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Versions: (draft-berger-avtext-framemarking) 00 01 02 03 04 05 06 07

Network Working Group                                          M. Zanaty
Internet-Draft                                                 E. Berger
Intended status: Standards Track                           S. Nandakumar
Expires: November 1, 2018                                  Cisco Systems
                                                          April 30, 2018


                   Frame Marking RTP Header Extension
                   draft-ietf-avtext-framemarking-07

Abstract

   This document describes a Frame Marking RTP header extension used to
   convey information about video frames that is critical for error
   recovery and packet forwarding in RTP middleboxes or network nodes.
   It is most useful when media is encrypted, and essential when the
   middlebox or node has no access to the media decryption keys.  It is
   also useful for codec-agnostic processing of encrypted or unencrypted
   media, while it also supports extensions for codec-specific
   information.

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
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on November 1, 2018.

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
   (http://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



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   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  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Key Words for Normative Requirements  . . . . . . . . . . . .   4
   3.  Frame Marking RTP Header Extension  . . . . . . . . . . . . .   4
     3.1.  Extension for Non-Scalable Streams  . . . . . . . . . . .   4
     3.2.  Extension for Scalable Streams  . . . . . . . . . . . . .   5
       3.2.1.  Layer ID Mappings for Scalable Streams  . . . . . . .   6
         3.2.1.1.  H265 LID Mapping  . . . . . . . . . . . . . . . .   6
         3.2.1.2.  H264-SVC LID Mapping  . . . . . . . . . . . . . .   7
         3.2.1.3.  H264 (AVC) LID Mapping  . . . . . . . . . . . . .   7
         3.2.1.4.  VP8 LID Mapping . . . . . . . . . . . . . . . . .   7
         3.2.1.5.  Future Codec LID Mapping  . . . . . . . . . . . .   7
     3.3.  Signaling Information . . . . . . . . . . . . . . . . . .   8
     3.4.  Usage Considerations  . . . . . . . . . . . . . . . . . .   8
       3.4.1.  Relation to Layer Refresh Request (LRR) . . . . . . .   8
       3.4.2.  Scalability Structures  . . . . . . . . . . . . . . .   8
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   5.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   9
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   9
     7.2.  Informative References  . . . . . . . . . . . . . . . . .   9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  11

1.  Introduction

   Many widely deployed RTP [RFC3550] topologies [RFC7667] used in
   modern voice and video conferencing systems include a centralized
   component that acts as an RTP switch.  It receives voice and video
   streams from each participant, which may be encrypted using SRTP
   [RFC3711], or extensions that provide participants with private media
   via end-to-end encryption where the switch has no access to media
   decryption keys.  The goal is to provide a set of streams back to the
   participants which enable them to render the right media content.  In
   a simple video configuration, for example, the goal will be that each
   participant sees and hears just the active speaker.  In that case,
   the goal of the switch is to receive the voice and video streams from
   each participant, determine the active speaker based on energy in the
   voice packets, possibly using the client-to-mixer audio level RTP
   header extension [RFC6464], and select the corresponding video stream
   for transmission to participants; see Figure 1.




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   In this document, an "RTP switch" is used as a common short term for
   the terms "switching RTP mixer", "source projecting middlebox",
   "source forwarding unit/middlebox" and "video switching MCU" as
   discussed in [RFC7667].

            +---+      +------------+      +---+
            | A |<---->|            |<---->| B |
            +---+      |            |      +---+
                       |   RTP      |
            +---+      |  Switch    |      +---+
            | C |<---->|            |<---->| D |
            +---+      +------------+      +---+


                           Figure 1: RTP switch

   In order to properly support switching of video streams, the RTP
   switch typically needs some critical information about video frames
   in order to start and stop forwarding streams.

   o  Because of inter-frame dependencies, it should ideally switch
      video streams at a point where the first frame from the new
      speaker can be decoded by recipients without prior frames, e.g
      switch on an intra-frame.
   o  In many cases, the switch may need to drop frames in order to
      realize congestion control techniques, and needs to know which
      frames can be dropped with minimal impact to video quality.
   o  Furthermore, it is highly desirable to do this in a payload
      format-agnostic way which is not specific to each different video
      codec.  Most modern video codecs share common concepts around
      frame types and other critical information to make this codec-
      agnostic handling possible.
   o  It is also desirable to be able to do this for SRTP without
      requiring the video switch to decrypt the packets.  SRTP will
      encrypt the RTP payload format contents and consequently this data
      is not usable for the switching function without decryption, which
      may not even be possible in the case of end-to-end encryption of
      private media.

   By providing meta-information about the RTP streams outside the
   encrypted media payload, an RTP switch can do codec-agnostic
   selective forwarding without decrypting the payload.  This document
   specifies the necessary meta-information in an RTP header extension.








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2.  Key Words for Normative Requirements

   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 [RFC2119].

3.  Frame Marking RTP Header Extension

   This specification uses RTP header extensions as defined in
   [RFC5285].  A subset of meta-information from the video stream is
   provided as an RTP header extension to allow an RTP switch to do
   generic selective forwarding of video streams encoded with
   potentially different video codecs.

   The Frame Marking RTP header extension is encoded using the one-byte
   header or two-byte header as described in [RFC5285].  The one-byte
   header format is used for examples in this memo.  The two-byte header
   format is used when other two-byte header extensions are present in
   the same RTP packet, since mixing one-byte and two-byte extensions is
   not possible in the same RTP packet.

   This extension is only specified for Source (not Redunadancy) RTP
   Streams [RFC7656] that carry video payloads.  It is not specified for
   audio payloads, nor is it specified for Redundancy RTP Streams.  The
   (separate) specifications for Redudancy RTP Streams often include
   provisions for recovering any header extensions that were part of the
   original source packet.  Such provisions SHALL be followed to recover
   the Frame Marking RTP header extension of the original source packet.

3.1.  Extension for Non-Scalable Streams

   The following RTP header extension is RECOMMENDED for non-scalable
   streams.  It MAY also be used for scalable streams if the sender has
   limited or no information about stream scalability.  The ID is
   assigned per [RFC5285], and the length is encoded as L=0 which
   indicates 1 octet of data.

    0                   1
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  ID=? |  L=0  |S|E|I|D|0 0 0 0|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



   The following information are extracted from the media payload and
   sent in the Frame Marking RTP header extension.




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   o  S: Start of Frame (1 bit) - MUST be 1 in the first packet in a
      frame; otherwise MUST be 0.
   o  E: End of Frame (1 bit) - MUST be 1 in the last packet in a frame;
      otherwise MUST be 0.
   o  I: Independent Frame (1 bit) - MUST be 1 for frames that can be
      decoded independent of temporally prior frames, e.g. intra-frame,
      VPX keyframe, H.264 IDR [RFC6184], H.265 IDR/CRA/BLA/RAP
      [RFC7798]; otherwise MUST be 0.
   o  D: Discardable Frame (1 bit) - MUST be 1 for frames that can be
      discarded, and still provide a decodable media stream; otherwise
      MUST be 0.
   o  The remaining (4 bits) - MUST be 0 for non-scalable streams.

3.2.  Extension for Scalable Streams

   The following RTP header extension is RECOMMENDED for scalable
   streams.  It MAY also be used for non-scalable streams, in which case
   TID, LID and TL0PICIDX MUST be 0.  The ID is assigned per [RFC5285],
   and the length is encoded as L=2 which indicates 3 octets of data.

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  ID=? |  L=2  |S|E|I|D|B| TID |   LID         |    TL0PICIDX  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



   The following information are extracted from the media payload and
   sent in the Frame Marking RTP header extension.

   o  S: Start of Frame (1 bit) - MUST be 1 in the first packet in a
      frame within a layer; otherwise MUST be 0.
   o  E: End of Frame (1 bit) - MUST be 1 in the last packet in a frame
      within a layer; otherwise MUST be 0.
   o  I: Independent Frame (1 bit) - MUST be 1 for frames that can be
      decoded independent of temporally prior frames, e.g. intra-frame,
      VPX keyframe, H.264 IDR [RFC6184], H.265 IDR/CRA/BLA/RAP
      [RFC7798]; otherwise MUST be 0.  Note that this bit only signals
      temporal independence, so it can be 1 in spatial or quality
      enhancement layers that depend on temporally co-located layers but
      not temporally prior frames.
   o  D: Discardable Frame (1 bit) - MUST be 1 for frames that can be
      discarded, and still provide a decodable media stream; otherwise
      MUST be 0.
   o  B: Base Layer Sync (1 bit) - MUST be 1 if this frame only depends
      on the base layer; otherwise MUST be 0.  If no scalability is
      used, this MUST be 0.



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   o  TID: Temporal ID (3 bits) - The base temporal layer starts with 0,
      and increases with 1 for each higher temporal layer/sub-layer.  If
      no scalability is used, this MUST be 0.
   o  LID: Layer ID (8 bits) - Identifies the spatial and quality layer
      encoded.  If no scalability is used, this MUST be 0 or omitted.
      When omitted, TL0PICIDX MUST also be omitted.
   o  TL0PICIDX: Temporal Layer 0 Picture Index (8 bits) - Running index
      of base temporal layer 0 frames when TID is 0.  When TID is not 0,
      this indicates a dependency on the given index.  If no scalability
      is used, this MUST be 0 or omitted.  When omitted, LID MUST also
      be omitted.

   The layer information contained in TID and LID convey useful aspects
   of the layer structure that can be utilized in selective forwarding.
   Without further information about the layer structure, these
   identifiers can only be used for relative priority of layers.  They
   convey a layer hierarchy with TID=0 and LID=0 identifying the base
   layer.  Higher values of TID identify higher temporal layers with
   higher frame rates.  Higher values of LID identify higher spatial
   and/or quality layers with higher resolutions and/or bitrates.

   With further information, for example, possible future RTCP SDES
   items that convey full layer structure information, it may be
   possible to map these TIDs and LIDs to specific frame rates,
   resolutions and bitrates.  Such additional layer information may be
   useful for forwarding decisions in the RTP switch, but is beyond the
   scope of this memo.  The relative layer information is still useful
   for many selective forwarding decisions even without such additional
   layer information.

3.2.1.  Layer ID Mappings for Scalable Streams

3.2.1.1.  H265 LID Mapping

   The following shows the H265 [RFC7798] LayerID (6 bits) and TID (3
   bits) from the NAL unit header mapped to the generic LID and TID
   fields.

   The I bit MUST be 1 when the NAL unit type is 16-23 (inclusive),
   otherwise it MUST be 0.

   The S and E bits MUST match the corresponding bits in PACI:PHES:TSCI
   payload structures.








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    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  ID=2 |  L=2  |S|E|I|D|B| TID |0|0|  LayerID  |    TL0PICIDX  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

3.2.1.2.  H264-SVC LID Mapping

   The following shows H264-SVC [RFC6190] Layer encoding information (3
   bits for spatial/dependency layer, 4 bits for quality layer and 3
   bits for temporal layer) mapped to the generic LID and TID fields.

   The S, E, I and D bits MUST match the corresponding bits in PACSI
   payload structures.

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  ID=2 |  L=2  |S|E|I|D|B| TID |0| DID |  QID  |    TL0PICIDX  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

3.2.1.3.  H264 (AVC) LID Mapping

   The following shows the header extension for H264 (AVC) [RFC6184]
   that contains only temporal layer information.

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  ID=2 |  L=2  |S|E|I|D|B| TID |0|0|0|0|0|0|0|0|    TL0PICIDX  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

3.2.1.4.  VP8 LID Mapping

   The following shows the header extension for VP8 [RFC7741] that
   contains only temporal layer information.

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  ID=2 |  L=2  |S|E|I|D|B| TID |0|0|0|0|0|0|0|0|    TL0PICIDX  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

3.2.1.5.  Future Codec LID Mapping

   The RTP payload format specification for future video codecs SHOULD
   include a section describing the LID mapping and TID mapping for the




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   codec.  For example, the LID/TID mapping for the VP9 codec is
   described in the VP9 RTP Payload Format [I-D.ietf-payload-vp9].

3.3.  Signaling Information

   The URI for declaring this header extension in an extmap attribute is
   "urn:ietf:params:rtp-hdrext:framemarking".  It does not contain any
   extension attributes.

   An example attribute line in SDP:

      a=extmap:3 urn:ietf:params:rtp-hdrext:framemarking

3.4.  Usage Considerations

   The header extension values MUST represent what is already in the RTP
   payload.

   When an RTP switch needs to discard a received video frame due to
   congestion control considerations, it is RECOMMENDED that it
   preferably drop frames marked with the D (Discardable) bit set, or
   the highest values of TID and LID, which indicate the highest
   temporal and spatial/quality enhancement layers, since those
   typically have fewer dependenices on them than lower layers.

   When an RTP switch wants to forward a new video stream to a receiver,
   it is RECOMMENDED to select the new video stream from the first
   switching point with the I (Independent) bit set and forward the
   same.  An RTP switch can request a media source to generate a
   switching point by sending Full Intra Request (RTCP FIR) as defined
   in [RFC5104], for example.

3.4.1.  Relation to Layer Refresh Request (LRR)

   Receivers can use the Layer Refresh Request (LRR)
   [I-D.ietf-avtext-lrr] RTCP feedback message to upgrade to a higher
   layer in scalable encodings.  The TID/LID values and formats used in
   LRR messages MUST correspond to the same values and formats specified
   in Section 3.2.

3.4.2.  Scalability Structures

   The LID and TID information is most useful for fixed scalability
   structures, such as nested hierarchical temporal layering structures,
   where each temporal layer only references lower temporal layers or
   the base temporal layer.  The LID and TID information is less useful,
   or even not useful at all, for complex, irregular scalability
   structures that do not conform to common, fixed patterns of inter-



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   layer dependencies and referencing structures.  Therefore it is
   RECOMMENDED to use LID and TID information for RTP switch forwarding
   decisions only in the case of temporally nested scalability
   structures, and it is NOT RECOMMENDED for other (more complex or
   irregular) scalability structures.

4.  Security Considerations

   In the Secure Real-Time Transport Protocol (SRTP) [RFC3711], RTP
   header extensions are authenticated but usually not encrypted.  When
   header extensions are used some of the payload type information are
   exposed and visible to middle boxes.  The encrypted media data is not
   exposed, so this is not seen as a high risk exposure.

5.  Acknowledgements

   Many thanks to Bernard Aboba, Jonathan Lennox, and Stephan Wenger for
   their inputs.

6.  IANA Considerations

   This document defines a new extension URI to the RTP Compact
   HeaderExtensions sub-registry of the Real-Time Transport Protocol
   (RTP) Parameters registry, according to the following data:

   Extension URI: urn:ietf:params:rtp-hdrext:framemarkinginfo
   Description: Frame marking information for video streams
   Contact: mzanaty@cisco.com
   Reference: RFC XXXX

   Note to RFC Editor: please replace RFC XXXX with the number of this
   RFC.

7.  References

7.1.  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>.

7.2.  Informative References








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   [I-D.ietf-avtext-lrr]
              Lennox, J., Hong, D., Uberti, J., Holmer, S., and M.
              Flodman, "The Layer Refresh Request (LRR) RTCP Feedback
              Message", draft-ietf-avtext-lrr-07 (work in progress),
              July 2017.

   [I-D.ietf-payload-vp9]
              Uberti, J., Holmer, S., Flodman, M., Lennox, J., and D.
              Hong, "RTP Payload Format for VP9 Video", draft-ietf-
              payload-vp9-05 (work in progress), March 2018.

   [RFC3550]  Schulzrinne, H., Casner, S., Frederick, R., and V.
              Jacobson, "RTP: A Transport Protocol for Real-Time
              Applications", STD 64, RFC 3550, DOI 10.17487/RFC3550,
              July 2003, <https://www.rfc-editor.org/info/rfc3550>.

   [RFC3711]  Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K.
              Norrman, "The Secure Real-time Transport Protocol (SRTP)",
              RFC 3711, DOI 10.17487/RFC3711, March 2004,
              <https://www.rfc-editor.org/info/rfc3711>.

   [RFC5104]  Wenger, S., Chandra, U., Westerlund, M., and B. Burman,
              "Codec Control Messages in the RTP Audio-Visual Profile
              with Feedback (AVPF)", RFC 5104, DOI 10.17487/RFC5104,
              February 2008, <https://www.rfc-editor.org/info/rfc5104>.

   [RFC5285]  Singer, D. and H. Desineni, "A General Mechanism for RTP
              Header Extensions", RFC 5285, DOI 10.17487/RFC5285, July
              2008, <https://www.rfc-editor.org/info/rfc5285>.

   [RFC6184]  Wang, Y., Even, R., Kristensen, T., and R. Jesup, "RTP
              Payload Format for H.264 Video", RFC 6184,
              DOI 10.17487/RFC6184, May 2011, <https://www.rfc-
              editor.org/info/rfc6184>.

   [RFC6190]  Wenger, S., Wang, Y., Schierl, T., and A. Eleftheriadis,
              "RTP Payload Format for Scalable Video Coding", RFC 6190,
              DOI 10.17487/RFC6190, May 2011, <https://www.rfc-
              editor.org/info/rfc6190>.

   [RFC6464]  Lennox, J., Ed., Ivov, E., and E. Marocco, "A Real-time
              Transport Protocol (RTP) Header Extension for Client-to-
              Mixer Audio Level Indication", RFC 6464,
              DOI 10.17487/RFC6464, December 2011, <https://www.rfc-
              editor.org/info/rfc6464>.






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   [RFC7656]  Lennox, J., Gross, K., Nandakumar, S., Salgueiro, G., and
              B. Burman, Ed., "A Taxonomy of Semantics and Mechanisms
              for Real-Time Transport Protocol (RTP) Sources", RFC 7656,
              DOI 10.17487/RFC7656, November 2015, <https://www.rfc-
              editor.org/info/rfc7656>.

   [RFC7667]  Westerlund, M. and S. Wenger, "RTP Topologies", RFC 7667,
              DOI 10.17487/RFC7667, November 2015, <https://www.rfc-
              editor.org/info/rfc7667>.

   [RFC7741]  Westin, P., Lundin, H., Glover, M., Uberti, J., and F.
              Galligan, "RTP Payload Format for VP8 Video", RFC 7741,
              DOI 10.17487/RFC7741, March 2016, <https://www.rfc-
              editor.org/info/rfc7741>.

   [RFC7798]  Wang, Y., Sanchez, Y., Schierl, T., Wenger, S., and M.
              Hannuksela, "RTP Payload Format for High Efficiency Video
              Coding (HEVC)", RFC 7798, DOI 10.17487/RFC7798, March
              2016, <https://www.rfc-editor.org/info/rfc7798>.

Authors' Addresses

   Mo Zanaty
   Cisco Systems
   170 West Tasman Drive
   San Jose, CA  95134
   US

   Email: mzanaty@cisco.com


   Espen Berger
   Cisco Systems

   Phone: +47 98228179
   Email: espeberg@cisco.com


   Suhas Nandakumar
   Cisco Systems
   170 West Tasman Drive
   San Jose, CA  95134
   US

   Email: snandaku@cisco.com






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