RFC 3038 (rfc3038) - Page 2 of 19

VCID Notification over ATM link for LDP

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 Procedures

2.1 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
      case.






Nagami, et al.              Standards Track