Internet Draft                                 Dave Allan, Ericsson ed.
Intended status: Informational               Donald Eastlake, Futurewei
Expires: August 2021                             David Woolley, Telstra
                                                          February 2021

    5G Wireless Wireline Convergence User Plane Encapsulation (5WE)


   As part of providing wireline access to the 5G Core (5GC), deployed
   wireline networks carry user data between 5G residential gateways
   and the 5G Access Gateway Function (AGF). The encapsulation method
   specified in this document supports the multiplexing of traffic for
   multiple PDU sessions within a VLAN delineated access circuit,
   permits legacy equipment in the data path to inspect certain packet
   fields, carries 5G QoS information associated with the packet data,
   and provides efficient encoding. It achieves this by specific points
   of similarity with the RFC 2516 PPPoE data packet encapsulation.

Status of this Memo

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Copyright and License Notice

   Copyright (c) 2021 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   This document is subject to BCP 78 and the IETF Trust's Legal
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   ( in effect on the date of
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   without warranty as described in the Simplified BSD License.

Table of Contents

   1. Introduction...................................................2
   1.1. Requirements Language........................................4
   1.2. Acronyms.....................................................4
   2. Data Encapsulation Format......................................5
   3. Acknowledgements...............................................6
   4. Security Considerations........................................6
   5. IANA Considerations............................................7
   6. References.....................................................7
   6.1. Normative References.........................................7
   6.2. Informative References.......................................8
   7. Authors' Addresses.............................................8

1. Introduction

   Converged 5G ("fifth generation") wireline networks carry user data
   between 5G residential gateways (5G-RG) and the 5G Access Gateway
   Function (identified as a Wireline-AGF (W-AGF) by 3GPP in [TS23316])
   across deployed access networks based on Broadband Forum [TR101] and
   [TR178]. This form of wireline access is considered to be trusted
   non-3GPP access by the 5G system.

   The transport encapsulation used needs to meet a variety of
   requirements including the following:

   -  The ability to multiplex multiple logical connections (Protocol
     Data Unit (PDU) Sessions as defined by 3GPP) within a VLAN
     identified point to point logical circuit between a 5G-RG and a W-

   - To allow unmodified legacy equipment in the data path to identify
      the encapsulation and inspect specific fields in the payload.
      Some access nodes in the data path between the 5G-RG and the W-
      AGF (Such as digital subscriber loop access multiplexers (DSLAMs)
      and optical line terminations (OLTs)) currently inspect packets
      identified by specific Ethertypes to identify protocols such as

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      the point to point protocol over ethernet (PPPoE), IP, ARP, and
      IGMP. This may be for the purpose of enhanced QoS, policing of
      identifiers and other applications. Some deployments are
      dependent upon this inspection. Such devices are able to do this
      for PPPoE or IP over ethernet (IPoE) packet encodings but would
      be unable to do so if a completely new encapsulation, or an
      existing encapsulation using a new Ethertype, were used.

   -  To carry per packet 5G QoS information.

   -  Fixed access residential gateways are sensitive to the complexity
     of packet processing, therefore an encapsulation that minimizes
     processing is an important consideration.

   A data encapsulation that uses a common Ethertype and has certain
   fields appearing at the same offset as the PPPoE [RFC2516] data
   encapsulation can address these requirements. This data
   encapsulation is referred to as the 5G WWC user plane Encapsulation
   or 5WE. Currently deployed access nodes do not police the VER, TYPE
   and CODE fields of an RFC 2516 header, and only perform limited
   policing of stateful functions with respect to the procedures
   documented in RFC 2516. Therefore, these fields have a different
   definition for 5WE and are used to:

   -  Identify that the mode of operation for packets encapsulated in
     such a fashion uses non-access stratum (NAS, a logical control
     interface between user equipment (UE) and 5GC as specified by
     3GPP) based 5G WWC session establishment and life cycle
     maintenance procedures as documented in [TS23502][TS23316] instead
     of legacy PPP/PPPoE session establishment procedures (i.e. PADI
     discipline, LCP, NCP etc.). In this scenario "discovery" is
     performed by means outside the scope of this document.

   -  Permit the session ID field to be used to identify the 5G PDU
     session the encapsulated packet is part of.

   -  Communicate per-packet 5G QoS Flow Identifier (QFI) and
     Reflective QoS Indication (RQI) information from the 5GC to the

   This 5G specific redesign of fields not inspected by deployed
   equipment results in an encapsulation uniquely applicable to the
   requirements for the communication of PDU session traffic between
   the subscriber premises and the 5G system over wireline networks.
   The 6 byte RFC 2516 data packet header followed by a 2 byte PPP
   protocol ID is also the most frugal of the encapsulations that are

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   currently supported by legacy access equipment that could be adapted
   to meet these requirements.

   This encapsulation is expected to be used in environments where RFC
   2516 is deployed. Therefore, implementations MUST examine the
   version number:

   - if the version number is 1, and PPPoE [RFC2516] is supported,
     process the frame further, else silently discard it.

   - if the version number is 2 and 5WE is supported, process the frame
     further, else silently discard it.

   In both cases frames for the supported version number should have
   session IDs corresponding to established sessions for the respective
   protocol models. A 5WE frame with an unrecognized session ID MUST be
   silently discarded.

   This encapsulation may have MTU issues when used for Ethernet
   multiplexing in networks where the underlying Ethernet payload is
   limited to 1500 bytes.

   This encapsulation is not suitable for other network environments,
   e.g., general use over the public Internet.

1.1. Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL
   "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.

1.2. Acronyms

   This document uses the following acronyms:

   3GPP  3rd Generation Partnership Project
   5WE   5G WWC Encapsulation
   5GC   5th Generation Core (network)
   DSLAM Digital Subscriber Loop Access Multiplexer
   W-AGF Wireline Access Gateway Function
   IPoE  IP over Ethernet
   NAS   Non-Access Stratum
   OLT   Optical Line Termination
   PDU   Protocol Data Unit

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   PPPoE PPP over Ethernet
   QFI   QoS Flow Identifier
   QoS   Quality of Service
   RG    Residential Gateway
   RQI   Reflective QoS Indicator
   WWC   Wireless Wireline Convergence

2. Data Encapsulation Format

   The Ethernet payload [IEEE802] for PPPoE [RFC2516] is indicated by
   an Ethertype of 0x8864. The information following that Ethertype
   uses a value of 2 in the VER field for the repurposing of the PPPoE
   data encapsulation as the 5G WWC user plane encapsulation (5WE). The
   5G WWC User Plane encapsulation is structured 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
     |  VER  |  TYPE |     QFI   |R|0|           SESSION_ID          |
     |            LENGTH             |          PROTOCOL ID          |
     |                         DATA PAYLOAD         ~

   The description of each field is as follows:

      VER is the version. It MUST be set to 0x02.

      TYPE is the message type. It MUST be set to 0x01.

      QFI encodes the 3GPP 5G QoS Flow Identifier [TS38415] to be used
          for mapping 5G QoS to IP DSCP/802.1 P-bits [IEEE802].

      R (short for Reflective QoS Indication [TS38415]) encodes the one
          bit RQI. It is set by the network side 5WE termination for
          downstream traffic and ignored by the network for upstream

      0 indicates the bit(s) MUST be sent as zero and ignored on

      SESSION_ID is a 16-bit unsigned integer in network byte order. It
          is used to distinguish different PDU sessions that are in the
          VLAN delineated multiplex. A value of 0xffff is reserved for
          future use and MUST NOT be used.

      LENGTH is the length in bytes of the data payload including

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          the initial Protocol ID. It is 16 bits in network byte order.

      PROTOCOL ID is the 16 bit identifier of the data payload type
          encoded using values from the IANA PPP DLL protocol numbers
          registry. (

          The following values are valid in this field for 5G
          WWC use:

               0x0021: IPv4

               0x0031: Ethernet (referred to in PPP as "bridging")

               0x0057: IPv6

          Packets received that do not contain one of the above
          protocol IDs are silently discarded.

      DATA PAYLOAD is encoded as per the protocol ID.

3. Acknowledgements

   This memo is a result of comprehensive discussions by the Broadband
   Forum's Wireline Wireless Convergence Work Area.
   The authors would also like to thank Joel Halpern and Dirk Von Hugo
   for their detailed review of this draft.

4. Security Considerations

   5G NAS procedures used for session life cycle maintenance employ
   ciphering and integrity protection [TS23502]. They can be considered
   to be a more secure session establishment discipline than existing
   RFC 2516 procedures, at least against on path attackers.
   The design of the 5WE encapsulation will not circumvent existing
   anti-spoofing and other security procedures in deployed equipment.
   The existing access equipment will be able to identify fields that
   they normally process and policed as per existing RFC 2516 traffic.

   Therefore, the security of a fixed access network using 5WE will be
   equivalent or superior to current practice.

   5WE encapsulated traffic is used on what the 5GC considers to be
   trusted non-3GPP interfaces, therefore is not ciphered. 5WE is not
   suitable for use over an untrusted non-3GPP interface.

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   The security requirements of the 5G system are documented in

5. IANA Considerations

   IANA is requested to create a registry on the Point-to-Point (PPP)
   Protocol Field Assignments IANA Web page as follows:

      Registry Name: PPP Over Ethernet Versions
      Registration Procedure: Specification Required
      References: [RFC2516] [this document]

          VER     Description                        Reference
         -----   -----------------------------      -----------
            0     reserved                          [this document]
            1     PPPoE                             [RFC2516]
            2     5G WWC User Plane Encapsulation   [this document]
         3-15     unassigned                        [this document]

   IANA is requested to add [this document] as an additional reference
   for Ethertype 0x8864 in the Ethertypes table on the IANA "IEEE 802
   Numbers" web page.(

6. References

6.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
          Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
          2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
          May 2017, <>.
[RFC2516] "A Method for Transmitting PPP Over Ethernet (PPPoE)",
          IETF RFC 2516, February 1999
[TS38415] 3rd Generation Partnership Project; Technical
          Specification Group Radio Access Network; NG-RAN; PDU
          Session User Plane Protocol (Release 15), 3GPP TS38.415
[TS23502] 3rd Generation Partnership Project; Technical
          Specification Group Services and System Aspects;
          Procedures for the 5G System (Release 16), 3GPP TS23.502
[TS23316] 3rd Generation Partnership Project; Technical
          Specification Group Services and System Aspects;
          Wireless and wireline convergence access support
          for the 5G System (5GS) (Release 16), 3GPP TS23.316,
          November 2018

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6.2. Informative References
[TR101]   "Migration to Ethernet Based Broadband Aggregation",
          Broadband Forum Technical Report: TR-101 issue 2, July
[TR178]   "Multi-service Broadband Network Architecture and Nodal
          Requirements", Broadband Forum Technical Report: TR-178,
          September 2014
[IEEE802] 802, IEEE, "IEEE Standard for Local and Metropolitan
          Networks: Overview and Architecture", IEEE Std 802-2014.
[TS33501] 3rd Generation Partnership Project; Technical
          Specification Group Services and System Aspects;
          Security Architecture and Procedures for 5G System
          (Release 16), 3GPP TS33.501, December 2019

7. Authors' Addresses
   Dave Allan (editor)
   2455 Augustine Drive
   San Jose, CA  95054 USA

   Donald E. Eastlake 3rd
   Futurewei Technologies
   2386 Panoramic Circle
   Apopka, FL 32703 USA
   Phone: +1-508-333-2270

   David Woolley
   Telstra Corporation
   242 Exhibition St
   Melbourne, 3000

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