Method and apparatus for transporting a client signal over an optical network

A method of transporting a client signal across an optical transport network (OTN) comprises dividing a received client signal into a plurality of parallel signals at a lower bit rate. The parallel signals are mapped into a respective number of optical data units (ODUs), each ODU having payload bytes and overhead bytes. Each ODU is mapped into a respective optical transport unit (OTUs) having payload bytes and overhead bytes. The OTUs are transmitted across respective optical carriers of a super-channel, the optical carriers of the super-channel being synchronously modulated. Optical channel control information is inserted into the overhead bytes of the ODU and/or OTU. The optical channel control information is used to manage and/or control the transport of the client signal using the super-channel.

TECHNICAL FIELD

This invention relates to optical transport networks and to methods and apparatus therefore.

BACKGROUND

Currently, the data traffic transported over the telecom optical transport networks is growing at a phenomenal pace and consequently the transmitted bit rates over a single optical wavelength in a DWDM transport systems are increasing rapidly. It is expected soon that the standardized 100 Gb/s bit rate will not meet the need and a higher digital rate is required.

Currently, transport equipment is designed with standardized interfaces and DWDM interfaces where multiple optical wavelengths are used to transport various digital bit rates. International Telecommunications Union (ITU-T) Recommendation G.709 defines the optical transport network (OTN) interfaces and hierarchy. G.709 also defines the largest container ODU4 to transport 100 Gbit/s of data traffic.

Standards for the transport of data traffic greater than 100 Gbit/s, for example 400 GBit/s or greater, are not yet defined.

SUMMARY

In one aspect there is provided a method of transporting a client signal across an optical transport network (OTN), the method comprising dividing a received client signal into a plurality of parallel signals at a lower bit rate; mapping the parallel signals into a respective number of optical data units (ODU) each having payload bytes and overhead bytes; mapping each ODU into a respective optical transport unit (OTU) having payload bytes and overhead bytes; transmitting the OTUs across respective optical carriers of a super-channel, the optical carriers of the super-channel being synchronously modulated; and inserting optical channel control information (OCCI) into the overhead bytes of the ODU and/or OTU, the OCCI being used to manage and/or control the transport of the client signal using the super-channel.

The use of super-channels together with in-band control and management signaling allows for increased transport capacity with minimum modifications to much existing transport equipment.

The OTN, ODU, OTU and the optical carriers of the super-channel may be constructed according to ITU-T standard G.709. Other types of containers (ODU/OTU) are however contemplated.

The super-channel may be transmitted using a single laser. The super-channel may consist of multiple frequency-locked carriers using coherent optical orthogonal frequency-division multiplexing (CO-OFDM), however other types of modulation may alternatively be used.

The OCCI may be used to identify which optical carriers are used to carry the respective OTU, and may also include information about structure, types, and management information about the signal/s transported.

The OCCI may be used to request a change in the optical carriers used to transport the client signal. This may include adding or subtracting sub-carriers, or re-allocating the same number of sub-carriers.

In a second aspect there is provided a method of transporting a client signal across an optical transport network (OTN), the method comprising: dividing a received client signal into a plurality of parallel signals at a lower bit rate; mapping the parallel signals into a respective number of optical data units (ODU) each having payload bytes and overhead bytes; mapping each ODU into a respective optical transport unit (OTU) having payload bytes and overhead bytes; mapping the resulting OTUs into a higher bit rate OTU having payload bytes and overhead bytes; transmitting the higher rate OTU across the OTN as an optical super-carrier, the optical super-carrier having a wavelength wider than the wavelength of an optical carrier normally allocated to transmitting a lower rate OTU across the OTN; inserting optical channel control information (OCCI) into the overhead bytes of the ODU and/or OTU, the OCCI being used to manage and/or control the transport of the client signal using the optical super-carrier.

The OTN, ODU, and OTU may operate according to G.709. The lower rate ODU and OTU may be ODU4 and OTU4 respectively, whilst the higher rate OTU may be OTU5.

The lower bit rate OTU may first be interleaved to form a single higher bit rate signal for mapping into the higher bit rate OTU. The interleaving may be performed using bit, byte or block interleaving. Circuit processing may be used to de-skew/align the signals.

In an embodiment, the optical carriers have a wavelength defined in ITU Recommendations G.694.1 and G.694.2 and the optical super-carrier has a wavelength wider than what would be used for the optical carriers.

The use of super-carriers together with in-band control and management signaling allows for increased transport capacity without modifications to much existing transport equipment.

In a third aspect there is provided a method of transporting a client signal across an optical transport network (OTN), the method comprising: dividing a received client signal into a plurality of parallel signals at a lower bit rate; mapping the parallel signals into a respective number of optical data units (ODU) each having payload bytes and overhead bytes; mapping each ODU into a respective optical transport unit (OTU) having payload bytes and overhead bytes; transmitting the OTUs across respective optical carriers; inserting optical channel control information (OCCI) into the overhead bytes of the ODU and/or OTU, the OCCI being used to request a change in the optical carriers used to transport the client signal.

The OTN, ODU, OTU may operate according to G.709. The optical carriers may be formed as part of a super-channel or as standard parallel wavelengths as defined in G.709, G.694.1 and G.694.2.

The use of in-band signaling to change the number of optical carriers used to transport the client signal allows for increased flexibility for handling the client signal.

There are also provided corresponding methods of receiving the optical channels and recovering the inserted OCCI. As noted, this may be used to assist in fully recovering all of the client signal, to manage the transport network, to control changes in the number and/or assignment of optical carriers used for transport of the client signal.

These methods can occur at a client signal ingress and egress node, as well as at intermediate nodes within the OTN.

There are also provided equipment such as optical nodes having optical-electrical-optical (OEO), optical-electrical (OE), electrical-optical (EO) capability which are arranged to carry out these methods. Similarly there are also provided computer code on a suitable carrier and executable by a suitable processor to carry out the above methods.

The functionality described here can be implemented in hardware, software executed by a processing apparatus, or by a combination of hardware and software. The processing apparatus can comprise a computer, a processor, a state machine, a logic array or any other suitable processing apparatus. The processing apparatus can be a general-purpose processor which executes software to cause the general-purpose processor to perform the required tasks, or the processing apparatus can be dedicated to perform the required functions. Another aspect of the invention provides machine-readable instructions (software) which, when executed by a processor, perform any of the described methods. The machine-readable instructions may be stored on an electronic memory device, hard disk, optical disk or other machine-readable storage medium. The machine-readable medium can be a non-transitory medium. The machine-readable instructions can be downloaded to the storage medium via a network connection.

DETAILED DESCRIPTION

FIG. 1shows an OTN network10and two nodes11,12forming part of the OTN network10at which client signals can ingress13the OTN network and/or egress14the OTN network10.

FIGS. 2A and 2Bshow one embodiment of apparatus at the nodes11,12ofFIG. 1in more detail.FIG. 2Ashows ingress functions at one of the nodes11,12. The node receives a 400 G client signal13and uses a demultiplexer/divider21to demultiplex/divide the client signal13into four parallel 100 G signals22which are mapped by a mapper23into ODU4 containers24as will be appreciated by those skilled in the art. For simplicity of explanation, not all steps of this process are described, however detailed explanations of these steps can be found in ITU-T standard G.709.

As will be appreciated by those skilled in the art, ODU4 containers24are able to transport 100 G client signals across the OTN network10, and thus the embodiment is able to transport the 400 G client signal13across four parallel ODU4 signals. The ODU4 containers24are mapped by a further mapper25into OTU4 containers26as is known. A channel managing entity31inserts32,33optical channel control information into the overhead bytes24A,26A of the ODU4 and/or OTU4 containers24,26. The channel managing entity31may be implemented by a suitably programmed processor and memory in the node11,12.

The set28of OTU4 signals are input to a super-channel multiplexer29which cooperates with a super-transponder30to generate an optical signal31comprising a group of optical sub-carriers or channels to transport the OTU4 containers across the OTN10. A super-channel can comprise a group of optical carriers which are synchronously modulated. In this example, four sub-carriers or wavelengths are used which correspond to the four parallel OTU4 streams. Various modulation schemes may be used such as QAM, QPSK, 16QPSK, etc. The sub-carriers may be further multiplexed to form part of a DWDM transport system.

The super-channel multiplexer29and super-channel transponder30can be implemented in various ways as will be appreciated by those skilled in the art. The Infinera DTN-X platform is a current commercially available product.

In one implementation, the optical carriers are modulated synchronously which provides improved optical performance. Such an implementation is described in the paper “Terabit Superchannels for High Spectral Efficiency Transmission” by S. Chandrasekhar and Xiang Liu, in ECOC 2010, 19-23 Sep., Torino Italy. The implementation described in this paper uses coherent optical orthogonal frequency division multiplexing (CO-OFDM), however alternative super-channel implementations could also be used.

The super-channel mux29and super-transponders30effectively integrate what would otherwise be the modulation of separate optical channels or wavelengths. The use of photonic integration has allowed the implementation of super-channels or groups of multiple wavelengths to be modulated together in a cost effective manner.

FIG. 2Bshows apparatus at a node11,12for egress of a client signal. A corresponding arrangement receives the four optical signals which form the super-channel79and recovers69the 4x OTU4 streams68, which are demapped65into 4x ODU4 streams. A channel manager entity71recovers optical channel control information73,72from the overheads66A,64A of the OTU4 and/or ODU466,64. A transponder70receives the optical signal79which comprises the super-channel. A demultiplexer69recovers the OTU4 streams68. The OTU4 streams are demapped65to ODU4 streams64. A set62of output signals recovered from the ODU4s are combined61and output as a client signal14.

FIG. 2Cshows two examples96,97of 400 G super-channel signals and, by way of contrast, a conventional 100 G signal95. The super-channel signal96shown inFIG. 2Cis of the type described above. It comprises four sub-carriers SC1, SC2, SC3, SC4. The super-channel signal97comprises two sub-carriers SC1, SC2. As can be seen from these examples, the number of sub-carriers and the bandwidth of each sub-carrier can vary. Modulation scheme can be selected from a range of possible modulation schemes. A different modulation scheme may be used for one or more of the sub-carriers in the plurality of sub-carriers.

In this embodiment, the number of sub-carriers of the super-channel and their particular wavelengths are referred to as the optical channels structure. The optical channel control information may include requests to change the optical channels structure used to transport the client signal. For example, should the client wish to increase the client signal from 400 G to 500 G, this may be accommodated by adding a fifth parallel OTU4 signal and corresponding optical sub-carrier. Alternatively, it may be necessary to change which sub-carriers are used (without changing their number) due to operational network considerations such as protection switching or congestion. In this case one or more of the OTU4 streams may need to be switched to a different optical sub-carrier.

Management information relating to the optical channels structure is communicated between nodes using optical channel control information (OCCI) which is inserted into and recovered from the overhead bytes of the ODU and/or OTU containers as will be described in more detail below. This management information may include the number of optical carriers used in the super-channel, their identities and other management information which would be familiar to those skilled in the art of optical transport network technologies. Alternatively or additionally, the OCCI may include requests, acknowledgements and other hand-shaking messages in order to control a change in the optical channels structure, such as adding or subtracting optical carriers from the super-channel.

The optical channel control information (OCCI) may be distributed in the overhead24A,26A of the ODU and OTU in any suitable manner. The information may be in the overhead of just one of the parallel streams of ODU/OTU or in any number of the parallel streams of ODU/OTN in any combination of unique or redundant formats.FIG. 3shows a standard OTUk frame structure which includes both OTUk OH (overhead) and ODUk OH as indicated. The client signal is mapped into the OPUk payload area as known and as indicated in the figure.FIG. 4shows the structure of the OH bytes24A,26A in more detail, where the acronyms represent:ACT: Activation/deactivation control channel;APS: Automatic Protection Switching coordination channel;EXP: Experimental;FAS: Frame Alignment Signal;FTFL: Fault Type & Fault Location reporting channel;GCC: General Communication Channel;MFAS: MultiFrame Alignment Signal;PCC: Protection Communication Control channel;PJO: Positive Justification Opportunity;PM: Path Monitoring;PSI: Payload Structure Identifier;RES: Reserved for future international standardisation;SM: Section Monitoring;TCM: Tandem Connection Monitoring.
In an example embodiment reserved bytes9-14in row4of the ODU OH could be used, as could reserve bytes13,14in row1of the OTU OH. Other ODU and/or OTU OH bytes might also or alternatively be used.

A method of transporting a client signal across an optical transport network (OTN) is shown inFIG. 5. The method can be performed by one of the nodes11,12. Step201comprises dividing a received client signal into a plurality of parallel signals at a lower bit rate. Step202comprises mapping the parallel signals into a respective number of optical data units, ODU, each having payload bytes and overhead bytes. Step203comprises mapping each ODU into a respective optical transport unit, OTU, having payload bytes and overhead bytes. Step204comprises transmitting the OTUs across respective optical carriers of a super-channel, the optical carriers of the super-channel being synchronously modulated. Step205comprises inserting optical channel control information into the overhead bytes of the ODU and/or OTU, the optical channel control information being used to manage and/or control the transport of the client signal using the super-channel.

A method of implementing a change in the optical channels structure is illustrated inFIG. 6. A step101can monitor the client signal. The client may indicate a need for a higher (e.g. 500 G) or lower (e.g. 300 G) rate signal, or the network may indicate a need to change the particular optical wavelengths to be used for transport. Step102determines if a change to the optical channel structure is needed. If a need for such a change to the optical channels structure arises, then suitable OCCI is inserted into the ODU/OTU OH24A,26A,64A,66A at step103. For example, if an additional wavelength is required to transport an increased bit rate 500 G client signal instead of the current 400 G signal, then predetermined “add wavelength” and “wavelength=21” type commands can be inserted into byte13of row1of the OTU OH26A,66A, for example. The wavelength=21 will most likely correspond to a wavelength adjacent the wavelengths transporting the current client signal, but need not be so limited. The method, which will be implemented by the channel manager, then awaits an acknowledgement from the second node or receiver.

The second node recovers the OCCI, and if it can receive the suggested optical signal and accommodate the addition OTU4 stream, will provide a positive acknowledgement signal, again typically using the ODU/OTU OH of optical signals in the reverse direction.

Step104determines if an acknowledgement is received from the second node. Once the acknowledgement is received, the channel manager of the first egress node sends a control signal (34) to the demux22to demultiplex to five parallel 100 G streams which are then mapped into five ODU4 and five OTU4. The channel manager31also controls35the super-channel mux29to generate a super-channel to accommodate the five OTU4 and controls36the super-transponder30to generate the corresponding five sub-wavelength optical channels.

Various other dynamic control operations can be achieved in this way, for example to reduce the number of optical carriers used (if the client signal rate reduces for example) or to change which wavelengths are used. The OCCI channel may also be used to send other commands, acknowledgements or implement other control operations.

Similarly, various static control information can also be transferred across the optical link for example confirming which optical channels and modulation types are being used.

A method of receiving a signal from an optical transport network (OTN) is shown inFIG. 7. The method can be performed by one of the nodes11,12. Step211comprises receiving optical carriers of a super-channel, the optical carriers of the super-channel being synchronously modulated. Step212comprises recovering optical transport units, OTU, each having payload bytes and overhead bytes. Step213comprises recovering optical data units, ODU, each having payload bytes and overhead bytes. Step214comprises recovering a plurality of parallel data signals from the ODUs. Step215comprises combining the plurality of parallel data signals into a client signal at a higher bit rate. Step216comprises recovering optical channel control information from the overhead bytes of the ODU and/or OTU, the optical channel control information being used to manage and/or control the transport of the client signal using the super-channel.

FIGS. 8A and 8Bshow an alternative embodiment which does not use super-channels but utilises the standard OTN/DWDM system of optical channels which are modulated separately (e.g. using OCh4) and then optically multiplexed to generate a DWDM signal. The initial stages of this embodiment are the same as described for the previous embodiment, and common reference numerals are used to indicate similar features. In this arrangement, each OTU4 is mapped into a respective OCh4 which is used to modulate41a respective separate laser. Four parallel optical wavelengths42are then used to transport the client signal across to the egress node. The process including the demux/divide22is still controlled by the channel manager entity31which inserts OCCI into the ODU and/or OTU OH24A,26A.FIG. 8Bshows apparatus at a second node12which receives the optical signal. In a corresponding manner, the second node12receives the four optical wavelengths82and recovers the four parallel OTU4 streams according to the G.709 standard. These containers are demapped into four ODU464which are fed to the mux/combiner61to reconstitute the client signal14. Any de-skewing processing can also be carried out. The channel manager71of the second node12recovers72,73, the OCCI from the ODU/OTU OH64A,66A.

FIG. 9shows a method of transporting a client signal across an optical transport network (OTN), which can be performed by one of the nodes11,12. Step301comprises dividing a received client signal into a plurality of parallel signals at a lower bit rate. Step302comprises mapping the parallel signals into a respective number of optical data units, ODU, each having payload bytes and overhead bytes. Step303comprises mapping each ODU into a respective optical transport unit, OTU, having payload bytes and overhead bytes. Step304comprises transmitting the OTUs across respective optical carriers. Step305comprises inserting optical channel control information into the overhead bytes of the ODU and/or OTU, the optical channel control information being used to request a change in the optical carriers used to transport the client signal.

FIG. 10shows a method of implementing changes to the optical channels structure, whether these are implemented using the super-channel embodiment or the separate optical channels DWDM embodiment. In this particular example a request to increase the client signal transport from 500 G to 700 G is received at step111. However, many alternative requests could also be accommodated as would be appreciated by those skilled in the art. The method can be implemented by the channel manager entity, which may receive the request upon completion of the method ofFIG. 6, for example. At step112the channel manager31instructs the demux/divider to split the incoming client signal into seven parallel streams of 100 G and to map these into seven ODU4 streams. At step113the method adjusts the OCCI input into the ODU/OTU OH. For example, the OCCI can indicate which optical channels are being used and in which order so that the client signal can be correctly reconstituted. At steps115,116the method then reconfigures the super-channel mux and super-transponder as appropriate. Alternatively, if a standard DWDM optical system is used, at step114the method maps seven OTU4 are mapped to seven OCh4 which are used to modulate seven separate wavelength lasers, as is known.

Alternatively, at step117the OCCI may be forwarded using control plane or management plane messaging in an out-of-band signal. At steps119,120the method then reconfigures the super-channel mux and super-transponder as appropriate. Alternatively, if a standard DWDM optical system is used, at step118the method maps seven OTU4 are mapped to seven OCh4 which are used to modulate seven separate wavelength lasers.

A method of receiving a signal from an optical transport network (OTN) is shown inFIG. 11. The method can be performed by one of the nodes11,12. Step311comprises receiving optical carriers. Step312comprises recovering optical transport units, OTU, each having payload bytes and overhead bytes. Step313comprises recovering optical data units, ODU, each having payload bytes and overhead bytes and can also include performing de-skewing. Step314comprises recovering a plurality of parallel data signals from the ODUs. Step315comprises combining the plurality of parallel data signals into a client signal at a higher bit rate. Step316comprises recovering optical channel control information from the overhead bytes of the ODU and/or OTU, the optical channel control information being used to manage and/or control the transport of the client signal using the super-channel.

Whilst various examples have been given, the invention is not so limited. For example any number of optical channels may be used, not just four optical channels for a 400 G client signal. Similarly ODU3/OTU3, ODU5/OTU5 or other variations of OTN containers could alternatively be used.

A further alternative embodiment is shown inFIGS. 12A and 12B, which utilises OTU5 containers from recent developments in the ITU-T G.709 standard. OTU5 are the next higher rate transport container for OTN as defined by G.709. Whilst the exact definition of the data rate to be used by ODU5 is still to be agreed, this will be significantly higher than the current highest OTU4 container which can support 100 G client signals over a single optical carrier. It is anticipated that ODU5 will support either 400 G or 1T (1000 G) client signals and will be capable of carrying multiple ODU4 containers. The current G.709 living list (Version 2011-05) is available from ITU-T and details the current specification options for ODU5 in more detail. However these will follow the G.709 principles for earlier defined data rates so that the skilled person will be fully understanding of the use of ODU5 as described in this embodiment.

In a similar manner to the embodiments ofFIGS. 2A, 2B and 8A, 8B, the incoming client signal13is divided21into four parallel digital signals22which are mapped23into four ODU4 containers24. These ODU4 are then mapped25into OTU4 containers26according to G.709. The channel manager entity31inserts OCCI into the overheads24A,26A of the ODU4 and/or OTU4 as previously described. The four OTU4 are then input to an interleaver45which bit, byte or block interleaves the four parallel OTU4 signals into a single digital stream46which is then mapped48into the payload bytes of an OTU5 container47. As per G.709, overhead bytes47A are added. The OTU5 container47shown corresponds to a 400 G data rate, however other container sizes could alternatively be used with the number of OTU4 containers added adjusted accordingly as would be appreciated by those skilled in the art. The OTU5 are then further processed according to G.709 in a manner corresponding to how older OTU containers are processed (e.g. OTU4, OTU3 etc.)—for example processing into OCh5. The OTU5 containers are applied to a super-carrier transponder which generates a wide bandwidth optical carrier modulated by the OTU5 data. As will be appreciated, a wider bandwidth optical signal allows a higher data rate signal to be transported using the same modulation rate and type.

FIG. 12Bshows apparatus at one of the nodes11,12which receives the optical signal90at a transponder/receiver89and recovers the higher rate (e.g. OTU5) container. A bitstream86is recovered from the higher-rate containers87and the bitstream is de-interleaved85to a parallel set of lower-rate OTUs (e.g. OTU4). These containers are demapped65into four ODU4 which are fed to the mux/combiner61to reconstitute the client signal14. The channel manager71of the second node12recovers72,73,77the OCCI from one or more of the ODU/OTU OH64A,66A,87A.

FIG. 13shows a wide bandwidth optical carrier50,90which can be used to carry the higher data rate signal, such as an OTU5, and a conventional, narrower bandwidth, optical carrier140which can be used to carry a lower rate signal. As an example, a conventional 100 G signal can have a bandwidth of 50 GHz while the higher rate signal can have a bandwidth of 75 GHz, although other carrier bandwidths can be used.

G.709 is associated with a grid of optical wavelengths which are used to carry ODU4 signals. This grid is defined in ITU-T G.694 and specifies the frequency grid, anchored to 193.1 THz. This supports a variety of channel spacings ranging from 12.5 GHz to 100 GHz. The wavelengths of the optical carriers fit within these spacings. The super-carrier has a wavelength broader than what would be used for the optical carriers and spans multiple defined spacings.

Using a super-carrier with a wavelength wider than the optical carrier wavelengths provides an alternative to using higher order modulation and/or higher optical bit rates to carry higher data rate signals like OTU5. This eases the requirements on optical components making them cheaper to implement. The super-carrier can co-exist with conventional carriers in the OTN10.

The super-carrier is received by a super-carrier transponder at the egress node and the OTU5 recovered using known G.709 technology. The OTU5 payload is de-interleaved to recover the original parallel OTU4 signals. These are de-mapped into 4 ODU4 signals which are combined to generate the original 400 G client signal. Signal processing and de-skewing/alignment of the individual signals are performed as necessary.

Meanwhile, the egress node's channel manager entity recovers OCCI from the overheads of the OTU and/or ODU as previously described. This allows for management as well as control of the super-carrier—for example to change the wavelength to accommodate a different size client signal.

As with the other embodiments, the specific examples given are not limiting, and could be altered—for example ten interleaved OTU4 could be mapped into a suitably sized OTU5.

FIG. 14shows a method of transporting a client signal across an optical transport network (OTN) which can be performed by one of the nodes11,12. Step401comprises dividing a received client signal into a plurality of parallel signals at a lower bit rate. Step402comprises mapping the parallel signals into a respective number of optical data units, ODU, each having payload bytes and overhead bytes. Step403comprises mapping each ODU into a respective optical transport unit, OTU, having payload bytes and overhead bytes. Step404comprises mapping the resulting OTUs into a higher bit rate OTU having payload bytes and overhead bytes. Step405comprises transmitting the higher rate OTU across the OTN as an optical super-carrier, the optical super-carrier having a bandwidth wider than the bandwidth of an optical carrier normally allocated to transmitting a lower rate OTU across the OTN. Step406comprises inserting optical channel control information into the overhead bytes of the ODU and/or OTU, the optical channel control information being used to manage and/or control the transport of the client signal using the optical super-carrier.

A method of receiving a signal from an optical transport network (OTN) is shown inFIG. 15. The method can be performed by one of the nodes11,12. Step411comprises receiving an optical super-carrier having a bandwidth wider than a bandwidth of an optical carrier normally allocated to transmitting a lower rate OTU across the OTN. Step412comprises recovering higher-rate optical transport units, OTU, each having payload bytes and overhead bytes. Step413comprises recovering lower-rate optical transport units, OTU, each having payload bytes and overhead bytes. Step414comprises recovering optical data units, ODU, each having payload bytes and overhead bytes. Step415comprises recovering a plurality of parallel data signals from the ODUs. Step416comprises combining the plurality of parallel data signals into a client signal at a higher bit rate and performing any de-skewing processing, if required. Step417comprises recovering optical channel control information from the overhead bytes of the ODU and/or OTU, the optical channel control information being used to manage and/or control the transport of the client signal using the optical super-carrier.

FIG. 16shows an exemplary processing apparatus130which may be implemented as any form of a computing and/or electronic device, and in which embodiments of the system and methods described above may be implemented. Processing apparatus130can be provided at one of the nodes11,12. Processing apparatus may implement any of the methods described above. Processing apparatus130comprises one or more processors131which may be microprocessors, controllers or any other suitable type of processors for executing instructions to control the operation of the device. The processor131is connected to other components of the device via one or more buses136. Processor-executable instructions133may be provided using any computer-readable media, such as memory132. The processor-executable instructions133can comprise instructions for implementing the functionality of the described methods. The memory132is of any suitable type such as read-only memory (ROM), random access memory (RAM), a storage device of any type such as a magnetic or optical storage device. Additional memory134can be provided to store data135used by the processor131. The processing apparatus130comprises one or more network interfaces138for interfacing with other network entities, such as other nodes11,12of the network10.