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RFC 8408

Proposed STD
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Conveying Path Setup Type in PCE Communication Protocol (PCEP) Messages

 


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Internet Engineering Task Force (IETF)                      S. Sivabalan
Request for Comments: 8408                           Cisco Systems, Inc.
Category: Standards Track                                    J. Tantsura
ISSN: 2070-1721                                           Nuage Networks
                                                                I. Minei
                                                            Google, Inc.
                                                                R. Varga
                                               Pantheon Technologies SRO
                                                             J. Hardwick
                                                     Metaswitch Networks
                                                               July 2018


                       Conveying Path Setup Type
             in PCE Communication Protocol (PCEP) Messages

Abstract

   A Path Computation Element (PCE) can compute Traffic Engineering (TE)
   paths through a network; these paths are subject to various
   constraints.  Currently, TE paths are Label Switched Paths (LSPs)
   that are set up using the RSVP-TE signaling protocol.  However, other
   TE path setup methods are possible within the PCE architecture.  This
   document proposes an extension to the PCE Communication Protocol
   (PCEP) to allow support for different path setup methods over a given
   PCEP session.

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 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc8408.

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Copyright Notice

   Copyright (c) 2018 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
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   4
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Path Setup Type Capability TLV  . . . . . . . . . . . . . . .   4
   4.  Path Setup Type TLV . . . . . . . . . . . . . . . . . . . . .   6
   5.  Operation . . . . . . . . . . . . . . . . . . . . . . . . . .   7
   6.  Manageability Considerations  . . . . . . . . . . . . . . . .   8
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
     8.1.  Additions to PCEP TLV Type Indicators Registry  . . . . .   9
     8.2.  New PCEP Path Setup Types Registry  . . . . . . . . . . .   9
     8.3.  Additions to PCEP-ERROR Object Error Types and Values
           Registry  . . . . . . . . . . . . . . . . . . . . . . . .  10
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  10
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  11
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  11
   Contributors  . . . . . . . . . . . . . . . . . . . . . . . . . .  11
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  12

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1.  Introduction

   [RFC5440] describes the PCE Communication Protocol (PCEP) for
   communication between a Path Computation Client (PCC) and a Path
   Computation Element (PCE) or between a PCE and a PCE.  A PCC
   requests, from a PCE, a path subject to various constraints and
   optimization criteria.  The PCE responds to the PCC with a hop-by-hop
   path in an Explicit Route Object (ERO).  The PCC uses the ERO to set
   up the path in the network.

   [RFC8231] specifies extensions to PCEP that allow a PCC to delegate
   its LSPs to a PCE.  The PCE can then update the state of LSPs
   delegated to it.  In particular, the PCE may modify the path of an
   LSP by sending a new ERO.  The PCC uses this ERO to reroute the LSP
   in a make-before-break fashion.  [RFC8281] specifies a mechanism that
   allows a PCE to dynamically instantiate an LSP on a PCC by sending
   the ERO and the characteristics of the LSP.  The PCC creates the LSP
   using the ERO and other attributes sent by the PCE.

   So far, PCEP and its extensions have assumed that the TE paths are
   label switched and are established via the RSVP-TE signaling
   protocol.  However, other methods of LSP setup are possible in the
   PCE architecture (see [RFC4655] and [RFC4657]).  This document
   generalizes PCEP to allow other LSP setup methods to be used.  It
   defines two new TLVs and specifies the base procedures to facilitate
   this:

   o  The PATH-SETUP-TYPE-CAPABILITY TLV allows a PCEP speaker to
      announce which LSP setup methods it supports when the PCEP session
      is established.

   o  The PATH-SETUP-TYPE TLV allows a PCEP speaker to specify which
      setup method should be used for a given LSP.  When multiple path
      setup types are deployed in a network, a given PCEP session may
      have to simultaneously support more than one path setup type.  A
      PCEP speaker uses the PATH-SETUP-TYPE TLV to explicitly indicate
      the intended path setup type in the appropriate PCEP messages,
      unless the path setup type is RSVP-TE (which is assumed to be the
      path setup type if no other setup type is indicated).  This is so
      that both the PCC and the PCE can take the necessary steps to set
      up the path.

   This document defines a path setup type code for RSVP-TE.  When a new
   path setup type (other than RSVP-TE) is introduced for setting up a
   path, a path setup type code and, optionally, a sub-TLV pertaining to
   the new path setup type will be defined by the document that
   specifies the new path setup type.

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1.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

2.  Terminology

   The following terminology is used in this document:

   ERO:  Explicit Route Object

   PCC:  Path Computation Client

   PCE:  Path Computation Element

   PCEP:  PCE Communication Protocol

   PST:  Path Setup Type

   TLV:  Type, Length, and Value

3.  Path Setup Type Capability TLV

   A PCEP speaker indicates which PSTs it supports during the PCEP
   initialization phase using the following process.  When the PCEP
   session is created, it sends an Open message with an OPEN object
   containing the PATH-SETUP-TYPE-CAPABILITY TLV.  The format of this
   TLV is 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 (34)           |             Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                           Reserved            |  Num of PSTs  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |     PST#1     |      ...      |     PST#N     |    Padding    |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      //               Optional sub-TLVs (variable)                  //
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                 Figure 1: PATH-SETUP-TYPE-CAPABILITY TLV

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   The TLV Type is 34.  Its Reserved field MUST be set to zero by the
   sender and MUST be ignored by the receiver.  The other fields in the
   TLV are as follows.

   Length:  The total length in bytes of the remainder of the TLV, that
      is, excluding the Type and Length fields.

   Num of PSTs:  The number of PSTs in the following list, excluding
      padding.

   List of PSTs:  A list of the PSTs that the PCEP speaker supports.
      Each PST is a single byte in length.  Duplicate entries in this
      list MUST be ignored.  The PCEP speaker MUST pad the list with
      zeros so that it is a multiple of four bytes in length.  This
      document defines the following PST value:

      *  PST = 0: Path is set up using the RSVP-TE signaling protocol

   Optional sub-TLVs:  A list of sub-TLVs associated with the supported
      PSTs.  Each PST has zero or one sub-TLVs associated with it, and
      each sub-TLV is associated with exactly one PST.  Each sub-TLV
      MUST obey the rules for TLV formatting defined in [RFC5440].  That
      is, each sub-TLV is padded to a four-byte alignment, and the
      Length field of each sub-TLV does not include the padding bytes.
      This document does not define any sub-TLVs; an example sub-TLV can
      be found in [PCEP-EXTENSIONS].

   A PCEP speaker MUST check that this TLV is correctly formatted, as
   follows.

   o  If there are no sub-TLVs, then the TLV Length field MUST be equal
      to four bytes plus the size of the PST list, excluding any padding
      bytes.

   o  If there are sub-TLVs, then the TLV Length field MUST be equal to
      four bytes plus the size of the PST list (rounded up to the
      nearest multiple of four) plus the size of the appended sub-TLVs,
      excluding any padding bytes in the final sub-TLV.

   o  The Num of PSTs field MUST be greater than zero.

   If a PCEP speaker receives a PATH-SETUP-TYPE-CAPABILITY TLV that
   violates these rules, then the PCEP speaker MUST send a PCErr message
   with Error-Type = 10 (Reception of an invalid object) and Error-value
   = 11 (Malformed object) and MUST close the PCEP session.  The PCEP
   speaker MAY include the malformed OPEN object in the PCErr message as
   well.

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   If a PCEP speaker receives an OPEN object with more than one PATH-
   SETUP-TYPE-CAPABILITY TLV, then it MUST ignore all but the first
   instance of this TLV.

   The absence of the PATH-SETUP-TYPE-CAPABILITY TLV from the OPEN
   object is equivalent to a PATH-SETUP-TYPE-CAPABILITY TLV containing a
   single PST value of 0 (Path is set up using the RSVP-TE signaling
   protocol) and no sub-TLVs.  A PCEP speaker MAY omit the PATH-SETUP-
   TYPE-CAPABILITY TLV if the only PST it supports is RSVP-TE.  If a
   PCEP speaker supports other PSTs besides RSVP-TE, then it SHOULD
   include the PATH-SETUP-TYPE-CAPABILITY TLV in its OPEN object.

   If a PCEP speaker does not recognize the PATH-SETUP-TYPE-CAPABILITY
   TLV, it will ignore the TLV in accordance with [RFC5440].

4.  Path Setup Type TLV

   When a PCEP session is used to set up TE paths using different
   methods, the corresponding PCE and PCC must be aware of the path
   setup method used.  This means that a PCE must be able to specify
   paths in the correct format, and a PCC must be able to take control-
   plane and forwarding-plane actions appropriate to the PST.

       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 (28)           |           Length (4)          |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                           Reserved            |      PST      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                       Figure 2: PATH-SETUP-TYPE TLV

   The PATH-SETUP-TYPE TLV is an optional TLV associated with the
   Request Parameters (RP) [RFC5440] and the Stateful PCE Request
   Parameters (SRP) [RFC8231] objects.  Its format is shown in Figure 2.
   The TLV type is 28.  Its Reserved field MUST be set to zero.  The
   one-byte PST field contains the PST as defined for the PATH-SETUP-
   TYPE-CAPABILITY TLV.

   The absence of the PATH-SETUP-TYPE TLV is equivalent to a PATH-SETUP-
   TYPE TLV with a PST value of 0 (Path is set up using the RSVP-TE
   signaling protocol).  A PCEP speaker MAY omit the TLV if the PST is
   RSVP-TE.  If the RP or SRP object contains more than one PATH-SETUP-
   TYPE TLV, only the first TLV MUST be processed, and the rest MUST be
   ignored.

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   If a PCEP speaker does not recognize the PATH-SETUP-TYPE TLV, it will
   ignore the TLV in accordance with [RFC5440] and use RSVP-TE to set up
   the path.

5.  Operation

   During the PCEP initialization phase, if a PCEP speaker receives a
   PATH-SETUP-TYPE-CAPABILITY TLV from its peer, it MUST assume that the
   peer supports only the PSTs listed in the TLV.  If the PCEP speaker
   and its peer have no PSTs in common, then the PCEP speaker MUST send
   a PCErr message with Error-Type = 21 (Invalid traffic engineering
   path setup type) and Error-value = 2 (Mismatched path setup type) and
   close the PCEP session.

   If the peer has sent no PATH-SETUP-TYPE-CAPABILITY TLV, then the PCEP
   speaker MUST infer that the peer supports path setup using at least
   RSVP-TE.  The PCEP speaker MAY also infer that the peer supports
   other path setup types, but the means of inference are outside the
   scope of this document.

   When a PCC sends a PCReq message to a PCE [RFC5440], it MUST include
   the PATH-SETUP-TYPE TLV in the RP object, unless the intended PST is
   RSVP-TE (in which case it MAY omit the PATH-SETUP-TYPE TLV).  If the
   PCE is capable of expressing the path in a format appropriate to the
   intended PST, it MUST use the appropriate ERO format in the PCRep
   message.

   When a PCE sends a PCRep message to a PCC [RFC5440], it MUST include
   the PATH-SETUP-TYPE TLV in the RP object, unless the PST is RSVP-TE
   (in which case it MAY omit the PATH-SETUP-TYPE TLV).  If the PCE does
   not support the intended PST, it MUST send a PCErr message with
   Error-Type = 21 (Invalid traffic engineering path setup type) and
   Error-value = 1 (Unsupported path setup type) and close the PCEP
   session.  If the PSTs corresponding to the PCReq and PCRep messages
   do not match, the PCC MUST send a PCErr message with Error-Type = 21
   (Invalid traffic engineering path setup type) and Error-value = 2
   (Mismatched path setup type) and close the PCEP session.

   When a stateful PCE sends a PCUpd message [RFC8231] or a PCInitiate
   message [RFC8281] to a PCC, it MUST include the PATH-SETUP-TYPE TLV
   in the SRP object, unless the intended PST is RSVP-TE (in which case
   it MAY omit the PATH-SETUP-TYPE TLV).  If the PCC does not support
   the PST associated with the PCUpd or PCInitiate message, it MUST send
   a PCErr message with Error-Type = 21 (Invalid traffic engineering
   path setup type) and Error-value = 1 (Unsupported path setup type)
   and close the PCEP session.

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   When a PCC sends a PCRpt message to a stateful PCE [RFC8231], it MUST
   include the PATH-SETUP-TYPE TLV in the SRP object, unless the PST is
   RSVP-TE (in which case it MAY omit the PATH-SETUP-TYPE TLV).  The PCC
   MUST include the SRP object in the PCRpt message if the PST is not
   RSVP-TE, even when the SRP-ID-number is the reserved value of
   0x00000000.  If the PCRpt message is triggered by a PCUpd or
   PCInitiate message, then the PST that the PCC indicates in the PCRpt
   message MUST match the PST that the stateful PCE intended in the
   PCUpd or PCInitiate message.  If it does not match, then the PCE MUST
   send a PCErr message with Error-Type = 21 (Invalid traffic
   engineering path setup type) and Error-value = 2 (Mismatched path
   setup type) and close the PCEP session.

6.  Manageability Considerations

   This document generalizes PCEP to allow path setup methods other than
   RSVP-TE to be used by the network (but does not define any new path
   setup types besides RSVP-TE).  It is possible that, in a given
   network, multiple path setup methods will be used.  It is also
   possible that not all devices will support the same set of path setup
   methods.  Managing networks that combine multiple path setup methods
   may therefore raise some challenges from a configuration and
   observability point of view.

   Each document that defines a new path setup type in the "PCEP Path
   Setup Types" registry (Section 8.2) must include a Manageability
   Considerations section.  The Manageability Considerations section
   must explain how operators can manage PCEP with the new path setup
   type.  It must address the following questions, which are generally
   applicable when working with multiple path setup types in PCEP.

   o  What are the criteria for when devices will use the new path setup
      type in PCEP, and how can the operator control this?

   o  How can the network be migrated to the new path setup type, and
      are there any backwards-compatibility issues that operators need
      to be aware of?

   o  Are paths set up using the new path setup type intended to coexist
      with other paths over the long term, and if so, how is this
      situation managed with PCEP?

   o  How can operators verify the correct operation of PCEP in the
      network with respect to the new path setup type?  Which fault
      conditions must be reported to the operators?

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   o  Are there any existing management interfaces (such as YANG models)
      that must be extended to model the operation of PCEP in the
      network with respect to the new path setup type?

   See [RFC5706] for further guidance on how to write Manageability
   Considerations sections in Standards Track documents.

7.  Security Considerations

   The security considerations described in [RFC5440] and [RFC8281] are
   applicable to this specification.  No additional security measure is
   required.

   Note that if the security mechanisms of [RFC5440] and [RFC8281] are
   not used, then the protocol described in this document could be
   attacked in the following new way.  An attacker, using a TCP man-in-
   the-middle attack, could inject error messages into the PCEP session
   when a particular PST is (or is not) used.  Doing this could
   potentially force the use of a specific PST, which may allow the
   attacker to subsequently attack a weakness in that PST.

8.  IANA Considerations

8.1.  Additions to PCEP TLV Type Indicators Registry

   IANA has allocated the following code points in the "PCEP TLV Type
   Indicators" registry.

     Value    Description                   Reference
     -----    --------------------------    ---------
     28       PATH-SETUP-TYPE               RFC 8408
     34       PATH-SETUP-TYPE-CAPABILITY    RFC 8408

8.2.  New PCEP Path Setup Types Registry

   IANA has created a new sub-registry within the "Path Computation
   Element Protocol (PCEP) Numbers" registry called "PCEP Path Setup
   Types".  The allocation policy for this new registry is IETF Review
   [RFC8126].  This new registry contains the following value:

     Value    Description                   Reference
     -----    --------------------------    ---------
     0        Path is set up using the      RFC 8408
              RSVP-TE signaling protocol

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8.3.  Additions to PCEP-ERROR Object Error Types and Values Registry

   IANA has allocated the following code points in the "PCEP-ERROR
   Object Error Types and Values" registry.

    Error-Type  Meaning                                        Reference
    ----------  -------------------------------------------    ---------
       10       Reception of an invalid object                 RFC 5440

                 Error-value = 11: Malformed object            RFC 8408

       21       Invalid traffic engineering path setup type    RFC 8408

                 Error-value = 0: Unassigned                   RFC 8408
                 Error-value = 1: Unsupported path setup type  RFC 8408
                 Error-value = 2: Mismatched path setup type   RFC 8408

9.  References

9.1.  Normative References

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

   [RFC5440]  Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation
              Element (PCE) Communication Protocol (PCEP)", RFC 5440,
              DOI 10.17487/RFC5440, March 2009,
              <https://www.rfc-editor.org/info/rfc5440>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8231]  Crabbe, E., Minei, I., Medved, J., and R. Varga, "Path
              Computation Element Communication Protocol (PCEP)
              Extensions for Stateful PCE", RFC 8231,
              DOI 10.17487/RFC8231, September 2017,
              <https://www.rfc-editor.org/info/rfc8231>.

   [RFC8281]  Crabbe, E., Minei, I., Sivabalan, S., and R. Varga, "Path
              Computation Element Communication Protocol (PCEP)
              Extensions for PCE-Initiated LSP Setup in a Stateful PCE
              Model", RFC 8281, DOI 10.17487/RFC8281, December 2017,
              <https://www.rfc-editor.org/info/rfc8281>.

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9.2.  Informative References

   [PCEP-EXTENSIONS]
              Sivabalan, S., Filsfils, C., Tantsura, J., Henderickx, W.,
              and J. Hardwick, "PCEP Extensions for Segment Routing",
              Work in Progress, draft-ietf-pce-segment-routing-12, June
              2018.

   [RFC4655]  Farrel, A., Vasseur, J., and J. Ash, "A Path Computation
              Element (PCE)-Based Architecture", RFC 4655,
              DOI 10.17487/RFC4655, August 2006,
              <https://www.rfc-editor.org/info/rfc4655>.

   [RFC4657]  Ash, J., Ed. and J. Le Roux, Ed., "Path Computation
              Element (PCE) Communication Protocol Generic
              Requirements", RFC 4657, DOI 10.17487/RFC4657, September
              2006, <https://www.rfc-editor.org/info/rfc4657>.

   [RFC5706]  Harrington, D., "Guidelines for Considering Operations and
              Management of New Protocols and Protocol Extensions",
              RFC 5706, DOI 10.17487/RFC5706, November 2009,
              <https://www.rfc-editor.org/info/rfc5706>.

   [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for
              Writing an IANA Considerations Section in RFCs", BCP 26,
              RFC 8126, DOI 10.17487/RFC8126, June 2017,
              <https://www.rfc-editor.org/info/rfc8126>.

Acknowledgements

   We would like to thank Marek Zavodsky for valuable comments.

Contributors

   The following people contributed to this document:

      - Jan Medved
      - Edward Crabbe

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Authors' Addresses

   Siva Sivabalan
   Cisco Systems, Inc.
   2000 Innovation Drive
   Kanata, Ontario  K2K 3E8
   Canada

   Email: msiva@cisco.com


   Jeff Tantsura
   Nuage Networks
   755 Ravendale Drive
   Mountain View, CA  94043
   United States of America

   Email: jefftant.ietf@gmail.com


   Ina Minei
   Google, Inc.
   1600 Amphitheatre Parkway
   Mountain View, CA  94043
   United States of America

   Email: inaminei@google.com



   Robert Varga
   Pantheon Technologies SRO
   Mlynske Nivy 56
   Bratislava, 821 05
   Slovakia

   Email: nite@hq.sk


   Jon Hardwick
   Metaswitch Networks
   100 Church Street
   Enfield, Middlesex
   United Kingdom

   Email: jonathan.hardwick@metaswitch.com