draft-ietf-mpls-multicast-07.txt   draft-ietf-mpls-multicast-08.txt 
Network Working Group D. Ooms, B. Sales Network Working Group D. Ooms, B. Sales
Internet Draft Alcatel Internet Draft Alcatel
Expiration Date: July 2002 W. Livens Expiration Date: October 2002 W. Livens
Colt Telecom Colt Telecom
A. Acharya A. Acharya
IBM IBM
F. Griffoul F. Griffoul
Ulticom Ulticom
F. Ansari F. Ansari
Bell Labs Bell Labs
January 2002 April 2002
Framework for IP Multicast in MPLS Framework for IP Multicast in MPLS
draft-ietf-mpls-multicast-07.txt draft-ietf-mpls-multicast-08.txt
Status of this Memo Status of this Memo
This document is an Internet-Draft and is in full conformance with This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026. all provisions of Section 10 of RFC2026.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet- other groups may also distribute working documents as Internet-
Drafts. Drafts.
skipping to change at page 22, line 25 skipping to change at page 22, line 25
can be maintained but the label advertisement is duplicated in space. can be maintained but the label advertisement is duplicated in space.
Since LSPs are only rewarding if they have a long lifetime and since Since LSPs are only rewarding if they have a long lifetime and since
the number of LSRs on a shared link is limited the second approach the number of LSRs on a shared link is limited the second approach
seems advantageous. seems advantageous.
Another issue with multicast in multi-access networks is whether to Another issue with multicast in multi-access networks is whether to
use upstream or downstream label assignment. For multicast traffic, use upstream or downstream label assignment. For multicast traffic,
upstream label allocation is simpler since there can be only one upstream label allocation is simpler since there can be only one
upstream node per link that belongs to a multicast tree. This upstream node per link that belongs to a multicast tree. This
(upstream) node can assign a label without any contention. With (upstream) node can assign a unique label for the FEC. With
downstream allocation, there may be multiple downstream nodes for a downstream allocation, there may be multiple downstream nodes for a
given tree on a multi-access link; each node may propose a label given tree on a multi-access link; each node may propose a different
assignment leading to contention and a contention resolution scheme label assignment for a FEC which would require some resolution
is required to chose one of them as the label allocator. process in order to come of with a single label per multicast FEC on
the link.
Once a label has been assigned, it is possible that the label Once a label has been assigned, it is possible that the label
assigner leaves the tree. With downstream label assignment, this assigner leaves the tree. With downstream label assignment, this
could happen when the label allocator leaves the group. With could happen when the label allocator leaves the group. With
upstream assignment this could happen when the upstream LSR changes upstream assignment this could happen when the upstream LSR changes
due to a unicast topology change. due to a unicast topology change.
10. More issues 10. More issues
10.1. TTL field 10.1. TTL field
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a) Easier label allocation in multi-access networks (see section 9). a) Easier label allocation in multi-access networks (see section 9).
b) The same label can be kept when the downstream LSR (which would b) The same label can be kept when the downstream LSR (which would
have been the label allocator in downstream mode in a multi-access have been the label allocator in downstream mode in a multi-access
network) leaves the group (see section 9). network) leaves the group (see section 9).
c) The upstream and implicit distribution mode allow a faster LSP c) The upstream and implicit distribution mode allow a faster LSP
setup when the LSP is traffic triggered. setup when the LSP is traffic triggered.
Whether to use upstream or downstream label distribution is outside
the scope of this framework. The relative complexity between the
necessary protocol extensions and the resolution mechanism needed,
as well as the relative operational complexity, will influence which
way to go.
10.5. Explicit vs. Implicit Label Distribution 10.5. Explicit vs. Implicit Label Distribution
Beside the explicit distribution modes (which use a signaling Beside the explicit distribution modes (which use a signaling
protocol), [ACHA] proposes an implicit label distribution method by protocol), [ACHA] proposes an implicit label distribution method by
using unknown labels. This method has all the advantages of the using unknown labels. This method has all the advantages of the
upstream label allocation method and is probably the fastest label upstream label allocation method and is probably the fastest label
advertisement method for traffic triggered LSPs. advertisement method for traffic triggered LSPs.
Implicit label distribution is not applicable if the FEC-to-label Implicit label distribution is not applicable if the FEC-to-label
binding has been advertised prior to traffic arrival, e.g. explicit binding has been advertised prior to traffic arrival, e.g. explicit
 End of changes. 

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