Internet Draft                                        Debanjan Saha
Expiration Date:  Sept., 1, 2000                      Bala Rajagopalan
                                                      Bo Tang
                                                       Tellium Inc.

               RSVP Extensions for Signaling Optical Paths


1. Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

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2. Abstact

   This document has two objectives. First, we identify signaling
   requirements for setting up and maintaining Optical Switched Paths
   (OSPs) in mesh-connected optical networks. We then propose
   extensions to RSVP to satisfy some of these requirements within the
   context of MPLS-based traffic engineering framework.

3. Introduction

   The IETF is currently in the process of defining and standardizing a
   control architecture for creating and managing switched OSPs. A
   number of contributions [2,3,5] submitted to IETF, and other
   standards bodies have already addressed some of the important
   aspects of this architecture. In this document we have identified
   several key requirements for signaling OSPs within the framework
   proposed in [2,3,5] that take into account some of the intricacies
   of an optical network. In light of these observations, we have
   proposed extensions to RSVP-TE to satisfy the signaling requirements
   of OSPs.

   Internet Draft             draft-saha-rsvp-optical-signaling-00.txt

4. Optical Network Architecture

   The optical network model considered in this draft consists of
   multiple Optical Cross-Connects (OXCs) interconnected by optical
   links in a general topology referred to as an "optical mesh
   network". In general, it can be expected that topologically adjacent
   OXCs in an optical mesh network will be connected via multiple,
   parallel bi-directional links. Each link can carry one or more
   optical channels or wavelengths. Each wavelength can be further
   demultiplexed into multiple Sub-channels. We also assume that one or
   more control channels exist between neighboring OXCs for signaling

   Each OXC is assumed to be capable of switching a wavelength from a
   given input port to a given output port. This switching function is
   controlled by appropriately configuring a cross-connect table. In
   the most general case, the cross-connect table consists of entries
   of the form <input port i, wavelength j, sub-channel k, output port
   m, output wavelength n, output sub-channel p>, indicating that the
   Sub-channel k, in wavelength j entering input port i will be
   switched to Sub-channel p in output wavelength n at output port j.
   An "optical path" from an ingress port in an OXC to an egress port
   in a remote OXC is established by setting up suitable cross-connects
   in the ingress, the egress and a set of intermediate OXCs such that
   a continuous physical path exists from the ingress to the egress

   Automated establishment of optical paths involves setting up the
   cross-connect table entries in the appropriate OXCs in a coordinated
   manner such that the desired physical path is realized. The request
   to establish an optical path may arise from either a router (or some
   other device) connected to the OXCs or from a management system.
   Such a request must identify the ingress and the egress OXC as
   endpoints of the optical path. In addition, it may also optionally
   specify the input and output ports, wavelengths, and Sub-channels.
   The request may also include bandwidth parameters and channel type
   (e.g., OC-48/OC-192, 10 GE/N), reliability parameters, restoration
   options, setup and holding priorities for the path etc. On receipt
   of the request, the ingress OXC computes a suitable route for the
   requested path, following applicable policies and constraints. Once
   the route has been computed, the ingress invokes RSVP to set up the
   path. The purpose of this draft is to identify special requirements
   for signaling OSPs and propose extensions to RSVP protocol to
   satisfy those requirements.

5. Signaling Requirements

5.1 Support for Bi-directional OSPs

   A OSP can be either unidirectional or bi-directional. However, bi-
   directional OSPs are far more typical than unidirectional OSPs.
   Although a bi-directional OSP can be modeled as a pair of
   unidirectional OSPs that can be setup independently, there are many
   limitations to this approach. Most importantly, two separately
   signaled unidirectional OSPs may follow two different paths

   Internet Draft             draft-saha-rsvp-optical-signaling-00.txt

   altogether. Even if they follow the same path, it is quite likely
   that they will use two different ports/wavelengths/Sub-channels (on
   the same OXC) for the forward and the backward directions. Either
   scenario makes it difficult for the network management system to
   manage and maintain the OSPs, especially in the event of failures
   that trigger automatic fault isolation and restoration events such
   as SONET APS (Automatic Protection Switching). The ability to setup
   bi-directional OSPs also reduces the signaling complexity and setup

   Since RSVP is designed to setup unidirectional paths, extensions are
   required for signaling bi-directional paths. The tricky part here is
   the handling of the potential race condition. Since different nodes
   may autonomously initiate the signaling for optical paths, it is
   possible that two path set-up attempts are in progress at the same
   time. Specifically, while setting up an optical path, an OXC A may
   select output port i, which is connected to input port j of the
   "next" OXC B. Concurrently, OXC B may select output port j for
   setting up a different optical path, where the next downstream OXC
   is A. If they also happen to choose the same wavelength and Sub-
   channel (when applicable) this results in a "collision".  There are
   two ways to deal with such collisions. First, collisions may be
   detected and the involved paths may be torn down and re-established.
   Or, collisions may be avoided altogether. The latter solution is
   preferred, if the complexity involved is acceptable. In Section 5 we
   propose extensions to RSVP-tunnel to handle this race condition
   which avoids collision.

5.2 Support for Protection Paths

   Another important requirement for lighpaths is protection. We
   consider two primary protection modes:

   1. Span protection: In this mode the optical channel between
   every two adjacent OXCs along the primary path is protected
   individually. There are different modes of span protection,
   such as 1+1, M:N etc.

   2. Path protection: In this mode end-to-end backup paths are
   provisioned for the primary paths. In path protection backup
   paths are typically link or link and node disjoint from the
   primary paths. There could be various levels of sharing among
   backup paths, such as completely dedicated backup paths (1+1
   style), backup paths that are shared by multiple primary paths
   (M:N style), and backup paths that share resources
   (wavelengths) among themselves. In the first two cases the
   backup paths span between the same source and the destination
   pair and can be pre-setup. The backup paths that share
   resources among themselves can be pre-provisioned but can not
   be pre-setup. In this scenario the backup paths can span
   between different source and destination pairs.

   RSVP-TE has limited support for setting up protection paths. In
   section 7 we introduce new C-types to signal protection requirements
   for both span and path protection. We also introduce a new shared
   reservation style to enable sharing of resources among backup paths.

   Internet Draft             draft-saha-rsvp-optical-signaling-00.txt

5.3 Support for Permanent OSPs

   RSVP relies on soft-state mechanisms to maintain OSPs. If the Path
   and Resv states corresponding to a OSPs are not refreshed within the
   configured timeout value, they are timed out and the OSP is deleted.
   The requirements for OSPs are quite different. Most OSPs are long-
   lived and should not be torn down unless explicitly requested. Also,
   the impact of transient partial failures must be minimized in an
   optical network. Specifically, optical paths that are not directly
   affected by a failure must not be torn down due to the failure. For
   example, the control processor in an OXC may fail, affecting
   signaling and other internodal control communication. Similarly, the
   control channel between OXCs may be affected temporarily by a
   failure. These failures may not affect already established OSPs
   passing through the OXC fabric. These requirements can be summarized
   as follows:

   1. During setup OSPs can be configured as permanent OSPs. Permanent
   OSPs should not be torn down unless explicitly requested.

   2. The Path and Resv states for permanent OSPs need not be refreshed
   and should not be timed out.

   3. We need explicit mechanisms for tearing down permanent OSPs. This
   requires enhancements to PathTear and ResvTear messages since these
   messages are not refreshed and are not transported reliably.

6. Extensions for Bi-directional OSPs

   To avoid the potential race condition and collision in label
   assignment we propose a solution where the OXC with the higher node
   ID (IP address) is always the owner of the label space between two
   adjacent OXCs. For the purpose of this discussion we assume that a
   label consists of three components: (1) the port ID, (2) the
   wavelength ID, and (3) the sub-channel ID. We also assume that if
   port i on OXC1 is connected to port j on OXC2, both OXCs have that
   information available to them via link layer discovery protocol. The
   wavelength ID and the sub-channel ID are assumed to be the same on
   both OXCs.

   We define a new C_type for the label request object defined in [2]
   as follows:

   Label Request with OSP

   Class = 19, C_type = 10  (OSP_Tunnel)

      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
      |    Reserved    |    Flags     |             L3PID             |
      |                             Port ID                           |
      |          Wavelength ID        |      Sub-channel ID           |

   Internet Draft             draft-saha-rsvp-optical-signaling-00.txt

   Reserved: This field is reserved. It MUST be set to zero on
   transmission and MUST be ignored on receipt.

   Flags (8 bits):
   xxxxxxx0 û If the upstream OXC is the slave and no label has been
   xxxxxxx1 û If the upstream OXC is the master has chosen the label
   for the OSP.

   L3PID (16 bits): An identifier of the layer 3 protocol using this
   path. Standard Ethertype values are used.

   Port ID (32 bits): Valid only when the LSB of the Flags is set. It
   is the Port ID of the downstream OXC.

   Wavelength ID (16 bits): Valid only when the LSB of the Flags is
   set. It is the wavelength ID within the port ID.

   Sub-channel ID (16 bits): Valid only when the LSB of the Flags is
   set. It is the sub-channel ID within the wavelength ID.

   The basic scheme is as follows. The upstream OXC sends the
   Label_Request object with of C_type 4 to the downstream OXC. If the
   upstream OXC is the master (has higher node ID) it picks the label
   and sets the LSB of Flags to 1. If the upstream OXC is the slave, it
   sets the LSB of the Flags to 0 and the label is picked by the
   downstream OXC. Since the master irrespective of the direction of
   the message flow always picks the label, no collision occurs.

   We also add a new C_Type (10: OSP_Tunnel) to the Label object.  The
   LABEL object has the following format:

   LABEL class = 16, C_Type = 10

      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
      |                                                               |
      //                      (Object contents)                      //
      |                                                               |
      |                          Port ID                              |
      |        Wavelength ID       |           Sub-channel ID         |

   The contents of a LABEL object are a stack of labels, where each
   label is encoded in 8 octets as shown above. The top of the stack
   is in the right 8 octets of the object contents.  A LABEL object
   that contains no labels is illegal.

   Internet Draft             draft-saha-rsvp-optical-signaling-00.txt

7. Extensions for Protection Paths

   To handle this issue we propose a new C_type for the SESSION_ATTRIBUTE

      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
     |   OSP type    |  Local Prot.  | Local Prot. Extension         |
     |  Setup Prio   | Holding Prio  |         Reserved              |
     |                                                               |
     //                   Optional Subobjects                       //
     |                                                               |

    Class-Num: The Class-Num indicates that the object is 207. (TBD)

     C-Type: The C-Type OSP_Tunnel (10). (TBD)

     OSP Type (8 bits):

   01 Permanent Uni-directional Primary Path
   02 Primary Bi-directional Primary Path
   03 Permanent Uni-directional Backup Path
   04 Permanent Bi-directional Backup Path
   05 Permanent Uni-directional Shared Backup Path
   06 Permanent Bi-directional Shared Backup Path
   07 Soft-state Uni-directional Primary Path
   08 Soft-state Bi-directional Primary Path
   09 Soft-state Uni-directional Backup Path
   10 Soft-state Bi-directional Backup Path

   Local Protection (8 bits):
   01 1+1
   02 1:N

   Local Protection Extension (16 bits): Protection scheme specific

   Setup Priority: The priority of the session with respect to taking
   resources, in the range of 0 to 7.  The value 0 is the highest
   priority. The Setup Priority is used in deciding whether this
   session can preempt another session.

   Holding Priority: The priority of the session with respect to
   holding resources, in the range of 0 to 7.  The value 0 is the
   highest priority. Holding Priority is used in deciding whether this
   session can be preempted by another session.

   Besides the mandatory fields described above, the session attribute
   object may contain one or more optional subobjects. The subobjects
   are formatted as TLVs and are defined below.

   Internet Draft             draft-saha-rsvp-optical-signaling-00.txt

      0                   1
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
     |    Type       |     Length    | (Subobject contents)          |

   Type: The Type indicates the type of contents of the subobject.
   Currently defined values are:
                0   Reserved
                1   PRIMARY_OSP subobject
                2   SHARING_POLICY subobject

   The PRIMARY_OSP subobject may be included in the SESSION_ATTRIBUTE
   object while setting up a backup path. This subobject includes
   information about the primary OSP and may be used for functions such
   as local admission control, sharing of backup etc. The format and
   content of this subobject is TBD.

   SHARING_POLICY subobject may be included in the SESSION_ATTRIBUTE
   object while signaling to setup shared backup paths. This
   information can be used to facilitate local sharing decision. The
   format and content of this subobject is TBD.

   Note that for the shared backup paths the cross-connects can not be
   setup during the signaling for the backup path since multiple backup
   paths may share the same resource and can over-subscribe it. The
   idea behind shared backups is to make soft reservations and to claim
   the resource only when it is required. A shared backup path can be
   converted to a primary path by sending Path refresh messages with
   OSP Type set to 01 or 02 depending on the type of the backup path.

8. Extensions for Permanent OSPs

   In order to satisfy the requirements for a permanent OSP we need to
   the followings:

   1. Add a new session attribute that identifies a OSP as a permanent
   OSP. If this new attribute is not present, by default an OSP is
   considered a ôsoft-stateö OSP. For permanent OSPs, the Path State
   Block (PSB) and the Resv State Block (RSB) are never timed out. The
   only way to delete a permanent OSP is through explicit signaling,
   that is via a PathTear or a ResvTear message.

   2. Since the permanent OSPs are never timed out and the PathTear and
   ResvTear messages are not refreshed, we need additional mechanisms
   that can be used to tear down the permanent OSPs in a reliable way.
   One way to achieve this is to add reliability to PathTear and
   ResvTear messages as suggested in [4]. The other option is to change
   the OSP_TYPE of a permanent OSP to a soft-state OSP and then rely on
   RSVP soft-state mechanisms along with PathTear to tear down the OSP.

   Internet Draft             draft-saha-rsvp-optical-signaling-00.txt

 9. Summary

   This draft described some issues that arise in developing signaling
   procedures for path provisioning and restoration in optical
   networks. The following signaling requirements were identified:
   support for support for bi-directional optical path set-up with
   collision avoidance features, support for protected paths, and
   support for permanent OSPs. Other requirements may arise as work
   proceeds in this area. In light of these observations, we propose
   extensions to RSVP-TE to satisfy these requirements.

10.  References

   1. Awduche, D., Rekhter, Y., Drake, J., Coltun, R., "Multi-Protocol
   Lambda Switching: Combining MPLS Traffic Engineering Control With
   Optical Crossconnects", draft-awduche-mpls-te-optical-01.txt.

   2. Awduche, et al, "Extensions to RSVP for LSR Tunnels," draft-ietf-
   mpls-rsvp-lsp-tunnel-04.txt, Work in progress, September 1999

   3. Basak, D., Awduche, D., Drake, J., Rekhter, Y., "Multi-protocol
   Lambda Switching: Issues in Combining MPLS Traffic Engineering
   Control With Optical Crossconnects", draft-basak-mpls-oxc-issues-

   4. Berger L., Gan D., Swallow G., Pan P., Tommasi F., Molendini S.,
   ôRSVP Refresh Overhead Reduction Extensionsö, draft-ietf-rsvp-

   5. Rajagopalan B., Saha D., Tang B., Krishna B., ôSignaling Framework
   for Automated Establishment and Restoration of Paths in Optical Mesh
   Networksö, dratf-rstb-optical-signaling-framework-00.txt, March

11. Author Information

   Debanjan Saha, Bala Rajagopalan, Bo Tang
   Tellium Inc.
   2 Crescent Place
   P.O Box 901
   Ocean Port, NJ  07757
   Email: {dsaha, braja, btang}

        ********** This draft expires on Sept. 1, 2000  ***********