5G Wireless Wireline Convergence User Plane Encapsulation (5WE)
draft-allan-5g-fmc-encapsulation-05

Internet Draft                                 Dave Allan, Ericsson ed.          
Intended status: Informational               Donald Eastlake, Futurewei         
Expires: September 2020                          David Woolley, Telstra 
                                                              July 2020 
             
 
    5G Wireless Wireline Convergence User Plane Encapsulation (5WE) 
                  draft-allan-5g-fmc-encapsulation-05 
 
 
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 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 snoop certain packet 
   fields, carries 5G QoS information associated with the packet data, 
   and provides efficient encoding. 
    
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.....................................................4 
   2. Data Encapsulation Format......................................4 
   3. Acknowledgements...............................................5 
   4. Security Considerations........................................5 
   5. IANA Considerations............................................6 
   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 [TS23716]) 
   across deployed access networks based on Broadband Forum [TR101] and 
   [TR178].  
    
   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 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 digital subscriber loop access multiplexers (DSLAMs) and 
      optical line terminations (OLTs)) currently snoop into packets 
      identified by specific Ethertypes to identify protocols such as 
      the point to point protocol over ethernet (PPPoE), IP, ARP, and 

 
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      IGMP. This may be for the purpose of enhanced QoS, policing of 
      identifiers and other applications. Some deployments are 
      dependent upon this snooping. 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 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 [RFC2516] 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 user equipment (UE) and 5GC as specified by 
     3GPP) based 5G WWC session establishment and life cycle 
     maintenance procedures as documented in [TS23502][TS23716] 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. 
      
   This 5G specific repurposing of fields 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 8 byte RFC 2516 data packet header is 
   also the most frugal of the encapsulations that are currently 
   supported by legacy access equipment that could be adapted to meet 
   these requirements. This encapsulation is not suitable for other 
   network environments, e.g., general use over the public Internet. 

    
1.1. Requirements Language 
    

 
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   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. 
 
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 
   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 
    
   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 2. 
 
 
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      TYPE is the message type. It MUST be set to 1.    
    
      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 RQI) encodes the one bit Reflective QoS Indicator. 
    
      0 indicates the bit(s) MUST be sent as zero and ignored on  
          receipt. 
    
      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.  
    
      LENGTH is the length in bytes of the data payload including 
          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. (https://www.iana.org/assignments/ppp-numbers/ppp-
          numbers.xhtml#ppp-numbers-2) 

          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. 

 
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   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 
      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.(https://www.iana.org/assignments/ieee-802-
   numbers/ieee-802-numbers.xhtml#ieee-802-numbers-1) 
    
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, <https://www.rfc-editor.org/info/rfc8174>. 
[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 
         
         
6.2. Informative References 
[TS23502] 3rd Generation Partnership Project; Technical  

 
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          Specification Group Services and System Aspects;    
          Procedures for the 5G System (Release 16), 3GPP TS23.502  
[TS23716] 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 
[TR101]   "Migrating to Ethernet Based Broadband Aggregation",  
          Broadband Forum Technical Report: TR-101 issue 2, July  
          2011 
[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. 
[RFC4937] "IANA Considerations for PPPoE", IETF RFC 4937, June  
          2007 
         
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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