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SPRING Working Group                                      Madhukar Anand
Internet-Draft                                            Sanjoy Bardhan
Intended Status: Informational                      Infinera Corporation

                                                     Ramesh Subrahmaniam
                                                              Individual

                                                           Jeff Tantsura
                                                              Individual

                                                     Utpal Mukhopadhyaya
                                                             Equinix Inc

                                                       Clarence Filsfils
                                                     Cisco Systems, Inc.

Expires: May 18, 2018                                  November 14, 2017


             Packet-Optical Integration in Segment Routing
                      draft-anand-spring-poi-sr-04


Abstract

   This document illustrates a way to integrate a new class of nodes and
   links in segment routing to represent transport networks in an opaque
   way into the segment routing domain.  An instance of this class would
   be optical networks that are typically transport centric.  In the IP
   centric network, this will help in defining a common control protocol
   for packet optical integration that will include optical paths as
   'transport segments' or sub-paths as an augmentation to packet paths.
   The transport segment option also defines a general mechanism to
   allow for future extensibility of segment routing into non-packet
   domains.


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 [RFC2119].

Status of this Memo

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




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Copyright and License Notice

   Copyright (c) 2017 IETF Trust and the persons identified as the
   document authors. All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
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   described in the Simplified BSD License.

Table of Contents

   1  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Reference Taxonomy . . . . . . . . . . . . . . . . . . . . . .  4
   3. Use case - Packet Optical Integration . . . . . . . . . . . . .  5
   4.  Mechanism overview . . . . . . . . . . . . . . . . . . . . . .  8
   5.  Transport Segments as SR Policy  . . . . . . . . . . . . . . .  9
   6.  PCEP extensions for supporting the transport segment . . . . . 10
   7.  BGP-LS extensions for supporting the transport segment . . . . 11
   8. Note about Transport Segments and Scalability . . . . . . . . . 13
   9. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
   10.  Security Considerations . . . . . . . . . . . . . . . . . . . 14
   11  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 14
     11.1 PCEP  . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
     11.2 BGP-LS  . . . . . . . . . . . . . . . . . . . . . . . . . . 15
   12  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 15



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   13  References . . . . . . . . . . . . . . . . . . . . . . . . . . 15
     13.1  Normative References . . . . . . . . . . . . . . . . . . . 15
     13.2  Informative References . . . . . . . . . . . . . . . . . . 16
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 16















































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1  Introduction

   Packet and optical transport networks have evolved independently with
   different control plane mechanisms that have to be provisioned and
   maintained separately. Consequently, coordinating packet and optical
   networks for delivering services such as end-to-end traffic
   engineering or failure response has proved challenging. To address
   this challenge, a unified control and management paradigm that
   provides an incremental path to complete packet-optical integration
   while leveraging existing signaling and routing protocols in either
   domains is needed. This document introduces such a paradigm based on
   Segment Routing (SR) [I-D.ietf-spring-segment-routing].

   This document introduces a new type of segment, Transport segment, as
   a special case of SR traffic engineering (SR-TE) policy [Type 1, Sec
   5. I-D.filsfils-spring-segment-routing-policy]. Specifically, the
   structure of SR-TE policy and constraints associated in the transport
   network are different from those outlined for the packet networks.
   Transport segment can be used to model abstracted paths through the
   optical transport domain and integrate it with the packet network for
   delivering end-to-end services. In addition, this also introduces a
   notion of a Packet optical gateway (POG). These are nodes in the
   network that map packet services to the optical domain that originate
   and terminate these transport segments. Given a transport segment, a
   POG will expand it to a path in the optical transport network. A POG
   can be viewed as SR traffic engineering policy headend.

   The concept of POG introduced here allows for multiple instantiations
   of the concept. In one case, the packet device is distinct from the
   optical transport device, and the POG is a logical entity that spans
   these two devices. In this case, the POG functionality is achieved
   with the help of external coordination between the packet and optical
   devices. In another case, the packet and optical components are
   integrated into one physical device, and the co-ordination required
   for functioning of the POG is performed by this integrated device.
   It must be noted that in either case, it is the packet/optical data
   plane that is either disaggregated or integrated. Control of the
   devices can be logically centralized or distributed in either
   scenario.  The focus of this document is to define the logical
   functions of a POG without going into the exact instantiations of the
   concept.

2.  Reference Taxonomy

   POG - Packet optical gateway Device

   SR Edge Router - The Edge Router which is the ingress device




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   CE - Customer Edge Device that is outside of the SR domain

   PCE - Path Computation Engine

   Controller - A network controller



3. Use case - Packet Optical Integration

   Many operators build and operate their networks that are both multi-
   layer and multi-domain. Services are built around these layers and
   domains to provide end-to-end services.  Due to the nature of the
   different domains, such as packet and optical,  the management and
   service creation has always been problematic and time consuming. With
   segment routing, enabling a head-end node to select a path and embed
   the information in the packet is a powerful construct that would be
   used in the Packet Optical Gateways (POG). The path is usually
   constructed for each domain that may be manually derived or through a
   stateful PCE which is run specifically in that domain.



                                P5
     P1 _                      .-'-._                    ,'P4
         `._                .-'      `-.               ,'
            `.          _.-'            `-._         ,'
              `-.    .-'                    `-.    ,'
               P2`.-'--------------------------`-.- P3
                  |\                            /|
                  | \                          / |   Packet
            ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,
                  |   \                      /   |
                  |    \                    /    |   Transport
                  |     \                  /     |
                  |      ................./      |
                  |    ,'O2              O3`.    |
                  |  ,'                      `.  |
                  |,'                          `.|
                O1\                              | O4
                   \                           ,'
                    \                        ,'
                     .......................-
                    O6                     O5

      Figure 1:  Representation of a packet-optical path





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In Figure 1 above, the nodes represent a packet optical network.
P1,...,P5 are packet devices. Nodes P2 and P3 are connected via optical
network comprising of nodes O1,...,O6. Nodes P2 and P3 are POGs that
communicate with other packet devices and also with the devices in the
optical transport domain. In defining a path between nodes P2 and P3, we
will need to specify the nodes and the links in both the packet and
optical transport domains.

To leverage segment routing to define a service between P1 and P4, the
ingress node P1 would append all outgoing packets in a SR header
consisting of the SIDs that constitute the path. In the packet domain
this would mean P1 would send its packets towards P4 using a segment
list {P2, P3, P4} or {P2, P5, P3, P4} as the case may be. The operator
would need to use a different mechanism in the optical domain to set up
the optical paths comprising the nodes O1, O2 and O3. Each POG would
announce the active optical path as a transport segment - for example,
the optical path {O1, O2, O3} could be represented as a label Om and the
optical path {O2, O3} could be represented as a transport label On. Both
Om and On will be advertised by Packet node P2. These paths are not
known to the packet SR domain and is only relevant to the optical domain
D between P2 and P3.   A PCE that is run in Domain D would be
responsible for calculating paths corresponding to label Om and On. The
expanded segment list would read as {P2, Om, P3, P4} or {P2, On, P3,
P4}. It is to be noted that there are other possible paths between P2
and P3 in the optical domain involving optical nodes O5, O6, and O4.
There may be multiple optical paths between P2 and P3 corresponding to
multiple SR policies. For example, some optical paths can be low-cost,
some are low-latency, and some others can be high-bandwidth paths.
Transport segments for all these candidate viable alternative paths may
be generated statically or dynamically.They may be pre-computed or may
be generated on the fly when a customer at node P1 requests a service
towards node P4.  A discussion on transport segments and scalability can
be found in Section 8.




Use-case examples of transport segments.

1. Consider the scenario where there are multiple fibers between two
packet end points. The network operator may choose to route packet
traffic on the first fiber, and reserve the second fiber only for
maintenance or low priority traffic.

2. As a second use-case, consider the case where the packet end points
are connected by optical transport provided by two different service
providers. The packet operator wants to preferentially route traffic
over one of the providers and use the second provider as a backup.



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3. Finally, let the packet end points be connected by optical paths that
may span multiple optical domains i.e. different administrative control.
For instance, one optical transport path may lie completely in one
country while the other optical transport path transits another country.
Weather, tariffs, security considerations and other factors may
determine how the packet operator wants to route different types of
traffic on this network.

All of the above use-cases can be supported by first mapping distinct
optical transport paths to different transport segments and then,
depending on the need, affixing appropriate transport segment identifier
to the specific packet to route it appropriately through the transport
domain.







                       +------------------------+
                       |                        |
   +--------------+----'    PCE or Controller   |----+---------------+
   |              |    |                        |    |               |
   |              |    +------------------------+    |               |
   |              |                                  |               |
   |              |            .-----.               |               |
   |              |           (       )              |               |
+-------+     +-------+   .--(         )--.     +-------+      +-------+
|  SR   |     |Packet |  (                 )    |Packet |      |  SR   |
| Edge  |     |Optical|-( Optical Transport )_  |Optical|      | Edge  |
|Router | ... |Gateway| (       Domain      )   |Gateway| ...  |Router |
+---+.--+     +-------+  (                 )    +-------+      +---+.--+
    |                      '--(         )--'                       |
  ,--+.                        (       )                         ,-+-.
 ( CE  )                        '-----'                         ( CE  )
  `---'                                                          `---'




       Figure 3. Reference Topology for Transport Segment Mechanism









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4.  Mechanism overview

      The current proposal assumes that the SR domains run standard
   protocols without any modification to discover the topology and
   distribute labels. There are also no modifications necessary in the
   control plane mechanisms in the optical transport domains.  The only
   requirement of a transport segment is that the optical path be setup
   before they are announced to the packet network. For example, the
   optical paths may be setup using a domain-specific controller or a
   PCE based on requirements from the packet domain (such as bandwidth,
   QoS, latency and cost) taking into consideration the constraints in
   the optical network.

   The mechanism for supporting the transport segment is as follows.

      1. Firstly, the Packet Optical Gateway (POG) devices are announced
   in the packet domain. This is indicated by advertising a new SR node
   capability flag. The exact extensions to support this capability are
   described in the subsequent sections of this document.

      2. Then, the POG devices announce candidate optical transport
   paths between that POG (Source POG) and other POGs (Destination POG)
   via appropriate mechanisms in the packet domain. The paths are
   announced with an appropriate optical transport domain ID and a
   Binding SID representing the transport segment from a source POG to a
   destination POG. The appropriate protocol-specific extensions to
   carry path characteristics and Binding SID corresponding to a optical
   path are described in the subsequent sections of this document.

      3.The transport SR policy can also optionally be announced with a
   set of attributes that characterizes the path in the optical
   transport domain between the two POG devices. For instance, those
   could define the path  attributes such as path identifier, latency,
   bandwidth, quality, directionality, or optical path protection
   schemes. These attributes can be used to determine the "color" of the
   SR-TE policy in the tuple <Source POG, Destination POG, color> used
   to prioritize different candidate paths between the POGs.

      4. The POG device is also responsible for programming its
   forwarding table to map every transport segment Binding SID entry
   into an appropriate forwarding action relevant in the optical domain,
   such as mapping it to a optical label-switched path.

      5. The transport SR policy is communicated to the PCE or
   Controller using extensions to BGP-LS or PCEP as described in
   subsequent sections of this document.

      6. Finally, the PCE or Controller in the packet domain then uses



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   the transport segment binding SID in the overall SR policy to
   influence the path traversed by the packet in the optical domain,
   thereby defining the end-to-end path for a given service.

   In the next few sections, we outline a few representative protocol
   specific extensions to carry the transport segment.

5.  Transport Segments as SR Policy

    The Segment Routing Traffic Engineering (SRTE) [I-D.filsfils-spring-
   segment-routing-policy] process installs the transport segment SR
   policy in the forwarding plane of the POG. The Transport SR policy is
   identified by using a transport segment Binding SID. Corresponding to
   each transport segment Binding SID, the SRTE process MAY learn about
   multiple candidate paths. The SRTE-DB includes information about the
   candidate paths including optical domain, topology and path
   characteristics. All of the information can be learned from different
   sources including but not limited to: Netconf/Restconf, PCEP and BGP-
   LS.

   The information model for Transport SR policy is as follows:

       Transport SR Policy FO1
              Candidate-paths
                path preference 200 (selected)
                    BSID1
                path preference 100
                    BSID2
                path preference 100
                    BSID3
                path preference 50
                    BSID4

A transport SR policy is identified through the tuple <Source POG,
Destination POG, color>. Each TSR policy is associated with one or more
candidate paths, each of them associated with a (locally) unique Binding
SID and a path preference. For each transport SR policy, the candidate
path with the highest path preference (at most one) is selected and used
for forwarding traffic that is being steered onto that policy. When
candidate paths change (or a new candidate path is set up), the path
selection process can be re-executed. The validity of each path is to be
verified by the POG before announcement in the packet domain. If there
are no valid paths, then the transport SR policy is deemed invalid.

The allocation of BSID to a path can include dynamic, explicit or
generic allocation strategies as discussed in [I-D.filsfils-spring-
segment-routing-policy]. We discuss PCEP and BGP-LS specific extensions
in the subsequent section.



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6.  PCEP extensions for supporting the transport segment

 To communicate the Packet-Optical Gateway capability of the device, we
introduce a new PCEP capabilities TLV is defined as follows(extensions
to [I-D.draft-sivabalan-pce-segment-routing]):

   Value    Meaning                                Reference
  --------  ------------------------------------ -----------------
     27     TRANSPORT-SR-PCE-CAPABILITY           This document


  A new type of TLV to accommodate a transport segment is defined
by extending Binding SIDs [I-D.draft-sivabalan-pce-binding-label-sid-01]










 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              |             Length            |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|        Binding Type (BT)      |             Domain ID         |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                        Binding Value                          |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~       Transport Segment Sub TLVs (variable length)            ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

 where:

 Type: TBD, suggested value 32

 Length: variable.

 Binding Type: 0 or 1 as defined in
              [I-D.draft-sivabalan-pce-binding-label-sid-01]

 Domain ID: An identifier for the transport domain

 Binding Value: is the transport segment label




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 Transport Segment Sub TLVs: TBD


IANA will be requested to allocate a new TLV type (recommended value
is 32) for TRANSPORT-SEGMENT-BINDING-TLV as specified in this document:

 1      Transport Segment Label (This document)




7.  BGP-LS extensions for supporting the transport segment


7.1 Node Attribuites TLV

  To communicate the Packet-Optical Gateway capability of the
  device, we introduce an new optical informational capability
  the following new Node Attribute TLV is defined:

   +-----------+----------------------------+----------+---------------+
   |  TLV Code | Description                |   Length |       Section |
   |   Point   |                            |          |               |
   +-----------+----------------------------+----------+---------------+
   |    1172   | SR-Optical-Node-Capability | variable |               |
   |           | TLV                        |          |               |
   +-----------+----------------------------+----------+---------------+

                       Table 1: Node Attribute TLVs

  These TLVs can ONLY be added to the Node Attribute associated with
  the node NLRI that originates the corresponding SR TLV.


7.2 SR-Optical-Node-Capability TLV

   The SR Capabilities sub-TLV has 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            |               Length          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      Flags    |   RESERVED    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

where:



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 Type : TBD, Suggested Value 1157

 Length: variable.

 Flags: The Flags field currently has only one bit defined. If the bit
 is set it has the capability of an Packet Optical Gateway.

9.3 Prefix Attribute TLVs
   The following Prefix Attribute Binding SID Sub-TLVs have been added:


   +------------+-------------------------+----------+-----------------+
   |  TLV Code  | Description             | Length   | Section         |
   |   Point    |                         |          |                 |
   +------------+-------------------------+----------+-----------------+
   |    1173    | TRANSPORT-SEGMENT-SID   | 12       |                 |
   |            |                         |          |                 |
   +------------+-------------------------+----------+-----------------+

   Table 4: Prefix Attribute - Binding SID Sub-TLVs

 The Transport segment TLV allows a node to advertise an transport
 segment within a single IGP domain. The transport segment SID TLV
 TRANSPORT-SEGMENT-TLV has the following format:

7.3.1  Transport Segment SID Sub-TLV

Further, a new sub-TLV (similar to the IPV4 ERO SubTLV) of
Binding SID Sub-TLV (TRANSPORT-SEGMENT-BINDING-SUBTLV) to carry the
transport segment label is defined as follows.


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             |             Length            |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|        Domain ID              |   Flags       |  Reserved     |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                     Packet-Optical Label                      |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~       Transport Segment Sub TLVs (variable length)           ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:

 Type : TBD

 Length: variable.




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 Domain ID: An identifier for the transport domain

 Flags: 1 octet field of following flags:
   V - Value flag.  If set, then the optical label carries a value.
       By default the flag is SET.
   L - Local. Local Flag.  If set, then the value/index carried by
       the Adj-SID has local significance.  By default the flag is SET.




   0 1 2 3 4 5 6 7
   +-+-+-+-+-+-+-+-+
   |V|L|
   +-+-+-+-+-+-+-+-+

 Packet-Optical Label : according to the V and L flags, it contains
        either:

      *  A 3 octet local label where the 20 rightmost bits are
        used for encoding the label value.  In this case the V and
        L flags MUST be set.

      *  A 4 octet index defining the offset in the label space
        advertised by this router. In this case V and L flags MUST
        be unset.

 Transport Segment Sub TLVs: TBD


Multiple TRANSPORT-SEGMENT-TLV MAY be associated with a pair
of POG devices to represent multiple paths within the optical domain


8. Note about Transport Segments and Scalability

In most operational scenarios, there would be multiple, distinct paths
between the POGs. There is no requirement that every distinct path in
the optical domain be advertised as a separate transport segment.
Transport segments are designed to be consumed in the packet domain,
and the correspondence between transport segments and exact paths in
the optical domain are determined by their utility to the packet world.
Therefore, the number of transport segments is to be determined by the
individual packet-optical use-case. The number of actual paths in the
optical domain between the POG is expected to be large (counting the
number of active and passive devices in the optical network), it is
likely that multiple actual paths are to be advertised as one transport
segment. Of course, in the degenerate case, it is possible that there



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is a one-to-one correspondence between an optical path and a transport
segment.  Given this view of network operation, the POG is not expected
to handle a large number of transport segments (and identifiers). This
framework does leave open the possibility of handling a large number
of transport segments in future. For instance, a hierarchical
partitioning of the optical domain along with stacking of multiple
transport segment identifiers could be explored towards reducing
the overall number of transport segment identifiers.

9. Summary

The motivation for introducing a new type of segment - transport
segment - is to integrate transport networks with the segment routing
domain and expose characteristics of the transport domain into the
packet domain. An end-to-end path across packet and transport domains
can then be specified by attaching appropriate SIDs to the packet.
An instance of transport segments has been defined here for optical
networks, where paths between packet-optical gateway devices have been
abstracted using binding SIDs. Extensions to various protocols to
announce the transport segment have been proposed in this document.

10.  Security Considerations

   This document does not introduce any new security considerations.


11  IANA Considerations

This documents request allocation for the following TLVs and subTLVs.


11.1 PCEP
Packet-Optical Gateway capability of the device

   Value    Meaning                                Reference
  --------  ------------------------------------ -----------------
     27     TRANSPORT-SR-PCE-CAPABILITY           This document


A new type of TLV to accommodate a transport segment is defined
by extending Binding SIDs [I-D.draft-sivabalan-pce-binding-label-sid-01]

  Value    Description                          Reference

     32    TRANSPORT-SR-PCEP-TLV                This document

This document requests that a registry is created to manage the value
of the Binding Type field in the TRANSPORT-SR-PCEP TLV.



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 Value    Description                Reference

   1      Transport Segment Label        This document



11.2 BGP-LS
Node Attributes TLV:

  Value    Description                          Reference

   1172    TRANSPORT-SR-BGPLS-CAPABILITY      This document

Prefix Attribute Binding SID SubTLV:

  Value    Description                          Reference

   1173    TRANSPORT-SR-BGPLS-TLV            This document


12  Acknowledgements
We would like to thank Peter Psenak, and Radhakrishna
Valiveti for their comments and review of this document.

13  References

13.1  Normative References



[I-D.ietf-spring-segment-routing]
              Filsfils, C., Previdi, S., Decraene, B., Litkowski, S.,
              and R. Shakir, "Segment Routing Architecture", draft-ietf-
              spring-segment-routing-12 (work in progress), June 2017.

[RFC7752]  Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and
              S. Ray, "North-Bound Distribution of Link-State and
              Traffic Engineering (TE) Information Using BGP", RFC 7752,
              DOI 10.17487/RFC7752, March 2016,
              <http://www.rfc-editor.org/info/rfc7752>.

[I-D.sivabalan-pce-binding-label-sid]
              Sivabalan, S., Filsfils, C., Previdi, S., Tantsura, J.,
              Hardwick, J., and Dhody, D., "Carrying Binding Label/
              Segment-ID in PCE-based Networks.", draft-sivabalan-pce-
              binding-label-sid-03 (work in progress), July 2017.

[I-D.ietf-pce-segment-routing]



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              Sivabalan, S., Filsfils, C., Tantsura, J., Henderickx, W.,
              and J. Hardwick, "PCEP Extensions for Segment Routing",
              draft-ietf-pce-segment-routing-10 (work in progress),
              October 2017.

[I-D.filsfils-spring-segment-routing-policy]
              Filsfils, C., Sivabalan, S., Raza, K., Liste, J., Clad,
              F., Lin, S., bogdanov@google.com, b., Horneffer, M.,
              Steinberg, D., Decraene, B., and S. Litkowski, "Segment
              Routing Policy for Traffic Engineering", draft-filsfils-
              spring-segment-routing-policy-01 (work in progress), July
              2017.





13.2  Informative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.


Authors' Addresses


   Madhukar Anand
   Infinera Corporation
   169 W Java Dr, Sunnyvale, CA 94089

   Email: manand@infinera.com



   Sanjoy Bardhan
   Infinera Corporation
   169 W Java Dr, Sunnyvale, CA 94089

   Email: sbardhan@infinera.com



   Ramesh Subrahmaniam
   Email: svr_fremont@yahoo.com





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   Jeff Tantsura
   Email: jefftant.ietf@gmail.com




   Utpal Mukhopadhyaya
   Equinix Inc
   1188 E. Arques, Sunnyvale, CA 94085
   Email: umukhopadhyaya@equinix.com



   Clarence Filsfils
   Cisco Systems, Inc.
   Brussels
   BE
   Email: cfilsfil@cisco.com

































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