GMPLS Synchronized Signaling for Optical Lightpath Setup
draft-martinelli-ccamp-synch-signaling-01.txt

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Abstract

In Generalized Multi-Protocol Label Switching (GMPLS) several extension are proposed to cope with constrain provide Wavelength Switched Optical Networks (WSON). One of the technology constrain related to Dense Wavelength Division Multiplexing (DWDM) systems is the bi-directionality of the lightpath. This memo provides some consideration about how extending the signaling phase to cope with the bi-directional requirements. The procedure is independent from the wavelength continuity constrain in both direction.

Table of Contents

1.  Introduction
2.  Information Required
3.  Bi-Directional Signaling Procedure
    3.1.  Synchronized Signaling Steps
    3.2.  Errors and Roll Back
    3.3.  Advantages and Disadvantages
4.  Backward Compatibility Considerations
5.  Error management
6.  Acknowledgments
7.  Contributing Authors
8.  IANA Considerations
9.  Security Considerations
10.  References
    10.1.  Normative References
    10.2.  Informative References
§  Authors' Addresses

1.  Introduction

The Generalized Multi-Protocol Label Switching (GMPLS) [RFC3945] (Mannie, E., “Generalized Multi-Protocol Label Switching (GMPLS) Architecture,” October 2004.) extension related to Wavelength Switched Optical Networks (WSON) has to cope with the bidirectional LSP issue.

The [RFC3471] (Berger, L., “Generalized Multi-Protocol Label Switching (GMPLS) Signaling Functional Description,” January 2003.) and [RFC3473] (Berger, L., “Generalized Multi-Protocol Label Switching (GMPLS) Signaling Resource ReserVation Protocol-Traffic Engineering (RSVP-TE) Extensions,” January 2003.) define the functional framework and encoding for bidirectional LSP setup. The presence of an Upstream Label Object (UL) during the signaling phase means that the LSP request is bidirectional and it also identifies the label to be used in the reverse direction.

In the WSON [I‑D.ietf‑ccamp‑rwa‑wson‑framework] (Bernstein, G., “Framework for GMPLS and PCE Control of Wavelength Switched Optical Networks (WSON),” March 2009.) context the bi-directionality appears as a strong requirement due to current available DWDM technology. The bidirectional LSP does not strictly require using the same wavelength in the two directions, however this could be a constrain in some deployed network while in other case this constrain can be relaxed (although keeping the bi-directionality).

In extending signaling to WSON requirements the following ID [I‑D.bernstein‑ccamp‑wson‑signaling] (Bernstein, G., “Signaling Extensions for Wavelength Switched Optical Networks,” February 2010.) explain a procedure regarding the signaling of a bidirectional LSP. The defined signaling extensions handle the setup of the upstream channel in the context of the downstream LSP session by adding additional objects to the request and requiring special node behaviors. This approach has some limitations in specific scenarios such as the case when path characteristics must be collected from source to destination (e.g. the optical signal parameters) as only the downstream direction can be evaluated. As an example considering a lightpath within an impairment aware control plane ([I‑D.ietf‑ccamp‑wson‑impairments] (Bernstein, G., “A Framework for the Control of Wavelength Switched Optical Networks (WSON) with Impairments,” June 2009.)) even if the same wavelength is used for both directions the optical impairments for the two directions can be very different.

This memo defines an operational procedure that exploits the bi-directionality with minimum requirements in term of protocol extensions and introducing a synchronization among the two signaling phases. [RFC3471] (Berger, L., “Generalized Multi-Protocol Label Switching (GMPLS) Signaling Functional Description,” January 2003.) list a set of disadvantages of using two unidirectional path to implement a bi-directional LSP. The memo also review some of advantages and disadvantages with focus on optical lightpath.

2.  Information Required

To set up a bidirectional LSP in a WSON environment we need to identify the information required. Some information is already defined in standards like [RFC3473] (Berger, L., “Generalized Multi-Protocol Label Switching (GMPLS) Signaling Resource ReserVation Protocol-Traffic Engineering (RSVP-TE) Extensions,” January 2003.), others might be identified as specific to WSON.

For the current purpose we identify the following information that need to be carried along the signaling phase:

• LSP bi-directionality. According to [RFC3471] (Berger, L., “Generalized Multi-Protocol Label Switching (GMPLS) Signaling Functional Description,” January 2003.) the Upstream Label Object presence is a trigger for bi-directionality.
• Wavelength Bi-directionality. In some specific cases the network might require the same wavelength used in both directions.

3.  Bi-Directional Signaling Procedure

3.1.  Synchronized Signaling Steps

The Bidirectional signaling is implemented through two independent signaling sessions (one for each direction) that are performed in synch keeping the upstream signaling nested in the downstream one. In this description we use the terms 'source' and 'destination' referring to the first request issued (downstream). For the upstream direction the destination is the node emitting the PATH and source the one emitting the RESV.

1. The source node signals a PATH request to the destination node for the downstream channel.
2. The destination node may apply any path validation procedure to asses the path feasibility.
3. The destination node signals a PATH request to the source node for the upstream channel with the path constrained by the ERO to use the same path as the downstream channel and, if requested, an initial LABEL_SET Object specifying the wavelengths available for the downstream LSPs (e.g. if the same wavelength is required for both direction).
4. The source node signals the RESV for the upstream channel to the destination node. The channel cross-connections are setup in the nodes.
5. The destination node signals the RESV for the downstream channel to the source node; if requested, the same wavelength selected by the upstream LSPs is signaled. The channel cross-connections are setup in the nodes.

+------+             +------+              +------+
| LSR  |             | LSR  |              | LSR  |
|  S   |             |  i   |              |  D   |
+------+             +------+              +------+
   |                     |                     |
   |      path-d         |                     |
   |---------            |                     |
   |         `---------->|                     |
   |                     |      path-d         |
   |                     |---------            |
   |                     |         `---------->|
   |                     |                     |
   |                     |      path-u         |
   |                     |          ___________|
   |                     |         /           |
   |       path-u        |<--------            |
   |          ___________|                     |
   |         /           |                     |
   |<--------            |                     |
   |      resv-u         |                     |
   |---------            |                     |
   |         `---------->|                     |
   |                     |      resv-u         |
   |                     |---------            |
   |                     |         `---------->|
   |                     |          ___________|
   |                     |         /           |
   |       resv-d        |<--------            |
   |          ___________|                     |
   |         /           |                     |
   |<--------            |                     |
   |                     |                     |

Message Sequence Chart for bidirectional synchronized LSP setup.

The Figure 1 shows in a graphical format how the upstream signaling phase is nested within the downstream one, where:

"LSR S" is the source node, "LSR i" is any intermediate node and "LSR D" is the destination node

path-d represents the path signaling phase downstream that has to be bidirectional

path-u represents the path signaling phase upstream

resv-u represent the reservation phase for upstream

resv-d represent the reservation phase for downstream

3.2.  Errors and Roll Back

In case of any error triggered the roll back procedure goes through a standard process apart from the processing at the destination node.

1. In case of error in the upstream LSP setup in the PATH or RESV signaling phase (PATHERR message received by the destination node), a PATHERR message is issued for the downstream node.
2. In case of error in the downstream RESV signaling phase, a PATHTEAR message is issued by the destination node for the upstream LSP

3.3.  Advantages and Disadvantages

The procedure has the following advantages

• standard processing of RSVP-TE messages (no additional operations performed in the RESV message processing)
• no need for ResvConf messages (each channel source point knows when the channel is setup by receiving the RESV message)
• the symmetrical resource allocation constraint could be removed: a different wavelength can be used for the upstream channel (the wavelength can be discovered with the usual LABEL_SET object management)
• in the MIBs (LSP MIB) both the upstream and downstream channel resources (labels, in-segment, out-segment) are explicitly reported

We can identify the following disadvantages:

• Longer setup time due to double signaling. This issue however has to be evaluated in term of lightpath. They have slow setup time.
• The two LSPs are not explicitly associated in the network nodes; only the destination node keeps track of the relation. Two possible options can be foreseen:
  1. additional info in the RSVP PATH message with associated LSP Id (and direction)
  2. associating the two LSP (upstream,downstream) to a CALL [RFC4974] (Papadimitriou, D. and A. Farrel, “Generalized MPLS (GMPLS) RSVP-TE Signaling Extensions in Support of Calls,” August 2007.) (even if you then need to signal the CALL too...)

4.  Backward Compatibility Considerations

A full WSON signaling solution could not be compatible, in this case the possibility to reject bidirectional signaling shall be implemented (Example in [I‑D.bernstein‑ccamp‑wson‑signaling] (Bernstein, G., “Signaling Extensions for Wavelength Switched Optical Networks,” February 2010.)).

5.  Error management

Specific Error management for the bidirectional case.

6.  Acknowledgments

7.  Contributing Authors

This document was the collective work of several authors. The text and content of this document was contributed by the editors and the co-authors listed below (the contact information for the editors appears in appropriate section and is not repeated below):

   Gabriele Maria Galimberti
   Cisco Systems
   via Philips 12
   Monza  20052
   Italy

   Email: ggalimbe@cisco.com

   Alberto Tanzi
   Cisco Systems
   via Philips 12
   Monza  20052
   Italy
   Email: atanzi@cisco.com

   Domenico La Fauci
   Cisco Systems
   via Philips 12
   Monza  20052
   Italy

   Email: dlafauci@cisco.com


   Elio Salvadori
   CREATE-NET
   via alla Cascata 56 C, Povo
   Trento  38100
   Italy

   Email: elio.salvadori@create-net.org


   Chava Vijaya Saradhi
   CREATE-NET
   via alla Cascata 56 C, Povo
   Trento  38100
   Italy

   Email: saradhi.chava@create-net.org

8.  IANA Considerations

This memo includes no request to IANA.

All drafts are required to have an IANA considerations section (see the update of RFC 2434 (Narten, T. and H. Alvestrand, “Guidelines for Writing an IANA Considerations Section in RFCs,” March 2008.) [I‑D.narten‑iana‑considerations‑rfc2434bis] for a guide). If the draft does not require IANA to do anything, the section contains an explicit statement that this is the case (as above). If there are no requirements for IANA, the section will be removed during conversion into an RFC by the RFC Editor.

9.  Security Considerations

This document introduces no new security considerations to [RFC3473] (Berger, L., “Generalized Multi-Protocol Label Switching (GMPLS) Signaling Resource ReserVation Protocol-Traffic Engineering (RSVP-TE) Extensions,” January 2003.). GMPLS security is described in section 11 of [RFC3471] (Berger, L., “Generalized Multi-Protocol Label Switching (GMPLS) Signaling Functional Description,” January 2003.).

10.  References

10.1. Normative References

10.2. Informative References

Authors' Addresses