User Plane Message Encoding
draft-murakami-dmm-user-plane-message-encoding-00

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Internet Engineering Task Force                         T. Murakami, Ed.
Internet-Draft                                               Arrcus, Inc
Intended status: Informational                             S. Matsushima
Expires: May 7, 2020                                            SoftBank
                                                              K. Ebisawa
                                                Toyota Motor Corporation
                                                               P. Garvia
                                                              R. Shekhar
                                                     Cisco Systems, Inc.
                                                        November 4, 2019

                      User Plane Message Encoding
           draft-murakami-dmm-user-plane-message-encoding-00

Abstract

   This document defines the encoding of User Plane messages into
   Segment Routing Header (SRH).  The SRH carries the User Plane
   messages over SRv6 Network.

Status of This Memo

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   to this document.  Code Components extracted from this document must
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   2
   3.  Conventions and Terminology . . . . . . . . . . . . . . . . .   3
   4.  Motivation  . . . . . . . . . . . . . . . . . . . . . . . . .   3
   5.  User Plane Message encoding into SRH  . . . . . . . . . . . .   3
     5.1.  GTP-U Header format . . . . . . . . . . . . . . . . . . .   3
     5.2.  Encoding of Tags Field  . . . . . . . . . . . . . . . . .   4
     5.3.  User Plane message Information Element Support  . . . . .   5
     5.4.  Consideration of PSP case . . . . . . . . . . . . . . . .   6
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   7.  IANA Consideration  . . . . . . . . . . . . . . . . . . . . .   6
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   7
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .   7
     9.2.  Informative References  . . . . . . . . . . . . . . . . .   7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

1.  Introduction

   3GPP defines User Plane messages.  The User Plane messages support
   in-band signaling for path and tunnel management.  Currently, User
   Plane messages are defined in TS 29.281 [TS29281].

   When applying SRv6 (Segment Routing IPv6) to the user plane of mobile
   networks based on draft-ietf-dmm-srv6-mobile-uplane
   [I-D.ietf-dmm-srv6-mobile-uplane], User Plane messages must be
   carried over SRv6 network.  This document defines which User Plane
   message must be encoded to SRv6 and also defines how to encode the
   User Plane messages into SRH.

   In addition, SRH is mandatory at the ultimate segment upon carrying
   the User Plane messages because User Plane message is encoded into
   SRH.  Hence, this document considers how to deal with the encoding of
   User Plane messages into SRH when PSP is applied that SRH is popped
   out at the penultimate segment.

2.  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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3.  Conventions and Terminology

   SRv6:                 Segment Routing IPv6.

   GTP-U:                GPRS Tunneling Protocol User Plane.

   UPF:                  User Plane Function.

   SRH:                  IPv6 Segment Routing Header.

   PSP:                  Penultimate Segment POP of the SRH.

   USP:                  Ultimate Segment Pop of the SRH.

4.  Motivation

   3GPP User Plane needs to support the user plane messages associated
   with a GTP-U tunnel defined in [TS29281].  In the case of SRv6 User
   Plane [I-D.ietf-dmm-srv6-mobile-uplane], those messages are also
   required when the user plane interworks with GTP-U.

   Segment Routing Header (SRH) [I-D.ietf-6man-segment-routing-header]
   is used for SRv6 User Plane.  SRH is able to associate additional
   information to the segments.  The Tag field of SRH is capable to
   indicate different properties within a SID.  SRH TLV is capable to
   provide meta-data to the endpoint node.

   The above capability of SRH motivates us to map the user plane
   messages into it because of the same encapsulation with the packets
   of carrying client packets.  It introduces no additional headers or
   extension headers to be chained in the packet just for carrying the
   user plane messages.

5.  User Plane Message encoding into SRH

   This section defines how to encode the User Plane messages into SRH
   in order to carry the User Plane messages over SRv6 network.

5.1.  GTP-U Header format

   3GPP defines GTP-U Header format as shown below.

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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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       | Ver |P|R|E|S|N| Message Type  |           Length              |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                Tunnel Endpoint Identifier                     |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |      Sequence Number          | N-PDU Number  |  Next-Ext-Hdr |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                       Figure 1: GTP-U Header format

   User Plane message type is encoded in Message Type field of GTP-U
   Header.  The following User Plane messages must be carried over SRv6
   network at least.  The value of each User Plane message type is
   defined as shown below.

   Echo Request:       1

   Echo Reply:         2

   Error Indication:   26

   End Marker:         254

5.2.  Encoding of Tags Field

   The Segment Routing Header is defined in draft-ietf-6man-segment-
   routing-header [I-D.ietf-6man-segment-routing-header].  This draft
   defines 16 bits Tag field but does not define the format or use of
   this Tag field in the Segment Routing Header.

   The User Plane message type encoding is defined in TS 29.281
   [TS29281].  Based on this definition, the User Plane message type
   must be encoded into the Tag field in the Segment Routing Header in
   order to indicate the type of the user plane messages for at least
   Echo Request, Echo Reply, Error Indication or End Marker.

   Only UPF must process the Tag field where the user plane message is
   encoded.  In addition, when the user plane message is encoded in the
   Tag field, the UPF should not encode any segments in the Segment
   Routing Header whose function modifies the Tag field value.  Any
   other transport router implementing SRv6 must ignore the Tag field
   upon processing the Segment Routing Header.

   The user plane messages must be encoded into the Tag filed as shown
   below.

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               0                             1
               0  1  2  3  4  5  6  7  8  9  0  1  2  3  4  5  6
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
               |         Reserved                  |B3|B2|B1|B0|
               +--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+

                       Figure 2: Tag Field Encoding

   Bit 0 [B0]:     End Marker

   Bit 1 [B1]:     Error Indication

   Bit 2 [B2]:     Echo Request

   Bit 3 [B3]:     Echo Reply

   End Marker, Echo Request and Echo reply messages do not require any
   additional information elements.  However, Error Indication message
   requires the additional information elements like Tunnel Endpoint
   Identifier Data IE, GSN Address, etc.  These additional information
   elements can be encoded into the SRH TLV that is defined in the next
   section.

5.3.  User Plane message Information Element Support

   End Maker, Echo Request and Echo Reply messages do not require any
   additional information elements.  However, Error Indication message
   requires additional 3GPP IEs (Information Element).  These additional
   information elements must be carried over SRv6 network as well.
   However SRv6 SID has limited space only.  Hence it cannot carry a lot
   of information elements.

   In order to carry more information elements, SRH TLV shall be
   leveraged.  SRH TLV is defined in draft-ietf-6man-segment-routing-
   header [I-D.ietf-6man-segment-routing-header] in order to carry the
   meta-data for the segment processing.  In order to carry 3GPP IEs,
   the new type named as "5GS Container" must be defined as the new SRH
   TLV.  The "5GS Container" can carry multiple 3GPP IEs with 1 TLV.

       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      |         3GPP IE TLVs        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      //                      3GPP IE TLVs                            //
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                             5GS Container TLV

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   Type:           to be assigned by IANA

   Length:         Length of 3GPP IE TLVs

   3GPP IE TLVs:   Multiple 3GPP IE TLV defined below

       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      |            Value            //
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                                3GPP IE TLV

   Type:           3GPP IE Type defined by 3GPP

   Length:         Length of Value

   Value:          3GPP IE value

5.4.  Consideration of PSP case

   This section considers PSP case where the SRH is popped out at the
   penultimate segment.

   In order to carry User Plane message over SRv6 network, SRH must be
   sustained over entire SRv6 network because User Plane message type
   and required information elements are encoded into SRH.  If the
   penultimate segment is popping out SRH, i.e., PSP, User Plane message
   can not be carried in entire SRv6 network.

   In order to avoid this problem, USP must be used in SRv6 network.  In
   this case, SRH is never popped out and User Plane message can be
   sustained over entire SRv6 network.  However, if PSP needs to be
   enabled in SRv6 network, it is also a possible solution to encap
   another SRH which carries User Plane message along with the outer
   IPv6 or SRH.

6.  Security Considerations

7.  IANA Consideration

   The type value of SRH TLV for 5GS Container must be assigned by IANA.

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8.  Acknowledgements

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>.

   [RFC2460]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", RFC 2460, DOI 10.17487/RFC2460,
              December 1998, <https://www.rfc-editor.org/info/rfc2460>.

   [RFC4291]  Hinden, R. and S. Deering, "IP Version 6 Addressing
              Architecture", RFC 4291, DOI 10.17487/RFC4291, February
              2006, <https://www.rfc-editor.org/info/rfc4291>.

9.2.  Informative References

   [I-D.ietf-6man-segment-routing-header]
              Filsfils, C., Dukes, D., Previdi, S., Leddy, J.,
              Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header
              (SRH)", draft-ietf-6man-segment-routing-header-26 (work in
              progress), October 2019.

   [I-D.ietf-dmm-srv6-mobile-uplane]
              Matsushima, S., Filsfils, C., Kohno, M., Camarillo, P.,
              Voyer, D., and C. Perkins, "Segment Routing IPv6 for
              Mobile User Plane", draft-ietf-dmm-srv6-mobile-uplane-06
              (work in progress), September 2019.

   [RFC1918]  Rekhter, Y., Moskowitz, B., Karrenberg, D., de Groot, G.,
              and E. Lear, "Address Allocation for Private Internets",
              BCP 5, RFC 1918, DOI 10.17487/RFC1918, February 1996,
              <https://www.rfc-editor.org/info/rfc1918>.

   [RFC3513]  Hinden, R. and S. Deering, "Internet Protocol Version 6
              (IPv6) Addressing Architecture", RFC 3513,
              DOI 10.17487/RFC3513, April 2003,
              <https://www.rfc-editor.org/info/rfc3513>.

   [TS29281]  3GPP, "General Packet Radio System (GPRS) Tunnelling
              Protocol User Plane (GTPv1-U)", 2019,
              <http://www.3gpp.org/ftp//Specs/
              archive/29_series/29.281/29281-f60.zip>.

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Authors' Addresses

   Tetsuya Murakami (editor)
   Arrcus, Inc
   2077 Gateway Place, Suite 400
   San Jose
   USA

   Email: tetsuya@arrcus.com

   Satoru Matsushima
   SoftBank
   1-9-1 Higashi-Shinbashi, Munato-ku
   Tokyo
   Japan

   Email: satoru.matsushima@g.softbank.co.jp

   Kentaro Ebisawa
   Toyota Motor Corporation
   Tokyo
   Japan

   Email: ebisawa@toyota-tokyo.tech

   Pablo Camarillo Garvia
   Cisco Systems, Inc.
   Spain

   Email: pcamaril@cisco.com

   Ravi Shekhar
   Cisco Systems, Inc.
   USA

   Email: ravishek@cisco.com

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