Message Encoding Parameter Reconfiguration in an Optical Network

Abstract

A method for reconfiguring a message encoding parameter used by a first channel node to transmit information to a second channel node via a first optical channel in an optical network comprises the steps of sending, via a second optical channel of the optical network, a reconfiguration request with a message encoding parameter from the first channel node to the second channel node of the first optical channel; receiving, via the second optical channel, a reply to the reconfiguration request from the second channel node; and modifying the first channel node in accordance with the message encoding parameter used to transmit information from the first channel node to the second channel node based on the reply.

Claims

1. A method for reconfiguring a message encoding parameter used by a first channel node to transmit information to a second channel node via a first optical channel in an optical network, the method comprising the steps of: sending, via the second optical channel of the optical network, a reconfiguration request with a message encoding parameter for the first optical channel from the first channel node to the second channel node; receiving, via the second optical channel, a reply to the reconfiguration request from the second channel node; and modifying the first channel node in accordance with the message encoding parameter used to transmit information from the first channel node to the second channel node via the first optical channel based on the reply.

2. The method of claim 1, wherein the message encoding parameter comprises at least one of a data rate, an FEC mode, a modulation mode and a baud rate.

3. The method of claim 1, wherein the information is transmitted from the first channel node to the second channel node through at least one additional node along the optical network, and/or wherein the optical network employs wavelength multiplexing.

4. The method of claim 1, wherein the second optical channel is an optical supervisory channel of the optical network, or wherein the second optical channel is implemented in an overhead data field of an optical channel using an independent message encoding scheme from the first optical channel in an overhead field reserved for operator use.

5. The method of claim 1, wherein the method further comprises the steps of: sending, via the second optical channel, an error suppression message instructing the second channel node to suppress errors from packet loss during a subsequent change of the message encoding parameter, and sending a transmitter reconfiguration completion message to the second channel node when the message encoding parameter has been successfully changed; and/or wherein the method further comprised the steps of: receiving, via the second optical channel, a receiver reconfiguration completion message from the second channel node, and reinitiating payload transfer via the first optical channel.

6. The method of claim 1, wherein the first channel node is identified by a first identifier, and the second channel node is identified by a second identifier, and wherein the first channel node is selected as a master of the first optical channel between the first channel node and the second channel node based on an unambiguous rule, said unambiguous rule depending on the first identifier of the first channel node and the second identifier of the second channel node in the optical network.

7. The method of claim 1, further comprising verifying compatibility of the first channel node with the message encoding parameter after receiving the message encoding parameter and before sending the reconfiguration request; and/or wherein the reconfiguration request comprises a set of supported parameter values for the message encoding parameter, said supported parameter values corresponding to parameter values for the message encoding parameter which are supported by the first channel node, wherein the method in particular further comprises receiving a selected parameter value from the second channel node, wherein the selected parameter value is a parameter value of the set of supported parameter values, and further comprises modifying the first channel node in accordance with the selected parameter value.

8. A method for reconfiguring a message encoding parameter used by an optical channel node to transmit information to a master channel node via a first optical channel in an optical network, the method comprising the steps of: receiving a reconfiguration request with a message encoding parameter for the first optical channel from the master channel node, via a second optical channel of the optical network; verifying compatibility of the optical channel node with the message encoding parameter; suppressing raising an alarm for the first optical channel; sending, via the second optical channel to the master channel node, a reply to the reconfiguration request; and modifying the message encoding parameter used to receive information from the master channel node via the first optical channel.

9. The method of claim 8, wherein the reconfiguration request comprises a set of supported parameter values for the message encoding parameter and the method further comprises selecting a suitable parameter value from the set of supported parameter values as a selected parameter value, in particular according to an order of the supported parameter values in the set of supported parameter values, wherein the suitable parameter value is supported by the optical channel node, and wherein the method further comprises sending the selected parameter value to the master channel node, in particular with the reply to the reconfiguration request.

10. An optical channel node of an optical network configured to transmit information to a second channel node via a first optical channel in the optical network, the optical channel node being configured to: send, via a second optical channel of the optical network, a reconfiguration request with a message encoding parameter for the first optical channel to the second channel node of the first optical channel; receive, via the second optical channel, a reply to the reconfiguration request from the second channel node; and modify the configuration of the optical channel node in accordance with the message encoding parameter used to transmit information from the optical channel node to the second channel node via the first optical channel based on the reply.

11. The optical channel node of claim 10, further comprising: a control unit; a transponder for modulating an optical beam of the first optical channel with the message encoding parameter to transmit information from the optical channel node to the second channel node, and a switch to receive the optical beam from the transponder and direct the optical beam into an optical fiber for the first optical channel, wherein the control unit is configured to modify the transponder according to the message encoding parameter.

12. The optical channel node of claim 11, wherein the optical beam remains switched on while the control unit changes the encoding parameter at the transponder.

Description

DETAILED DESCRIPTION OF EMBODIMENTS

[0070] The features and numerous advantages of the method and optical channel nodes according to the present invention will best be understood from a detailed description of preferred embodiments with reference to the accompanying drawings, in which:

[0071] FIG. 1 shows a schematic optical transport system according to an example;

[0072] FIG. 2 schematically illustrates a dense wavelength division multiplexing (DWDM) system according to an example;

[0073] FIG. 3 shows a method for modifying a message encoding parameter used in a first optical channel according to an example;

[0074] FIG. 4 illustrates a method for reconfiguring a message encoding parameter used by a first channel node to communicate via a first optical channel according to an example;

[0075] FIG. 5 illustrates a method for reconfiguring a message encoding parameter used by a second channel node to receive messages via a first optical channel according to an example; and

[0076] FIG. 6 illustrates a method for abandoning a reconfiguration of the message encoding parameter according to an example.

[0077] FIG. 1 shows a schematic optical transport system 10 according to an example. The system 10 comprises a first channel node 12 and a second channel node 14 coupled via optical fibers 16a, 16b to intermediate optical channel nodes 18a, 18b of an intermediate transport section 16a, 16b, 20 connecting the first channel node 12 and the second channel node 14. The first channel node 12 comprises a first transponder 22 and the second channel node 14 comprises a second transponder 24, wherein the first transponder 22 is configured to modulate an optical beam accommodated in a band of wavelengths and added into the first optical fiber 16a. The second transponder 24 is configured to receive said optical beam at said band of wavelengths after it is dropped from the second optical fiber 16b at the second channel node 14.

[0078] The optical beam at said band of wavelengths added by the first channel node 12 to the optical beam traversing the optical fibers 16a, 16b and the intermediate transport section 16a, 16b, 20 comprising intermediate optical channel nodes 18a, 18b defines an optical channel between the first and second channel nodes 12, 14 for transferring payload data from the first channel node 12 to the second channel node 14. The first transponder 22 encodes the payload data in the optical beam with a given modulation format, such as quadrature amplitude modulation, pulse amplitude modulation, or the like, and using a given forward error correction (FEC) mode with a modulation frequency given by a predefined baud rate. Since each symbol encoded at the modulation frequency can encode a plurality of bits depending on the modulation format, an effectively transferred data rate for the optical channel can depend on both the baud rate and the modulation format.

[0079] A given data packet transferred from the first channel node 12 to the second channel node 14 is transferred in one or more data frames encapsulating the data packet together with overhead data providing service information as well as partially redundant data for forward error correction of transmission errors inadvertently modifying the symbols encoding the data packet. The FEC mode can specify a degree of redundancy in the data frame as well as the encoding format for providing the redundant data for forward error correction. Accordingly, the second channel node 14 receives, at the second transponder 24, the optical beam dropped from the second optical fiber 16b and decodes the data frame according to a predetermined message encoding parameter and potentially corrects transmission errors occurring during the transfer from the first channel node 12 to the second channel node 14.

[0080] FIG. 2 schematically illustrates a dense wavelength division multiplexing (DWDM) system 10 according to an example to illustrate an exemplary network element configuration for the first and second channel nodes 12, 14. The system 10 comprises a first channel node 12 and a second channel node 14 connected via the optical fiber connection 16 to provide an optical channel accommodated in a predefined frequency band depicted as wavelength p (i.e. a band of wavelengths), such as a DWDM band of the C-band between 191.7 THz to 196.1 THz or an extended C-band between 186 THz to 201 THz having a bandwidth of 100 GHz, 50 GHz or 25 GHz. Although not explicitly shown in FIG. 2 (but schematically shown in FIG. 1), said optical fiber connection 16 generally includes a plurality of intermediate passive (erbium doped fiber) amplifiers as well as intermediate channel nodes 16a, 16b configured to forward and/or passively amplify an optical beam traversing the optical fiber connection 16.

[0081] The first channel node 12 receives an optical input beam B1 from a DWDM network, which is amplified by a preamplifier 26a of the first channel node 12 and guided towards a first optical multiplexing section 28a allowing to add/drop a wavelength p to/from the optical beam B1. A first transponder 22 of the first channel node 12 is configured to receive a client layer data signal and to encode the client layer data signal according to a set of message encoding parameters for the first transponder 22 specifying, among other parameters, an FEC mode, a modulation format and/or a baud rate for modulating the wavelength p. The wavelength p accommodating the first optical channel is received by the first multiplexer section 28a of the first channel node 12 and added to the DWDM network, such as by switching said wavelength p to the DWDM network using a wavelength selective switch. The optical beam . . . +p including the added first optical channel is then guided past an optional second multiplexing section 30a of the first channel node 12 to a post-amplifier 32a of the first channel node 12 to amplify the optical beam and insert the optical beam into the optical fiber connection 16.

[0082] The optical beam . . . +p including the added first optical channel can be received by the second channel node 14 and preamplified at the second preamplifier 26b of the second channel node 14. A first multiplexing section 28 to be of the second channel node 14 can deterministically switch/drop the wavelength p accommodating the first optical channel from the optical beam towards the second transponder 24 of the second channel node 14 while the optical beam . . . p from which the wavelength p accommodating the first optical channel has been dropped can be switched towards the second multiplexing section 30b of the second channel node 14 and further guided to a post-amplifier 32b of the second channel node 14 which amplifies the optical beam for transmission as an outgoing beam B2 of the DWDM network.

[0083] In an initial configuration, the second transponder 24 receives the wavelength p accommodating the first optical channel and decodes data frames according to the message encoding parameter, wherein the second transponder 24 is configured to sample the wavelength p accommodating the first optical channel at a predefined baud rate and using a predefined modulation format as well as FEC mode shared with the first transponder 22 of the first channel node 12.

[0084] Although only a single wavelength p is illustrated, the first and second channel nodes 12, 14 may communicate via a plurality of optical channels accommodated in a number of different wavelengths p and one optical channel may comprise a plurality of bands of wavelengths and/or may be accommodated in a set of timeslots of said plurality of bands of wavelengths. However, for the sake of conciseness, the first and second optical channel will be referred to as corresponding to a respective different band of wavelengths. Nonetheless, in some embodiments, the first and second channel may equally share a frequency band and be accommodated in different timeslots of said shared frequency band without loss of generality.

[0085] In addition, the first and second channel nodes 12, 14 can listen to an additional frequency band outside of the C-band, such as an optical supervisory channel (OSC), which can be transmitted via the same physical optical fibers 16, 16a, 16b. The additional frequency band may be terminated and re-transmitted at intermediate nodes 16a, 16b, wherein each of the intermediate nodes 16a, 16b may add service-level information to the additional frequency band.

[0086] In addition, a second (symmetric) unidirectional optical service may be provided connecting the second channel node 14 and the first channel node 12 in the reverse direction. However, for the sake of simplicity, the optical channels supported by the optical network will be discussed as being bidirectional and the reverse connection between the second channel node 14 and the first channel node 12 is supposed to be implicitly provided. The skilled person will nonetheless appreciate that the reverse connection between the second channel node 14 and the first channel node 12 may be independently configured from the first optical channel and messages transferred via the reverse optical connection may be encoded according to different message encoding parameters.

[0087] In the prior art, the shared message encoding parameters shared between the first channel node 12 and the second channel node 14 are usually configured during commissioning of the first optical channel. Reconfiguration of the message encoding parameters shared by the first channel node 12 and the second channel 14 is possible by decommissioning the first optical channel including intermediate channel nodes 16a, 16b along the optical fiber connection 16 and then recommissioning the first optical channel with the modified message encoding parameters.

[0088] In contrast, using the techniques of the present disclosure, the first, head-end channel node 12, and the second, tail-end channel node 14 may also negotiate modified message encoding parameters avoiding decommissioning of the first optical channel, for instance by means of the method illustrated in FIG. 3.

[0089] FIG. 3 shows a sequence of method steps for modifying a message encoding parameter used for encoding a message in the first optical channel between a first, head-end node 12 and a second, tail-end node 14 following a request for modified message encoding parameters, such as by a management system for the optical transport network, according to an example. The method begins by nominating the first channel node 12 as a master node for the first optical channel (step S10). Said nominating may be performed according to an unambiguous rule, such as a comparison of alphabetical to decimal value conversion of the trail trace identifier portion identifying the network elements, e.g. the source/destination access point identifier (SAPI/DAPI) of the end nodes 12, 14 of the first optical channel. However, since optical channel nodes 12, 14 are, despite the general unidirectionality of optical connections, generally bi-directionally connected, one of the optical channel nodes 12, 14 of an optical connection may also assume the designation as master node 12 and may consequently inform the other optical channel node 14 of said assumed designation as head-end node 12, i.e. as first channel node 12, for the first optical channel connecting it to the other, tail-end node 14, i.e. the second channel node 14.

[0090] In a next step S12, which may however equally precede step S10, the first channel node 12 receives or generates modified message encoding parameters for transferring data frames via the first optical channel to the second channel node 14. In preferred examples, the first channel node 12 receives the message encoding parameter from a management node of the optical network. In step S14, the first channel node 12 inserts the modified message encoding parameter into the second optical channel, wherein said second optical channel features independent message encoding parameters from the first channel, such as a second optical channel in a different band of wavelengths transmitted via the optical fiber connection 16 to the second channel node 14 or a wavelength/band of wavelengths lying outside of the passively amplified band of wavelengths, such as the OSC which can be terminated and retransmitted at intermediate nodes 16a, 16b of the optical fiber connection 16.

[0091] In step S16, the second channel node 14 receives the modified message encoding parameters transmitted via the second optical channel from the first channel node 12 and verifies a compatibility of the second transponder 24 of the second channel node 14 with said modified message encoding parameters. If the modified message encoding parameters are supported by the second channel node 14, the second channel node 14 acknowledges the reconfiguration request by the first channel node 12 via the second optical channel 14 and enables the suppression of alarms for the second optical transponder 24 resulting from unsuccessful decoding of signals transmitted by the first optical channel during the reconfiguration of the message encoding parameters by the first and second channel nodes 12, 14.

[0092] The first channel node 12 receives the acknowledgment of the second channel node 14 via the second optical channel in step S18 and subsequently changes the configuration of the first transponder 22 in accordance with the modified message encoding parameter.

[0093] When the first channel node 12 finishes reconfiguration of the first transponder 22 and associated hardware, it sends a channel lock clearing message to the second channel nodes 14 via the second optical channel (step S20), indicating the successful change of the message encoding parameter to the second channel node 14 and the readiness to recommence payload data transfer.

[0094] The second channel node 14 receives the channel lock clearing message and changes the configuration of the second transponder 24 in accordance with the modified message encoding parameter (step S22). In some embodiments, the second channel node 14 initiates reconfiguration of the second transponder 24 in accordance with the modified message encoding parameter following the acknowledgment of the modified message encoding parameter by the second channel node 14, e.g. before the first channel node 12 finishes reconfiguration of the message encoding parameter. For example, the second channel node 14 may change the configuration of the second transponder 24 following a received message from the first channel node 12 via the second optical channel indicating the start of the reconfiguration of the first transponder 22 in the first channel node 12 or immediately after receiving the channel lock message. The synchronous reconfiguration of the first and second transponders 22, 24 in the first and second channel nodes 12, 14 may reduce a total time necessary for reconfiguration of the first optical channel with the modified message encoding parameters. However, in some examples, the second channel node 14 waits for the first channel node 12 to finish reconfiguration of the first transponder 22 to limit an impact of reconfiguration failure in the first channel node 12 on data transmission.

[0095] In step S24 the second channel node 14 finishes reconfiguration of the second transponder 24 and subsequently disables error suppression in the second transponder 24 or error suppression with respect to errors generated by the second transponder 24. The successful change of the message encoding parameter in the second transponder 24 is further indicated towards the first channel node 12, preferably via the second optical channel, such that payload data transfer can be reinitiated by the first channel node 12.

[0096] In accordance with the example of the reconfiguration method illustrated in FIG. 3, the first channel node 12 can be configured to perform the method of FIG. 4 illustrating a method to reconfigure a message encoding parameter used by a first channel node 12 to transmit payload data via a first optical channel to a second channel node 14. Following a generation or a reception of a new message encoding parameter by the first channel node 12, the method comprises sending, via a second optical channel of the optical network, a reconfiguration request with a message encoding parameter from the first channel node 12 to the second channel node 14 of the first optical channel (step S26). The method further comprises receiving, via the second optical channel, a reply to the reconfiguration request from the second channel node 14 (step S28). Said reply may indicate a compatibility of the second channel node 14 with the modified message encoding parameter. The method then further comprises modifying the first channel node 12 in accordance with the message encoding parameter used to transmit information from the first channel node 12 to the second channel node 14 based on reply (step S30).

[0097] Said modification of the first channel node 12 may modify the minimum amount of attributes in the optical connection to reuse most of the configuration of the first optical channel. In particular, the reconfiguration of the first channel node 12 may be substantially limited to the reconfiguration of the first transponder 22 at the first channel node 12 and associated hardware. Additionally, the method of reconfiguring the first channel node 12 with the new message encoding parameter may avoid switching off an optical beam transmitted by the first optical channel from the first channel node 12 to the second channel node 14, such that transient effects due to a power-dependent optical characteristic of the first optical channel between the first channel node 12 and the second channel 14 is substantially unchanged during the reconfiguration of the first channel node 12. Preferably, no or minimal resynchronization of (intermediate) channel nodes 12, 14, 16a, 16b is triggered due to the reconfiguration of the method encoding parameter of the first optical channel.

[0098] An example of such a modified message encoding parameter may be a change of the FEC mode used to add overhead data to data frames for forward error correction at the receiver due to a high optical performance/SNR of the first optical channel, such as a change from EFEC (25% SD FEC) to EFEC (15% SDEFEC-AC100) reducing the amount of bytes used for forward error correction in the data frame thereby increasing the available data rate for the first optical channel.

[0099] Equally, the message encoding parameter may be a combination of a modified modulation format and baud rate, such as a change from 4 QAM to 8 QAM and an associated modification of the baud rate to leave the effective data rate for the client layer of the optical network unaffected. However, the data rate may also be changed by changing any combination of baud rate, modulation format and FEC mode, such as to render the first optical channel compatible with an increased data rate requested by a client layer.

[0100] Accordingly, the second channel node 14 may perform a corresponding reconfiguration method for modifying the message encoding parameter used to receive payload data from the first channel node 12.

[0101] FIG. 5 illustrates a method for reconfiguring the second channel node 14 according to an example. The method comprises receiving a reconfiguration request with a new message encoding parameter for the first optical channel from the master channel node 12, i.e. the first, head-end channel node 12, via a second optical channel of the optical network (step S32). The method further comprises verifying compatibility of the optical channel node 14, i.e. the second channel node 14, with the new message encoding parameter (step S34). If this verification of the compatibility of the second channel 14 with the new message encoding parameter is successful, the second channel node 14 may continue reconfiguration of the message encoding parameter. The method then further comprises suppressing raising alarms for the first optical channel (step S36), such as by suppressing alarms raised by the second transponder 24 used to receive payload data in the second channel node 14 via the first optical channel; and sending, via the second optical channel to the master channel node 12, a positive reply to the reconfiguration request (step S38). Furthermore, the method comprises modifying the message encoding parameter used to receive information from the master channel node 12 (step S40).

[0102] In some embodiments, the second channel node 14 may receive a channel lock message transmitted by the first channel node 12 via the second optical channel prior to modifying the message encoding parameter to avoid frame loss before the first channel node 12 starts changing the message encoding parameter. In some embodiments, the second channel node 14 waits for a channel lock clearing message transmitted by the first channel node 12 via the second optical channel indicating successful completion of the reconfiguration of the message encoding parameter in the first channel node 12 prior to modifying the message encoding parameter for receiving information via the first optical channel from the first, master channel node 12. Additionally, instead of raising alarms during suppressing raising alarms, the second channel node 14 may issue an error message to the client layer indicating temporary unavailability of the first optical channel for payload data transfer due to an active reconfiguration of message encoding parameters.

[0103] The method of FIG. 5 may also be used to setup message encoding parameters for one or more newly created optical channels between the first and second channel nodes 12, 14 already sharing an optical connection, such as a preconfigured optical channel or an OSC. The preconfigured optical channel or the OSC may then act as the second optical channel for configuring message encoding parameters of one or more newly created first optical channels.

[0104] For example, a network management system may indicate a wavelength selective switch configuration to an optical fiber connection 16 and corresponding optical nodes 12, 14, 16a, 16b of the optical network to connect the first and second channel nodes 12, 14 via said one or more newly created first optical channels. The network management system may then designate the first channel node 12 as the master, head-end node for said one or more newly created optical channels and may indicate message encoding parameters for use with said one or more channels. The first channel node 12 may then send, via the second optical channel, i.e. the preconfigured optical channel, an overhead field thereof, or via the OSC connecting the first and the second channel nodes 12, 14, a reconfiguration request with a message encoding parameter for information transfer via said one or more newly created optical channels from the first channel node 12 to the second channel node 14. The first channel node 12 may then receive for at least one newly created optical channel a (positive) reply to the reconfiguration request from the second channel node 14 indicating a compatibility of the second channel node 14 with the message encoding parameters for said at least one newly created optical channel, and may modify a configuration of the first channel node 12, e.g. a configuration of a transponder 22 of the first channel node 12 for transmitting data via said at least one newly created optical channel to the second channel node 14.

[0105] Equally, the second channel node 14 may perform initialization of the second transponder 24 for said one or more newly created optical channels after receiving the reconfiguration request from the first channel node 12 via the second optical channel with the new message encoding parameter in accordance with the method illustrated in FIG. 5 by verifying compatibility of the second channel node 14 with the message according parameters received for each of the one or more newly created optical channels and acknowledging the reconfiguration request based on the verification of the compatibility with the message encoding parameters. However, the skilled person will appreciate that for an initialization of said one or more newly created optical channels, a suppression of errors may not be required. Additionally, the second channel node 14 may immediately commence configuring an associated second transponder 24 for receiving payload data via said one or more newly created optical channels before the first channel node 12 finishes reconfiguration of the message encoding parameters for transferring payload data via said one or more newly created optical channels.

[0106] FIG. 6 illustrates a method, wherein the second, tail-end channel node 14 receives a reconfiguration request with at least one modified message encoding parameter (step S42), but may be at least partially or temporarily not compatible with said reconfiguration request. The second channel node 14 then acknowledges the reception of the reconfiguration requests with a negative reply to the first channel node 12 and ignores a channel lock message sent from the first channel node 12 via the second optical channel (step S44). The first channel node 12 receives the negative reply via the second optical channel and reports the failed reconfiguration attempt (step S46). The network management system then responds negatively to the user having requested the change of message encoding parameters (step S48), and the previous message encoding parameters are maintained.

[0107] The preceding examples have mostly focused on message encoding for payload data transfer from the first channel node 12 to the second channel node 14 via the first optical channel. However, message encoding for data transfer in the reverse direction from the second channel node 14 to the first channel node 12 via the first optical channel, i.e. a corresponding unidirectional optical connection providing a reverse service for the first optical channel, may equally be reconfigured during the method.

[0108] For example, the first channel node 12 may simultaneously change a message encoding parameter of the first channel node 12 for receiving payload data from the second channel node 14 via the first optical channel when modifying the message encoding parameter for sending data from the first channel node 12 to the second channel node 14. Similarly, the second channel node 14 may simultaneously modify a message encoding parameter for sending payload data from the second channel node 14 to the first channel node 12 via the first optical channel when modifying the second channel node 14 in accordance with the new message encoding parameter for receiving payload data from the first channel 12 via the first optical channel.

[0109] However in some embodiments, the reverse connection via the first optical channel is not reconfigured according to the modified message encoding parameters or is independently, and in particular only subsequently, reconfigured after a reconfiguration of the message encoding parameter for transferring payload data from the first channel node 12 to the second channel node 14 via the first optical channel has been successfully completed in both nodes 12, 14.

[0110] In some embodiments, a bilateral simultaneous message encoding parameter reconfiguration is performed in both nodes, wherein a transponder 22 of both the first channel node 12 and the second channel node 14 is modified according to the message encoding parameters to send information to the respective tail-end node of the corresponding optical connection of the first optical channel after the reconfiguration request has been acknowledged by the second channel node 14. When successful completion of one or both transponder reconfigurations of the first and second channel node 12, 14 have been indicated to the other channel node, a corresponding receiver reconfiguration of the second and first channel node 14, 12 according to the modified message encoding parameter is performed, respectively, to receive payload data transmitted via the first optical channel according to the modified message encoding parameter in one or both directions.

[0111] The description of the preferred embodiments and the figures merely serve to illustrate the invention and the beneficial effects associated therewith, but should not be understood to imply any limitation. The scope of the invention is to be determined solely by the appended claims.

LIST OF REFERENCE SIGNS

[0112] 10 system

[0113] 12 first channel node

[0114] 14 second channel node

[0115] 16 optical fiber connection

[0116] 16a first optical fiber

[0117] 16b second optical fiber

[0118] 18a, 18b intermediate optical channel nodes

[0119] 20 intermediate transport section

[0120] 22 first transponder

[0121] 24 second transponder

[0122] 26a preamplifier of the first channel node

[0123] 26b preamplifier of the second channel node

[0124] 28a first multiplexing section of the first channel node

[0125] 28b first multiplexing section of the second channel node

[0126] 30a second multiplexing section of the first channel node

[0127] 30b second multiplexing section of the second channel node

[0128] 32a post-amplifier of the first channel node

[0129] 32b post-amplifier of the second channel node

[0130] .sub.p wavelength of the first optical channel

[0131] . . . +.sub.p optical beam including added first optical channel

[0132] . . . .sub.p optical beam from which first optical channel has been dropped

[0133] B1 input beam

[0134] B2 output beam