CCAMP Working Group                            Vishnu Pavan Beeram (Ed)
 Internet Draft                                         Juniper Networks
 Intended status: Standards Track                      Igor Bryskin (Ed)
                                                 ADVA Optical Networking
 Expires: April 23, 2015                                October 23, 2014
                       Network Assigned Upstream-Label
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    Section 4.e of the Trust Legal Provisions and are provided without
    warranty as described in the Simplified BSD License.
    This document discusses a GMPLS RSVP-TE protocol mechanism that
    enables the network to assign an upstream-label for a given LSP.
    This is useful in scenarios where a given node does not have
    sufficient information to assign the correct upstream-label on its
    own and needs to rely on the network to pick an appropriate label.
 Conventions used in this document
    The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
    document are to be interpreted as described in RFC-2119 [RFC2119].
 Table of Contents
    1. Introduction...................................................2
    2. Use-Case: Alien Wavelength Setup...............................3
    3. The "crank-back" approach......................................3
    4. Symmetric Labels...............................................5
    5. Unassigned Upstream Label......................................5
       5.1. Processing Rules..........................................5
       5.2. Backwards Compatibility...................................6
    6. Applicability..................................................6
       6.1. Initial Setup.............................................7
       6.2. Wavelength Change.........................................8
    7. Security Considerations........................................8
    8. IANA Considerations............................................8
    9. Normative References...........................................8
    10. Acknowledgments...............................................8
 1. Introduction
    The GMPLS RSVP-TE extensions for setting up a Bidirectional LSP are
    discussed in [RFC3473]. The Bidirectional LSP setup is indicated by
    the presence of an UPSTREAM_LABEL Object in the PATH message. As per
    the existing setup procedure outlined for a Bidirectional LSP, each
    upstream-node must allocate a valid upstream-label on the outgoing
    interface before sending the initial PATH message downstream.
    However, there are certain scenarios where it is not desirable or
    possible for a given node to pick the upstream-label on its own.
    This document defines the protocol mechanism to be used in such
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    scenarios. This mechanism enables a given node to offload the task
    of assigning the upstream-label for a given LSP onto the network.
 2. Use-Case: Alien Wavelength Setup
    Consider the network topology depicted in Figure 1. Nodes A and B
    are client IP routers that are connected to an optical WDM transport
    network. F, H and I represent WDM nodes. The transponder sits on the
    router and is directly connected to the add-drop port on a WDM node.
    The optical signal originating on "Router A" is tuned to a
    particular wavelength. On "WDM-Node F", it gets multiplexed with
    optical signals at other wavelengths. Depending on the
    implementation of this multiplexing function, it may not be
    acceptable to have the router send signal into the optical network
    unless it is at the appropriate wavelength. In other words, having
    the router send signal with a wrong wavelength may adversely impact
    existing optical trails. If the clients do not have full visibility
    into the optical network, they are not in a position to pick the
    correct wavelength up-front.
                               | +---+            /-\
                               | |   | Router    (   ) WDM
                               | +---+ Node       \-/  node
      +---+          /-\           /-\           /-\          +---+
      | A |---------( F )---------( H )---------( I )---------| B |
      +---+          \-/           \-/           \-/          +---+
                     Figure 1: Sample topology
 3. The "crank-back" approach
    There are currently no GMPLS RSVP-TE protocol mechanisms that an
    upstream-node can use for indicating that it does not know what
    upstream-label to use and that it needs the downstream-node to pick
    the label on its behalf.
    The following setup sequence is an attempt to address the above use-
    case using existing protocol mechanisms:
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      +---+                 /-\             /-\                 +---+
      | A |----------------( F ) ~~~~~~~~~ ( I )----------------| B |
      +---+                 \-/             \-/                 +---+
           Upstream Label (any available value)
           Routing problem/Unacceptable Label Value
           Acceptable Label Set (L1, L2 .. Ln)
           Upstream Label (L2)
                               -- ~~ -- ~~ -->
                               <-- ~~ -- ~~ --
           Label (Assigned)
              Figure 2: Setup Sequence - Crank-back Approach
    The above approach does sort of work, but there are a few obvious
    - Since "Router-A" does not know which upstream-label to use, it
      picks some random label and signals it without programming its
      data-plane. As a result, the outgoing PATH message has no
      indication of whether the upstream-label has been installed along
      the data-path or not.
    - If "Router-A" somehow correctly guesses (by sheer luck) an
      acceptable upstream label upfront, the network may end up finding
      a path which is suboptimal (there could be a different acceptable
      upstream label which corresponds to a better path in the network)
    - The "Path-Error with Acceptable Label Set" retry approach is
      usually used for exception handling. The above solution uses it
      for almost every single setup request (except in the rare scenario
      where the appropriate upstream-label is guessed correctly).
    - There is an awkward window between the time the network sends out
      the Path-Error (with the ACCEPTABLE_LABEL_SET) and receives the
      corresponding Path (with the selected UPSTREAM_LABEL); this window
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      opens up the possibility of the selected UPSTREAM_LABEL to be
      stale by the time the network receives the retry PATH.
    - The above solution assumes the use of "symmetric labels" by
    The rest of the sections in this draft discuss a solution proposal
    that is devoid of any of the above concerns.
 4. Symmetric Labels
    As per [RFC3471], the upstream-label and the downstream-label for an
    LSP at a given hop need not be the same. The use-case discussed in
    this document pertains to Lambda Switch Capable (LSC) LSPs and it is
    an undocumented fact that in practice, LSC LSPs always have
    symmetric labels at each hop along the path of the LSP.
    The use of the protocol mechanism discussed in this document
    mandates "Label Symmetry". This mechanism is meant to be used only
    for Bidirectional LSPs that assign Symmetric Labels at each hop
    along the path of the LSP.
 5. Unassigned Upstream Label
    This document proposes the use of a special label value -
    "0xFFFFFFFF" - to indicate an Unassigned Label. The presence of this
    value in the UPSTREAM_LABEL object of a PATH message indicates that
    the upstream-node has not assigned an upstream label on its own and
    has requested the downstream-node to provide a label that it can use
    in both forward and reverse directions. The presence of this value
    in the UPSTREAM LABEL object of a PATH message can also be
    interpreted as a request to mandate "symmetric labels" for the LSP
    at the given hop.
 5.1. Processing Rules
    The Unassigned Upstream Label is used by an upstream-node when it is
    not in a position to pick the upstream label on its own. In such a
    scenario, the upstream-node sends a PATH message downstream with an
    Unassigned Upstream Label and requests the downstream-node to
    provide a symmetric label. If the upstream-node desires to make the
    downstream-node aware of its limitations with respect to label
    selection, it has the option to specify a list of valid labels via
    the LABEL_SET object.
    In response, the downstream-node picks an appropriate symmetric
    label and sends it via the LABEL object in the RESV message. The
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    upstream-node would then start using this symmetric label for both
    directions of the LSP. If the downstream-node cannot pick the
    symmetric label, it MUST issue a PATH-ERR message with a "Routing
    Problem/Unacceptable Label Value" indication.
    The upstream-node will continue to signal the Unassigned Upstream
    Label in the PATH message even after it receives an appropriate
    symmetric label in the RESV message. This is done to make sure that
    the downstream-node would pick a symmetric label if and when it
    needs to change the RESV label at a later point in time.
               +----------+                    +------------+
            ---| Upstream |--------------------| Downstream |---
               +----------+                    +------------+
                            Upstream Label (Unassigned)
                            Label-Set (L1, L2 ... Ln)
                            Label (Assigned - L2)
                       Figure 3: Unassigned UPSTREAM_LABEL
 5.2. Backwards Compatibility
    If the downstream-node is running an older implementation (which may
    be using the "crank-back" approach discussed in Section 3) and
    doesn't understand the semantics of an Unassigned UPSTREAM LABEL, it
    will either (a) reject the special label value and generate an error
    or (b) accept it and treat it as a valid label.
    If the behavior that is exhibited is (a), then there are obviously
    no backwards compatibility concerns. Ingress implementations may
    even choose to adopt the "crank-back" approach in such cases. If
    there is some existing implementation that exhibits the behavior in
    (b), then there could be some potential issues. The use-case
    discussed in this draft pertains to LSC LSPs and it is safe to
    assume that the behavior in (b) will not be exhibited for such LSPs.
 6. Applicability
    Let us revisit the "alien wavelength" use-case discussed in Section
    2 and examine how the mechanism proposed in this document allows the
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    optical network to select and communicate the correct wavelength to
    its clients.
 6.1. Initial Setup
      +---+                 /-\             /-\                 +---+
      | A |----------------( F ) ~~~~~~~~~ ( I )----------------| B |
      +---+                 \-/             \-/                 +---+
           Upstream Label (Unassigned)
                               -- ~~ -- ~~ -->
                               <-- ~~ -- ~~ --
           Label (Assigned)
                 Figure 4: Alien Wavelength - Initial Setup
      - "Router A" does not have enough information to pick an
        appropriate client wavelength. It sends a PATH downstream
        requesting the network to assign an appropriate symmetric label
        for it to use. Since the client wavelength is unknown, the
        laser is off at the ingress client.
      - The network receives the PATH, chooses the appropriate
        wavelength values and forwards them in appropriate label fields
        to the egress client ("Router B")
      - "Router B" receives the PATH, turns the laser ON and tunes it
        to the appropriate wavelength (received in the
        UPSTREAM_LABEL/LABEL_SET of the PATH) and sends out a RESV
      - The RESV received by the ingress client carries a valid
        symmetric label in the LABEL object. "Router A" turns on the
        laser and tunes it to the wavelength specified in the network
        assigned symmetric LABEL.
    For cases where the egress-node relies on RSVP signaling to
    determine exactly when to start using the LSP, this draft recommends
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    integrating the above sequence with any of the existing graceful
    setup procedures:
      - "RESV-CONF" setup procedure (or)
      - 2-step "ADMIN STATUS" based setup procedure ("A" bit set in the
        first step; "A" bit cleared when the LSP is ready for use).
 6.2. Wavelength Change
    After the LSP is set up, the network MAY decide to change the
    wavelength for the given LSP. This could be for a variety of reasons
    - policy reasons, restoration within the core, preemption etc.
    In such a scenario, if the ingress client receives a changed label
    via the LABEL object in a RESV modify, it MUST retune the laser at
    the ingress to the new wavelength. Similarly if the egress client
    receives a changed label via UPSTREAM_LABEL/LABEL_SET in a PATH
    modify, it MUST retune the laser at the egress to the new
 7. Security Considerations
 8. IANA Considerations
 9. Normative References
    [RFC2119]    Bradner, S., "Key words for use in RFCs to Indicate
                 Requirement Levels", BCP 14, RFC 2119, March 1997.
    [RFC3471]    Berger, L., "Generalized Multi-Protocol Label Switching
                 Signaling Functional Description", RFC 3471, January
    [RFC3473]    Berger, L., "Generalized Multi-Protocol Label Switching
                 Signaling Resource Reservation Protocol-Traffic
                 Engineering Extensions", RFC 3473, January 2003.
 10. Acknowledgments
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 Authors' Addresses
    Vishnu Pavan Beeram
    Juniper Networks
    John Drake
    Juniper Networks
    Gert Grammel
    Juniper Networks
    Igor Bryskin
    ADVA Optical Networking
    Pawel Brzozowski
    ADVA Optical Networking
    Daniele Ceccarelli
    Oscar Gonzalez de Dios
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