5G Wireless Wireline Convergence User Plane Encapsulation (5WE)
draft-allan-5g-fmc-encapsulation-03

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Internet Draft                                 Dave Allan, Ericsson ed.          
Intended status: Informational               Donald Eastlake, Futurewei         
Expires: September 2020                          David Woolley, Telstra 
                                                             March 2020 
             
 
    5G Wireless Wireline Convergence User Plane Encapsulation (5WE) 
                  draft-allan-5g-fmc-encapsulation-03 
 
 
Abstract 
 
   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 used 
   needs to meet a variety of requirements including being able to 
   multiplex the traffic of multiple PDU sessions within a VLAN 
   delineated access circuit, to permit legacy equipment in the data 
   path to snoop certain packet fields, to carry 5G QoS information 
   associated with the data, and to be efficiently encoded. This memo 
   specifies an encapsulation that meets these requirements. 
    
Status of this Memo 
    
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Copyright and License Notice 
    
   Copyright (c) 2020 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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Table of Contents 
    
   1. Introduction...................................................2 
   1.1. Requirements Language........................................3 
   1.2. Acronyms.....................................................3 
   2. Data Encapsulation Format......................................4 
   3. Acknowledgements...............................................5 
   4. Security Considerations........................................5 
   5. IANA Considerations............................................5 
   6. References.....................................................6 
   6.1. Normative References.........................................6 
   6.2. Informative References.......................................6 
   7. Authors' Addresses.............................................7 
    
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 an Fixed-AGF (FAGF) by 3GPP in [5]) across 
   deployed access networks based on BBF TR-101[6] and TR-178[7].  
    
   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 p2p logical circuit between a 5G-RG and an FAGF. 
    
   - To allow unmodified legacy equipment in the data path to identify 
      the encapsulation and snoop specific fields in the payload. Some 
      access nodes in the data path between the 5G-RG and the FAGF 
      (Such as DSLAMs and OLTs) currently snoop into packets identified 
      by specific Ethertypes to identify protocols such as PPPoE, IP, 
      ARP, and IGMP. This may be for the purpose of enhanced QoS, 
      policing of identifiers and other applications. Some deployments 
      are depended upon this snooping. Such devices are currently able 
      to do so for PPPoE or IPoE packet encodings but would be unable 

 
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      to do so if a new encapsulation, or an existing encapsulation 
      using a new Ethertype, were used. 
    
   -  To carry per packet 5G QoS information.  
    
   -  Fixed access is very sensitive to the complexity of residential 
      gateways, therefore encapsulation overhead and efficiency is an 
      important consideration.  
    
   A modified RFC 2516[3] PPPoE data encapsulation (referred to as the 
   5G WWC user plane Encapsulation or 5WE) can address these 
   requirements. 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 may be repurposed 
   to: 
       
   -  Identify that the mode of operation for packets encapsulated in 
     such a fashion uses non-access stratum(NAS, a logical control 
     interface between UE and 5GC as specified by 3GPP) based 5G WWC 
     session establishment and life cycle maintenance procedures as 
     documented in [4][5] instead of legacy PPP/PPPoE session 
     establishment procedures (i.e. PADI discipline, LCP, NCP etc.). 
    
   - 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 
     5G-RG. 
      
   The 8 byte RFC 2516 data packet header is the most frugal of the 
   encapsulations that are currently supported by legacy access 
   equipment that can also meet all the requirements.   
    
1.1. 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 [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 
 
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   5WE   5G WWC Encapsulation 
   5GC   5th Generation Core (network) 
   DSLAM Digital Subscriber Loop Access Multiplexer 
   FAGF  Fixed Network Access Gateway Function 
   IPoE  IP over Ethernet 
   NAS   Non-Access Stratum 
   OLT   Optical Line Termination 
   PDU   Protocol Data Unit 
   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 
    
   PPPoE data packet encapsulation is indicated in an IEEE 802[8] 
   Ethernet frame 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 2. 
 
      TYPE is the message type. It MUST be set to 1.    
    
      QFI encodes the 3GPP 5G QoS Flow Identifier to be used for    
          mapping 5G QoS to IP DSCP/802.1 P-bits[9]. 
    
      R (short for RQI) encodes the one bit Reflective QoS Indicator. 
    
      0 indicates the bit(s) MUST be sent as zero and ignored on  
          receipt. 
    

 
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      SESSION_ID is a 16-bit unsigned integer. It is used to   
          distinguish different PDU sessions that are in the VLAN  
          delineated multiplex.  
    
      LENGTH is the length in bytes of the data payload including 
          the initial Protocol ID. 
    
      PROTOCOL ID is the 16 bit identifier of the data payload type  
          encoded as per RFC 2516. The following values are valid in   
          this field for 5G WWC use: 
    
               0x0021: IPv4 
    
               0x0031: Ethernet (referred to in PPP as "bridging") 
    
               0x0057: IPv6 
    
      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. They can be considered to be a 
   more secure session establishment discipline than existing RFC 2516 
   procedures, at least against man in the middle attacks. 
   The document"s re-purposing of the RFC 2516 data 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 police as per 
   existing RFC 2516 traffic. 
    
   Therefore, the security of a fixed access network using 5WE will be 
   equivalent or superior to current practice. 
    
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 

 
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      Registration Procedure: Expert Review 
      References: [RFC2516] [this document] 
    
          VER     Description                        Reference 
         -----   -----------------------------      ----------- 
            0     reserved                          [this document] 
            1     Classic 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  
  [1]   Bradner, S., "Key words for use in RFCs to Indicate              
        Requirement Levels", BCP 14, RFC 2119, March 1997. 
  [2]   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>. 
  [3]   "A Method for Transmitting PPP Over Ethernet (PPPoE)", 
        IETF RFC 2516, February 1999 
         
6.2. Informative References 
  [4]   3rd Generation Partnership Project; Technical 
        Specification Group Services and System Aspects; 
        Procedures for the 5G System (Release 16), 3GPP TS23.502  
  [5]   3rd Generation Partnership Project; Technical 
        Specification Group Services and System Aspects; Study on 
        the Wireless and Wireline Convergence for the 5G system 
        architecture (Release 16), 3GPP TR23.716, November 2018 
  [6]   "Migrating to Ethernet Based Broadband Aggregation", 
        Broadband Forum Technical Report: TR-101 issue 2, July 
        2011 
  [7]   "Multi-service Broadband Network Architecture and Nodal 
        Requirements", Broadband Forum Technical Report: TR-178, 
        September 2014 
  [8]   802, IEEE, "IEEE Standard for Local and Metropolitan 
        Networks: Overview and Architecture", IEEE Std 802-2014. 
  [9]   3rd Generation Partnership Project; Technical 
        Specification Group Radio Access Network; NG-RAN; PDU 
        Session User Plane Protocol (Release 15), 3GPP TS38.415 
  [10]  "IANA Considerations for PPPoE", IETF RFC 4937, June 2007 
         

 
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7. Authors' Addresses 
   Dave Allan (editor) 
   Ericsson 
   2455 Augustine Drive 
   San Jose, CA  95054 USA 
   Email: david.i.allan@ericsson.com  
    
    
   Donald E. Eastlake 3rd 
   Futurewei Technologies 
   2386 Panoramic Circle 
   Apopka, FL 32703 USA 
   Phone: +1-508-333-2270 
   Email: d3e3e3@gmail.com 
    
    
   David Woolley 
   Telstra Corporation 
   242 Exhibition St 
   Melbourne, 3000 
   Australia 
   Email: david.woolley@team.telstra.com 

 
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