Network Working Group J. Meuric, Ed.
Internet-Draft E. Le Rouzic
Updates: RFC7689 (if approved) Orange
Intended status: Standards Track L. Alahdab
Expires: January 27, 2021 Individual
G. Galimberti
July 26, 2020

Conveying Transceiver-Related Information within RSVP-TE Signaling


The ReSource Reservation Protocol with Traffic Engineering extensions (RSVP-TE) allows to carry optical information so as to set up channels over Wavelength Division Multiplexing (WDM) networks between a pair of transceivers. Nowadays, there are many transceivers that not only support tunable lasers, but also multiple modulation formats. This memo leverages the Generalized Multiprotocol Label Switching protocol extensions to support the signaling of the associated information as a "mode" parameter within a "transceiver type" context.

Requirements Language

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119.

Status of This Memo

This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.

Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at

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This Internet-Draft will expire on January 27, 2021.

Copyright Notice

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Table of Contents

1. Introduction

The ITU-T's recommendation [G.694.1] defines the flexi-grid technology as the latest evolution of the WDM data plane. [RFC7689] defines the extensions to the RSVP-TE signaling ([RFC3473]) to provision lightpaths in WDM networks, from transceiver to transceiver, including transit Reconfigurable Optical Add-Drop Multiplexers (ROADMs). [RFC7792] specifies the encoding of the flex-grid label to be carried within RSVP-TE signaling messages, leveraging the reconfiguration capability of optical switches and the wavelength tunability of the transceivers at both ends of the optical signal.

To address the various requirements of optical networks, some transceivers are supporting multiple modulation formats, baudrates, FECs, etc. This capability enables to select at setup time the right trade-off between bitrate, baudrate, reach, spectral width, etc. This memo defines the required fields to explicitly addresses this case of "elastic" transceivers. Two options are proposed to address this issue. The first extension relies on a two-stage identifier: a Transceiver Type, allowing to summarize the set of capabilities and consistently correlate both ends of a given optical channel, and a Transceiver ModeID, i.e. a hardware-related identifier to be interpreted within the Type context. The second extension replaces the aforementioned ModeID by a set of optical parameters. In the latter, the exact list of fields will follow [I-D.ietf-ccamp-dwdm-if-param-yang]

2. Main Use Cases

In the following section, it is assumed that, to be able to meet optical performance requirements, the Routing and Wavelength Assignment (RWA) tasks are performed before the signaling messages leave the ingress ROADM. This could happen in various ways, provided the network topology is available, including optical parameters (e.g., advertised using [I-D.ietf-ccamp-wson-iv-encode]). This includes ROADM-local computation process, passive PCE responding to the ingress ROADM's request [I-D.ietf-pce-wson-rwa-ext]), as well centralized controllers relying on PCEP to trigger the RSVP-TE signaling in the ingress node ([RFC8281]).

2.1. Single Control Domain

We consider that transceivers are in the same control domain as the optical switches. In many deployments, transceivers are embedded in the edge ROADM shelves, where both the transceiver and the optical switching are configured by the same set of local control processes. In this case, carrying the Mode parameter in RSVP-TE signaling is required to configure the egress side of the signaling session. Even though some receiver implementations may be able to detect the modulation format without configuration, most operational deployments rely on bidirectional signals, thus making the modulation information a mandatory parameter to fully configure the egress transceiver in most cases.

The specification below allows to address this use case.

2.2. Open Line Systems

We now consider that transceivers are installed in shelves independant from the ROADMs. The set of ROADMs is referred to as the "optical line", the shelves carrying the transceivers are named "client devices". This use case is aligned with the problem statement specified in [I-D.ietf-ccamp-dwdm-if-mng-ctrl-fwk] and is consistent with [RFC7698].

    --Path-->  --Path-->                           --Path-->
            ___  _ _ _                    _ _ _  ___
   ___     |   |/              _ _ _  ___      \|   |     ___
  |   |____|   |_ _ _               \|   |      |   |____|   |
  |___|    |   |                     |   |      |   |    |___|
    Ti     |___|\_ _ _               |   |_____/|___|      Te
             Ri                _ _ _/|___|        Re
    <--Resv--  <--Resv--               R           <--Resv--

Figure 1: Transceivers (Ti, Te) Connected to an Open Line System

T is a transceiver shelf.

R is a ROADM. Only edge ROADMs are depicted here but le line system is typically a mesh of multiple ROADMs and amplifiers.

From the signaling perspective, T and R are refered to as Ti/Ri (Te/Re) to identify the ingress end (egress end, respectively).

The network topology and the associated optical parameters are only advertised among the ROADMs, part of the line system, i.e. the topology information does not leak up to the transceiver shelves (otherwise, that is a specific case of [CREF1]Section 2.1). Therefore, beyond the usual signaling features, the resulting signaling messages serve 3 additional purposes:

The specification below allows to address this use case.

3. Signaling Messages

The following sections specify the fields used in the RSVP-TE Path and Resv messages to address the requirements above.

3.1. Encodings

This documents specifies two sub-TLVs. Both serve the same purpose, with a different level of details: the transceiver mode is described either using an identifier or a detailed set of parameters. As a result, an RSVP-TE message SHOULD only carry one of the sub-TLV for a given hop. In case several of the sub-TLVs below are included, the first one takes precedence and the following ones are ignored.

3.1.1. WDM-Transceiver-ModeID Sub-TLV

This document introduces the WDM-Transceiver-ModeID sub-TLV so as to carry the Transceiver Type and ModeID. It has the following format:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   |  Type = TBD1  |  Length = 16  |   Reserved    |AppID Type=TBD6|
   |                              OUI                              |
   |          OUI (cont'd)         |            ModeID             |
   |                            Tsv-Type                           |

Application ID Type (8 bits): As per section 5 of [I-D.ietf-ccamp-dwdm-if-lmp], this field allows to distinguish between the possible encodings of the trailing "Application ID" field. This specification defines a new Application ID Type (value TBD6) that extends the "Proprietary" type and specifies specific fields within the "value" bytes:

Tsv-Type (32 bits): A transponder-specific value allowing to identify a compatible Tsv-Type at the remote end, and supporting a set of optical ModeIDs. This value MUST be included by the ingress transceiver, i.e. from the signaling first hop. 0 is a Reserved value that MUST trigger a PathErr message in response, with Error Code 24 (Routing Problem) and Error Sub-code TBD3 ("Unsupported Tsv-Type").

ModeID (16 bits): Within a given Tsv-Type, this ID allows to specify how the transceiver should be configured among the set of options supported by Tsv-Type; e.g. optical modulation format or baudrate. The value 0 means that the sending device has not chosen a particular ModeID and expects this information to be determined by a downstream node (e.g., the ingress ROADM of the optical line). If the Tsv-Type resolves into a single ModeID, the ModeID field SHOULD use a non-zero value and MAY be ignored. A transceiver receiving a ModeID with the value 0 MAY select a mode based on local policies combined to other signaling information, e.g. channel spectral width.

3.1.2. WDM-Tranceiver-Param Sub-TLV

This document introduces the WDM-Transceiver-Param sub-TLV so as to carry the Transceiver Type identifier and the "detailed mode" description, which is a subset of the ones specified in [I-D.ietf-ccamp-dwdm-if-param-yang]. It is aligned on figure 3 in [I-D.ggalimbe-ccamp-flexigrid-carrier-label] and has the following format:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   |          Type = TBD           |          Length = 20          |
   |       Modulation Format       |        Bits per Symbol        |
   |            FEC-ID             |      Min OSNR Threshold       |
   |                           Baud-rate                           |
   |      Channel output power     |           Tsv-Type            |

Modulation Format: A codepoint identifying the modulation format of the transceiver signal. Knowing this parameter is not mandatory to perform an optical path computation, thus the value 0 is acceptable within a successful signaling session.

Bits per Symbol (16 bits): A nonnegative integer specifying the number of bits encoded per symbol value in case of hybrid modulation format. It is an off-set with values from 0 to 127 to be applied to the specified Modulation Format and indicates the mix between the selected Modulation Format and its upper adjacent (e.g. QPSK + 63 bits per symbol indicates that there is a 50% MIX between QPSK and 8-QAM = 2.5 bits per symbol). If value = 0 the standard Modulation Format is applied.

FEC-ID (16 bits): A codepoint identifying the Forward Error Correction of the transceiver.

Min OSNR Threshold (16 bits): An integer specifying the minimum accepted threshold for the Optical Signal-Noise Ratio in 0.1 nm.

Baud-rate (32 bits): A nonnegative integer specifying the number of symbols per second.

Channel Ouput Power (16 bits): An integer specifying the signal power coming out of the transceiver (in dB or W?). The value 0 means "unspecified". If a transceiver receives an unspecified value, its data plane SHOULD be configured according to its local policy (e.g. fixed or default value).

Tsv-Type (16 bits): A transponder-specific value allowing to identify a compatible Tsv-Type at the remote end. This field MAY be set to 0, which is a reserved value to disable Tsv-Type checking between end transceivers (e.g. because it is useless).

3.2. Processing

3.2.1. Downstream Direction

The parameters to be used by the egress transceivers are carried in Path messages. In RSVP-TE signaling, hop-specific information is encoded within the ERO as hop attributes and WDM parameters are to be carried as sub-TLVs within the Type 4 TLV of the Hop Attribute subobject [RFC7689].

When sending a Path message, if a signaling head end node includes one of the WDM-Transceiver sub-TLVs specified in this document, the entity in charge of the path computation (e.g. the ingress ROADM) MUST include (unless an error is raised), as part of the ERO population step, the same sub-TLV to specify the Hop Attibutes of the tail end transceiver, allowing this information to be propagated along the RSVP-TE Path messages.

A signaling head end node sending a Path message including one of the WDM-Transceiver sub-TLVs specified in the previous section with unallocated values, i.e. Mode-defining fields set to 0 (e.g. "ModeID = 0" in the WDM-Transceiver-ModeID sub-TLV), MUST include an empty RRO to request its population by some downstream nodes [RFC3209]. In case the Mode specification is fully defined before the first signaling hop (e.g. operator-specified), the use of the RRO remains OPTIONAL.

3.2.2. Upstream Direction

When the mode selection happens after the signaling has left the signaling head node, which carries the ingress transceiver, the selected value needs to be sent back to the head node. As specified in [RFC7570], it can be included in the Record Route Object (RRO) within RSVP-TE Resv messages. Starting from the fact that both end transceivers share a common mode to properly set up a channel, this leads to the following processing:

4. IANA Considerations

The IANA is requested to allocate, from the "Sub-TLV Types for WSON Processing Hop Attribute TLV" section within the "RSVP-TE Parameters" registry:

Value Meaning Reference
TDB1 WDM-Transceiver-ModeID [This I-D]
TDB2 WDM-Transceiver-Param [This I-D]

The IANA is requested to allocate, from the "Error Codes and Globally-Defined Error Value Sub-Codes" section within the "RSVP Parameters" registry:

Error Code Sub-code Meaning Reference
24 TBD3 Unsupported Tsv-Type [This I-D]
TBD4 Unsupported Transceiver Mode [This I-D]
TBD5 Unable to Select Transceiver Mode [This I-D]

The IANA is requested to create, within the "GMPLS Signaling Parameters" registry, two new sub-registries named "WDM Modulation Formats" and "WDM FEC Types".

For both of them:

The "WDM Modulation Format" sub-registry is initialized as follows:

Value Modulation Format
0 Pending selection
2 8-QAM
3 16-QAM
4 32-QAM
5 64-QAM
6-63999 Unallocated
64000-65535 Vendor-specific use

The "WDM FEC Types" sub-registry is initialized as follows:

Value FEC Types
0 Pending selection
1 Reed Solomon FEC
2 Staircase FEC
4-63999 Unallocated
64000-65535 Vendor-specific use

The IANA is requested to allocate, from the "Application ID Type" section within the "LMP" registry:

Type Meaning Reference
TBA G.698.2 [I-D.ietf-ccamp-dwdm-if-lmp]
TBA OUI + proprietary value [I-D.ietf-ccamp-dwdm-if-lmp]
TBD6 OUI + Tsv-Type + ModeID [This document]

5. Security Considerations

This specification only adds TLVs to RSVP-TE signaling messages. As a result, it relies on security guidelines documented in [RFC5920].

6. Acknowledgements

The authors would like to thank Ramon Casellas for his valuable feedback on the work related to this document.

7. References

7.1. Normative References

[I-D.ggalimbe-ccamp-flexigrid-carrier-label] Galimberti, G., Fauci, D., Zanardi, A., Galvagni, L. and J. Meuric, "Signaling extensions for Media Channel sub-carriers configuration in Spectrum Switched Optical Networks (SSON) in Lambda Switch Capable (LSC) Optical Line Systems.", Internet-Draft draft-ggalimbe-ccamp-flexigrid-carrier-label-09, March 2020.
[I-D.ietf-ccamp-dwdm-if-lmp] Hiremagalur, D., Grammel, G., Galimberti, G., Kunze, R. and D. Beller, "Extension to the Link Management Protocol (LMP/DWDM -rfc4209) for Dense Wavelength Division Multiplexing (DWDM) Optical Line Systems to manage the application code of optical interface parameters in DWDM application", Internet-Draft draft-ietf-ccamp-dwdm-if-lmp-02, May 2020.
[I-D.ietf-pce-wson-rwa-ext] Lee, Y. and R. Casellas, "PCEP Extension for WSON Routing and Wavelength Assignment", Internet-Draft draft-ietf-pce-wson-rwa-ext-16, March 2019.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997.
[RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V. and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001.
[RFC3473] Berger, L., "Generalized Multi-Protocol Label Switching (GMPLS) Signaling Resource ReserVation Protocol-Traffic Engineering (RSVP-TE) Extensions", RFC 3473, DOI 10.17487/RFC3473, January 2003.
[RFC5920] Fang, L., "Security Framework for MPLS and GMPLS Networks", RFC 5920, DOI 10.17487/RFC5920, July 2010.
[RFC7570] Margaria, C., Martinelli, G., Balls, S. and B. Wright, "Label Switched Path (LSP) Attribute in the Explicit Route Object (ERO)", RFC 7570, DOI 10.17487/RFC7570, July 2015.
[RFC7689] Bernstein, G., Xu, S., Lee, Y., Martinelli, G. and H. Harai, "Signaling Extensions for Wavelength Switched Optical Networks", RFC 7689, DOI 10.17487/RFC7689, November 2015.
[RFC7792] Zhang, F., Zhang, X., Farrel, A., Gonzalez de Dios, O. and D. Ceccarelli, "RSVP-TE Signaling Extensions in Support of Flexi-Grid Dense Wavelength Division Multiplexing (DWDM) Networks", RFC 7792, DOI 10.17487/RFC7792, March 2016.
[RFC8281] Crabbe, E., Minei, I., Sivabalan, S. and R. Varga, "Path Computation Element Communication Protocol (PCEP) Extensions for PCE-Initiated LSP Setup in a Stateful PCE Model", RFC 8281, DOI 10.17487/RFC8281, December 2017.

7.2. Informative References

[I-D.ietf-ccamp-dwdm-if-mng-ctrl-fwk] Kunze, R., Grammel, G., Beller, D., Galimberti, G. and J. Meuric, "A framework for Management and Control of DWDM optical interface parameters", Internet-Draft draft-ietf-ccamp-dwdm-if-mng-ctrl-fwk-13, July 2019.
[I-D.ietf-ccamp-dwdm-if-param-yang] Galimberti, G., Kunze, R., Burk, A., Hiremagalur, D. and G. Grammel, "A YANG model to manage the optical interface parameters for an external transponder in a WDM network", Internet-Draft draft-ietf-ccamp-dwdm-if-param-yang-04, May 2020.
[I-D.ietf-ccamp-wson-iv-encode] Martinelli, G., Lee, Y., Galimberti, G. and F. Zhang, "Information Encoding for WSON with Impairments Validation", Internet-Draft draft-ietf-ccamp-wson-iv-encode-02, January 2019.
[RFC7698] Gonzalez de Dios, O., Casellas, R., Zhang, F., Fu, X., Ceccarelli, D. and I. Hussain, "Framework and Requirements for GMPLS-Based Control of Flexi-Grid Dense Wavelength Division Multiplexing (DWDM) Networks", RFC 7698, DOI 10.17487/RFC7698, November 2015.

Authors' Addresses

Julien Meuric (editor) Orange 2 avenue Pierre Marzin Lannion, 22300 France EMail:
Esther Le Rouzic Orange 2 avenue Pierre Marzin Lannion, 22300 France EMail:
Luay Alahdab Individual Lannion, 22300 France EMail:
Gabriele Galimberti Cisco Via S. Maria Molgora, 48 c Vimercate, 20871 Italy EMail: