PPP Working Group Pat R. Calhoun
INTERNET DRAFT Sun Microsystems, Inc.
Category: Informational Ken Peirce
Title: draft-ietf-pppext-l2tp-ds-02.txt 3Com Corporation
Date: July 1998
Layer Two Tunneling Protocol "L2TP"
IP Differential Services Extension
<draft-ietf-pppext-l2tp-ds-02.txt>
Status of this Memo
This document is an Internet-Draft. Internet-Drafts are working
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Abstract
The L2TP document [1] defines the base protocol which describes the
method of tunneling PPP [2] data. The L2TP base protocol does not
address any Differential Services extensions.
Since the market is reluctant to outsource dial access without any
Quality of Service assurances, this draft addresses this problem by
allowing each L2TP Data Session to be assigned an appropriate
differential services indicator.
Table of Contents
1.0 Introduction
1.1 Conventions
2.0 Quality of Service/Diferential Services Negotiation
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2.1 Differential Sevices Indicator Exchange
2.2 Error Reporting
3.0 References
4.0 Authors' Addresses
1.0 Introduction
The L2TP protocol specification does not discuss Quality of
Service/Differential Services in any way. The current state of the
market has shown that many customers are reluctant to adopt L2TP
without any quality of service assurances.
This document will describe how two L2TP peers can negotiate a
differential services indicator for a dial-in user. Note that each
individual session within a tunnel can have its own Diff Serv
Indicator.
The mechanism defined in this document assumes that the Tunnel
Initiator determines what the user's appropriate service level is and
sends the value in either the ICRQ or OCRQ messages. The Tunnel
Terminator can respond to the message by stating what it believes is
the user's appropriate service level. The values of the indicator
supplied by the Tunnel Terminator will supercede those provided by
the Tunnel Initiator if a difference is found. However, the Tunnel
Terminator MUST NOT propose a higher differential service level than
was proposed by the Tunnel Initiator.
In the case where the Tunnel Terminator does not propose ANY
indicator (which is infered by the absence of the QOS AVPs in either
the ICRP or OCRP) the Tunnel Initiator will assume no QOS is assigned
to the session.
A tunnel peer which violates the negotiated differential service
level is liable to have it's tunnel shutdown.
1.1 Conventions
The following language conventions are used in the items of specifi-
cation in this document:
o MUST, SHALL, or MANDATORY -- This item is an absolute
requirement of the specification.
o SHOULD or RECOMMEND -- This item should generally be followed
for all but exceptional circumstances.
o MAY or OPTIONAL -- This item is truly optional and may be
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followed or ignored according to the needs of the
implementor.
2.0 Quality of Service/Diferential Services Negotiation
This section will define the new AVPs which are required for the
Quality of Service extension of the L2TP protocol. The AVPs allow
designation of a Quality of Service level for a specific data
channel.
2.1 Differential Services Indicator AVP
The Differential Services indicator AVP is found in the IPv4 header's
Type of Service octet. This is the second octet in the header. The
actual bit interpretation of the IP Precedence and Type of Service
bit fields is left to the appropriate documentation[2][3][4]. This
document is concerned with defining a uniform exchange mechanism for
the indicator only.
The Differential Services Indicator AVP MAY be present in ICRQ, ICRP,
OCRQ and OCRP. This message is used to inform the tunnel peer that a
set of differential service indicator value SHOULD be used for all
packets related to the data channel associated with the Tunnel and
Call Identifiers in the L2TP header [1].
The presence of this AVP in the ICRQ or OCRQ indicates that the
tunnel initiator wishes to use a specific differential service
indicator value on all data packets. However, the value found in the
ICRP or OCRP indicate the value which the Tunnel Terminator is
willing to accept. However, the Tunnel Terminator MUST NOT propose a
higher differential service level than was proposed by the Tunnel
Initiator.
A tunnel peer which violates the negotiated indicator value is liable
to have it's tunnel shutdown.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1|1|0|0| Length | 43 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 1 | Diff Serv Indicator Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
This AVP MAY be present in the messages shown above. It is encoded
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with a Vendor ID of 43 (3Com Corporation) with the attribute set
to 1, marked as optional, with the indicator value as data. This
AVP SHOULD NOT be hidden and is optional. When present, the L2TP
peer is indicating that differential services are to be used on IP
packets within the session's data channel.
2.2 Error Reporting
In the event that the peer did not accept the Diff Serv Indicator
provided, or is unable to support Differential Services a Call-
Disconnect-Notify is returned to the peer.
If the indicator provided cannot be used by the peer, the Call-
Disconnect-Notify message will include the Diff Serv Indicator AVP as
provided in the message that caused the Call-Disconnect-Notify.
3.0 References
[1] K. Hamzeh, T. Kolar, M. Littlewood, G. Singh Pall, J. Taarud,
A. J. Valencia, W. Verthein, W.M. Townsley, B. Palter,
A. Rubens "Layer Two Tunneling Protocol (L2TP)",
Internet draft, October 1997
[2] D. Clark, J. Wroclawski, "An Approach to Service Allocation in
the Internet", draft-clark-diff-svc-alloc-00.txt, July 1997.
[3] P. Ferguson, "Simple Differential Services: IP TOS and
Precedence, Delay Indication, and Drop Preference,",
draft-ferguson-delay-drop-00.txt, November 1997
[4] J. Heinanen, "Use of the IPv4 TOS Octet to Support Differential
Services", draft-heinanen-diff-tos-octet-01.txt, November 1997
4.0 Authors' Addresses
Questions about this memo can be directed to:
Pat R. Calhoun
Technology Development
Sun Microsystems, Inc.
15 Network Circle
Menlo Park, California, 94025
USA
Phone: 1-650-786-7733
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Fax: 1-650-786-6445
E-mail: pcalhoun@eng.sun.comt
Ken Peirce
3Com Corporation
1800 Central Ave.
Mount Prospect, Il, 60056
Phone: 1-847-342-6794
Fax: 1-847-222-2424
E-mail: Ken_Peirce@mw.3com.com
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