VCAT/LCAS GMPLS: Operating Virtual Concatenation (VCAT) and the Link Capacity Adjustment Scheme (LCAS) with Generalized Multi-Protocol Label Switching (GMPLS)

Internet Engineering Task Force (IETF)                 G. Bernstein, Ed.
Request for Comments: 6344                             Grotto Networking
Updates: 4606                                                D. Caviglia
Category: Standards Track                                       Ericsson
ISSN: 2070-1721                                                R. Rabbat
                                                                  Google
                                                         H. van Helvoort
                                                                  Huawei
                                                             August 2011


               Operating Virtual Concatenation (VCAT) and
               the Link Capacity Adjustment Scheme (LCAS)
        with Generalized Multi-Protocol Label Switching (GMPLS)

Abstract

   This document describes requirements for, and the use of, the
   Generalized Multi-Protocol Label Switching (GMPLS) control plane in
   support of the Virtual Concatenation (VCAT) layer 1 inverse
   multiplexing data plane mechanism and its companion Link Capacity
   Adjustment Scheme (LCAS).  LCAS can be used for hitless dynamic
   resizing of the inverse multiplex group.  These techniques apply to
   Optical Transport Network (OTN), Synchronous Optical Network (SONET),
   Synchronous Digital Hierarchy (SDH), and Plesiochronous Digital
   Hierarchy (PDH) signals.  This document updates RFC 4606 by making
   modifications to the procedures for supporting virtual concatenation.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc6344.

Copyright Notice

   Copyright (c) 2011 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   described in the Simplified BSD License.

Table of Contents

   1. Introduction ....................................................3
      1.1. Conventions Used in This Document ..........................4
   2. VCAT/LCAS Scenarios and Specific Requirements ...................4
      2.1. VCAT/LCAS Interface Capabilities ...........................4
      2.2. Member Signal Configuration Scenarios ......................5
      2.3. VCAT Operation with or without LCAS ........................6
      2.4. VCGs and VCG Members .......................................7
   3. VCAT Data and Control Plane Concepts ............................7
   4. VCGs Composed of a Single Member Set (One LSP) ..................8
      4.1. One-Shot VCG Setup .........................................8
      4.2. Incremental VCG Setup ......................................9
      4.3. Procedure for VCG Reduction by Removing a Member ...........9
      4.4. Removing Multiple VCG Members in One Shot .................10
      4.5. Teardown of Whole VCG .....................................10
   5. VCGs Composed of Multiple Member Sets (Multiple LSPs) ..........10
      5.1. Signaled VCG Service Layer Information ....................11
      5.2. CALL_ATTRIBUTES Object VCAT TLV ...........................12
      5.3. Procedures for Multiple Member Sets .......................14
           5.3.1. Setting Up a New VCAT Call and VCG Simultaneously ..14
           5.3.2. Setting Up a VCAT Call and LSPs without a VCG ......14
           5.3.3. Associating an Existing VCAT Call with a New VCG ...15
           5.3.4. Removing the Association between a Call and VCG ....15
           5.3.5. VCG Bandwidth Modification .........................15
   6. Error Conditions and Codes .....................................16
   7. IANA Considerations ............................................17
      7.1. RSVP Call Attribute TLV ...................................17
      7.2. RSVP Error Codes and Error Values .........................17
      7.3. VCAT Elementary Signal Registry ...........................18
      7.4. VCAT VCG Operation Actions ................................18
   8. Security Considerations ........................................18
   9. Contributors ...................................................19
   10. Acknowledgments ...............................................19
   11. References ....................................................19
      11.1. Normative References .....................................19
      11.2. Informative References ...................................20

1.  Introduction

   The Generalized Multi-Protocol Label Switching (GMPLS) suite of
   protocols allows for the automated control of different switching
   technologies, including the Synchronous Optical Network (SONET),
   Synchronous Digital Hierarchy (SDH), Optical Transport Network (OTN),
   and Plesiochronous Digital Hierarchy (PDH).  This document updates
   the procedures described in [RFC4606] to allow supporting additional
   applications of the Virtual Concatenation (VCAT) layer 1 inverse
   multiplexing mechanism that has been standardized for SONET, SDH,
   OTN, and PDH [ANSI-T1.105] [ITU-T-G.707] [ITU-T-G.709] [ITU-T-G.7043]
   technologies, along with its companion Link Capacity Adjustment
   Scheme (LCAS) [ITU-T-G.7042].

   VCAT is a time-division multiplexing (TDM)-oriented byte striping
   inverse multiplexing method that works with a wide range of existing
   and emerging TDM framed signals, including very-high-bit-rate OTN and
   SDH/SONET signals.  VCAT enables the selection of an optimal signal
   server bandwidth (size) utilizing a group of server signals and
   provides for efficient use of bandwidth in a mesh network.  When
   combined with LCAS, hitless dynamic resizing of bandwidth and fast
   graceful degradation in the presence of network faults can be
   supported.  To take full advantage of VCAT/LCAS functionality,
   additional extensions to GMPLS signaling are needed that enable the
   setup of diversely routed signals that are members of the same VCAT
   group.  Note that the scope of this document is limited to scenarios
   where all member signals of a VCAT group are controlled using
   mechanisms defined in this document and related RFCs.  Scenarios
   where a subset of member signals are controlled by a management plane
   or a proprietary control plane are outside the scope of this
   document.

1.1.  Conventions Used in This Document

   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 [RFC2119].

2.  VCAT/LCAS Scenarios and Specific Requirements

   There are a number of specific requirements for the support of
   VCAT/LCAS in GMPLS that can be derived from the carriers'
   applications for the use of VCAT/LCAS.  These are set out in the
   following section.

2.1.  VCAT/LCAS Interface Capabilities

   In general, a label switched router (LSR) can be an ingress/egress of
   one or more VCAT groups.  VCAT and LCAS are data plane interface
   capabilities.  An LSR may have, for example, VCAT-capable interfaces
   that are not LCAS-capable.  It may at the same time have interfaces
   that are neither VCAT-capable nor LCAS-capable.

2.2.  Member Signal Configuration Scenarios

   We list in this section the different scenarios.  Here we use the
   [ITU-T-G.707] term "VCG" to refer to the VCAT group and the
   terminology "set" and "subset" to refer to the subdivision of the
   group and the individual VCAT group member signals.  As noted above,
   the scope of these scenarios is limited to scenarios where all member
   signals are controlled using mechanisms defined in this document.

   The scenarios listed here are dependent on the terms "co-routed" and
   "diversely routed".  In the context of this document, "co-routed"
   refers to a set of VCAT signals that all traverse the same sequence
   of switching nodes.  Furthermore, a co-routed set of signals between
   any pair of adjacent nodes utilizes a set of links that have similar
   delay characteristics.  Thus, "diversely routed" means a set of
   signals that are not classed as "co-routed".

   Fixed, co-routed: A fixed-bandwidth VCG, transported over a co-routed
      set of member signals.  This is the case where the intended
      bandwidth of the VCG does not change and all member signals follow
      the same route to minimize differential delay.  The application
      here is the capability to allocate an amount of bandwidth close to
      that required at the client layer.

   Fixed, diversely routed: A fixed-bandwidth VCG, transported over at
      least two diversely routed subsets of member signals.  In this
      case, the subsets are link-disjoint over at least one link of the
      route.  The application here is more efficient use of network
      resources, e.g., no unique route has the required bandwidth.

   Fixed, member sharing: A fixed-bandwidth VCG, transported over a set
      of member signals that are allocated from a common pool of
      available member signals without requiring member connection
      teardown and setup.  This document only covers the case where this
      pool of "potential" member signals has been established via
      mechanisms defined in this document.  Member signals need not be
      co-routed or be guaranteed to be diversely routed.  Note that by
      the nature of VCAT, a member signal can only belong to one VCG at
      a time.  To be used in a different VCG, a signal must first be
      removed from any VCG to which it may belong.

   Dynamic, co-routed: A dynamic VCG (bandwidth can be increased or
      decreased via the addition or removal of member signals),
      transported over a co-routed set of members.  The application here
      is dynamic resizing and resilience of bandwidth.

   Dynamic, diversely routed: A dynamic VCG (bandwidth can be increased
      or decreased via the addition or removal of member signals),
      transported over at least two diversely routed subsets of member
      signals.  The application here is efficient use of network
      resources, dynamic resizing, and resilience of bandwidth.

   Dynamic, member sharing: A dynamic-bandwidth VCG, transported over a
      set of member signals that are allocated from a common pool of
      available member signals without requiring member connection
      teardown and setup.

2.3.  VCAT Operation with or without LCAS

   VCAT capabilities may be present with or without the presence of
   LCAS.  The use of LCAS is beneficial in the provisioning of flexible
   bandwidth services, but in the absence of LCAS, VCAT is still a valid
   technique.  Therefore, GMPLS mechanisms for the operation of VCAT are
   REQUIRED for both the case where LCAS is available and the case where
   it is not available.  The GMPLS procedures for the two cases SHOULD
   be identical.

   o  GMPLS signaling for LCAS-capable interfaces MUST support all
      scenarios described in Section 2.2 with no loss of traffic.

   o  GMPLS signaling for non-LCAS-capable interfaces MUST support the
      "fixed" scenarios described in Section 2.2.

   To provide for these requirements, GMPLS signaling MUST carry the
   following information on behalf of the VCAT endpoints:

   o  The type of the member signal that the VCG will contain, e.g.,
      VC-3, VC-4, etc.

   o  The total number of members to be in the VCG.  This provides the
      endpoints in both the LCAS and non-LCAS case with information on
      which to accept or reject the request, and in the non-LCAS case
      will let the receiving endpoint know when all members of the VCG
      have been established.

   o  Identification of the VCG and its associated members.  This
      provides information that allows the endpoints to differentiate
      multiple VCGs and to tell what member, label switched paths
      (LSPs), to associate with a particular VCG.

2.4.  VCGs and VCG Members

   The signaling solution SHOULD provide a mechanism to support these
   scenarios:

   o  VCG members (server-layer connections) may be set up prior to
      their use in a VCG.

   o  VCG members (server-layer connections) may exist after their
      corresponding VCG has been removed.

   However, it is not required that any arbitrarily created server-layer
   connection be supported in the above scenarios, i.e., connections
   established without following the procedures described in this
   document.

3.  VCAT Data and Control Plane Concepts

   When utilizing GMPLS with VCAT/LCAS, we use a number of control and
   data plane concepts described below.

   VCG - This is the group of data plane server-layer signals used to
      provide the bandwidth for the virtual concatenation link
      connection through a network ([ITU-T-G.7042]).

   VCG member - This is an individual data plane server-layer signal
      that belongs to a VCG ([ITU-T-G.7042]).

   Member set - One or more VCG members (or potential members) set up
      via the same control plane signaling exchange.  Note that all
      members in a member set follow the same route.

   Data plane LSP - This is an individual VCG member.

   Control plane LSP - A control plane entity that can control multiple
      data plane LSPs.  For our purposes here, this is equivalent to the
      member set.

   Call - A control plane mechanism for providing association between
      endpoints and possibly key transit points.

4.  VCGs Composed of a Single Member Set (One LSP)

   In this section and the next section, we will describe the procedures
   for supporting the applications described in Section 2.

   This section describes the support of a single VCG composed of a
   single member set (in support of the fixed, co-routed application and
   the dynamic, co-routed application) using existing GMPLS procedures
   [RFC4606].  Note that this section is included for informational
   purposes only and does not modify [RFC4606].  It is provided to show
   how the existing GMPLS procedures may be used.  [RFC4606] provides
   the normative definition for GMPLS processing of VCGs composed of a
   single member set, and in the event of any conflict between this
   section and that document, [RFC4606] takes precedence.

   The existing GMPLS signaling protocols support a VCG composed of a
   single member set.  Setup using the Number of Virtual Components
   (NVC) field is explained in Section 2.1 of [RFC4606].  In this case,
   one (single) control plane LSP is used in support of the VCG.

   There are two options for setting up the VCG, depending on policy
   preferences: one-shot setup and incremental setup.

   The following sections explain the procedure based on an example of
   setting up a VC-4-7v SDH VCAT group (corresponding to an STS-3c-7v
   SONET VCAT group), which is composed of 7 virtually concatenated
   VC-4s (or STS-3c).

4.1.  One-Shot VCG Setup

   This section describes establishment of an LSP that supports all VCG
   members as part of the initial LSP establishment.  To establish such
   an LSP, an RSVP-TE (Resource Reservation Protocol - Traffic
   Engineering) Path message is sent containing the SONET/SDH traffic
   parameters defined in [RFC4606].  In the case of this example:

   o  Elementary signal is set to 6 (for VC-4/STS-3c_SPE).

   o  NVC is set to 7 (number of members).

   o  Per [RFC4606], a Multiplier Transform greater than 1 (say N > 1)
      may be used if the operator wants to set up N identical VCAT
      groups (for the same LSP).

   o  SDH or SONET labels have to be assigned for each member of the VCG
      and concatenated to form a single Generalized Label constructed as
      an ordered list of 32-bit timeslot identifiers of the same format
      as TDM labels.  [RFC4606] requires that the order of the labels
      reflect the order of the payloads to concatenate, and not the
      physical order of timeslots.

   o  Refer to [RFC4606] for other traffic parameter settings.

4.2.  Incremental VCG Setup

   In some cases, it may be necessary or desirable to set up the VCG
   members individually, or to add group members to an existing group.

   One example of this need is when the local policy requires that VCAT
   can only add VCAT members one at a time or cannot automatically match
   the members at the ingress and egress for the purposes of inverse
   multiplexing.  Serial or incremental setup solves this problem.

   In order to accomplish incremental setup, an iterative process is
   used to add group members.  For each iteration, NVC is incremented up
   to the final value required.  A successful iteration consists of the
   successful completion of Path and Resv signaling.  At first, NVC = 1,
   and the label includes just one timeslot identifier.

   At each of the next iterations, NVC is set to (NVC + 1), and one more
   timeslot identifier is added to the ordered list in the Generalized
   Label (in the Path or Resv message).  A node that receives a Path
   message that contains changed fields will process the full Path
   message and, based on the new value of NVC, it will add a component
   signal to the VCAT group, and switch the new timeslot based on the
   new label information.

   Following the addition of the new label (identifying the new member)
   to the LSP, in the data plane, LCAS may be used to add the new member
   at the endpoints into the existing VCAT group.  LCAS (data plane)
   signaling is described in [ITU-T-G.7042].

4.3.  Procedure for VCG Reduction by Removing a Member

   The procedure to remove a component signal is similar to that used to
   add components as described in Section 4.2.  In the data plane, LCAS
   signaling is used first to take the component out of service from the
   group.  LCAS signaling is described in [ITU-T-G.7042].

   In this case, the NVC value is decremented by 1, and the timeslot
   identifier for the dropped component is removed from the ordered list
   in the Generalized Label.

   Note that for interfaces that are not LCAS-capable, removing one
   component of the VCG will result in failure detection of the member
   at the endpoint and failure of the whole group.  So, this is a
   feature that only LCAS-capable VCAT interfaces can support without
   management intervention at the endpoints.

   Note that if using LCAS, a VCG member can be temporarily removed from
   the VCG due to a failure of the component signal.  The LCAS data
   plane signaling will take appropriate actions to adjust the VCG as
   described in [ITU-T-G.7042].

4.4.  Removing Multiple VCG Members in One Shot

   The procedure is similar to that described in Section 4.3.  In this
   case, the NVC value is changed to the new value, and all relevant
   timeslot identifiers for the components to be torn down are removed
   from the ordered list in the Generalized Label.  This procedure is
   also not supported for VCAT-only interfaces without management
   intervention, as removing one or more components of the VCG will tear
   down the whole group.

4.5.  Teardown of Whole VCG

   The entire LSP is deleted in a single step (i.e., all components are
   removed in one go) using the deletion procedures described in
   [RFC3473].

5.  VCGs Composed of Multiple Member Sets (Multiple LSPs)

   The motivation for VCGs composed of multiple member sets comes from
   the requirement to support VCGs with diversely routed members.  The
   initial GMPLS specification did not support diversely routed signals
   using the NVC construct.  [RFC4606] says:

      [...] The standard definition for virtual concatenation allows
      each virtual concatenation component to travel over diverse paths.
      Within GMPLS, virtual concatenation components must travel over
      the same (component) link if they are part of the same LSP.  This
      is due to the way that labels are bound to a (component) link.
      Note, however, that the routing of components on different paths
      is indeed equivalent to establishing different LSPs, each one
      having its own route.  Several LSPs can be initiated and
      terminated between the same nodes, and their corresponding
      components can then be associated together (i.e., virtually
      concatenated).

   The setup of diversely routed VCG members requires multiple VCG
   member sets, i.e., multiple control plane LSPs.

   The support of a VCG with multiple VCG member sets requires being
   able to identify separate sets of control plane LSPs with a single
   VCG and exchange information pertaining to the VCG as a whole between
   the endpoints.  This document updates the procedures described in
   [RFC4606] to provide this capability by using the call procedures and
   extensions described in [RFC4974].  The VCG makes use of one or more
   calls (VCAT calls) to associate control plane LSPs in support of VCG
   server-layer connections (VCG members) in the data plane.  Note that
   the trigger for the VCG (by management plane or client layer) is
   outside the scope of this document.  These procedures provide for
   autonomy of the client layer and server layer with respect to their
   management.

   In addition, by supporting the identification of a VCG (VCG ID) and
   VCAT call identification (VCAT Call ID), support can be provided for
   the member-sharing scenarios, i.e., by explicitly separating the VCG
   ID from the VCAT call ID.  Note that per [RFC4974], LSPs
   (connections) cannot be moved from one call to another; hence, to
   support member sharing, the procedures in this document provide
   support by moving call(s) and their associated LSPs from one VCG to
   another.  Figure 1 below illustrates these relationships; however,
   note that VCAT calls can exist independently of a VCG (for connection
   pre-establishment), as will be described later in this document.

    +-------+      +-------------+      +-------+      +------------+
    |       |1    n|             |1    n|       |1    n| Data Plane |
    |  VCG  |<>----|  VCAT Call  |<>----|  LSP  |<>----| Connection |
    |       |      |             |      |       |      |(co-routed) |
    +-------+      +-------------+      +-------+      +------------+

     Figure 1.  Conceptual Containment Relationship between VCG, VCAT
           Calls, Control Plane LSPs, and Data Plane Connections

5.1.  Signaled VCG Service Layer Information

   In this section, we provide information that will be communicated at
   the VCG level, i.e., between the VCG signaling endpoints using the
   call procedures described in [RFC4974].  To accommodate the VCG
   information, a new TLV is defined in this document for the
   CALL_ATTRIBUTES object [RFC6001] for use in the Notify message
   [RFC4974].  The Notify message is a targeted message and does not
   need to follow the path of LSPs through the network; i.e., there is
   no dependency on the member signaling for establishing the VCAT call,
   and the use of external call managers as described in [RFC4974] is
   not precluded.

   The following information is needed:

   1. Signal type

   2. Number of VCG members

   3. LCAS requirements:

      a. LCAS required

      b. LCAS desired

      c. LCAS not supported

   4. VCG Identifier - Used to identify a particular VCG separately from
      the call ID so that call members can be reused with different VCGs
      per the requirements for member sharing and the requirements of
      Section 2.4.

5.2.  CALL_ATTRIBUTES Object VCAT TLV

   This document defines a CALL_ATTRIBUTES object VCAT TLV for use in
   the CALL_ATTRIBUTES object [RFC6001] as follows:

      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 = 4               |     Length = 12               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     | Signal Type                   |      Number of Members        |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |LCR| Reserved  |  Action       |               VCG ID          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type, as defined in [RFC6001].  This field MUST be set to 2.

   Length, as defined in [RFC6001].  This field MUST be set to 12.

   Signal Type: 16 bits

      The signal types can never be mixed in a VCG; hence, a VCAT call
      contains only one signal type.  This field can take the following
      values and MUST never change over the lifetime of a VCG
      [ANSI-T1.105] [ITU-T-G.707] [ITU-T-G.709] [ITU-T-G.7043]:

         Value  Type (Elementary Signal)
         -----  -------------------------
           1     VT1.5  SPE / VC-11
           2     VT2    SPE / VC-12
           3     STS-1  SPE / VC-3
           4     STS-3c SPE / VC-4
          11     ODU1 (i.e., 2.5 Gbit/s)
          12     ODU2 (i.e., 10 Gbit/s)
          13     ODU3 (i.e., 40 Gbit/s)
          21     T1   (i.e., 1.544 Mbps)
          22     E1   (i.e., 2.048 Mbps)
          23     E3   (i.e., 34.368 Mbps)
          24     T3   (i.e., 44.736 Mbps)

   Number of Members: 16 bits

      This field is an unsigned integer that MUST indicate the total
      number of members in the VCG (not just the call).  This field MUST
      be changed (over the life of the VCG) to indicate the current
      number of members.

   LCR (LCAS Required): 2 bits

      This field can take the following values and MUST NOT change over
      the life of a VCG:

         Value         Meaning
         -----    ------------------
           0      LCAS required
           1      LCAS desired
           2      LCAS not supported

   Action: 8 bits

      This field is used to indicate the relationship between the call
      and the VCG and has the following values:

       Value                     Meaning
       -----    -------------------------------------------------------
         0      No VCG ID (set up call prior to VCG creation)
         1      New VCG for Call
         2      Modification of Number of Members (no change in VCG ID)
         3      Remove VCG from Call

   VCG Identifier (ID): 16 bits

      This field carries an unsigned integer that is used to identify a
      particular VCG within a session.  The value of the field MUST NOT
      change over the lifetime of a VCG but MAY change over the lifetime
      of a call.

5.3.  Procedures for Multiple Member Sets

   The creation of a VCG based on multiple member sets requires the
   establishment of at least one VCAT-layer call.  VCAT-layer calls and
   related LSPs (connections) MUST follow the procedures as defined in
   [RFC4974], with the addition of the inclusion of a CALL_ATTRIBUTES
   object containing the VCAT TLV.  Multiple VCAT layer calls per VCG
   are not required to support member sets, but are needed to support
   certain member-sharing scenarios.

   The remainder of this section provides specific procedures related to
   VCG signaling.  The procedures described in [RFC4974] are only
   modified as discussed in this section.

   When LCAS is supported, the data plane will add or decrease the
   members per [ITU-T-G.7042].  When LCAS is not supported across LSPs,
   the data plane coordination across member sets is outside the scope
   of this document.

5.3.1.  Setting Up a New VCAT Call and VCG Simultaneously

   To simultaneously set up a VCAT call and identify it with an
   associated VCG, a CALL_ATTRIBUTES object containing the VCAT TLV MUST
   be included in the Notify message at the time of call setup.  The
   VCAT TLV Action field MUST be set to 1, which indicates that this is
   a new VCG for this call.  LSPs MUST then be added to the call until
   the number of members reaches the number specified in the VCAT TLV.

5.3.2.  Setting Up a VCAT Call and LSPs without a VCG

   To provide for pre-establishment of the server-layer connections for
   a VCG, a VCAT call MAY be established without an associated VCG
   identifier.  In fact, to provide for the member-sharing scenarios, a
   pool of VCAT calls with associated connections (LSPs) can be
   established, and then one or more of these calls (with accompanying
   connections) can be associated with a particular VCG (via the VCG
   ID).  Note that multiple calls can be associated with a single VCG
   but that a call MUST NOT contain members used in more than one VCG.

   To establish a VCAT call with no VCG association, a CALL_ATTRIBUTES
   object containing the VCAT TLV MUST be included at the time of call
   setup in the Notify message.  The VCAT TLV Action field MUST be set
   to 0, which indicates that this is a VCAT call without an associated
   VCG.  LSPs can then be added to the call.  The Number of Members
   parameter in the VCAT TLV has no meaning at this point, since it
   reflects the intended number of members in a VCG and not in a call.

5.3.3.  Associating an Existing VCAT Call with a New VCG

   A VCAT call that is not otherwise associated with a VCG may be
   associated with a VCG.  To establish such an association, a Notify
   message MUST be sent with a CALL_ATTRIBUTES object containing a
   VCAT TLV.  The TLV's Action field MUST be set to 1, and the VCG
   Identifier field MUST be set to correspond to the VCG.  The Number of
   Members field MUST equal the sum of all LSPs associated with the VCG.
   Note that the total number of VCGs supported by a node may be
   limited; hence, on reception of any message with a change of VCG ID,
   this limit should be checked.  Likewise, the sender of a message with
   a change of VCG ID MUST be prepared to receive an error response.
   Again, any error in a VCG may result in the failure of the
   complete VCG.

5.3.4.  Removing the Association between a Call and VCG

   To reuse the server-layer connections in a call in another VCG, the
   current association between the call and a VCG MUST first be removed.
   To do this, a Notify message MUST be sent with a CALL_ATTRIBUTES
   object containing a VCAT TLV.  The Action field of the TLV MUST be
   set to 3 (Remove VCG from Call).  The VCG ID field is ignored and MAY
   be set to any value.  The Number of Members field is also ignored and
   MAY be set to any value.  When the association between a VCG and all
   existing calls has been removed, then the VCG is considered torn
   down.

5.3.5.  VCG Bandwidth Modification

   The following cases may occur when increasing or decreasing the
   bandwidth of a VCG:

   1. LSPs are added to or, in the case of a decrease, removed from a
      VCAT call already associated with a VCG.

   2. An existing VCAT call (and corresponding LSPs) is associated with
      a VCG or, in the case of a decrease, has its association removed.
      Note that in the case of an increase, the call MUST NOT have any
      existing association with a VCG.

   The following sequence SHOULD be used when modifying the bandwidth of
   a VCG:

   1. In both cases, prior to any other change, a Notify message MUST be
      sent with a CALL_ATTRIBUTES object containing a VCAT TLV for each
      of the existing VCAT calls associated with the VCG.  The Action
      field of the TLV MUST be set to 2.  The VCG ID field MUST be set
      to match the VCG.  The Number of Members field MUST equal the sum
      of all LSPs that are anticipated to be associated with the VCG
      after the bandwidth change.  The Notify message is otherwise
      formatted and processed to support call establishment as described
      in [RFC4974].  If an error is encountered while processing any of
      the Notify messages, the number of members is reverted to the
      pre-change value, and the increase is aborted.  The reverted
      number of members MUST be signaled in a Notify message as
      described above.  Failures encountered in processing these Notify
      messages are handled per [RFC4974].

   2. Once the existing calls have successfully been notified of the new
      number of members in the VCG, the bandwidth change can be made.
      The next step is dependent on the two cases defined above.  In the
      first case defined above, the bandwidth change is made by adding
      (in the case of an increase) or removing (in the case of a
      decrease) LSPs to or from the VCAT call per the procedures defined
      in [RFC4974].  In the second case, the procedure defined in
      Section 5.3.3 is followed for an increase, and the procedure
      defined in Section 5.3.4 is followed for a decrease.

6.  Error Conditions and Codes

   VCAT call and member LSP setup can be denied for various reasons.  In
   addition to the call procedures and related error codes described in
   [RFC4974], below is a list of error conditions that can be
   encountered while using the procedures defined in this document.
   These fall under RSVP error code 39.

   These can occur when setting up a VCAT call or associating a VCG with
   a VCAT call.

      Error                                      Value
      ------------------------------------      --------
      VCG signal type not supported                1
      LCAS option not supported                    2
      Max number of VCGs exceeded                  3
      Max number of VCG members exceeded           4
      LSP Type incompatible with VCAT call         5
      Unknown LCR (LCAS required) value            6
      Unknown or unsupported ACTION                7
   Any failure in call or LSP establishment MUST be treated as a failure
   of the VCG as a whole and MAY trigger the calls and LSPs associated
   with the VCG being deleted.

7.  IANA Considerations

7.1.  RSVP Call Attribute TLV

   IANA has made the following assignments in the "Call Attributes TLV"
   section of the "RSVP PARAMETERS" registry available from
   http://www.iana.org.

   IANA has made assignments from the Call Attributes TLV [RFC6001]
   portions of this registry.

   This document introduces a new Call Attributes TLV:

           TLV Value     Name                       Reference
           ---------     ----------------------     ---------
           4             VCAT TLV                   [RFC6344]

7.2.  RSVP Error Codes and Error Values

   A new RSVP Error Code and new Error Values are introduced.  IANA
   assigned the following from the "RSVP Parameters" registry using the
   sub-registry "Error Codes and Globally-Defined Error Value
   Sub-Codes".

   o  Error Codes:

      - VCAT Call Management (39)

   o  Error Values:

         Meaning                                    Value
         ------------------------------------      --------
         VCG signal type not supported                1
         LCAS option not supported                    2
         Max number of VCGs exceeded                  3
         Max number of VCG members exceeded           4
         LSP Type incompatible with VCAT call         5
         Unknown LCR (LCAS required) value            6
         Unknown or unsupported ACTION                7

7.3.  VCAT Elementary Signal Registry

   IANA created a registry to track elementary signal types as defined
   in Section 5.2.  New allocations are by "IETF Review" [RFC5226].

   IANA maintains the following information:

      - Value
      - Type (Elementary Signal)
      - RFC

   The available range is 0 - 65535.

   The registry has been initially populated with the values shown in
   Section 5.2 of this document.  Value 0 is Reserved.  Other values are
   marked Unassigned.

7.4.  VCAT VCG Operation Actions

   IANA created a registry to track VCAT VCG operation actions as
   defined in Section 5.2.  New allocations are by "IETF Review"
   [RFC5226].

   IANA maintains the following information:

      - Value
      - Meaning
      - RFC

   The available range is 0 - 255.

   The registry has been initially populated with the values shown in
   Section 5.2 of this document.  Other values are marked Unassigned.

8.  Security Considerations

   This document introduces a specific use of the Notify message and
   ADMIN_STATUS object for GMPLS signaling as originally specified in
   [RFC3473] and as modified by [RFC4974].  It does not introduce any
   new signaling messages, nor does it change the relationship between
   LSRs that are adjacent in the control plane.  The call information
   associated with diversely routed control plane LSPs, in the event of
   an interception, may indicate that these are members of the same VCAT
   group that take a different route, and may indicate to an interceptor
   that the VCG call desires increased reliability.

   See [RFC5920] for additional information on GMPLS security.

9.  Contributors

   Wataru Imajuku (NTT)
   1-1 Hikari-no-oka Yokosuka Kanagawa 239-0847
   Japan

   Phone +81-46-859-4315
   EMail: imajuku.wataru@lab.ntt.co.jp


   Julien Meuric
   France Telecom
   2, avenue Pierre Marzin
   22307 Lannion Cedex
   France

   Phone: +33 2 96 05 28 28
   EMail: julien.meuric@orange-ft.com


   Lyndon Ong
   Ciena
   PO Box 308
   Cupertino, CA  95015
   USA

   Phone: +1 408 705 2978
   EMail: lyong@ciena.com

10.  Acknowledgments

   The authors would like to thank Adrian Farrel, Maarten Vissers,
   Trevor Wilson, Evelyne Roch, Vijay Pandian, Fred Gruman, Dan Li,
   Stephen Shew, Jonathan Saddler, and Dieter Beller for extensive
   reviews and contributions to this document.

11.  References

11.1.  Normative References

   [RFC2119]      Bradner, S., "Key words for use in RFCs to Indicate
                  Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC3473]      Berger, L., Ed., "Generalized Multi-Protocol Label
                  Switching (GMPLS) Signaling Resource ReserVation
                  Protocol-Traffic Engineering (RSVP-TE) Extensions",
                  RFC 3473, January 2003.

   [RFC4606]      Mannie, E. and D. Papadimitriou, "Generalized Multi-
                  Protocol Label Switching (GMPLS) Extensions for
                  Synchronous Optical Network (SONET) and Synchronous
                  Digital Hierarchy (SDH) Control", RFC 4606,
                  August 2006.

   [RFC4974]      Papadimitriou, D. and A. Farrel, "Generalized MPLS
                  (GMPLS) RSVP-TE Signaling Extensions in Support of
                  Calls", RFC 4974, August 2007.

   [RFC6001]      Papadimitriou, D., Vigoureux, M., Shiomoto, K.,
                  Brungard, D., and JL. Le Roux, "Generalized MPLS
                  (GMPLS) Protocol Extensions for Multi-Layer and Multi-
                  Region Networks (MLN/MRN)", RFC 6001, October 2010.

11.2.  Informative References

   [ANSI-T1.105]  American National Standards Institute, "Synchronous
                  Optical Network (SONET) - Basic Description including
                  Multiplex Structure, Rates, and Formats", ANSI
                  T1.105-2001, May 2001.

   [ITU-T-G.707]  International Telecommunication Union, "Network Node
                  Interface for the Synchronous Digital Hierarchy
                  (SDH)", ITU-T Recommendation G.707, December 2003.

   [ITU-T-G.709]  International Telecommunication Union, "Interfaces for
                  the Optical Transport Network (OTN)", ITU-T
                  Recommendation G.709, March 2003.

   [ITU-T-G.7042] International Telecommunication Union, "Link Capacity
                  Adjustment Scheme (LCAS) for Virtual Concatenated
                  Signals", ITU-T Recommendation G.7042, March 2006.

   [ITU-T-G.7043] International Telecommunication Union, "Virtual
                  Concatenation of Plesiochronous Digital Hierarchy
                  (PDH) Signals", ITU-T Recommendation G.7043,
                  July 2004.

   [RFC5226]      Narten, T. and H. Alvestrand, "Guidelines for Writing
                  an IANA Considerations Section in RFCs", BCP 26,
                  RFC 5226, May 2008.

   [RFC5920]      Fang, L., Ed., "Security Framework for MPLS and GMPLS
                  Networks", RFC 5920, July 2010.

Authors' Addresses

   Greg M. Bernstein (editor)
   Grotto Networking
   Fremont, CA
   USA

   Phone: (510) 573-2237
   EMail: gregb@grotto-networking.com


   Diego Caviglia
   Ericsson
   Via A. Negrone 1/A 16153
   Genoa Italy

   Phone: +39 010 600 3736
   EMail: diego.caviglia@ericsson.com


   Richard Rabbat
   Google, Inc.
   1600 Amphitheatre Parkway
   Mountain View, CA  94043
   USA

   EMail: rabbat@alum.mit.edu


   Huub van Helvoort
   Huawei Technologies, Ltd.
   Kolkgriend 38, 1356 BC Almere
   The Netherlands

   Phone: +31 36 5315076
   EMail: hhelvoort@huawei.com