(19)
(11)EP 3 266 131 B1

(12)EUROPEAN PATENT SPECIFICATION

(45)Mention of the grant of the patent:
15.12.2021 Bulletin 2021/50

(21)Application number: 15709140.6

(22)Date of filing:  04.03.2015
(51)International Patent Classification (IPC): 
H04J 3/16(2006.01)
(52)Cooperative Patent Classification (CPC):
H04J 3/1664; H04J 3/1652
(86)International application number:
PCT/EP2015/054502
(87)International publication number:
WO 2016/138950 (09.09.2016 Gazette  2016/36)

(54)

ENCAPSULATING DIGITAL COMMUNICATIONS SIGNALS FOR TRANSMISSION ON AN OPTICAL LINK

VERKAPSELUNG VON DIGITALEN KOMMUNIKATIONSSIGNALEN ZUR ÜBERTRAGUNG ÜBER EINE OPTISCHE VERBINDUNG

ENCAPSULATION DE SIGNAUX DE COMMUNICATION NUMÉRIQUES POUR UNE ÉMISSION SUR UNE LIAISON OPTIQUE


(84)Designated Contracting States:
AL AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HR HU IE IS IT LI LT LU LV MC MK MT NL NO PL PT RO RS SE SI SK SM TR

(43)Date of publication of application:
10.01.2018 Bulletin 2018/02

(73)Proprietor: Telefonaktiebolaget LM Ericsson (publ)
164 83 Stockholm (SE)

(72)Inventors:
  • CAVALIERE, Fabio
    I-56100 Pisa (IT)
  • STRACCA, Stefano
    I-56100 Pisa (IT)
  • BOTTARI, Giulio
    I-56100 Pisa (IT)

(74)Representative: Zacco Sweden AB 
Valhallavägen 117 Box 5581
114 85 Stockholm
114 85 Stockholm (SE)


(56)References cited: : 
US-A1- 2007 091 896
US-A1- 2008 075 110
US-A1- 2007 104 485
US-A1- 2011 229 133
  
      
    Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention).


    Description

    Technical Field



    [0001] The invention relates to a method of encapsulating digital communications signals for transmission on an optical link, encapsulation apparatus for a communications network transmitter and a communications network transmitter.

    Background



    [0002] The Mobile Backhaul, MBH, segment is the part of a communications network located between the Base Stations, BS, of a wireless communications network, located at cell sites, and the communications network core segment. In traditional radio access network, RAN, architectures, radio and baseband processing are integrated in a BS which typically outputs a Gigabit Ethernet (GbE/10GbE) signal. GbE clients are transported across the MBH segment using microwave signals and/or over optical fibre. Wavelength division multiplexing, WDM, can be used to increase the aggregated capacity of the optical fibre, especially in situations when fibre availability is scarce or limited by topology or cost constraints.

    [0003] In the Coordinated RAN, C-RAN, architecture, radio and baseband processing are separated. Remote Radio Units, RRU, which include radio, amplification/filtering, and digital-to-analogue, D/A, conversion, are located at the cell site. Digital Units, DU, for performing baseband processing, are separated from the RRUs, and are sometimes aggregated to form a DU pool. Decentralizing the DU enables improved coordination of radio capabilities across a set of RRUs, faster service delivery, and cost savings. Common Public Radio Interface, CPRI, as defined in the CPRI Specification, is the radio interface protocol widely used for IQ data transmission between RRUs and DUs.

    [0004] Both RAN and C-RAN architectures can benefit from using a transport layer based on optical technologies, which ensures low propagation delays, high data throughput, and low power consumption, while being an economical choice in exploiting fibre resources. In RAN, GbE clients can be transported over optical channels, directly mapped over wavelengths or as Optical Transport Network, OTN, clients as defined in ITU-T Recommendation G.709. In C-RAN, CPRI flows can also be transported over optical channels. ITU-T has recently included CPRI as a further OTN client in an appendix to G.709. However, the actual implementation of CPRI over OTN still presents unsolved issues. A simpler alternative to OTN has been proposed in PCT/EP2014/052056 in which CPRI is mapped over WDM optical channels with no or only a small additional overhead for Operations, Administration and Maintenance, OAM, and forward error correction, FEC, purposes. This may be referred to as CPRI over WDM.

    [0005] A third option is CPRI over Ethernet, CoE, which replaces a direct dedicated link between DU and RRU, using the CPRI protocol, with an Ethernet link having a CoE adapter at both the RRU and DU. There are two primary functions of a CoE adapter: implementation of the precision CoE clock; and mapping ingress CPRI basic frames received from the RRU or DU into outgoing CoE packets. The inverse mapping is applied to incoming CoE packets. CoE is appealing since it allows, in principle, management of any kind of traffic in the same Ethernet switch. However, due to the nature of Ethernet, CoE packets arrive asynchronously and some of them may be missing. Hence, a CoE Packet Buffer is needed to assemble arriving CoE packets in the order of egress from the originator. While the CoE packets arrive asynchronously at the adapter over the Ethernet interface, they must be delivered into the CPRI interface synchronously in order to be transparent to the CPRI interface.

    [0006] This is accomplished by transferring CPRI basic frames extracted from the CoE packets into the CPRI interface at both a precise known latency and at a clocking rate that is regulated by the local CoE clock.

    [0007] Document US 2007104485 A1 discloses a data traffic transmitting device in the OTN to realize high efficient data traffic mapping on the OTN frame structure.

    [0008] Document US 2011229133 A1 describes technique for mapping data between frames of different bit rates using buffer memory units.

    Summary



    [0009] It is an object to provide an improved method of encapsulating digital communications signals for transmission on an optical link. It is a further object to provide an improved encapsulation apparatus for a communications network transmitter. It is a further object to provide an improved communications network transmitter.

    [0010] A first aspect of the invention provides a method of encapsulating digital communications signals for transmission on a communications link. The method comprises steps a. to d. Step a. comprises receiving a first digital communications signal of a first signal type and receiving a second digital communications signal of a second signal type, different to the first signal type. The first digital communications signal comprises a first clock signal and the second digital communications signal comprises a second clock signal, different to the first clock signal. Each clock signal has a respective clock value and accuracy. Step b. comprises obtaining the first clock signal. Step c. comprises obtaining a difference between at least one of the clock values of the first and second clock signals and the accuracies of the first and second clock signals. Step b. also comprises buffering the second digital communications signal for a time at least long enough to compensate for the difference. Step d. comprises assembling the first digital communications signal and the buffered second digital communications signal into a frame for transmission. The frame comprises an overhead and a payload, the payload comprising a first portion and a second portion. The first digital communications signal is mapped into the first portion and the second digital communications signal is mapped into the second portion. Step d. is performed using the first clock signal.

    [0011] The method may enable transmission of digital communications signals of different types, having different clock signals, in a single frame on a single carrier signal without degradation of a synchronization accuracy of the first digital communications signal. The method may enable use of a communications link used to transport digital communications signals of different types to be optimized. The frame format may enable digital communications signals of different types to be carried on a single carrier signal and may provide an overhead for both types of signal. By performing the framing using the first clock signal the frame is synchronous with the first digital communications signal, and introduction of jitter onto the first digital communications signal may be avoided.

    [0012] In an embodiment, the communications link is an optical link.

    [0013] The method may enable transmission of digital communications signals of different types, having different clock signals, in a single frame on a single optical channel without degradation of a synchronization accuracy of the first digital communications signal. The method may enable use of an optical link used to transport digital communications signals of different types to be optimized. The frame format may enable digital communications signals of different types to be carried on a single optical channel and may provide an overhead for both types of signal. By performing the framing using the first clock signal the frame is synchronous with the first digital communications signal, and introduction of jitter onto the first digital communications signal may be avoided.

    [0014] In an embodiment, the communications link is one of a radio link and an electrical link.

    [0015] In an embodiment, a plurality of digital communications signals of the first signal type are received and are mapped into the first portion of the payload. The method may enable use of a communications link used to transport digital communications signals of different types to be optimized. The method may enable use of the traffic capacity of a carrier signal to be optimized.

    [0016] In an embodiment, a plurality of digital communications signals of the second signal type are received and are mapped into the second portion of the payload. The method may enable use of a communications link used to transport digital communications signals of different types to be optimized. The method may enable use of the traffic capacity of a carrier signal to be optimized.

    [0017] In an embodiment, at least some of the digital communications signals have different traffic bit rates. Each of the digital communications signals of the first signal type comprises the first clock signal and each of the digital communications signals of the second signal type comprises the second clock signal. The method may enable use of a communications link used to transport digital communications signals of different types to be optimized. The method may enable use of the traffic capacity of a carrier signal to be optimized.

    [0018] In an embodiment, each digital communications signal of the first signal type has the same traffic bit rate and each second digital communications signal of the second signal type has the same traffic bit rate, different to the traffic bit rate of the digital communications signal of the first signal type. The method may enable use of a communications link used to transport digital communications signals of different types to be optimized. The method may enable use of the traffic capacity of a carrier signal to be optimized.

    [0019] In an embodiment, at least two communications signals of the first signal type are received, a first of said signals having a first traffic bit rate and a second of said signals having a second traffic bit rate, different to the first traffic bit rate. The method may enable use of a communications link used to transport digital communications signals of different types to be optimized. The method may enable use of the traffic capacity of a carrier signal to be optimized.

    [0020] In an embodiment, at least two communications signals of the second signal type are received, a first of said signals having a third traffic bit rate and a second of said signals having a fourth traffic bit rate, different to the third traffic bit rate. The method may enable use of a communications link used to transport digital communications signals of different types to be optimized. The method may enable use of the traffic capacity of a carrier signal to be optimized.

    [0021] In an embodiment, the frame comprises at least three timeslots. The first portion of the payload comprising at least a first timeslot. The second portion of the payload comprising at least a second timeslot. The overhead comprises a third timeslot. The frame may provide an overhead for both types of signal.

    [0022] In an embodiment, the frame comprises at least four timeslots. The payload also comprises a fourth timeslot for receiving at least one of control characters and bits of a said digital communications signal which cannot be mapped within a capacity of a respective one of the first portion and the second portion. Providing a timeslot for receiving control characters and/or bits which cannot be mapped into the capacity of the respective portion may optimize the amount of communications traffic which may be mapped into the frame and may provide flexibility in the choice of digital communications signals which may be mapped into the frame.

    [0023] In an embodiment, the method comprises allocating timeslots to the first portion and the second portion of the payload in proportion to a respective weight of traffic of the communications signals of each of said signal types.

    [0024] In an embodiment, the method comprises determining the number of timeslots to be allocated to each of the first portion and the second portion in proportion to a respective weight of traffic of the communications signals of each of said signal types.

    [0025] In an embodiment, the method comprises determining which timeslots to allocate to each of the first portion and the second portion in proportion to a respective weight of traffic of the communications signals of each of said signal types.

    [0026] In an embodiment, the method comprises allocating timeslots to the first portion and the second portion of the payload depending a network configuration of a communications network comprising the optical link and the relative weight of traffic of the communications signals of each of said signal types.

    [0027] In an embodiment, each said first digital communications signal has a first latency requirement and each said second digital communications signal has a second latency requirement, less stringent than the first latency requirement. The method may enable transmission of digital communications signals having different latency requirements in a single frame on a single optical channel without degradation of the synchronization accuracy of the signal with the more stringent latency requirement. By enabling the transport of signals having different latency requirements using the same optical channel, the method may optimize the use of fibre infrastructure where used to transport both types of signal. Compared to the OTN client agnostic multiplexing based on ODUflex, the method does not introduce additional impairments on latency sensitive traffic. The advantages which the method may provide with respect to CoE are the absence of buffers (i.e. delay) on the latency sensitive signals and the absence of lost traffic. By performing the framing using the first clock signal the frame is synchronous with the first digital communications signal, and introduction of jitter onto the more sensitive first digital communications signal may be avoided.

    [0028] In an embodiment, each said first digital communications signal is a continuous bit rate signal and each said second digital communications signal is a packet signal. The method may enable transmission of continuous bit rate, CBR, signals and packet signals in a single frame on a single optical channel without degradation of the synchronization accuracy of the continuous bit rate signal. By enabling the transport of CBR signals and packet signals using the same optical channel, the method may optimize the use of fibre infrastructure where used to transport both types of signal. Compared to the OTN client agnostic multiplexing based on ODUflex, the method does not introduce additional impairments on performance sensitive CBR traffic while the impact on packet traffic, due to buffers, is expected to be tolerable, due to the inherent statistical nature of packet traffic. The advantages which the method may provide with respect to CoE are the absence of buffers (i.e. delay) on the CBR signals and the absence of lost CBR traffic. By performing the framing using the first clock signal the frame is synchronous with the CBR signal, and introduction of jitter onto the CBR signal may be avoided.

    [0029] In an embodiment, each said first digital communications signal is a common public radio interface, CPRI, signal as defined in the CPRI Specification and each said second digital communications signal is an Ethernet signal as defined in IEEE 802.3.

    [0030] The method may enable framing of Ethernet, including Gigabit Ethernet, signals and CPRI signals together into a single frame, for transmission on a single optical channel without degradation of the synchronization accuracy of the CPRI signal. The method may provide a unified transport method for mixing traffic originating from traditional radio base stations, BS, and remote radio units, RRU. By enabling the transport of Ethernet traffic and CPRI traffic in the same optical channel, the method may optimize the use of the optical channel capacity and may thus optimise the use of fibre infrastructure for transporting fronthaul traffic (CPRI) and conventional backhaul traffic (GbE/lOGbE). This may provide an advantage with respect to CPRI over WDM and CPRI over OTN using BMP, since it may enable problems of fibre scarcity in this network segment to be overcome and it may reduce leased fibre costs. The CPRI Specification sets stringent constraints for latency, jitter and delay symmetry in downstream and upstream. By performing the framing using the CPRI clock signal the frame is synchronous with the CPRI signal, and introduction of jitter onto the CPRI signal may be avoided. Compared to the OTN client agnostic multiplexing based on ODUflex, the method does not introduce additional impairments on performance sensitive CPRI traffic while the impact on Ethernet packets, due to buffers, is expected to be tolerable, due to the inherent statistical nature of Ethernet packets. The advantages which the method may provide with respect to CoE are the absence of buffers (i.e. delay) on the CPRI signals and the absence of lost CPRI traffic, which can compromise the target 10-12 bit error rate, BER. Moreover, the method may avoid the need for additional mechanisms to manage network synchronization.

    [0031] The method is applicable to present optical rates, i.e. around 10 Gbps, and may be extended with increasing benefits to higher bit rates, i.e. 40 Gbps and 100 Gbps.

    [0032] In an embodiment, each digital communications signal of the first signal type is mapped into the first portion of the frame using the following steps i. to v. Step i. comprises performing data recovery on each digital communications signal of the first signal type to obtain line coded digital communications traffic. Step ii. comprises decoding the input digital communications traffic to obtain information bits and non-information bits. Step iii. comprises removing the non-information bits. Step iv. comprises adding service channel bits for monitoring or maintenance, and step v. comprises mapping the service channel bits and information bits into the first portion of the frame. Each of steps ii. to v. is performed using the first clock signal. Each digital communications signal of the second signal type is mapped into the second portion of the frame using the Generic Framing Procedure, GFP, according to ITU-T Recommendation G.7041. Removing the non-information bits from each digital communications signal of the first type makes capacity available to add the service channel bits, so a service channel for monitoring or maintenance may be added to the received digital communications signals. The method may enable a 'light optical transport layer' to be added to digital communications traffic client signals without one or more of the disadvantages of standard OTN framing.

    [0033] In an embodiment, the first clock signal is obtained by performing clock recovery in step i.

    [0034] In an embodiment, the first clock signal is obtained from a digital unit which transmitted the digital communications signal of the first signal type.

    [0035] In an embodiment, the fourth timeslot is for receiving at least one of CPRI control characters and bits of a said Ethernet signal which cannot be mapped within a capacity of the second portion. The frame structure may enable CPRI signal control characters and bits of an Ethernet signal which cannot be mapped into the capacity of the second portion to be mapped into the allocated timeslot. By enabling the transport of Ethernet traffic and CPRI traffic in the same optical channel, and providing an allocated timeslot for CPRI control characters and Ethernet bits beyond the capacity of the second portion, the method may optimize the use of the optical channel capacity and may thus optimise the use of fibre infrastructure for transporting fronthaul traffic (CPRI) and conventional backhaul traffic (GbE/lOGbE).

    [0036] In an embodiment, the method comprises providing a forward error correction code and service channel bits for each of the communications signals in the overhead. The same forward error correction code may be provided for both the communications signals of the first type and the communications signals of the second type, or a first forward error correction code may be provided for the communications signals of the first type and a second forward error correction code for the communications signals of the second type. The frame may therefore carry FEC and OAM for both types of signal.

    [0037] In an embodiment, the forward error correction code is a Reed-Solomon (255, 239) forward error correction code having a plurality of interleaved codecs proportional to a preselected latency value. The method may therefore use a forward error correction, FEC, scheme which complies with the ITU-T G.709 standard for OTN but which has a lower latency, acceptable for CPRI signals.

    [0038] In an embodiment, the method comprises calculating respective bit-interleaved parity, BIP, bytes for the whole payload including both communications signals of the first and second type.

    [0039] In an embodiment, the time for which each second communications signal is buffered for is set using a local clock.

    [0040] In an embodiment, the method comprises receiving a value of a delay applied at another location in a communications network comprising the optical link. The time for which each second communications signal is buffered for is adjusted in proportion to said delay.

    [0041] In an embodiment, the value of said delay is received in a precision timing protocol signal according to IEEE 1588.

    [0042] A second aspect of the invention provides encapsulation apparatus for a communications network transmitter. The encapsulation apparatus comprises at least one input, a buffer and a framer. The at least one input is arranged to receive a first digital communications signal of a first signal type and a second digital communications signal of a second signal type, different to the first signal type. The first digital communications signal comprises a first clock signal and the second digital communications signal comprises a second clock signal different to the first clock signal. Each clock signal has a respective clock value and accuracy. The buffer is arranged to buffer the second digital communications signal for a time at least long enough to compensate for a difference between at least one of the clock values of the first and second clock signals and the accuracies of the first and second clock signals. The framer is arranged to receive the first digital communications signal and to receive the buffered second digital communications signal from the buffer. The framer is arranged to frame the first digital communications signal and the buffered second digital communications signal into a frame for transmission. The frame comprises an overhead and a payload, which comprising a first portion and a second portion. The framer is arranged to map the first digital communications signal into the first portion and being arranged to map the buffered second digital communications signal into the second portion. The encapsulation apparatus is arranged to obtain the first clock signal and the framer is arranged to operate using the first clock signal.

    [0043] The apparatus may enable digital communications signals of different types, having different clock signals, to be framed in a single frame for transmission on a single carrier signal without degradation of a synchronization accuracy of the first digital communications signal. This may enable use of a communications link used to transport digital communications signals of different types to be optimized. The frame format may enable digital communications signals of different types to be carried on a single carrier signal and may provide an overhead for both types of signal. By performing the framing using the first clock signal the frame is synchronous with the first digital communications signal, and introduction of jitter onto the first digital communications signal may be avoided.

    [0044] In an embodiment, the encapsulation apparatus is for an optical communications network transmitter.

    [0045] The apparatus may enable digital communications signals of different types, having different clock signals, to be framed in a single frame for transmission on a single optical channel without degradation of a synchronization accuracy of the first digital communications signal. This may enable use of an optical link used to transport digital communications signals of different types to be optimized. The frame format may enable digital communications signals of different types to be carried on a single optical carrier and may provide an overhead for both types of signal. By performing the framing using the first clock signal the frame is synchronous with the first digital communications signal, and introduction of jitter onto the first digital communications signal may be avoided.

    [0046] In an embodiment, the encapsulation apparatus is for radio communications network transmitter.

    [0047] In an embodiment, the encapsulation apparatus is for an electrical communications network transmitter.

    [0048] In an embodiment, the input is arranged to receive a plurality of digital communications signals of the first signal type. The framer is arranged to map said plurality of digital communications signals of the first signal type into the first portion of the payload. The apparatus may enable use of a communications link used to transport digital communications signals of different types to be optimized. The apparatus may enable use of the traffic capacity of a carrier signal to be optimized.

    [0049] In an embodiment, the input is arranged to receive a plurality of digital communications signals of the second signal type. The framer is arranged to map said plurality of digital communications signals of the second signal type into the second portion of the payload. The apparatus may enable use of a communications link used to transport digital communications signals of different types to be optimized. The apparatus may enable use of the traffic capacity of a carrier signal to be optimized.

    [0050] In an embodiment, at least some of the digital communications signals have different traffic bit rates. Each of the digital communications signals of the first signal type comprises the first clock signal and each of the digital communications signals of the second signal type comprises the second clock signal. The apparatus may enable use of a communications link used to transport digital communications signals of different types to be optimized. The apparatus may enable use of the traffic capacity of a carrier signal to be optimized.

    [0051] In an embodiment, each digital communications signal of the first signal type has the same traffic bit rate and each second digital communications signal of the second signal type has the same traffic bit rate, different to the traffic bit rate of the digital communications signal of the first signal type. The apparatus may enable use of a communications link used to transport digital communications signals of different types to be optimized. The apparatus may enable use of the traffic capacity of a carrier signal to be optimized.

    [0052] In an embodiment, at least two communications signals of the first signal type are received, a first of said signals having a first traffic bit rate and a second of said signals having a second traffic bit rate, different to the first traffic bit rate. The apparatus may enable use of a communications link used to transport digital communications signals of different types to be optimized. The apparatus may enable use of the traffic capacity of a carrier signal to be optimized.

    [0053] In an embodiment, at least two communications signals of the second signal type are received, a first of said signals having a third traffic bit rate and a second of said signals having a fourth traffic bit rate, different to the third traffic bit rate. The apparatus may enable use of a communications link used to transport digital communications signals of different types to be optimized. The apparatus may enable use of the traffic capacity of a carrier signal to be optimized.

    [0054] In an embodiment, the frame comprises at least three timeslots. The first portion of the payload comprising at least a first timeslot. The second portion of the payload comprising at least a second timeslot. The overhead comprises a third timeslot. The frame may provide an overhead for both types of signal.

    [0055] In an embodiment, the frame comprises at least four timeslots. The payload also comprises a fourth timeslot for receiving at least one of control characters and bits of a said digital communications signal which cannot be mapped within a capacity of a respective one of the first portion and the second portion. Providing a timeslot for receiving control characters and/or bits which cannot be mapped into the capacity of the respective portion may optimize the amount of communications traffic which may be mapped into the frame and may provide flexibility in the choice of digital communications signals which may be mapped into the frame.

    [0056] In an embodiment, each said first digital communications signal has a first latency requirement and each said second digital communications signal has a second latency requirement, less stringent than the first latency requirement. The apparatus may enable digital communications signals having different latency requirements to be framed in a single frame for transmission on a single optical channel without degradation of the synchronization accuracy of the signal with the more stringent latency requirement. By enabling the transport of signals having different latency requirements using the same optical channel, the apparatus may optimize the use of fibre infrastructure where used to transport both types of signal. Compared to the OTN client agnostic multiplexing based on ODUflex, the apparatus does not introduce additional impairments on latency sensitive traffic. The advantages which the apparatus may provide with respect to CoE are the absence of buffers (i.e. delay) on the latency sensitive signals and the absence of lost traffic. By performing the framing using the first clock signal the frame is synchronous with the first digital communications signal, and introduction of jitter onto the more sensitive first digital communications signal may be avoided.

    [0057] In an embodiment, each said first digital communications signal is a continuous bit rate signal and each said second digital communications signal is a packet signal. The apparatus may enable of continuous bit rate, CBR, signals and packet signals to be framed in a single frame for transmission on a single optical channel without degradation of the synchronization accuracy of the CBR signal. By enabling the transport of CBR signals and packet signals using the same optical channel, the apparatus may optimize the use of fibre infrastructure where used to transport both types of signal. Compared to the OTN client agnostic multiplexing based on ODUflex, the apparatus does not introduce additional impairments on performance sensitive CBR traffic. The advantages which the apparatus may provide with respect to CoE are the absence of buffers (i.e. delay) on the CBR signals and the absence of lost CBR traffic. By performing the framing using the first clock signal the frame is synchronous with the CBR signal, and introduction of jitter onto CBR signal may be avoided.

    [0058] In an embodiment, each said first digital communications signal is a common public radio interface, CPRI, signal as defined in the CPRI Specification and each said second digital communications signal is an Ethernet signal, as defined in IEEE 802.3.

    [0059] The apparatus may enable framing of Ethernet, including Gigabit Ethernet, signals and CPRI signals together into a single frame, for transmission on a single optical channel without degradation of the synchronization accuracy of the CPRI signal. The apparatus may provide a unified transport approach, mixing traffic originating from traditional radio base stations, BS, and remote radio units, RRU. By enabling the transport of Ethernet traffic and CPRI traffic in the same optical channel, the apparatus may optimize the use of the optical channel capacity and may thus optimise the use of fibre infrastructure for transporting fronthaul traffic (CPRI) and conventional backhaul traffic (GbE/lOGbE). This may provide an advantage with respect to CPRI over WDM and CPRI over OTN using BMP, since it may enable problems of fibre scarcity in this network segment to be overcome and it may reduce leased fibre costs. The CPRI Specification sets stringent constraints for latency, jitter and delay symmetry in downstream and upstream. By performing the framing using the CPRI clock signal the frame is synchronous with the CPRI signal, and introduction of jitter onto the CPRI signal may be avoided. Compared to the OTN client agnostic multiplexing based on ODUflex, the apparatus does not introduce additional impairments on performance sensitive CPRI traffic while the impact on Ethernet packets, due to buffers, is expected to be tolerable, due to the inherent statistical nature of Ethernet packets. The advantages which the apparatus may provide with respect to CoE are the absence of buffers (i.e. delay) on the CPRI signals and the absence of lost CPRI traffic, which can compromise the target 10-12bit error rate, BER. Moreover, the apparatus may avoid the need for additional mechanisms to manage network synchronization.

    [0060] The apparatus is operable with present optical rates, i.e. around 10 Gbps, and may be extended with increasing benefits to higher bit rates, i.e. 40 Gbps and 100 Gbps.

    [0061] In an embodiment, the framer is arranged to map each digital communications signal of the first signal type into the first portion of the frame using the following steps i. to v. Step i. comprises performing data recovery on each digital communications signal of the first signal type to obtain line coded digital communications traffic. Step ii. comprises decoding the input digital communications traffic to obtain information bits and non-information bits. Step iii. comprises removing the non-information bits. Step iv. comprises adding service channel bits for monitoring or maintenance, and step v. comprises mapping the service channel bits and information bits into the first portion of the frame. Each of steps ii. to v. is performed using the first clock signal.. The framer is arranged to map each digital communications signal of the second signal type into the second portion of the frame using the Generic Framing Procedure, GFP, according to ITU-T Recommendation G.7041. Removing the non-information bits from each digital communications signal of the first type makes capacity available to add the service channel bits, so a service channel for monitoring or maintenance may be added to the received digital communications signals. The method may enable a 'light optical transport layer' to be added to digital communications traffic client signals without one or more of the disadvantages of standard OTN framing.

    [0062] In an embodiment, the framer is arranged to map at least one of CPRI control characters and bits of a said Ethernet signal which cannot be mapped within a capacity of the second portion into the fourth timeslot. The frame structure may enable CPRI signal control characters and bits of an Ethernet signal which cannot be mapped into the capacity of the second portion to be mapped into the allocated timeslot. By enabling the transport of Ethernet traffic and CPRI traffic in the same optical channel, and providing an allocated timeslot for CPRI control characters and Ethernet bits beyond the capacity of the second portion, the apparatus may optimize the use of the optical channel capacity and may thus optimise the use of fibre infrastructure for transporting fronthaul traffic (CPRI) and conventional backhaul traffic (GbE/lOGbE).

    [0063] In an embodiment, the framer is arranged to provide a forward error correction code and service channel bits for each of the communications signals in the overhead. The same forward error correction code may be provided for both the communications signals of the first type and the communications signals of the second type, or a first forward error correction code may be provided for the communications signals of the first type and a second forward error correction code for the communications signals of the second type. The frame may therefore carry FEC and OAM for both types of signal.

    [0064] In an embodiment, the forward error correction code is a Reed-Solomon (255, 239) forward error correction code having a plurality of interleaved codecs proportional to a preselected latency value. The apparatus may therefore apply a forward error correction, FEC, scheme which complies with the ITU-T G.709 standard for OTN but which has a lower latency, acceptable for CPRI signals.

    [0065] In an embodiment, the framer is arranged to calculate respective bit-interleaved parity, BIP, bytes for the payload including both communications signals of the first type and the second type.

    [0066] In an embodiment, the buffer is arranged to operate using a local clock.

    [0067] In an embodiment, the apparatus is arranged to receive a value of a delay applied at another location in a communications network comprising the optical link. The time for which each second communications signal is buffered for is adjusted in proportion to said delay.

    [0068] In an embodiment, the value of said delay is received in a precision timing protocol signal according to IEEE 1588.

    [0069] A third aspect of the invention provides a communications network transmitter comprising encapsulation apparatus and a carrier signal transmitter arranged to generate and transmit a carrier signal carrying the frame for transmission. The encapsulation apparatus comprises at least one input, a buffer and a framer. The at least one input is arranged to receive a first digital communications signal of a first signal type and a second digital communications signal of a second signal type, different to the first signal type. The first digital communications signal comprises a first clock signal and the second digital communications signal comprises a second clock signal different to the first clock signal. Each clock signal has a respective clock value and accuracy. The buffer is arranged to buffer the second digital communications signal for a time at least long enough to compensate for a difference between at least one of the clock values of the first and second clock signals and the accuracies of the first and second clock signals. The framer is arranged to receive the first digital communications signal and to receive the buffered second digital communications signal from the buffer. The framer is arranged to frame the first digital communications signal and the buffered second digital communications signal into a frame for transmission. The frame comprises an overhead and a payload, which comprising a first portion and a second portion. The framer is arranged to map the first digital communications signal into the first portion and being arranged to map the buffered second digital communications signal into the second portion. The encapsulation apparatus is arranged to obtain the first clock signal and the framer is arranged to operate using the first clock signal.

    [0070] The encapsulation apparatus may enable digital communications signals of different types, having different clock signals, to be framed in a single frame for transmission on a single carrier signal without degradation of a synchronization accuracy of the first digital communications signal. Use of the communications network transmitter may enable use of a communications link used to transport digital communications signals of different types to be optimized. The frame format may enable digital communications signals of different types to be carried on a single carrier signal and may provide an overhead for both types of signal. By performing the framing using the first clock signal the frame is synchronous with the first digital communications signal, and introduction of jitter onto the first digital communications signal may be avoided.

    [0071] In an embodiment, the carrier signal transmitter is an optical transmitter for generating an optical carrier signal.

    [0072] The encapsulation apparatus may enable digital communications signals of different types, having different clock signals, to be framed in a single frame for transmission on a single optical carrier signal, also known as an "optical channel", without degradation of a synchronization accuracy of the first digital communications signal. Use of the communications network transmitter may enable use of an optical link used to transport digital communications signals of different types to be optimized. The frame format may enable digital communications signals of different types to be carried on a single optical channel and may provide an overhead for both types of signal. By performing the framing using the first clock signal the frame is synchronous with the first digital communications signal, and introduction of jitter onto the first digital communications signal may be avoided.

    [0073] In an embodiment, the carrier signal transmitter is a radio transmitter for generating a radio frequency carrier signal.

    [0074] In an embodiment, the carrier signal transmitter is an electrical signal transmitter for generating an electrical carrier signal.

    [0075] In an embodiment, the input is arranged to receive a plurality of digital communications signals of the first signal type. The framer is arranged to map said plurality of digital communications signals of the first signal type into the first portion of the payload. The communications network transmitter may enable use of a communications link used to transport digital communications signals of different types to be optimized. The communications network transmitter may enable use of the traffic capacity of a carrier signal to be optimized.

    [0076] In an embodiment, the input is arranged to receive a plurality of digital communications signals of the second signal type. The framer is arranged to map said plurality of digital communications signals of the second signal type into the second portion of the payload. The communications network transmitter may enable use of a communications link used to transport digital communications signals of different types to be optimized. The communications network transmitter may enable use of the traffic capacity of a carrier signal to be optimized.

    [0077] In an embodiment, at least some of the digital communications signals have different traffic bit rates. Each of the digital communications signals of the first signal type comprises the first clock signal and each of the digital communications signals of the second signal type comprises the second clock signal. The transmitter may enable use of a communications link used to transport digital communications signals of different types to be optimized. The communications network transmitter may enable use of the traffic capacity of a carrier signal to be optimized.

    [0078] In an embodiment, each digital communications signal of the first signal type has the same traffic bit rate and each second digital communications signal of the second signal type has the same traffic bit rate, different to the traffic bit rate of the digital communications signal of the first signal type. The communications network transmitter may enable use of a communications link used to transport digital communications signals of different types to be optimized. The communications network transmitter may enable use of the traffic capacity of a carrier signal to be optimized.

    [0079] In an embodiment, at least two communications signals of the first signal type are received, a first of said signals having a first traffic bit rate and a second of said signals having a second traffic bit rate, different to the first traffic bit rate. The communications network transmitter may enable use of a communications link used to transport digital communications signals of different types to be optimized. The communications network transmitter may enable use of the traffic capacity of a carrier signal to be optimized.

    [0080] In an embodiment, at least two communications signals of the second signal type are received, a first of said signals having a third traffic bit rate and a second of said signals having a fourth traffic bit rate, different to the third traffic bit rate. The communications network transmitter may enable use of a communications link used to transport digital communications signals of different types to be optimized. The communications network transmitter may enable use of the traffic capacity of a carrier signal to be optimized.

    [0081] In an embodiment, the frame comprises at least three timeslots. The first portion of the payload comprising at least a first timeslot. The second portion of the payload comprising at least a second timeslot. The overhead comprises a third timeslot. The frame may provide an overhead for both types of signal.

    [0082] In an embodiment, the frame comprises at least four timeslots. The payload also comprises a fourth timeslot for receiving at least one of control characters and bits of a said digital communications signal which cannot be mapped within a capacity of a respective one of the first portion and the second portion. Providing a timeslot for receiving control characters and/or bits which cannot be mapped into the capacity of the respective portion may optimize the amount of communications traffic which may be mapped into the frame and may provide flexibility in the choice of digital communications signals which may be mapped into the frame.

    [0083] In an embodiment, each said first digital communications signal has a first latency requirement and each said second digital communications signal has a second latency requirement, less stringent than the first latency requirement. The apparatus may enable digital communications signals having different latency requirements to be framed in a single frame for transmission on a single optical channel without degradation of the synchronization accuracy of the signal with the more stringent latency requirement. By enabling the transport of signals having different latency requirements using the same optical channel, the transmitter may optimize the use of fibre infrastructure where used to transport both types of signal. Compared to the OTN client agnostic multiplexing based on ODUflex, the transmitter does not introduce additional impairments on latency sensitive traffic. The advantages which the apparatus may provide with respect to CoE are the absence of buffers (i.e. delay) on the latency sensitive signals and the absence of lost traffic. By performing the framing using the first clock signal the frame is synchronous with the first digital communications signal, and introduction of jitter onto the more sensitive first digital communications signal may be avoided.

    [0084] In an embodiment, each said first digital communications signal is a continuous bit rate signal and each said second digital communications signal is a packet signal. The encapsulation apparatus may enable of continuous bit rate, CBR, signals and packet signals to be framed in a single frame for transmission on a single optical channel without degradation of the synchronization accuracy of the CBR signal. By enabling the transport of CBR signals and packet signals using the same optical channel, the transmitter may optimize the use of fibre infrastructure where used to transport both types of signal. Compared to the OTN client agnostic multiplexing based on ODUflex, the encapsulation apparatus does not introduce additional impairments on performance sensitive CBR traffic. The advantages which the encapsulation apparatus may provide with respect to CoE are the absence of buffers (i.e. delay) on the CBR signals and the absence of lost CBR traffic. By performing the framing using the first clock signal the frame is synchronous with the CBR signal, and introduction of jitter onto CBR signal may be avoided.

    [0085] In an embodiment, each said first digital communications signal is a common public radio interface, CPRI, signal as defined in the CPRI Specification and each said second digital communications signal is an Ethernet signal, as defined in IEEE 802.3.

    [0086] The communications network transmitter may enable framing of Ethernet, including Gigabit Ethernet, signals and CPRI signals together into a single frame, and transmission of the framed signals on a single optical channel without degradation of the synchronization accuracy of the CPRI signal. The communications network transmitter may provide a unified transport approach, mixing traffic originating from traditional radio base stations, BS, and remote radio units, RRU. By enabling the transport of Ethernet traffic and CPRI traffic in the same optical channel, the communications network transmitter may optimize the use of the optical channel capacity and may thus optimise the use of fibre infrastructure for transporting fronthaul traffic (CPRI) and conventional backhaul traffic (GbE/lOGbE). This may provide an advantage with respect to CPRI over WDM and CPRI over OTN using BMP, since it may enable problems of fibre scarcity in this network segment to be overcome and it may reduce leased fibre costs. The CPRI Specification sets stringent constraints for latency, jitter and delay symmetry in downstream and upstream. By performing the framing using the CPRI clock signal the frame is synchronous with the CPRI signal, and introduction of jitter onto the CPRI signal may be avoided. Compared to the OTN client agnostic multiplexing based on ODUflex, the encapsulation apparatus does not introduce additional impairments on performance sensitive CPRI traffic while the impact on Ethernet packets, due to buffers, is expected to be tolerable, due to the inherent statistical nature of Ethernet packets. The advantages which the encapsulation apparatus may provide with respect to CoE are the absence of buffers (i.e. delay) on the CPRI signals and the absence of lost CPRI traffic, which can compromise the target 10-12bit error rate, BER. Moreover, the communications network transmitter may avoid the need for additional mechanisms to manage network synchronization.

    [0087] The communications network transmitter is operable with present optical rates, i.e. around 10 Gbps, and may be extended with increasing benefits to higher bit rates, i.e. 40 Gbps and 100 Gbps.

    [0088] In an embodiment, the framer is arranged to map each digital communications signal of the first signal type into the first portion of the frame using the following steps i. to v. Step i. comprises performing data recovery on each digital communications signal of the first signal type to obtain line coded digital communications traffic. Step ii. comprises decoding the input digital communications traffic to obtain information bits and non-information bits. Step iii. comprises removing the non-information bits. Step iv. comprises adding service channel bits for monitoring or maintenance, and step v. comprises mapping the service channel bits and information bits into the first portion of the frame. Each of steps ii. to v. is performed using the first clock signal.. The framer is arranged to map each digital communications signal of the second signal type into the second portion of the frame using the Generic Framing Procedure, GFP, according to ITU-T Recommendation G.7041. Removing the non-information bits from each digital communications signal of the first type makes capacity available to add the service channel bits, so a service channel for monitoring or maintenance may be added to the received digital communications signals. The method may enable a 'light optical transport layer' to be added to digital communications traffic client signals without one or more of the disadvantages of standard OTN framing.

    [0089] In an embodiment, the framer is arranged to map at least one of CPRI control characters and bits of a said Ethernet signal which cannot be mapped within a capacity of the second portion into the fourth timeslot. The frame structure may enable CPRI signal control characters and bits of an Ethernet signal which cannot be mapped into the capacity of the second portion to be mapped into the allocated timeslot. By enabling the transport of Ethernet traffic and CPRI traffic in the same optical channel, and providing an allocated timeslot for CPRI control characters and Ethernet bits beyond the capacity of the second portion, the transmitter may optimize the use of the optical channel capacity and may thus optimise the use of fibre infrastructure for transporting fronthaul traffic (CPRI) and conventional backhaul traffic (GbE/lOGbE).

    [0090] In an embodiment, the framer is arranged to provide a forward error correction code and service channel bits for each of the communications signals in the overhead. The same forward error correction code may be provided for both the communications signals of the first type and the communications signals of the second type, or a first forward error correction code may be provided for the communications signals of the first type and a second forward error correction code for the communications signals of the second type. The frame may therefore carry FEC and OAM for both types of signal.

    [0091] In an embodiment, the forward error correction code is a Reed-Solomon (255, 239) forward error correction code having a plurality of interleaved codecs proportional to a preselected latency value. The communications network transmitter may therefore apply a forward error correction, FEC, scheme which complies with the ITU-T G.709 standard for OTN but which has a lower latency, acceptable for CPRI signals.

    [0092] In an embodiment, the framer is arranged to calculate respective bit-interleaved parity, BIP, bytes for the payload including both communications signals of the first type and the second type.

    [0093] In an embodiment, the buffer is arranged to operate using a local clock.

    [0094] In an embodiment, the communications network transmitter is arranged to receive a value of a delay applied at another location in a communications network comprising the optical link. The time for which each second communications signal is buffered for is adjusted in proportion to said delay.

    [0095] In an embodiment, the value of said delay is received in a precision timing protocol signal according to IEEE 1588.

    [0096] A fourth aspect of the invention provides a communications network node comprising a communications network transmitter. The communications network transmitter comprises encapsulation apparatus and a carrier signal transmitter arranged to generate and transmit a carrier signal carrying the frame for transmission. The encapsulation apparatus comprises at least one input, a buffer and a framer. The at least one input is arranged to receive a first digital communications signal of a first signal type and a second digital communications signal of a second signal type, different to the first signal type. The first digital communications signal comprises a first clock signal and the second digital communications signal comprises a second clock signal different to the first clock signal. Each clock signal has a respective clock value and accuracy. The buffer is arranged to buffer the second digital communications signal for a time at least long enough to compensate for a difference between at least one of the clock values of the first and second clock signals and the accuracies of the first and second clock signals. The framer is arranged to receive the first digital communications signal and to receive the buffered second digital communications signal from the buffer. The framer is arranged to frame the first digital communications signal and the buffered second digital communications signal into a frame for transmission. The frame comprises an overhead and a payload, which comprising a first portion and a second portion. The framer is arranged to map the first digital communications signal into the first portion and being arranged to map the buffered second digital communications signal into the second portion. The encapsulation apparatus is arranged to obtain the first clock signal and the framer is arranged to operate using the first clock signal.

    [0097] The encapsulation apparatus may enable digital communications signals of different types, having different clock signals, to be framed in a single frame for transmission on a single carrier signal without degradation of a synchronization accuracy of the first digital communications signal. Use of the communications network transmitter may enable use of a communications link used to transport digital communications signals of different types to be optimized. The frame format may enable digital communications signals of different types to be carried on a single carrier signal and may provide an overhead for both types of signal. By performing the framing using the first clock signal the frame is synchronous with the first digital communications signal, and introduction of jitter onto the first digital communications signal may be avoided.

    [0098] In an embodiment, the carrier signal transmitter is an optical transmitter arranged to generate and transmit an optical signal carrying the frame for transmission.

    [0099] The encapsulation apparatus may enable digital communications signals of different types, having different clock signals, to be framed in a single frame for transmission on a single optical channel without degradation of a synchronization accuracy of the first digital communications signal. Use of the communications network transmitter may enable use of a communications link used to transport digital communications signals of different types to be optimized. The frame format may enable digital communications signals of different types to be carried on a single optical channel and may provide an overhead for both types of signal. By performing the framing using the first clock signal the frame is synchronous with the first digital communications signal, and introduction of jitter onto the first digital communications signal may be avoided.

    [0100] In an embodiment, the carrier signal transmitter is a radio transmitter arranged to generate and transmit a radio frequency carrier signal carrying the frame for transmission.

    [0101] In an embodiment, the carrier signal transmitter is an electrical signal transmitter arranged to generate and transmit an electrical carrier signal carrying the frame for transmission.

    [0102] In an embodiment, the input is arranged to receive a plurality of digital communications signals of the first signal type. The framer is arranged to map said plurality of digital communications signals of the first signal type into the first portion of the payload. The communications network transmitter may enable use of a communications link used to transport digital communications signals of different types to be optimized. The communications network transmitter may enable use of the traffic capacity of a carrier signal to be optimized.

    [0103] In an embodiment, the input is arranged to receive a plurality of digital communications signals of the second signal type. The framer is arranged to map said plurality of digital communications signals of the second signal type into the second portion of the payload. The communications network transmitter may enable use of a communications link used to transport digital communications signals of different types to be optimized. The communications network transmitter may enable use of the traffic capacity of a carrier signal to be optimized.

    [0104] In an embodiment, at least some of the digital communications signals have different traffic bit rates. Each of the digital communications signals of the first signal type comprises the first clock signal and each of the digital communications signals of the second signal type comprises the second clock signal. The communications network transmitter may enable use of a communications link used to transport digital communications signals of different types to be optimized. The communications network transmitter may enable use of the traffic capacity of a carrier signal to be optimized.

    [0105] In an embodiment, each digital communications signal of the first signal type has the same traffic bit rate and each second digital communications signal of the second signal type has the same traffic bit rate, different to the traffic bit rate of the digital communications signal of the first signal type. The communications network transmitter may enable use of a communications link used to transport digital communications signals of different types to be optimized. The communications network transmitter may enable use of the traffic capacity of a carrier signal to be optimized.

    [0106] In an embodiment, at least two communications signals of the first signal type are received, a first of said signals having a first traffic bit rate and a second of said signals having a second traffic bit rate, different to the first traffic bit rate. The communications network transmitter may enable use of a communications link used to transport digital communications signals of different types to be optimized. The communications network transmitter may enable use of the traffic capacity of a carrier signal to be optimized.

    [0107] In an embodiment, at least two communications signals of the second signal type are received, a first of said signals having a third traffic bit rate and a second of said signals having a fourth traffic bit rate, different to the third traffic bit rate. The communications network transmitter may enable use of a communications link used to transport digital communications signals of different types to be optimized. The communications network transmitter may enable use of the traffic capacity of a carrier signal to be optimized.

    [0108] In an embodiment, the frame comprises at least three timeslots. The first portion of the payload comprising at least a first timeslot. The second portion of the payload comprising at least a second timeslot. The overhead comprises a third timeslot. The frame may provide an overhead for both types of signal.

    [0109] In an embodiment, the frame comprises at least four timeslots. The payload also comprises a fourth timeslot for receiving at least one of control characters and bits of a said digital communications signal which cannot be mapped within a capacity of a respective one of the first portion and the second portion. Providing a timeslot for receiving control characters and/or bits which cannot be mapped into the capacity of the respective portion may optimize the amount of communications traffic which may be mapped into the frame and may provide flexibility in the choice of digital communications signals which may be mapped into the frame.

    [0110] In an embodiment, each said first digital communications signal has a first latency requirement and each said second digital communications signal has a second latency requirement, less stringent than the first latency requirement. The apparatus may enable digital communications signals having different latency requirements to be framed in a single frame for transmission on a single optical channel without degradation of the synchronization accuracy of the signal with the more stringent latency requirement. By enabling the transport of signals having different latency requirements using the same optical channel, the transmitter may optimize the use of fibre infrastructure where used to transport both types of signal. Compared to the OTN client agnostic multiplexing based on ODUflex, the transmitter does not introduce additional impairments on latency sensitive traffic. The advantages which the apparatus may provide with respect to CoE are the absence of buffers (i.e. delay) on the latency sensitive signals and the absence of lost traffic. By performing the framing using the first clock signal the frame is synchronous with the first digital communications signal, and introduction of jitter onto the more sensitive first digital communications signal may be avoided.

    [0111] In an embodiment, each said first digital communications signal is a continuous bit rate signal and each said second digital communications signal is a packet signal. The encapsulation apparatus may enable of continuous bit rate, CBR, signals and packet signals to be framed in a single frame for transmission on a single optical channel without degradation of the synchronization accuracy of the CBR signal. By enabling the transport of CBR signals and packet signals using the same optical channel, the transmitter may optimize the use of fibre infrastructure where used to transport both types of signal. Compared to the OTN client agnostic multiplexing based on ODUflex, the encapsulation apparatus does not introduce additional impairments on performance sensitive CBR traffic. The advantages which the encapsulation apparatus may provide with respect to CoE are the absence of buffers (i.e. delay) on the CBR signals and the absence of lost CBR traffic. By performing the framing using the first clock signal the frame is synchronous with the CBR signal, and introduction of jitter onto CBR signal may be avoided.

    [0112] In an embodiment, each said first digital communications signal is a common public radio interface, CPRI, signal as defined in the CPRI Specification and each said second digital communications signal is an Ethernet signal, as defined in IEEE 802.3.

    [0113] The communications network transmitter may enable framing of Ethernet, including Gigabit Ethernet, signals and CPRI signals together into a single frame, and transmission of the framed signals on a single optical channel without degradation of the synchronization accuracy of the CPRI signal. The communications network transmitter may provide a unified transport approach, mixing traffic originating from traditional radio base stations, BS, and remote radio units, RRU. By enabling the transport of Ethernet traffic and CPRI traffic in the same optical channel, the communications network transmitter may optimize the use of the optical channel capacity and may thus optimise the use of fibre infrastructure for transporting fronthaul traffic (CPRI) and conventional backhaul traffic (GbE/lOGbE). This may provide an advantage with respect to CPRI over WDM and CPRI over OTN using BMP, since it may enable problems of fibre scarcity in this network segment to be overcome and it may reduce leased fibre costs. The CPRI Specification sets stringent constraints for latency, jitter and delay symmetry in downstream and upstream. By performing the framing using the CPRI clock signal the frame is synchronous with the CPRI signal, and introduction of jitter onto the CPRI signal may be avoided. Compared to the OTN client agnostic multiplexing based on ODUflex, the encapsulation apparatus does not introduce additional impairments on performance sensitive CPRI traffic while the impact on Ethernet packets, due to buffers, is expected to be tolerable, due to the inherent statistical nature of Ethernet packets. The advantages which the encapsulation apparatus may provide with respect to CoE are the absence of buffers (i.e. delay) on the CPRI signals and the absence of lost CPRI traffic, which can compromise the target 10-12bit error rate, BER. Moreover, the transmitter may avoid the need for additional mechanisms to manage network synchronization.

    [0114] The communications network transmitter is operable with present optical rates, i.e. around 10 Gbps, and may be extended with increasing benefits to higher bit rates, i.e. 40 Gbps and 100 Gbps.

    [0115] In an embodiment, the framer is arranged to map each digital communications signal of the first signal type into the first portion of the frame using the following steps i. to v. Step i. comprises performing data recovery on each digital communications signal of the first signal type to obtain line coded digital communications traffic. Step ii. comprises decoding the input digital communications traffic to obtain information bits and non-information bits. Step iii. comprises removing the non-information bits. Step iv. comprises adding service channel bits for monitoring or maintenance, and step v. comprises mapping the service channel bits and information bits into the first portion of the frame. Each of steps ii. to v. is performed using the first clock signal.. The framer is arranged to map each digital communications signal of the second signal type into the second portion of the frame using the Generic Framing Procedure, GFP, according to ITU-T Recommendation G.7041. Removing the non-information bits from each digital communications signal of the first type makes capacity available to add the service channel bits, so a service channel for monitoring or maintenance may be added to the received digital communications signals. The method may enable a 'light optical transport layer' to be added to digital communications traffic client signals without one or more of the disadvantages of standard OTN framing.

    [0116] In an embodiment, the framer is arranged to map at least one of CPRI control characters and bits of a said Ethernet signal which cannot be mapped within a capacity of the second portion into the fourth timeslot. The frame structure may enable CPRI signal control characters and bits of an Ethernet signal which cannot be mapped into the capacity of the second portion to be mapped into the allocated timeslot. By enabling the transport of Ethernet traffic and CPRI traffic in the same optical channel, and providing an allocated timeslot for CPRI control characters and Ethernet bits beyond the capacity of the second portion, the transmitter may optimize the use of the optical channel capacity and may thus optimise the use of fibre infrastructure for transporting fronthaul traffic (CPRI) and conventional backhaul traffic (GbE/lOGbE).

    [0117] In an embodiment, the framer is arranged to provide a forward error correction code and service channel bits for each of the communications signals in the overhead. The same forward error correction code may be provided for both the communications signals of the first type and the communications signals of the second type, or a first forward error correction code may be provided for the communications signals of the first type and a second forward error correction code for the communications signals of the second type. The frame may therefore carry FEC and OAM for both types of signal.

    [0118] In an embodiment, the forward error correction code is a Reed-Solomon (255, 239) forward error correction code having a plurality of interleaved codecs proportional to a preselected latency value. The apparatus may therefore apply a forward error correction, FEC, scheme which complies with the ITU-T G.709 standard for OTN but which has a lower latency, acceptable for CPRI signals.

    [0119] In an embodiment, the framer is arranged to calculate respective bit-interleaved parity, BIP, bytes for the payload including both communications signals of the first type and the second type.

    [0120] In an embodiment, the buffer is arranged to operate using a local clock.

    [0121] In an embodiment, the transmitter is arranged to receive a value of a delay applied at another location in a communications network comprising the optical link. The time for which each second communications signal is buffered for is adjusted in proportion to said delay.

    [0122] In an embodiment, the value of said delay is received in a precision timing protocol signal according to IEEE 1588.

    [0123] A fifth aspect of the invention provides a communications network comprising a communications network node. The communications network node comprises a communications network transmitter. The communications network transmitter comprises encapsulation apparatus and a carrier signal transmitter arranged to generate and transmit carrier signal carrying the frame for transmission. The encapsulation apparatus comprises at least one input, a buffer and a framer. The at least one input is arranged to receive a first digital communications signal of a first signal type and a second digital communications signal of a second signal type, different to the first signal type. The first digital communications signal comprises a first clock signal and the second digital communications signal comprises a second clock signal different to the first clock signal. Each clock signal has a respective clock value and accuracy. The buffer is arranged to buffer the second digital communications signal for a time at least long enough to compensate for a difference between at least one of the clock values of the first and second clock signals and the accuracies of the first and second clock signals. The framer is arranged to receive the first digital communications signal and to receive the buffered second digital communications signal from the buffer. The framer is arranged to frame the first digital communications signal and the buffered second digital communications signal into a frame for transmission. The frame comprises an overhead and a payload, which comprising a first portion and a second portion. The framer is arranged to map the first digital communications signal into the first portion and being arranged to map the buffered second digital communications signal into the second portion. The encapsulation apparatus is arranged to obtain the first clock signal and the framer is arranged to operate using the first clock signal.

    [0124] The encapsulation apparatus may enable digital communications signals of different types, having different clock signals, to be framed in a single frame for transmission on a single carrier signal without degradation of a synchronization accuracy of the first digital communications signal. Use of the transmitter may enable use of a communications link used to transport digital communications signals of different types to be optimized. The frame format may enable digital communications signals of different types to be carried on a single carrier signal and may provide an overhead for both types of signal. By performing the framing using the first clock signal the frame is synchronous with the first digital communications signal, and introduction of jitter onto the first digital communications signal may be avoided.

    [0125] In an embodiment, the carrier signal transmitter is an optical transmitter for generating an optical carrier signal.

    [0126] The encapsulation apparatus may enable digital communications signals of different types, having different clock signals, to be framed in a single frame for transmission on a single optical carrier signal, also known as an "optical channel", without degradation of a synchronization accuracy of the first digital communications signal. Use of the communications network transmitter may enable use of an optical link used to transport digital communications signals of different types to be optimized. The frame format may enable digital communications signals of different types to be carried on a single optical channel and may provide an overhead for both types of signal. By performing the framing using the first clock signal the frame is synchronous with the first digital communications signal, and introduction of jitter onto the first digital communications signal may be avoided.

    [0127] In an embodiment, the carrier signal transmitter is a radio transmitter for generating a radio frequency carrier signal.

    [0128] In an embodiment, the carrier signal transmitter is an electrical signal transmitter for generating an electrical carrier signal.

    [0129] In an embodiment, the input is arranged to receive a plurality of digital communications signals of the first signal type. The framer is arranged to map said plurality of digital communications signals of the first signal type into the first portion of the payload. The communications network transmitter may enable use of a communications link used to transport digital communications signals of different types to be optimized. The communications network transmitter may enable use of the traffic capacity of a carrier signal to be optimized.

    [0130] In an embodiment, the input is arranged to receive a plurality of digital communications signals of the second signal type. The framer is arranged to map said plurality of digital communications signals of the second signal type into the second portion of the payload. The communications network transmitter may enable use of a communications link used to transport digital communications signals of different types to be optimized. The communications network transmitter may enable use of the traffic capacity of a carrier signal to be optimized.

    [0131] In an embodiment, at least some of the digital communications signals have different traffic bit rates. Each of the digital communications signals of the first signal type comprises the first clock signal and each of the digital communications signals of the second signal type comprises the second clock signal. The transmitter may enable use of a communications link used to transport digital communications signals of different types to be optimized. The communications network transmitter may enable use of the traffic capacity of a carrier signal to be optimized.

    [0132] In an embodiment, each digital communications signal of the first signal type has the same traffic bit rate and each second digital communications signal of the second signal type has the same traffic bit rate, different to the traffic bit rate of the digital communications signal of the first signal type. The communications network transmitter may enable use of a communications link used to transport digital communications signals of different types to be optimized. The communications network transmitter may enable use of the traffic capacity of a carrier signal to be optimized.

    [0133] In an embodiment, at least two communications signals of the first signal type are received, a first of said signals having a first traffic bit rate and a second of said signals having a second traffic bit rate, different to the first traffic bit rate. The communications network transmitter may enable use of a communications link used to transport digital communications signals of different types to be optimized. The communications network transmitter may enable use of the traffic capacity of a carrier signal to be optimized.

    [0134] In an embodiment, at least two communications signals of the second signal type are received, a first of said signals having a third traffic bit rate and a second of said signals having a fourth traffic bit rate, different to the third traffic bit rate. The communications network transmitter may enable use of a communications link used to transport digital communications signals of different types to be optimized. The communications network transmitter may enable use of the traffic capacity of a carrier signal to be optimized.

    [0135] In an embodiment, the frame comprises at least three timeslots. The first portion of the payload comprising at least a first timeslot. The second portion of the payload comprising at least a second timeslot. The overhead comprises a third timeslot. The frame may provide an overhead for both types of signal.

    [0136] In an embodiment, the frame comprises at least four timeslots. The payload also comprises a fourth timeslot for receiving at least one of control characters and bits of a said digital communications signal which cannot be mapped within a capacity of a respective one of the first portion and the second portion. Providing a timeslot for receiving control characters and/or bits which cannot be mapped into the capacity of the respective portion may optimize the amount of communications traffic which may be mapped into the frame and may provide flexibility in the choice of digital communications signals which may be mapped into the frame.

    [0137] In an embodiment, each said first digital communications signal has a first latency requirement and each said second digital communications signal has a second latency requirement, less stringent than the first latency requirement. The apparatus may enable digital communications signals having different latency requirements to be framed in a single frame for transmission on a single optical channel without degradation of the synchronization accuracy of the signal with the more stringent latency requirement. By enabling the transport of signals having different latency requirements using the same optical channel, the transmitter may optimize the use of fibre infrastructure where used to transport both types of signal. Compared to the OTN client agnostic multiplexing based on ODUflex, the transmitter does not introduce additional impairments on latency sensitive traffic. The advantages which the apparatus may provide with respect to CoE are the absence of buffers (i.e. delay) on the latency sensitive signals and the absence of lost traffic. By performing the framing using the first clock signal the frame is synchronous with the first digital communications signal, and introduction of jitter onto the more sensitive first digital communications signal may be avoided.

    [0138] In an embodiment, each said first digital communications signal is a continuous bit rate signal and each said second digital communications signal is a packet signal. The encapsulation apparatus may enable of continuous bit rate, CBR, signals and packet signals to be framed in a single frame for transmission on a single optical channel without degradation of the synchronization accuracy of the CBR signal. By enabling the transport of CBR signals and packet signals using the same optical channel, the transmitter may optimize the use of fibre infrastructure where used to transport both types of signal. Compared to the OTN client agnostic multiplexing based on ODUflex, the encapsulation apparatus does not introduce additional impairments on performance sensitive CBR traffic. The advantages which the encapsulation apparatus may provide with respect to CoE are the absence of buffers (i.e. delay) on the CBR signals and the absence of lost CBR traffic. By performing the framing using the first clock signal the frame is synchronous with the CBR signal, and introduction of jitter onto CBR signal may be avoided.

    [0139] In an embodiment, each said first digital communications signal is a common public radio interface, CPRI, signal as defined in the CPRI Specification and each said second digital communications signal is an Ethernet signal, as defined in IEEE 802.3.

    [0140] The communications network transmitter may enable framing of Ethernet, including Gigabit Ethernet, signals and CPRI signals together into a single frame, and transmission of the framed signals on a single optical channel without degradation of the synchronization accuracy of the CPRI signal. The communications network transmitter may provide a unified transport approach, mixing traffic originating from traditional radio base stations, BS, and remote radio units, RRU. By enabling the transport of Ethernet traffic and CPRI traffic in the same optical channel, the transmitter may optimize the use of the optical channel capacity and may thus optimise the use of fibre infrastructure for transporting fronthaul traffic (CPRI) and conventional backhaul traffic (GbE/lOGbE). This may provide an advantage with respect to CPRI over WDM and CPRI over OTN using BMP, since it may enable problems of fibre scarcity in this network segment to be overcome and it may reduce leased fibre costs. The CPRI Specification sets stringent constraints for latency, jitter and delay symmetry in downstream and upstream. By performing the framing using the CPRI clock signal the frame is synchronous with the CPRI signal, and introduction of jitter onto the CPRI signal may be avoided. Compared to the OTN client agnostic multiplexing based on ODUflex, the encapsulation apparatus does not introduce additional impairments on performance sensitive CPRI traffic while the impact on Ethernet packets, due to buffers, is expected to be tolerable, due to the inherent statistical nature of Ethernet packets. The advantages which the encapsulation apparatus may provide with respect to CoE are the absence of buffers (i.e. delay) on the CPRI signals and the absence of lost CPRI traffic, which can compromise the target 10-12bit error rate, BER. Moreover, the communications network transmitter may avoid the need for additional mechanisms to manage network synchronization.

    [0141] The communications network transmitter is operable with present optical rates, i.e. around 10 Gbps, and may be extended with increasing benefits to higher bit rates, i.e. 40 Gbps and 100 Gbps.

    [0142] In an embodiment, the framer is arranged to map each digital communications signal of the first signal type into the first portion of the frame using the following steps i. to v. Step i. comprises performing data recovery on each digital communications signal of the first signal type to obtain line coded digital communications traffic. Step ii. comprises decoding the input digital communications traffic to obtain information bits and non-information bits. Step iii. comprises removing the non-information bits. Step iv. comprises adding service channel bits for monitoring or maintenance, and step v. comprises mapping the service channel bits and information bits into the first portion of the frame. Each of steps ii. to v. is performed using the first clock signal.. The framer is arranged to map each digital communications signal of the second signal type into the second portion of the frame using the Generic Framing Procedure, GFP, according to ITU-T Recommendation G.7041. Removing the non-information bits from each digital communications signal of the first type makes capacity available to add the service channel bits, so a service channel for monitoring or maintenance may be added to the received digital communications signals. The method may enable a 'light optical transport layer' to be added to digital communications traffic client signals without one or more of the disadvantages of standard OTN framing.

    [0143] In an embodiment, the framer is arranged to map at least one of CPRI control characters and bits of a said Ethernet signal which cannot be mapped within a capacity of the second portion into the fourth timeslot. The frame structure may enable CPRI signal control characters and bits of an Ethernet signal which cannot be mapped into the capacity of the second portion to be mapped into the allocated timeslot. By enabling the transport of Ethernet traffic and CPRI traffic in the same optical channel, and providing an allocated timeslot for CPRI control characters and Ethernet bits beyond the capacity of the second portion, the transmitter may optimize the use of the optical channel capacity and may thus optimise the use of fibre infrastructure for transporting fronthaul traffic (CPRI) and conventional backhaul traffic (GbE/lOGbE).

    [0144] In an embodiment, the framer is arranged to provide a forward error correction code and service channel bits for each of the communications signals in the overhead. The same forward error correction code may be provided for both the communications signals of the first type and the communications signals of the second type, or a first forward error correction code may be provided for the communications signals of the first type and a second forward error correction code for the communications signals of the second type. The frame may therefore carry FEC and OAM for both types of signal.

    [0145] In an embodiment, the forward error correction code is a Reed-Solomon (255, 239) forward error correction code having a plurality of interleaved codecs proportional to a preselected latency value. The apparatus may therefore apply a forward error correction, FEC, scheme which complies with the ITU-T G.709 standard for OTN but which has a lower latency, acceptable for CPRI signals.

    [0146] In an embodiment, the framer is arranged to calculate respective bit-interleaved parity, BIP, bytes for the payload including both communications signals of the first type and the second type.

    [0147] In an embodiment, the buffer is arranged to operate using a local clock.

    [0148] In an embodiment, the communications network transmitter is arranged to receive a value of a delay applied at another location in a communications network comprising the optical link. The time for which each second communications signal is buffered for is adjusted in proportion to said delay.

    [0149] In an embodiment, the value of said delay is received in a precision timing protocol signal according to IEEE 1588.

    [0150] A sixth aspect of the invention provides a computer program comprising instructions which, when executed on at least one processor, cause the at least one processor to carry out any of the above steps of the method of encapsulating digital communications signals for transmission on a communications link.

    [0151] A seventh aspect of the invention provides a data carrier having computer readable instructions embodied therein. The said computer readable instructions are for providing access to resources available on a processor. The computer readable instructions comprise instructions to cause the processor to perform any of the above steps of the method of encapsulating digital communications signals for transmission on a communications link.

    [0152] In an embodiment, the data carrier is a non-transitory data carrier.

    [0153] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings.

    Brief Description of the drawings



    [0154] 

    Figure 1 illustrates part of a prior art communications network transporting mobile backhaul (Ethernet, 10GbE, over WDM) and fronthaul (CPRI over WDM) in different optical channels of the same WDM signal;

    Figure 2 shows the steps of a method according to a first embodiment of the invention of encapsulating digital communications signals for transmission on a communications link;

    Figure 3 shows the steps of a method according to a second embodiment of the invention of encapsulating digital communications signals for transmission on a communications link;

    Figure 4 shows the steps of a method according to a third embodiment of the invention of encapsulating digital communications signals for transmission on a communications link;

    Figure 5 shows the steps of a method according to an eighth embodiment of the invention of encapsulating digital communications signals for transmission on a communications link;

    Figure 6 illustrates Ethernet and CPRI signals framed according to the method according to a tenth embodiment of the invention being transported over a single optical channel of a WDM signal;

    Figure 7 illustrates a frame for use in a method according to twelfth embodiment of the invention;

    Figure 8 illustrates a frame for use in a method according to a thirteenth embodiment of the invention;

    Figure 9 is a schematic representation of encapsulation apparatus according to a fourteenth embodiment of the invention;

    Figure 10 is a schematic representation of encapsulation apparatus according to a twenty-first embodiment of the invention;

    Figure 11 is a schematic representation of a communications network transmitter according to a twenty-second embodiment of the invention;

    Figure 12 is a schematic representation of a communications network node according to a twenty-fourth embodiment of the invention;

    Figure 13 is a schematic representation of a communications network according to a twenty-fifth embodiment of the invention; and

    Figure 14 is a schematic representation of a communications network according to a twenty-sixth embodiment of the invention.


    Detailed description



    [0155] The same reference numbers will used for corresponding features in different embodiments.

    [0156] Figure 1 illustrates how a common fibre infrastructure 1 may be used to transport both backhaul traffic, for example Ethernet over WDM, and fronthaul traffic using CPRI over WDM, in different optical channels of the same WDM signal. A first group of optical channels 2 is used to connect a set of RBSs to the backhaul segment (High Radio Access Network, HRAN, or Metro) by transporting 10GbE clients, one per optical channel. A second group of optical channels 3 is used to connect RRUs to DUs by transporting CPRI flows at 9.8304 Gbps, equal to CPRI option 7 bit rate, using the method described in PCT/EP2014/052056. The output of the DUs can then be transmitted over Ethernet to the remaining part of the backhaul area.

    [0157] Referring to Figure 2, a first embodiment of the invention provides a method 10 of encapsulating digital communications signals for transmission on a communications link.

    [0158] The method comprises steps a. to d., as follows. Step a. comprises receiving a first digital communications signal of a first signal type and receiving a second digital communications signal of a second signal type, different to the first signal type 12. The first digital communications signal comprises a first clock signal and the second digital communications signal comprises a second clock signal, different to the first clock signal. Each clock signal has a respective clock value and accuracy. As will be well known to the skilled person, clock values are usually defined in Hz, or some multiple Hz units, and clock accuracy is usually defined in parts per million, ppm.

    [0159] Step b. comprises obtaining the first clock signal 14. Step c. comprises obtaining a difference between the clock value of the first clock signal and the clock value of the second clock signal, and/or between the accuracy of the first clock signal and accuracy of the second clock signal 16. Step c. also comprises buffering the second digital communications signal for a time at least long enough to compensate for the difference. So after buffering, the second digital communications signal is synchronous with the first digital communications signal.

    [0160] Step d. comprises assembling the first digital communications signal and the buffered second digital communications signal into a frame for transmission 20. The frame comprises an overhead and a payload, comprising a first portion and a second portion. The first digital communications signal is mapped into the first portion and the second digital communications signal is mapped into the second portion. Step d. is performed using the first clock signal, so the entire frame is synchronous with the first digital communications signal, and no jitter is introduced onto the first digital communications signal.

    [0161] In a method 30 according to a second embodiment, shown in Figure 3, step a. comprises receiving a plurality of digital communications signals of a first type 32. In step d. the plurality of digital communications signals of the first type are mapped into the first portion of the frame 32.

    [0162] In a method 40 according to a third embodiment, shown in Figure 4, step a. comprises receiving a plurality of digital communications signals of a first type and receiving a plurality of digital communications signals of a second type 42. In step c. the plurality of digital communications signals of the second type are buffered 44. In step d. the plurality of digital communications signals of the first type are mapped into the first portion of the frame and the plurality of digital communications signals of the second type are mapped into the second portion of the frame 46.

    [0163] In a fourth embodiment, described with reference to Figure 3, the digital communications signals of the first type have a first traffic bit rate and the second digital communications signal has a second traffic bit rate, different to the first traffic bit rate. The digital communications signals of the first type may each have a different traffic bit rate, which may be different to the second traffic bit rate.

    [0164] In a fifth embodiment, described with reference to Figure 4, the digital communications signals of the first type have a first traffic bit rate and the digital communications signals of the second type have a second traffic bit rate, different to the first traffic bit rate. The digital communications signals of the first type may each have a different traffic bit rate, which may be different to the second traffic bit rate.

    [0165] In a sixth embodiment, described with reference to Figure 2, the first digital communications signal has a first latency requirement and the second digital communications signal has a second latency requirement, less stringent than the first latency requirement.

    [0166] In a seventh embodiment, described with reference to Figure 2, in step d. the first digital communications signal is mapped into the first portion of the frame using the following steps i. to v.:
    1. i. performing data recovery on each digital communications signal of the first signal type to obtain line coded digital communications traffic;
    2. ii. decoding the input digital communications traffic to obtain information bits and non-information bits;
    3. iii. removing the non-information bits;
    4. iv. adding service channel bits for monitoring or maintenance; and
    5. v. mapping the service channel bits and information bits into the first portion of the frame.


    [0167] Each of steps ii. to v. is performed using the first clock signal.

    [0168] The first clock signal may be obtained by performing clock recovery in step i. or it may obtained from a digital unit which transmitted the digital communications signal of the first signal type. The second digital communications signal is mapped into the second portion of the frame using the Generic Framing Procedure, GFP, according to ITU-T Recommendation G.7041.

    [0169] An eighth embodiment of the invention provides a method 50 of encapsulating digital communications signals for transmission on a communications link having the steps shown in Figure 5.

    [0170] The method comprises steps a. to d., as follows. Step a. comprises receiving a CBR signal and receiving a packet signal 52. The CBR signal comprises a first clock signal and the packet signal comprises a second clock signal, different to the first clock signal. Each clock signal has a respective clock value and accuracy.

    [0171] Step b. comprises obtaining the first clock signal 54. Step c. comprises obtaining a difference between at least one of the clock values of the first and second clock signals and the accuracies of the first and second clock signals 16. Step c. also comprises buffering the packet signal for a time at least long enough to compensate for the difference. So after buffering, the packet signal is synchronous with the CBR signal.

    [0172] Step d. comprises assembling the CBR signal and the buffered packet signal into a frame for transmission 20. The frame comprises an overhead and a payload, comprising a first portion and a second portion. The CBR signal is mapped into the first portion and the packet signal is mapped into the second portion. Step d. is performed using the CBR clock signal, so the entire frame is synchronous with the CBR signal, and no jitter is introduced onto the CBR signal.

    [0173] Referring to Figure 6, a ninth embodiment of the invention provides a method of encapsulating digital communications signals for transmission on communications link in the form of an optical link. The method comprises steps a. to d., as follows.

    [0174] Step a. comprises receiving a CPRI signal and receiving a Gigabit Ethernet, GbE, signal 52. The CPRI signal comprises a CPRI clock signal and the Ethernet signal comprises an Ethernet clock signal, different to the CPRI clock signal. Each clock signal has a respective clock value and accuracy.

    [0175] Step b. comprises obtaining the CPRI clock signal 54. This may be done by recovering the CPRI clock signal from the CPRI signal or by obtaining the CPRI clock signal from a digital unit, DU, which transmitted the CPRI signal. The Ethernet clock signal is recovered from the Ethernet signal.

    [0176] Step c. comprises obtaining a difference between the clock value of the CPRI clock signal and the Ethernet clock signal 16. Step c. also comprises buffering the Ethernet packets for a time at least long enough to compensate for the difference. So after buffering, the Ethernet signal is synchronous with the CPRI signal.

    [0177] Step d. comprises assembling the CPRI signal and buffered Ethernet packets into a frame for transmission 20. The frame comprises an overhead and a payload, comprising a first portion and a second portion. The CPRI signal is mapped into the first portion and the Ethernet packets are mapped into the second portion. Step d. is performed using the CPRI clock signal, so the entire frame is synchronous with the CPRI signal, and no jitter is introduced onto the CPRI signal.

    [0178] The CPRI signal is mapped into the first portion of the frame using the following steps i. to v.:
    1. i. performing data recovery on the CPRI signal to obtain line coded digital communications traffic;
    2. ii. decoding the input digital communications traffic to obtain information bits and non-information bits;
    3. iii. removing the non-information bits;
    4. iv. adding service channel bits for monitoring or maintenance; and
    5. v. mapping the service channel bits and information bits into the first portion of the frame.


    [0179] Each of steps ii. to v. is performed using the CPRI clock signal obtained in step b. The CPRI clock signal may alternatively be obtained by additionally performing clock recovery in step i.

    [0180] The buffered Ethernet packets are mapped into the frame using the Generic Framing Procedure, GFP, defined in ITU-T Recommendation G.7041.

    [0181] Figure 6 illustrates a hybrid transport link 72 comprising an optical channel, λ3, 82 carrying both CPRI and GbE digital communications signals, encapsulated using the method of a tenth embodiment of the invention. A first set of optical channels, λ1 and λ2, is used to transport 10GbE traffic originated by radio base stations, RBS 76. A second set of optical channels, λ4 to λN is used to transport 10G CPRI traffic between remote radio units, RRU, 80 and digital units, DU, 84.

    [0182] The third optical channel, λ3, is used to transport a mix of GbE and 2.5G CPRI traffic, encapsulated as described above with reference to Figures 3 and 4.

    [0183] The CPRI signals bit rate and the digital communications signals of the second type have a second traffic bit rate, different to the first traffic bit rate. The digital communications signals of the first type may each have a different traffic bit rate, which may be different to the second traffic bit rate.

    [0184] Various combinations of bit rates for the CPRI and GbE signals can be used, depending on the optical bit rate of the optical channel. For example: two GbE signals, one 2.4576 Gbit/s CPRI signal and one 4.9152 Gbit/s CPRI signal can be mapped into a frame for transmission on a 10 Gbit/s optical channel; one 10 GbE and three 9.8304 Gbit/s CPRI signals can be mapped into a frame for transmission on a 40 Gbit/s optical channels; or four 10 GbE and six 9.8304 Gbit/s CPRI signals can be mapped into a frame for transmission on a 100Gbit/s optical channel. It will be appreciated that many other combinations are possible.

    [0185] In a method according to an eleventh embodiment of the invention of encapsulating digital communications signals for transmission on a communications link, the frame comprises at least three timeslots. The first portion of the payload comprises at least a first timeslot and the second portion of the payload comprises at least a second timeslot. The frame overhead comprises a third timeslot.

    [0186] Referring to Figure 7, in a twelfth embodiment of the invention the frame comprises a plurality, N, of timeslots, t1-tN. The first portion 92 of the payload comprises a plurality of timeslots, t1 to tn. The second portion 94 of the payload comprises a plurality of timeslots, tn+1 to tN-2. The payload also comprises a timeslot, tN-1, 96 for receiving control characters and/or bits of a digital communications signal which cannot be mapped within a capacity of a respective one of the first portion and the second portion. The overhead 98 comprises a further timeslot, tN.

    [0187] The method comprises allocating timeslots to the first portion 92 and to the second portion 94 in proportion to a respective weight of traffic of the communications signals of each of the first and second signal types.

    [0188] Figure 8 illustrates a frame 100 for use in a method according to a thirteenth embodiment of the invention of encapsulating digital communications signals for transmission on a communications link, in the form of an optical link.

    [0189] In this embodiment, two GbE signals, one 2.4576 Gbit/s CPRI signal and one 4.9152 Gbit/s CPRI signal are mapped into the frame 100 for transmission on a 9.8304 Gbit/s optical channel.

    [0190] The frame has ten timeslots, t0 to t9, which may also be referred to as "channels" 0 to 6, X and Y. Each of the timeslots can accommodate 1/10th of the 9.8403 Gb capacity of the optical channel, i.e. 0.98403 Gb. Timeslots t0 to t5 are allocated to the first portion of the payload, timeslots t6 and t7 are allocated to the second portion of the payload, timeslot t8 is also allocated to the payload and timeslot t9 is allocated to the overhead. The number timeslots which are allocated to CPRI signals and to Ethernet signals depends on the relative weight of traffic of each type expected to be transmitted on the optical link. Network configuration of the network that the optical link is part of may also be taken into consideration. It will be appreciated that how the timeslots allocated to each signal type, the control character and additional bits, and the overhead may be provided in a different arrangement to that shown in Figure 8.

    [0191] In step d., the 2.4576 Gbit/s CPRI signal is mapped into timeslots t0 and t1, and the 4.9152 Gbit/s CPRI signal is mapped into timeslots t2 to t5. The control characters, also known as 'K codes', of the CPRI signals are mapped into timeslot t8. A first of the GbE signals is mapped into timeslot t6 and bit 6 of timeslot t8, and the second GbE signal is mapped into timeslot t7 and bit 7 of timeslot t8. Since each timeslot has a capacity of 0.98403 Gb, there are some bits of each of the GbE signals which cannot be mapped into the capacity of the allocated timeslot. These additional bits are mapped into timeslot t8. The overhead for all of the signals, namely frame alignment word, FEC coding and operation and maintenance channel traffic, are mapped into timeslot t9.

    [0192] Referring to Figure 9, a fourteenth embodiment of the invention provides encapsulation apparatus 200 for a communications network transmitter. The encapsulation apparatus comprises an input 204 arranged to receive a first digital communications signal of a first signal type and an input 202 arranged to receive a second digital communications signal of a second signal type, different to the first signal type. The first digital communications signal has a first clock signal and the second digital communications signal has a second clock signal, which is different to the first clock signal. Each clock signal has a respective clock value and accuracy.

    [0193] The encapsulation apparatus also comprises a buffer 206 and a framer 208. The buffer is arranged to buffer the second digital communications signal for a time at least long enough to compensate for a difference between the clock value of the first clock signal and the clock value of the second clock signal and/or the accuracy of the first clock signal and the accuracy of the second clock signal. The framer is arranged to receive the first digital communications signal and to receive the buffered second digital communications signal from the buffer. The framer is arranged to frame the first digital communications signal and the buffered second digital communications signal into a frame for transmission. The frame comprises an overhead and a payload, comprising a first portion and a second portion. The framer is arranged to map first digital communications signal into the first portion and to map the second digital communications signal into the second portion. The encapsulation apparatus is arranged to obtain the first clock signal and the framer is arranged to operate using the first clock signal, so the entire frame is synchronous with the first digital communications signal, and no jitter is introduced onto the first digital communications signal.

    [0194] A fifteenth embodiment of the invention provides encapsulation apparatus for a communications network transmitter which has the same general structure as the encapsulation apparatus 200 of the previous embodiment. In this embodiment, the input 204 is arranged to receive a plurality of digital communications signals of the first signal type. The framer 208 is arranged to map the digital communications signals of the first signal type into the first portion of the payload.

    [0195] A sixteenth embodiment of the invention provides encapsulation apparatus for a communications network transmitter which has the same general structure as the encapsulation apparatus 200 of the previous embodiment. In this embodiment, the input 204 is arranged to receive a plurality of digital communications signals of the first signal type and the input 202 is arranged to receive a plurality of digital communications signals of the second signal type. The framer 208 is arranged to map the digital communications signals of the first signal type into the first portion of the payload and to map the digital communications signals of the second signal type into the second portion of the payload.

    [0196] A seventeenth embodiment of the invention provides encapsulation apparatus for a communications network transmitter which has the same general structure as the encapsulation apparatus 200 of the previous embodiment. In this embodiment, the digital communications signals of the first type have a first traffic bit rate and the second digital communications signal has a second traffic bit rate, different to the first traffic bit rate. The digital communications signals of the first type may each have a different traffic bit rate, which may be different to the second traffic bit rate. The framer 208 is arranged to map the digital communications signals of the first signal type into the first portion of the payload and to map the digital communications signals of the second signal type into the second portion of the payload.

    [0197] An eighteenth embodiment of the invention provides encapsulation apparatus for a communications network transmitter which has the same general structure as the encapsulation apparatus 200 of the previous embodiment. In this embodiment, the first digital communications signal has a first latency requirement and the second digital communications signal has a second latency requirement, less stringent than the first latency requirement. The buffer 206 is arranged to buffer the second digital communications signal for a time at least long enough to compensate for a difference between at least one of the clock values of the first and second clock signals and the accuracies of the first and second clock signals. The buffering time is less than a maximum acceptable latency of the second digital communications signal.

    [0198] A nineteenth embodiment of the invention provides encapsulation apparatus for a communications network transmitter which has the same general structure as the encapsulation apparatus 200 of the previous embodiment. In this embodiment, the framer 208 is arranged to map the first digital communications signal into the first portion of the frame by:

    performing data recovery on each digital communications signal of the first signal type to obtain line coded digital communications traffic;

    decoding the input digital communications traffic to obtain information bits and non-information bits;

    removing the non-information bits;

    adding service channel bits for monitoring or maintenance; and

    mapping the service channel bits and information bits into the first portion of the frame.



    [0199] The framer is arranged to perform the above steps using the first clock signal.

    [0200] The first clock signal may be obtained by performing clock recovery in step i. or it may obtained from a digital unit which transmitted the digital communications signal of the first signal type.

    [0201] The framer 208 is arranged to map the second digital communications signal into the second portion of the frame using the Generic Framing Procedure, GFP.

    [0202] A twentieth embodiment of the invention provides encapsulation apparatus for a communications network transmitter which has the same general structure as the encapsulation apparatus 200 of the previous embodiment. In this embodiment, each said first digital communications signal is a CBR signal and each second digital communications signal is a packet signal. The framer 208 is arranged to map the CBR signal into the first portion of the payload and to map the packet signal into the second portion of the payload.

    [0203] Figure 10 shows encapsulation apparatus 220 according to a twenty-first embodiment of the invention. The encapsulation apparatus comprises a first input 224 arranged to receive a CPRI signal 234 and a second input 222 arranged to receive an Ethernet signal 232. The CPRI signal has a first clock signal and the Ethernet signal has a second clock signal, which is different to the first clock signal. Each clock signal has a respective clock value and accuracy.

    [0204] The encapsulation apparatus also comprises a buffer 226 and a framer 228. The buffer is arranged to buffer the Ethernet signal for a time at least long enough to compensate for a difference between at least one of the clock values of the first and second clock signals and the accuracies of the first and second clock signals. The framer 228 is arranged to receive the CPRI signal and to receive the buffered Ethernet signal from the buffer. The framer is arranged to frame the CPRI signal and the buffered Ethernet signal into a frame for transmission. The frame comprises an overhead and a payload, comprising a first portion and a second portion. The framer is arranged to map the CPRI signal into the first portion by:

    performing data recovery on each digital communications signal of the first signal type to obtain line coded digital communications traffic;

    decoding the input digital communications traffic to obtain information bits and non-information bits;

    removing the non-information bits;

    adding service channel bits for monitoring or maintenance; and

    mapping the service channel bits and information bits into the first portion of the frame.



    [0205] The framer is arranged to map the Ethernet signal into the second portion using the Generic Framing Procedure, GFP.

    [0206] The encapsulation apparatus is arranged to obtain the first clock signal and the framer is arranged to operate using the first clock signal, so the entire frame is synchronous with the CPRI signal, and no jitter is introduced onto the CPRI signal.

    [0207] A twenty-second embodiment of the invention provides communications network transmitter 300 as shown in Figure 11. The communications network transmitter 300 comprises encapsulation apparatus 200 and a carrier signal transmitter 302.

    [0208] The encapsulation apparatus 200 is as shown in Figure 9 and described above according to any of the thirteenth to twentieth embodiments. It will be appreciated that the encapsulation apparatus 220 described with reference to Figure 10 may alternatively be used. The carrier signal transmitter 302 is arranged to generate and transmit carrier signal 304 carrying the frame generated by the encapsulation apparatus 200.

    [0209] In a twenty-third embodiment of the invention the carrier signal transmitter 302 is an optical transmitter arranged to generate and transmit an optical signal 304 carrying the frame generated by the encapsulation apparatus 200.

    [0210] It will be appreciated that the carrier signal transmitter may alternatively be a radio transmitter arranged to generate and transmit a radio frequency signal carrying the frame or an electrical transmitter arranged to generate and transmit an electrical signal carrying the frame.

    [0211] A twenty-fourth embodiment of the invention provides a communications network node 400, as shown in Figure 12, comprising a communications network transmitter 300 as described in the previous embodiment.

    [0212] A twenty-fifth embodiment of the invention provides a communications network 500 as shown in Figure 13. The communications network 500 comprises a radio base station, RBS, 510, a remote radio unit, RRU, 512, a communications network node 400 as described in the previous embodiment, an optical link 514, an optical receiver 516, a GbE link 518 for connection to a Metro or HRAN network, and a digital unit, DU, 520.

    [0213] The carrier signal transmitter 302 in this embodiment is a grey optics transmitter and the optical receiver 516 is a grey optics receiver. The optical link 514 is a single optical fibre, therefore the RBS and RRU are connected to the optical receiver 516 on a point-to-point connection using low cost grey optics.

    [0214] A twenty-sixth embodiment of the invention provides a wavelength division multiplexing, WDM, communications network 520 as shown in Figure 14. The communications network 520 comprises radio base stations, RBS, 510, 526, remote radio units, RRU, 512, 528, a communications network node 400 as shown in Figure 12, optical transmitters 530, 532, optical add-drop multiplexers 522, 524, a WDM transport network 540, optical receivers 516, 534, 536 a GbE links 542 for connection to a Metro or HRAN network, and a digital unit pool, DU, 538.

    [0215] Radio equipment, RBSs and RRUs are connected to a WDM multiplexer 522 via dedicated drop fibres 544, with one wavelength/optical channel per fibre. RBS 510 and RRU 512 share the same wavelength in the same drop fibre 546 without requiring additional fibres or modifications of the network topology. Communication is bidirectional so the location of eastbound transmitter is also the location for the westbound receiver and vice versa.

    [0216] For sake of simplicity Figure 14 shows a single WDM distribution node but it will be appreciated that the communications network node 400 may also be used in ring or meshed WDM networks.

    [0217] A twenty-seventh embodiment of the invention provides a computer program comprising instructions which, when executed on at least one processor, cause the at least one processor to carry out any steps of the method 10, 30, 40, 50 of encapsulating digital communications signals for transmission on a communications link, as described above.

    [0218] A twenty-eighth embodiment of the invention provides a data carrier having computer readable instructions embodied therein. The computer readable instructions are for providing access to resources available on a processor. The computer readable instructions comprise instructions to cause the processor to perform any of the steps of the method 10, 30, 40, 50 of encapsulating digital communications signals for transmission on a communications link, as described above.

    [0219] In an embodiment, the data carrier is a non-transitory data carrier.


    Claims

    1. A method of encapsulating digital communications signals for transmission on a communications link, the method comprising steps of:

    a. receiving (12) a first digital communications signal of a first signal type, the first digital communications signal comprising a first clock signal and receiving a second digital communications signal of a second signal type, different to the first signal type, the second digital communications signal comprising a second clock signal different to the first clock signal, each clock signal having a respective clock value and accuracy;

    b. obtaining (14) the first clock signal;

    c. obtaining a difference (16) between at least one of the clock values of the first and second clock signals and the accuracies of the first and second clock signals, and buffering (18) the second digital communications signal for a time at least long enough to compensate for the difference, wherein after buffering (18) the second digital communications signal, the second digital communications signal is synchronous with the first digital communications signal; and

    d. assembling (20) the first digital communications signal and the buffered second digital communications signal into a frame (90, 100) for transmission, the frame (90, 100) comprising an overhead and a payload, the payload comprising a first portion and a second portion, the first digital communications signal being mapped into the first portion and the second digital communications signal being mapped into the second portion,

    wherein step d. is performed using the first clock signal.
     
    2. The method as claimed in claim 1, wherein a plurality of digital communications signals of the first signal type are received and are mapped into the first portion of the payload.
     
    3. The method as claimed in claim 1 or claim 2, wherein a plurality of digital communications signals of the second signal type are received and are mapped into the second portion of the payload.
     
    4. The method as claimed in claim 2 or claim 3, wherein at least some of the digital communications signals have different traffic bit rates.
     
    5. The method as claimed in any preceding claim, wherein the frame (90, 100) comprises at least four timeslots, the first portion of the payload comprising at least a first timeslot, the second portion of the payload comprising at least a second timeslot, the payload also comprising a third timeslot for receiving at least one of control characters and bits of a digital communications signal which cannot be mapped within a capacity of a respective one of the first portion and the second portion, and the overhead comprising a fourth timeslot.
     
    6. The method as claimed in claim 5, further comprising allocating timeslots (t0 ― tN) to the first portion and the second portion of the payload in proportion to a respective weight of traffic of the digital communications signals of each of said signal types.
     
    7. The method as claimed in any preceding claim, wherein each said first digital communications signal is a continuous bit rate signal and each said second digital communications signal is a packet signal.
     
    8. An encapsulation apparatus (200) for a communications network transmitter (300), the encapsulation apparatus (200) comprising:

    at least one input (202, 204) arranged to receive a first digital communications signal of a first signal type, the first digital communications signal comprising a first clock signal and a second digital communications signal of a second signal type, different to the first signal type, the second digital communications signal comprising a second clock signal different to the first clock signal, each clock signal having a respective clock value and accuracy;

    a buffer (206) arranged to buffer the second digital communications signal for a time at least long enough to compensate for a difference between at least one of the clock values of the first and second clock signals and the accuracies of the first and second clock signals, wherein after buffering the second digital communications signal, the second digital communications signal is synchronous with the first digital communications signal; and

    a framer arranged (208) to receive the first digital communications signal and to receive the buffered second digital communications signal from the buffer (206) and

    arranged to frame the first digital communications signal and the buffered second digital communications signal into a frame for transmission, the frame comprising an overhead and a payload, the payload comprising a first portion and a second portion,

    and the framer (208) being arranged to map the first digital communications signal into the first portion and being arranged to map the buffered second digital communications signal into the second portion,

    wherein the encapsulation apparatus (200) is arranged to obtain the first clock signal and the framer (208) is arranged to operate using the first clock signal.


     
    9. The encapsulation apparatus (200) as claimed in claim 8, wherein the at least one input (202, 204) is arranged to receive a plurality of digital communications signals of the first signal type and the framer (208) is arranged to map said plurality of digital communications signals of the first signal type into the first portion of the payload.
     
    10. The encapsulation apparatus (200) as claimed in claim 8 or claim 9, wherein the at least one input (202, 204) is arranged to receive a plurality of digital communications signals of the second signal type and the framer (208) is arranged to map said plurality of digital communications signals of the second signal type into the second portion of the payload.
     
    11. The encapsulation apparatus (200) as claimed in any of claims 8 to 10, wherein at least some of the digital communications signals have different traffic bit rates.
     
    12. The encapsulation apparatus (200) as claimed in any of claims 8 to 11, wherein the frame comprises at least four timeslots, the first portion of the payload comprising at least a first timeslot, the second portion of the payload comprising at least a second timeslot, the payload also comprising at least a third timeslot for receiving at least one of control characters and bits of a digital communications signal which cannot be mapped within a capacity of a respective one of the first portion and the second portion, and the overhead comprising a fourth timeslot.
     
    13. The encapsulation apparatus (200) as claimed in any of claims 8 to 12, wherein each said first digital communications signal has a first latency requirement and each said second digital communications signal has a second latency requirement, less stringent than the first latency requirement.
     
    14. A communications network transmitter (300) comprising:

    an encapsulation apparatus (200) as claimed in any of claims 8 to 13; and

    a carrier signal transmitter (302) arranged to generate and transmit a carrier signal carrying the frame for transmission.


     
    15. A computer program comprising instructions which, when executed on at least one processor, cause the at least one processor to carry out the method according to any one of claims 1 to 7.
     


    Ansprüche

    1. Verfahren zur Verkapselung digitaler Kommunikationssignale zur Übertragung auf einer Kommunikationsverbindung, wobei das Verfahren die folgenden Schritte umfasst:

    a. Empfangen (12) eines ersten digitalen Kommunikationssignals eines ersten Signaltyps, wobei das erste digitale Kommunikationssignal ein erstes Taktsignal umfasst, und Empfangen eines zweiten digitalen Kommunikationssignals eines zweiten Signaltyps, der sich von dem ersten Signaltyp unterscheidet, wobei das zweite digitale Kommunikationssignal ein zweites Taktsignal umfasst, das sich von dem ersten Taktsignal unterscheidet, wobei jedes Taktsignal einen entsprechenden Taktwert und eine entsprechende Genauigkeit aufweist;

    b. Gewinnen (14) des ersten Taktsignals;

    c. Erhalten einer Differenz (16) zwischen mindestens einem der Taktwerte des ersten und zweiten Taktsignals und den Genauigkeiten des ersten und zweiten Taktsignals, und Puffern (18) des zweiten digitalen Kommunikationssignals für eine Zeit, die mindestens lang genug ist, um die Differenz auszugleichen, wobei nach dem Puffern (18) des zweiten digitalen Kommunikationssignals das zweite digitale Kommunikationssignal synchron mit dem ersten digitalen Kommunikationssignal ist; und

    d. Zusammenfügen (20) des ersten digitalen Kommunikationssignals und des gepufferten zweiten digitalen Kommunikationssignals zu einem Rahmen (90, 100) für die Übertragung, wobei der Rahmen (90, 100) einen Overhead und eine Nutzlast umfasst, wobei die Nutzlast einen ersten Teil und einen zweiten Teil umfasst, wobei das erste digitale Kommunikationssignal in den ersten Teil abgebildet wird und das zweite digitale Kommunikationssignal in den zweiten Teil abgebildet wird,

    wobei Schritt d. unter Verwendung des ersten Taktsignals durchgeführt wird.
     
    2. Verfahren nach Anspruch 1, wobei eine Vielzahl von digitalen Kommunikationssignalen des ersten Signaltyps empfangen und in den ersten Teil der Nutzlast abgebildet werden.
     
    3. Verfahren nach Anspruch 1 oder Anspruch 2, wobei eine Vielzahl von digitalen Kommunikationssignalen des zweiten Signaltyps empfangen und in den zweiten Teil der Nutzlast abgebildet werden.
     
    4. Verfahren nach Anspruch 2 oder Anspruch 3, wobei mindestens einige der digitalen Kommunikationssignale unterschiedliche Datenverkehrsbitraten aufweisen.
     
    5. Verfahren nach einem der vorhergehenden Ansprüche, wobei der Rahmen (90, 100) mindestens vier Zeitschlitze umfasst, wobei der erste Teil der Nutzlast mindestens einen ersten Zeitschlitz umfasst, der zweite Teil der Nutzlast mindestens einen zweiten Zeitschlitz umfasst, die Nutzlast auch einen dritten Zeitschlitz zum Empfangen von mindestens einem von Steuerzeichen und Bits eines digitalen Kommunikationssignals, das nicht innerhalb einer Kapazität eines jeweiligen des ersten Teils und des zweiten Teils abgebildet werden kann, umfasst und der Overhead einen vierten Zeitschlitz umfasst.
     
    6. Verfahren nach Anspruch 5, das ferner das Zuweisen von Zeitschlitzen (t0 - tN) zu dem ersten Teil und dem zweiten Teil der Nutzlast im Verhältnis zu einem jeweiligen Gewicht des Datenverkehrs der digitalen Kommunikationssignale jedes der Signaltypen umfasst.
     
    7. Verfahren nach einem der vorhergehenden Ansprüche, wobei jedes erste digitale Kommunikationssignal ein Signal mit kontinuierlicher Bitrate ist und jedes zweite digitale Kommunikationssignal ein Paketsignal ist.
     
    8. Verkapselungsvorrichtung (200) für einen Kommunikationsnetzwerksender (300), wobei die Verkapselungsvorrichtung (200) Folgendes umfasst:

    mindestens einen Eingang (202, 204), der zum Empfang eines ersten digitalen Kommunikationssignals eines ersten Signaltyps eingerichtet ist, wobei das erste digitale Kommunikationssignal ein erstes Taktsignal und ein zweites digitales Kommunikationssignal eines zweiten Signaltyps, der sich von dem ersten Signaltyp unterscheidet, umfasst, wobei das zweite digitale Kommunikationssignal ein zweites Taktsignal umfasst, das sich von dem ersten Taktsignal unterscheidet, wobei jedes Taktsignal einen entsprechenden Taktwert und eine entsprechende Genauigkeit aufweist;

    einen Puffer (206), der dafür ausgelegt ist, das zweite digitale Kommunikationssignal für eine Zeit zu puffern, die mindestens lang genug ist, eine Differenz zwischen mindestens einem der Taktwerte des ersten und zweiten Taktsignals und den Genauigkeiten des ersten und zweiten Taktsignals auszugleichen, wobei nach dem Puffern des zweiten digitalen Kommunikationssignals das zweite digitale Kommunikationssignal synchron mit dem ersten digitalen Kommunikationssignal ist; und

    einen Framer (208), der dafür ausgelegt ist, das erste digitale Kommunikationssignal zu empfangen und das gepufferte zweite digitale Kommunikationssignal aus dem Puffer (206) zu empfangen und der dafür ausgelegt ist, das erste digitale Kommunikationssignal und das gepufferte zweite digitale Kommunikationssignal in einen Rahmen für die Übertragung einzurahmen, wobei der Rahmen einen Overhead und eine Nutzlast umfasst, wobei die Nutzlast einen ersten Teil und einen zweiten Teil umfasst, und der Framer (208) dafür ausgelegt ist, das erste digitale Kommunikationssignal in den ersten Teil abzubilden und dafür ausgelegt ist, das gepufferte zweite digitale Kommunikationssignal in den zweiten Teil abzubilden,

    wobei die Verkapselungsvorrichtung (200) dafür ausgelegt ist, das erste Taktsignal zu erhalten, und der Framer (208) dafür ausgelegt ist, unter Verwendung des ersten Taktsignals zu arbeiten.


     
    9. Verkapselungsvorrichtung (200) nach Anspruch 8, wobei der mindestens eine Eingang (202, 204) dafür ausgelegt ist, eine Vielzahl von digitalen Kommunikationssignalen des ersten Signaltyps zu empfangen, und der Framer (208) dafür ausgelegt ist, die mehreren digitalen Kommunikationssignale des ersten Signaltyps auf den ersten Teil der Nutzlast abzubilden.
     
    10. Verkapselungsvorrichtung (200) nach Anspruch 8 oder Anspruch 9, wobei der mindestens eine Eingang (202, 204) dafür ausgelegt ist, eine Vielzahl von digitalen Kommunikationssignalen des zweiten Signaltyps zu empfangen, und der Framer (208) dafür ausgelegt ist, die mehreren digitalen Kommunikationssignale des zweiten Signaltyps auf den zweiten Teil der Nutzlast abzubilden.
     
    11. Verkapselungsvorrichtung (200) nach einem der Ansprüche 8 bis 10, wobei mindestens einige der digitalen Kommunikationssignale unterschiedliche Datenverkehrsbitraten aufweisen.
     
    12. Verkapselungsvorrichtung (200) nach einem der Ansprüche 8 bis 11, wobei der Rahmen mindestens vier Zeitschlitze umfasst, wobei der erste Teil der Nutzlast mindestens einen ersten Zeitschlitz umfasst, der zweite Teil der Nutzlast mindestens einen zweiten Zeitschlitz umfasst, die Nutzlast auch mindestens einen dritten Zeitschlitz zum Empfangen von mindestens einem von Steuerzeichen und Bits eines digitalen Kommunikationssignals, das nicht innerhalb einer Kapazität eines jeweiligen des ersten Teils und des zweiten Teils abgebildet werden kann, umfasst und der Overhead einen vierten Zeitschlitz umfasst.
     
    13. Verkapselungsvorrichtung (200) nach einem der Ansprüche 8 bis 12, wobei jedes erste digitale Kommunikationssignal eine erste Latenzanforderung aufweist und jedes zweite digitale Kommunikationssignal eine zweite Latenzanforderung aufweist, die weniger streng ist als die erste Latenzanforderung.
     
    14. Kommunikationsnetzwerk-Sender (300), der Folgendes umfasst:
    eine Verkapselungsvorrichtung (200) nach einem der Ansprüche 8 bis 13; und einen Trägersignalsender (302), der dafür ausgelegt ist, ein Trägersignal zu erzeugen und zu sendeen, das den zu übertragenden Rahmen trägt.
     
    15. Computerprogramm mit Anweisungen, die, wenn sie auf mindestens einem Prozessor ausgeführt werden, den mindestens einen Prozessor veranlassen, das Verfahren nach einem der Ansprüche 1 bis 7 auszuführen.
     


    Revendications

    1. Procédé d'encapsulation de signaux de communications numériques pour une transmission sur une liaison de communications, le procédé comprenant les étapes consistant à :

    a. recevoir (12) un premier signal de communications numérique d'un premier type de signal, le premier signal de communications numérique comprenant un premier signal d'horloge et la réception d'un deuxième signal de communications numérique d'un deuxième type de signal, différent du premier type de signal, le deuxième signal de communications numérique comprenant un deuxième signal d'horloge différent du premier signal d'horloge, chaque signal d'horloge ayant une valeur d'horloge et une précision respectives ;

    b. obtenir (14) le premier signal d'horloge ;

    c. obtenir une différence (16) entre au moins l'une des valeurs d'horloge des premier et deuxième signaux d'horloge et des précisions des premier et deuxième signaux d'horloge, et mettre en mémoire tampon (18) le deuxième signal de communications numérique pendant une durée assez longue pour compenser la différence, dans lequel après la mise en mémoire tampon (18) du deuxième signal de communications numérique, le deuxième signal de communications numérique est synchrone avec le premier signal de communications numérique ; et

    d. assembler (20) le premier signal de communications numérique et le deuxième signal de communications numérique mis en mémoire tampon dans une trame (90, 100) pour une transmission, la trame (90, 100) comprenant un en-tête et une charge utile, la charge utile comprenant une première portion et une deuxième portion, le premier signal de communications numérique étant mappé dans la première portion et le deuxième signal de communications numérique étant mappé dans la deuxième portion, dans lequel l'étape d. est réalisée à l'aide du premier signal d'horloge.


     
    2. Procédé selon la revendication 1, dans lequel une pluralité de signaux de communications numériques du premier type de signal sont reçus et sont mappés dans la première portion de la charge utile.
     
    3. Procédé selon la revendication 1 ou la revendication 2, dans lequel une pluralité de signaux de communications numériques du deuxième type de signal sont reçus et sont mappés dans la deuxième portion de la charge utile.
     
    4. Procédé selon la revendication 2 ou la revendication 3, dans lequel au moins certains des signaux de communications numériques ont des débits binaires de trafic différents.
     
    5. Procédé selon l'une quelconque des revendications précédentes, dans lequel la trame (90, 100) comprend au moins quatre intervalles temporels, la première portion de la charge utile comprenant au moins un premier intervalle temporel, la deuxième portion de la charge utile comprenant au moins un deuxième intervalle temporel, la charge utile comprenant également un troisième intervalle temporel pour recevoir au moins les uns parmi des caractères de commande et des bits d'un signal de communications numérique qui ne peut pas être mappé au sein d'une capacité de l'une respective de la première portion et de la deuxième portion, et l'en-tête comprenant un quatrième intervalle temporel.
     
    6. Procédé selon la revendication 5, comprenant en outre l'attribution d'intervalles temporels (t0 à tN) à la première portion et à la deuxième portion de la charge utile proportionnellement à un poids respectif de trafic des signaux de communications numériques de chacun desdits types de signal.
     
    7. Procédé selon l'une quelconque des revendications précédentes, dans lequel chaque dit premier signal de communications numérique est un signal à débit binaire continu et chaque dit deuxième signal de communications numérique est un signal par paquets.
     
    8. Appareil d'encapsulation (200) pour un émetteur de réseau de communications (300), l'appareil d'encapsulation (200) comprenant :

    au moins une entrée (202, 204) agencée pour recevoir un premier signal de communications numérique d'un premier type de signal,

    le premier signal de communications numérique comprenant un premier signal d'horloge et un deuxième signal de communications numérique d'un deuxième type de signal, différent du premier type de signal, le deuxième signal de communications numérique comprenant un deuxième signal d'horloge différent du premier signal d'horloge, chaque signal d'horloge ayant une valeur d'horloge et une précision respectives ;

    une mémoire tampon (206) agencée pour mettre en mémoire tampon le deuxième signal de communications numérique pendant une durée assez longue pour compenser une différence entre au moins l'une parmi les valeurs d'horloge des premier et deuxième signaux d'horloge et les précisions des premier et deuxième signaux d'horloge, dans lequel après la mise en mémoire tampon du deuxième signal de communications numérique, le deuxième signal de communications numérique est synchrone avec le premier signal de communications numérique ; et

    un dispositif de mise en trame (208) pour recevoir le premier signal de communications numérique et pour recevoir le deuxième signal de communications numérique mis en mémoire tampon depuis la mémoire tampon (206) et agencé pour mettre en trame le premier signal de communications numérique et le deuxième signal de communications numérique mis en mémoire tampon dans une trame pour une transmission, la trame comprenant un en-tête et une charge utile, la charge utile comprenant une première portion et une deuxième portion, et le dispositif de mise en trame (208) étant agencé pour mapper le premier signal de communications numérique dans la première portion et étant agencé pour mapper le deuxième signal de communications numérique dans la deuxième portion,

    dans lequel l'appareil d'encapsulation (200) est agencé pour obtenir le premier signal d'horloge et le dispositif de mise en trame (208) est agencé pour fonctionner à l'aide du premier signal d'horloge.


     
    9. Appareil d'encapsulation (200) selon la revendication 8, dans lequel l'au moins une entrée (202, 204) est agencée pour recevoir une pluralité de signaux de communications numériques du premier type de signal et le dispositif de mise en trame (208) est agencé pour mapper ladite pluralité de signaux de communications numériques du premier type de signal dans la première portion de la charge utile.
     
    10. Appareil d'encapsulation (200) selon la revendication 8 ou la revendication 9, dans lequel l'au moins une entrée (202, 204) est agencée pour recevoir une pluralité de signaux de communications numériques du deuxième type de signal et le dispositif de mise en trame (208) est agencé pour mapper ladite pluralité de signaux de communications numériques du deuxième type de signal dans la deuxième portion de la charge utile.
     
    11. Appareil d'encapsulation (200) selon l'une quelconque des revendications 8 à 10, dans lequel au moins certains des signaux de communications numériques ont des débits binaires de trafic différents.
     
    12. Appareil d'encapsulation (200) selon l'une quelconque des revendications 8 à 11, dans lequel la trame comprend au moins quatre intervalles temporels, la première portion de la charge utile comprenant au moins un premier intervalle temporel, la deuxième portion de la charge utile comprenant au moins un deuxième intervalle temporel, la charge utile comprenant également au moins un troisième intervalle temporel pour recevoir au moins les uns parmi des caractères de commande et des bits d'un signal de communications numériques qui ne peut pas être mappé au sein d'une capacité de l'une respective de la première portion et de la deuxième portion, et l'en-tête comprenant un quatrième intervalle temporel.
     
    13. Appareil d'encapsulation (200) selon l'une quelconque des revendications 8 à 12, dans lequel chaque dit premier signal de communications numérique a une première exigence de latence et chaque dit deuxième signal de communications numérique a une deuxième exigence de latence, moins stricte que la première exigence de latence.
     
    14. Émetteur de réseau de communications (300) comprenant :

    un appareil d'encapsulation (200) tel que revendiqué dans l'une quelconque des revendications 8 à 13 ; et

    un émetteur de signal porteur (302) agencé pour générer un signal porteur acheminant la trame pour une transmission.


     
    15. Programme informatique comprenant des instructions qui, lorsqu'elles sont exécutées sur au moins un processeur, amènent l'au moins un processeur à exécuter le procédé selon l'une quelconque des revendications 1 à 7.
     




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    Cited references

    REFERENCES CITED IN THE DESCRIPTION



    This list of references cited by the applicant is for the reader's convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard.

    Patent documents cited in the description