Network Working Group K. Nagami
Request for Comments: 3038 Y. Katsube
Category: Standards Track Toshiba Corp.
Univ. of Tokyo
VCID Notification over ATM link for LDP
Status of this Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright (C) The Internet Society (2001). All Rights Reserved.
The Asynchronous Transfer Mode Label Switching Router (ATM-LSR) is
one of the major applications of label switching. Because the ATM
layer labels (VPI and VCI) associated with a VC rewritten with new
value at every ATM switch nodes, it is not possible to use them to
identify a VC in label mapping messages. The concept of Virtual
Connection Identifier (VCID) is introduced to solve this problem.
VCID has the same value at both ends of a VC. This document
specifies the procedures for the communication of VCID values between
neighboring ATM-LSRs that must occur in order to ensure this
Several label switching schemes have been proposed to integrate Layer
2 and Layer 3. The ATM Label Switching Router (ATM-LSR) is one of
the major applications of label switching.
In the case of ATM VCs, the VPI and VCI labels are, in the general
case, rewritten with new values at every switch node through which
the VC passes and cannot be used to provide end to end identification
of a VC.
Nagami, et al. Standards Track [Page 1]RFC 3038 VCID Notification for LDP January 2001
In the context of MPLS 'stream', which are classes of packets that
have some common characteristic that may be deduced by examination of
the layer 3 header in the packets, are bound to layer 2 'labels'. We
speak of stream being 'bound' to labels. These bindings are conveyed
between peer LSRs by means of a Label Distribution Protocol [LDP].
In order to apply MPLS to ATM links, we need some way to identify ATM
VCs in LDP mapping messages. An identifier called a Virtual
Connection ID (VCID) is introduced. VCID has the same value at both
ends of a VC. This document specifies the procedures for the
communication of VCID values between neighboring ATM-LSRs that must
occur in order to ensure this property.
2. Overview of VCID Notification Procedures2.1 VCID Notification procedures
The ATM has several types of VCs (transparent point-to-point
link/VP/PVC/SVC). A transparent point-to-point link is defined as
one that has the same VPI/VCI label at both ends of a VC. For
example, two nodes are directly connected (i.e., without intervening
ATM switches) or are connected through a VP with the same VPI value
at both ends of the VP.
There are two broad categories of VCID notification procedures;
inband and outband. The categorization refers to the connection over
which the messages of the VCID notification procedure are forwarded.
In the case of the inband procedures, those messages are forwarded
over the VC to which they refer. In contrast the out of band
procedures transmit the messages over some other connection (than the
VC to which they refer).
We list below the various types of link and briefly mention the VCID
notification procedures employed and the rational for that choice.
The procedures themselves are discussed in detail in later sections.
Transparent point-to-point link : no VCID notification
VCID notification procedure is not necessary because the label
(i.e., VPI/VCI) is the same at each end of the VC.
VP : inband notification or VPID notification or no notification
- Inband notification
VCID notification is needed because the VPI at each end of the VC
may not be the same. Inband VCID notification is used in this