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Versions: 00 01 02 03 draft-ietf-spring-segment-routing-mpls

Network Working Group                                   C. Filsfils, Ed.
Internet-Draft                                           S. Previdi, Ed.
Intended status: Standards Track                             A. Bashandy
Expires: February 1, 2015                            Cisco Systems, Inc.
                                                             B. Decraene
                                                            S. Litkowski
                                                                  Orange
                                                            M. Horneffer
                                                        Deutsche Telekom
                                                            I. Milojevic
                                                          Telekom Srbija
                                                               R. Shakir
                                                         British Telecom
                                                                 S. Ytti
                                                                  TDC Oy
                                                           W. Henderickx
                                                          Alcatel-Lucent
                                                             J. Tantsura
                                                                Ericsson
                                                               E. Crabbe
                                                            Google, Inc.
                                                           July 31, 2014


                  Segment Routing with MPLS data plane
             draft-filsfils-spring-segment-routing-mpls-03

Abstract

   Segment Routing (SR) leverages the source routing paradigm.  A node
   steers a packet through a controlled set of instructions, called
   segments, by prepending the packet with an SR header.  A segment can
   represent any instruction, topological or service-based.  SR allows
   to enforce a flow through any topological path and service chain
   while maintaining per-flow state only at the ingress node to the SR
   domain.

   Segment Routing can be directly applied to the MPLS architecture with
   no change in the forwarding plane.  This drafts describes how Segment
   Routing operates on top of the MPLS data plane.

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].





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Status of This Memo

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

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on February 1, 2015.

Copyright Notice

   Copyright (c) 2014 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
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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Illustration  . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  MPLS Instantiation of Segment Routing . . . . . . . . . . . .   4
   4.  IGP Segments Examples . . . . . . . . . . . . . . . . . . . .   6
     4.1.  Example 1 . . . . . . . . . . . . . . . . . . . . . . . .   7
     4.2.  Example 2 . . . . . . . . . . . . . . . . . . . . . . . .   7
     4.3.  Example 3 . . . . . . . . . . . . . . . . . . . . . . . .   7
     4.4.  Example 4 . . . . . . . . . . . . . . . . . . . . . . . .   7
     4.5.  Example 5 . . . . . . . . . . . . . . . . . . . . . . . .   8
   5.  Other Examples of MPLS Segments . . . . . . . . . . . . . . .   8
     5.1.  LDP LSP segment combined with IGP segments  . . . . . . .   8
     5.2.  RSVP-TE LSP segment combined with IGP segments  . . . . .   9
   6.  Segment List History  . . . . . . . . . . . . . . . . . . . .  10
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  10



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   8.  Manageability Considerations  . . . . . . . . . . . . . . . .  11
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .  11
   10. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  11
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  11
     11.1.  Normative References . . . . . . . . . . . . . . . . . .  11
     11.2.  Informative References . . . . . . . . . . . . . . . . .  11
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  12

1.  Introduction

   The Segment Routing architecture
   [I-D.filsfils-spring-segment-routing] can be directly applied to the
   MPLS architecture with no change in the MPLS forwarding plane.  This
   drafts describes how Segment Routing operates on top of the MPLS data
   plane.

   The Segment Routing use cases are described in in
   [I-D.filsfils-spring-segment-routing-use-cases].

   Link State protocol extensions for Segment Routing are described in
   [I-D.ietf-isis-segment-routing-extensions],
   [I-D.ietf-ospf-segment-routing-extensions] and
   [I-D.psenak-ospf-segment-routing-ospfv3-extension].

2.  Illustration

   Segment Routing, applied to the MPLS data plane, offers the ability
   to tunnel services (VPN, VPLS, VPWS) from an ingress PE to an egress
   PE, without any other protocol than ISIS or OSPF
   ([I-D.ietf-isis-segment-routing-extensions] and
   [I-D.ietf-ospf-segment-routing-extensions]).  LDP and RSVP-TE
   signaling protocols are not required.

   Note that [I-D.filsfils-spring-segment-routing-ldp-interop] documents
   SR co-existence and interworking with other MPLS signaling protocols,
   if present in the network during a migration, or in case of non-
   homogeneous deployments.

   The operator only needs to allocate one node segment per PE and the
   SR IGP control-plane automatically builds the required MPLS
   forwarding constructs from any PE to any PE.










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                 P1---P2
                /       \
   A---CE1---PE1         PE2---CE2---Z
                \       /
                 P4---P4

                    Figure 1: IGP-based MPLS Tunneling

   In Figure 1 above, the four nodes A, CE1, CE2 and Z are part of the
   same VPN.

   PE2 advertises (in the IGP) a host address 192.0.2.2/32 with its
   attached node segment 102.

   CE2 advertises to PE2 a route to Z.  PE2 binds a local label LZ to
   that route and propagates the route and its label via MPBGP to PE1
   with nhop 192.0.2.2 (PE2 loopback address).

   PE1 installs the VPN prefix Z in the appropriate VRF and resolves the
   next-hop onto the node segment 102.  Upon receiving a packet from A
   destined to Z, PE1 pushes two labels onto the packet: the top label
   is 102, the bottom label is LZ. 102 identifies the node segment to
   PE2 and hence transports the packet along the ECMP-aware shortest-
   path to PE2.  PE2 then processes the VPN label LZ and forwards the
   packet to CE2.

   Supporting MPLS services (VPN, VPLS, VPWS) with SR has the following
   benefits:

      Simple operation: one single intra-domain protocol to operate: the
      IGP.  No need to support IGP synchronization extensions as
      described in [RFC5443] and [RFC6138].

      Excellent scaling: one Node-SID per PE.

3.  MPLS Instantiation of Segment Routing

   MPLS instantiation of Segment Routing fits in the MPLS architecture
   as defined in [RFC3031] both from a control plane and forwarding
   plane perspective:

   o  From a control plane perspective [RFC3031]does not mandate a
      single signaling protocol.  Segment Routing proposes to use the
      Link State IGP as its use of information flooding fits very well
      with label stacking on ingress.

   o  From a forwarding plane perspective, Segment Routing does not
      require any change to the forwarding plane.



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   When applied to MPLS, a Segment is a LSP and the 20 right-most bits
   of the segment are encoded as a label.  This implies that, in the
   MPLS instantiation, the SID values are allocated within a reduced
   20-bit space out of the 32-bit SID space.

   The notion of indexed global segment fits the MPLS architecture
   [RFC3031] as the absolute value allocated to any segment (global or
   local) can be managed by a local allocation process (similarly to
   other MPLS signaling protocols).

   If present, SR can coexist and interwork with LDP and RSVP
   [I-D.filsfils-spring-segment-routing-ldp-interop].

   The source routing model described in
   [I-D.filsfils-spring-segment-routing] is inherited from the ones
   proposed by [RFC1940] and [RFC2460].  The source routing model offers
   the support for explicit routing capability.

   Contrary to RSVP-based explicit routes where tunnel midpoints
   maintain states, SR-based explicit routes only require per-flow
   states at the ingress edge router where the traffic engineer policy
   is applied.

   Contrary to RSVP-based explicit routes which consist in non-ECMP
   circuits (similar to ATM/FR), SR-based explicit routes can be built
   as list of ECMP-aware node segments and hence ECMP-aware traffic
   engineering is natively supported by SR.

   When Segment Routing is instantiated over the MPLS data plane the
   following applies:

      A list of segments is represented as a stack of labels.

      The active segment is the top label.

      The CONTINUE operation is implemented as an MPLS swap operation.
      When the same Segment Routing Global Block (SRGB, defined in
      [I-D.filsfils-spring-segment-routing] is used throughout the SR
      domain, the outgoing label value is equal to the incoming label
      value . Else, the outgoing label value is [SRGB(next_hop)+index]

      The NEXT operation is implemented as an MPLS pop operation.

      The PUSH operation is implemented as an MPLS push of a label
      stack.

   In conclusion, there are no changes in the operations of the data-
   plane currently used in MPLS networks.



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4.  IGP Segments Examples

   Assuming the network diagram of Figure 2 and the IP address and IGP
   Segment allocation of Figure 3, the following examples can be
   constructed.

            +--------+
           /          \
   R1-----R2----------R3-----R8
          | \        / |
          |  +--R4--+  |
          |            |
          +-----R5-----+

                   Figure 2: IGP Segments - Illustration

   +-----------------------------------------------------------+
   | IP address allocated by the operator:                     |
   |                      192.0.2.1/32 as a loopback of R1     |
   |                      192.0.2.2/32 as a loopback of R2     |
   |                      192.0.2.3/32 as a loopback of R3     |
   |                      192.0.2.4/32 as a loopback of R4     |
   |                      192.0.2.5/32 as a loopback of R5     |
   |                      192.0.2.8/32 as a loopback of R8     |
   |              198.51.100.9/32 as an anycast loopback of R4 |
   |              198.51.100.9/32 as an anycast loopback of R5 |
   |                                                           |
   | SRGB defined by the operator as 1000-5000                 |
   |                                                           |
   | Global IGP SID allocated by the operator:                 |
   |                      1001 allocated to 192.0.2.1/32       |
   |                      1002 allocated to 192.0.2.2/32       |
   |                      1003 allocated to 192.0.2.3/32       |
   |                      1004 allocated to 192.0.2.4/32       |
   |                      1008 allocated to 192.0.2.8/32       |
   |                      2009 allocated to 198.51.100.9/32    |
   |                                                           |
   | Local IGP SID allocated dynamically by R2                 |
   |                     for its "north" adjacency to R3: 9001 |
   |                     for its "north" adjacency to R3: 9003 |
   |                     for its "south" adjacency to R3: 9002 |
   |                     for its "south" adjacency to R3: 9003 |
   +-----------------------------------------------------------+

        Figure 3: IGP Address and Segment Allocation - Illustration






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4.1.  Example 1

   R1 may send a packet P1 to R8 simply by pushing an SR header with
   segment list {1008}.

   1008 is a global IGP segment attached to the IP prefix 192.0.2.8/32.
   Its semantic is global within the IGP domain: any router forwards a
   packet received with active segment 1008 to the next-hop along the
   ECMP-aware shortest-path to the related prefix.

   In conclusion, the path followed by P1 is R1-R2--R3-R8.  The ECMP-
   awareness ensures that the traffic be load-shared between any ECMP
   path, in this case the two north and south links between R2 and R3.

4.2.  Example 2

   R1 may send a packet P2 to R8 by pushing an SR header with segment
   list {1002, 9001, 1008}.

   1002 is a global IGP segment attached to the IP prefix 192.0.2.2/32.
   Its semantic is global within the IGP domain: any router forwards a
   packet received with active segment 1002 to the next-hop along the
   shortest-path to the related prefix.

   9001 is a local IGP segment attached by node R2 to its north link to
   R3.  Its semantic is local to node R2: R2 switches a packet received
   with active segment 9001 towards the north link to R3.

   In conclusion, the path followed by P2 is R1-R2-north-link-R3-R8.

4.3.  Example 3

   R1 may send a packet P3 along the same exact path as P1 using a
   different segment list {1002, 9003, 1008}.

   9003 is a local IGP segment attached by node R2 to both its north and
   south links to R3.  Its semantic is local to node R2: R2 switches a
   packet received with active segment 9003 towards either the north or
   south links to R3 (e.g. per-flow loadbalancing decision).

   In conclusion, the path followed by P3 is R1-R2-any-link-R3-R8.

4.4.  Example 4

   R1 may send a packet P4 to R8 while avoiding the links between R2 and
   R3 by pushing an SR header with segment list {1004, 1008}.





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   1004 is a global IGP segment attached to the IP prefix 192.0.2.4/32.
   Its semantic is global within the IGP domain: any router forwards a
   packet received with active segment 1004 to the next-hop along the
   shortest-path to the related prefix.

   In conclusion, the path followed by P4 is R1-R2-R4-R3-R8.

4.5.  Example 5

   R1 may send a packet P5 to R8 while avoiding the links between R2 and
   R3 while still benefitting from all the remaining shortest paths (via
   R4 and R5) by pushing an SR header with segment list {2009, 1008}.

   2009 is a global IGP segment attached to the anycast IP prefix
   198.51.100.9/32.  Its semantic is global within the IGP domain: any
   router forwards a packet received with active segment 2009 to the
   next-hop along the shortest-path to the related prefix.

   In conclusion, the path followed by P5 is either R1-R2-R4-R3-R8 or
   R1-R2-R5-R3-R8 .

5.  Other Examples of MPLS Segments

   In addition to the IGP segments previously described, the SPRING
   source routing policy applied to MPLS can include MPLS LSP's signaled
   by LDP, RSVPTE and BGP.  The list of examples is non exhaustive.
   Other form of segments combination can be instantiated through
   Segment Routing (e.g.: RSVP LSPs combined with LDP or IGP or BGP
   LSPs).

5.1.  LDP LSP segment combined with IGP segments

   The example illustrates a segment-routing policy including IGP
   segments and LDP LSP segments.

                      SL1---S2---SL3---L4---SL5---S6
                                  |               |
                                  +---------------+

           Figure 4: LDP LSP segment combined with IGP segments

   We assume that:

   o  All links have an IGP cost of 1 except SL3-S6 link which has cost
      2.

   o  All nodes are in the same IGP area.




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   o  Nodes SL1, S2, SL3, SL5 and S6 are IGP-SR capable.

   o  SL3 and S6 have, respectively, index 3 and 6 assigned to them.

   o  All SR nodes have the same SRGB consisting of: [1000, 1999]

   o  SL1, SL3, L4 and SL5 are LDP capable.

   o  SL1 has a directed LDP session with SL3 and is able to retrieve
      the SL3 local LDP mapping for FEC SL5: 35

   o  The following source-routed policy is defined in S1 for the
      traffic destined to S6: use path SL1-S2-SL3-L4-SL5-S6 (instead of
      shortest-path SL1-S2-SL3-S6).

   This is realized by programming the following segment-routing policy
   at S1: for traffic destined to S6, push the ordered segment list:
   {1003, 35, 1006}, where:

   o  1003 gets the packets from S1 to SL3 via S2.

   o  35 gets the packets from SL3 to SL5 via L4.

   o  1006 gets the packets from SL5 to S6.

   The above allows to steer the traffic into path SL1-S2-SL3-L4-SL5-S6
   instead of the shortest path SL1-S2-SL3-S6.

5.2.  RSVP-TE LSP segment combined with IGP segments

   The example illustrates a segment-routing policy including IGP
   segments and RSVP-TE LSP segments.

                       S1---S2---RS3---R4---RS5---S6
                                  |               |
                                  +---------------+

         Figure 5: RSVP-TE LSP segment combined with IGP segments

   We assume that:

   o  All links have an IGP cost of 1 except link RS3-S6 which has cost
      2.

   o  All nodes are IGP-SR capable except R4.

   o  RS3 and R6 have, respectively, index 3 and 6 assigned to them.




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   o  All SR nodes have the same SRGB consisting of: [1000, 1999]

   o  RS3, R4 and RS5 are RSVP-TE capable.

   o  An RSVP-TE LSP has been provisioned from RS3 to RS5 via R4.

   o  RS3 allocates a binding SID (with value of 135) for this RSVP-TE
      LSP and signals it in the igp.

   o  The following source-routed policy is defined at S1 for the
      traffic destined to S6: use path S1-S2-RS3-R4-RS5-S6 instead of
      shortest-path S1-S2-RS3-S6.

   This is realized by programming the following segment-routing policy
   at S1: - for traffic destined to S6, push the ordered segment list:
   {1003, 135, 1006}, where:

   o  1003 gets the packets from S1 to RS3 via S2.

   o  135 gets the packets from RS3 into the RSVP-TE LSP to RS5 via R4.

   o  1006 gets the packets from RS5 to S6.

   The above allows to steer the traffic into path S1-S2-RS3-R4-RS5-S6
   instead of the shortest path S1-S2-RS3-S6.

6.  Segment List History

   In the abstract SR routing model
   [I-D.filsfils-spring-segment-routing], any node N along the journey
   of the packet is able to determine where the packet P entered the SR
   domain and where it will exit.  The intermediate node is also able to
   determine the paths from the ingress edge router to itself, and from
   itself to the egress edge router.

   In the MPLS instantiation, as the packet travels through the SR
   domain, the stack is depleted and the segment list history is
   gradually lost.

   Future version of this document will describe how this information
   can be preserved in MPLS domains.

7.  IANA Considerations

   TBD






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8.  Manageability Considerations

   TBD

9.  Security Considerations

   TBD

10.  Acknowledgements

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.

   [RFC2460]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", RFC 2460, December 1998.

   [RFC3031]  Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
              Label Switching Architecture", RFC 3031, January 2001.

11.2.  Informative References

   [I-D.filsfils-spring-segment-routing]
              Filsfils, C., Previdi, S., Bashandy, A., Decraene, B.,
              Litkowski, S., Horneffer, M., Milojevic, I., Shakir, R.,
              Ytti, S., Henderickx, W., Tantsura, J., and E. Crabbe,
              "Segment Routing Architecture", draft-filsfils-spring-
              segment-routing-04 (work in progress), July 2014.

   [I-D.filsfils-spring-segment-routing-ldp-interop]
              Filsfils, C., Previdi, S., Bashandy, A., Decraene, B.,
              Litkowski, S., Horneffer, M., Milojevic, I., Shakir, R.,
              Ytti, S., Henderickx, W., Tantsura, J., and E. Crabbe,
              "Segment Routing interoperability with LDP", draft-
              filsfils-spring-segment-routing-ldp-interop-01 (work in
              progress), April 2014.

   [I-D.filsfils-spring-segment-routing-use-cases]
              Filsfils, C., Francois, P., Previdi, S., Decraene, B.,
              Litkowski, S., Horneffer, M., Milojevic, I., Shakir, R.,
              Ytti, S., Henderickx, W., Tantsura, J., Kini, S., and E.
              Crabbe, "Segment Routing Use Cases", draft-filsfils-
              spring-segment-routing-use-cases-00 (work in progress),
              March 2014.




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   [I-D.ietf-isis-segment-routing-extensions]
              Previdi, S., Filsfils, C., Bashandy, A., Gredler, H.,
              Litkowski, S., Decraene, B., and J. Tantsura, "IS-IS
              Extensions for Segment Routing", draft-ietf-isis-segment-
              routing-extensions-02 (work in progress), June 2014.

   [I-D.ietf-ospf-segment-routing-extensions]
              Psenak, P., Previdi, S., Filsfils, C., Gredler, H.,
              Shakir, R., Henderickx, W., and J. Tantsura, "OSPF
              Extensions for Segment Routing", draft-ietf-ospf-segment-
              routing-extensions-01 (work in progress), July 2014.

   [I-D.psenak-ospf-segment-routing-ospfv3-extension]
              Psenak, P., Previdi, S., Filsfils, C., Gredler, H.,
              Shakir, R., Henderickx, W., and J. Tantsura, "OSPFv3
              Extensions for Segment Routing", draft-psenak-ospf-
              segment-routing-ospfv3-extension-02 (work in progress),
              July 2014.

   [RFC1940]  Estrin, D., Li, T., Rekhter, Y., Varadhan, K., and D.
              Zappala, "Source Demand Routing: Packet Format and
              Forwarding Specification (Version 1)", RFC 1940, May 1996.

   [RFC5443]  Jork, M., Atlas, A., and L. Fang, "LDP IGP
              Synchronization", RFC 5443, March 2009.

   [RFC6138]  Kini, S. and W. Lu, "LDP IGP Synchronization for Broadcast
              Networks", RFC 6138, February 2011.

   [draft-filsfils-rtgwg-segment-routing-ldp-interop-00]
              Filsfils, C. and S. Previdi, "Segment Routing
              interoperability with LDP", October 2013.

Authors' Addresses

   Clarence Filsfils (editor)
   Cisco Systems, Inc.
   Brussels
   BE

   Email: cfilsfil@cisco.com










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   Stefano Previdi (editor)
   Cisco Systems, Inc.
   Via Del Serafico, 200
   Rome  00142
   Italy

   Email: sprevidi@cisco.com


   Ahmed Bashandy
   Cisco Systems, Inc.
   170, West Tasman Drive
   San Jose, CA  95134
   US

   Email: bashandy@cisco.com


   Bruno Decraene
   Orange
   FR

   Email: bruno.decraene@orange.com


   Stephane Litkowski
   Orange
   FR

   Email: stephane.litkowski@orange.com


   Martin Horneffer
   Deutsche Telekom
   Hammer Str. 216-226
   Muenster  48153
   DE

   Email: Martin.Horneffer@telekom.de


   Igor Milojevic
   Telekom Srbija
   Takovska 2
   Belgrade
   RS

   Email: igormilojevic@telekom.rs



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   Rob Shakir
   British Telecom
   London
   UK

   Email: rob.shakir@bt.com


   Saku Ytti
   TDC Oy
   Mechelininkatu 1a
   TDC  00094
   FI

   Email: saku@ytti.fi


   Wim Henderickx
   Alcatel-Lucent
   Copernicuslaan 50
   Antwerp  2018
   BE

   Email: wim.henderickx@alcatel-lucent.com


   Jeff Tantsura
   Ericsson
   300 Holger Way
   San Jose, CA  95134
   US

   Email: Jeff.Tantsura@ericsson.com


   Edward Crabbe
   Google, Inc.
   1600 Amphitheatre Parkway
   Mountain View, CA  94043
   US

   Email: edc@google.com









Filsfils, et al.        Expires February 1, 2015               [Page 14]

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