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Network Working Group                                      Abel Wang
Category: Internet-Draft                                   Wenxiu Xu
                                                           Yanqing Lu
                                                           Lei Cao
                                                           Rong Zhang
                                                           Tao Zhang
                                                           Maowen Guo



 Category: Informational                                  October 2003

                 Virtual Broadband Access Server Protocol
                for communicating between BAS and IP-DSLAM
                       draft-abel-vbas-01.txt

Status of this Memo

This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.

Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups.  Note that
other groups may also distribute working documents as
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Copyright Notice

Copyright (C) The Internet Society (2003).  All Rights Reserved.

Abstract

The virtual broadband access server (VBAS) protocol looks BAS and
IP-DSLAM as a whole and provides an applicable method for
communicating between BAS and IP-DSLAM.

This document describes a communication process, which is added
in the existing access control modes. It also describes how to
encapsulate VBAS packets over Ethernet.

Applicability

This specification is intended to provide the facilities, which are
defined for VBAS.


Wang/Xu/Lu/Cao                                  [Page 2]

VBAS Protocol                                    Oct 2003

This specification can support ADSL or VDSL or LAN access modes that
use IP uplink. It is independent of authentication mode.

This document describes the VBAS over Ethernet encapsulation that is
being deployed by China Telecom-Guangzhou Research and Development
Center.

1       Introduction

DSL technologies, which use twisted pairs as transport medium, are
the dominant broadband technologies for subscribers to access
broadband services. Broadband deployment has focused on DSLAM in
the past two years. Traditional uplink interface of DSLAM is ATM
that is suitable for telecom service providers who have the ATM
metropolitan area networks. With the DSLAM construction increasing,
the ATM resource is limited and being exhausted. As a result, the
new metropolitan area networks are based on Ethernet and IP-DSLAM
is introduced for DSLAM to link Ethernet metropolitan area networks.

Switches are used between IP-DSLAM and BAS as aggregation network,
whose VLAN ID is limited (vary from 0 to 4095). Subscribers must
share a VLAN and the subscribers¯ detailed information can¯t be
sent to the BAS and Radius server. Many issues, such as tracking
of hackers and security of subscribers etc, emerged in the use
of IP-DSLAM.

VBAS protocol adds a communication process between BAS and
IP-DSLAM, which can get the subscribers¯ detailed information
of physical address.

2       Conventions

The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD,
SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL, when they appear in
this document, are to be interpreted as described in [1].

3       Protocol Overview

There are three access control modes for IP-uplink ADSL
subscribers: PPPOE802.1X and DHCP+WEB. Below PPPOE is
used for example.

In order to resolving the problems introduced by IP-DSLAM,
VBAS protocol”ÀVirtual Broadband Access Server”¿is submitted.
That is, a communication process is added between an IP-DSLAM
and a BAS in the existing authentication process. After a BAS
sends a PADS packet of PPPOE to a new subscriber, it will
query the IP-DSLAM about the physical-port information which
corresponding to the MAC-address of the new subscriber. When
the IP-DSLAM gets the VBAS Query packet, it will respond a
VBAS Response packet, which includes the physical-port
information.


Wang/Xu/Lu/Cao                                  [Page 3]

VBAS Protocol                                    Oct 2003

To avoid broadcast packets between BAS and IP-DSLAM in
network, the communication process is point to point between
 a BAS and an IP-DSLAM in MAC layer.

4       Payloads

The following packet formats are defined here.  The payload contents
will be defined in the VBAS sections.

An Ethernet frame is as follows:

                                       1
                   0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
                  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                  |       DESTINATION_ADDR        |
                  |          (6 octets)           |
                  |                               |
                  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                  |         SOURCE_ADDR           |
                  |          (6 octets)           |
                  |                               |
                  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                  |    ETHER_TYPE  (2 octets)     |
                  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                  ~                               ~
                  ~           payload             ~
                  ~                               ~
                  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                  |           CHECKSUM            |
                  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

The DESTINATION_ADDR field contains a unicast Ethernet destination
address.

The SOURCE_ADDR field MUST contain the Ethernet MAC address of the
source device.

The ETHER_TYPE is set to 0x8200 (suggested for VBAS).

The Ethernet payload for VBAS is as follows:


Wang/Xu/Lu/Cao                                  [Page 4]

VBAS Protocol                                    Oct 2003

                        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      |                Reserved Field 1               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   Transferred info Type       | Operation Type|Operation Result|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                VBAS Session ID                                |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |Hardware Address length|Information length|Hardware Interface Type|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |              Source Hardware Address                          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Source Hardware Address    |         Source Vlan ID        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        Source Port            | Destination Hardware Address  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  Destination Hardware Address                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Destination Vlan ID           |      Destination Port         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |User Port Info Length|   User Port Information                 |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   ~                                                               ~
   ~              User Port Information                            ~
   ~                                                               ~
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

The VER field is eight bits and MUST be set to 0x1 for this version
of the VBAS specification.

The Reserved field 1 is twenty-four bits and MUST be set to 0x000
for this version of the VBAS specification.

The Transferred info Type field is sixteen bits and MUST be set to
0x01 for this version of the VBAS specification. A value of 0xff
MUST NOT be used.

The Operation Type field is eight bits and defined below for VBAS
Query and Response stage.

The Operation Result field is eight bits and defined below for VBAS
Query and Response stage.

The VBAS Session ID field is thirty-two bits. It is an unsigned
value in network byte order. Its value is defined below for VBAS Query
packets. The value is fixed for a given VBAS session and, in fact,
defines a VBAS session along with the Ethernet SOURCE_ADDR and
DESTINATION_ADDR.  A value of 0xffff is reserved for future use and
MUST NOT be used.

The Hardware Address Length field is eight bits and MUST be set to
0x6 that refers to the MAC address length for this version of the
VBAS specification.


Wang/Xu/Lu/Cao                                  [Page 5]

VBAS Protocol                                    Oct 2003

The Information Length field is eight bits and MUST be set to 0x4
for this version of the VBAS specification.

The Hardware Interface Type field is sixteen bits and defined below
for VBAS Query and Response stage.

The Source Hardware Address field is forty-eight bits and defined below
for VBAS Query and Response stage.

The Source VLAN ID field is sixteen bits and defined below for VBAS Query
and Response stage.

The Source Port field is sixteen bits and MUST be set to ox00 for this
version of the VBAS specification.

The Destination Hardware Address field is forty-eight bits and defined
below for VBAS Query and Response stage.

The Destination VLAN ID field is sixteen bits and MUST be set the same
value as Source VLAN ID field.

The Destination Port field is sixteen bits and MUST be set to ox00 for
this version of the VBAS specification.

The User Port Info Length field is eight bits and defined below for VBAS
Query and Response stage.

The User Port Information field is no more tran 127 bytes and defined below
for VBAS Query and Response stage.


5.VBAS protocol

There are two stages in VBAS protocol.  When it completes, BAS can get the
physical address of a new subscriber.  First step is VBAS Query; second
step is VBAS Response.

All VBAS Ethernet frames are suggested to have the ETHER_TYPE field set to
the value 0x8200.

The VBAS communication process is shown in Figure 1, below.

PC                               IP-DSLAM                  BAS
|------------------------------------|----------------------|
|            PPPOE Discovery Stage                          |
|------------------------------------|----------------------|
                                     |  VBAS Query Stage    |
                                     |<---------------------|
                                     |  VBAS Response Stage |
                                     |--------------------->|
|               PPPOE Session Stage                         |
|-----------------------------------------------------------|

    Figure 1 VBAS communication process


Wang/Xu/Lu/Cao                                  [Page 6]

VBAS Protocol                                    Oct 2003

5.1     The VBAS Query Packet
After a BAS send a PADS packet of PPPOE to a new subscriber, it will
prepare to begin a VBAS session. It generates a unique SESSION_ID for
the VBAS session and sends the VBAS Query Packet to an IP-DSLAM about
the physical-port information which corresponding to the MAC address
of the new subscriber.

The Operation Type field MUST be set to 0x1 that indicates it is the
VBAS query operation.

The Operation Result field MUST be set to 0x0. The Hardware Interface
field MUST be set to 0x0.The Source Hardware Address is the MAC address
of BAS. The Destination Hardware Address is the MAC address of the new
subscriber.

If the packet received in PADR stage of PPPOE is untagged, the Source
Vlan ID field MUST be set to 0xFFFF; If the packet received in PADR
stage of PPPOE is tagged, the Source VLAN ID field is the same value
as it in PADR packet of PPPOE.

The User Port Information Length field and the User Port Information field
in the VBAS Query stage is not available.


5.2     The VBAS Response Packet

When an IP-DSLAM gets the VBAS Query packet, it will send a VBAS
Response Packet to the BAS, which includes the physical-port
information of the new subscriber.

The Operation Type field MUST be set to 0x2 that indicates it is the
VBAS response operation.

The Operation Result field MUST be set to 0x0 for successful request
and 0x1 for failure.

The VBAS Session ID MUST be set the value as it in VBAS Query packet.

The Hardware Interface field MUST be set to 0x10 for DSL subscriber,
which is same as the value of NAS-Port-Type defined in RFC 2865.

The Source Hardware Address is the MAC address of the new subscriber.
The Destination Hardware Address is the MAC address of BAS. The
Destination Vlan ID field is the same value of the Source VLAN ID
field.

The Source VLAN ID field is valid in low 12 bits and contains
the physical-port information of the new subscriber. It is
transported from BAS to RADIUS Server.

If the Source VLAN ID can accurately identify the DSLAM port such as
slot number, subslot number and port number,the value of the User Port
Info Length field is 0 and the User Port Information field does not exist.
Otherwise,the User Port Information field must be included in the VBAS
Response Packet and its length will be filled in the User Port Information
Length field.

The reference format of the User Port Information field is as follows:
"frame=0~31; slot=0~63; port=0~127;"


6       Other Considerations

When a BAS does not receive a VBAS Repose packet within a specified
amount of time, it SHOULD resend its VBAS Query packet and double
the waiting period. This is repeated many times as desired;
otherwise the VBAS Query is failed.

A BAS MUST receives a VBAS Response packet before it began to send
an authentication access packet to Radius Server; otherwise the VBAS
Query is failed.


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VBAS Protocol                                    Oct 2003


7       Security considerations

8       Acknowledgments

This document is based on concepts discussed in our team.

9       References

[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.

[2] Simpson, W., Editor, "The Point-to-Point Protocol (PPP)", STD 51,
RFC 1661, July 1994

[3] L. Mamakos, Editor, ÿA Method for Transmitting PPP Over Ethernet
    (PPPoE)ÿ,  RFC 2516, February 1999

10      Authors¯ Addresses

 Abel Wang
   China Telecom-Guangzhou Research and Development Center
   109 ZhongShan Ave
   TianHe District, Guangzhou
   China

   Email: wangab@gsta.com


  Wenxiu Xu
   China Telecom-Guangzhou Research and Development Center
   109 ZhongShan Ave
   TianHe District, Guangzhou
   China

   Email: xuwx@gsta.com



  Yanqing Lu
   China Telecom-Guangzhou Research and Development Center
   109 ZhongShan Ave
   TianHe District, Guangzhou
   China

   Email: luyq@gsta.com


  Lei Cao
   Guangdong Telecom
   TianHe District, Guangzhou
   China

   Email: cao@spring.gd.cn



Wang/Xu/Lu/Cao                                  [Page 8]

VBAS Protocol                                    Oct 2003

   Rong Zhang
   China Telecom-Guangzhou Research and Development Center
   109 ZhongShan Ave
   TianHe District, Guangzhou
   China

   Email: zhangr@gsta.com


Tao Zhang
   China Telecom-Guangzhou Research and Development Center
   109 ZhongShan Ave
   TianHe District, Guangzhou
   China

   Email: zhangt@gsta.com


Maowen Guo
   China Telecom-Guangzhou Research and Development Center
   109 ZhongShan Ave
   TianHe District, Guangzhou
   China

   Email: guomw@gsta.com



11      Glossary
ADSL      Asymmetric Digital Subscriber Line
ATM       Asynchronous Transport Mode
BAS       Broadband Access Server
DHCP      Dynamic Host Configuration Protocol
DSLAM     Digital Subscriber Line Access Multiplexer
IMA       Inverse Multiplexing for ATM
IP        Internet Protocol
LAN       Local Area Network
MAC       Media Access Control
PADS      PPPoE Active Discovery Session-confirmation
PPPOE     PPP Over Ethernet
ID        Identification
RADIUS    Remote Authorization Dial In User Service
STM       Synchronous Transport Mode
VBAS      Virtual BAS
VDSL      Very-high-speed Digital Subscriber Line
VLAN      Virtual LAN

12      Full Copyright Statement

Copyright (C) The Internet Society (2003).  All Rights Reserved.



Wang/Xu/Lu/Cao                                  [Page 9]

VBAS Protocol                                    Oct 2003

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