VPLS Multicast Challenges
and Options
Marc Lasserre
Riverstone Networks
MPLS Japan 2005

1

Problem Statement

2Multicast Optimizations

Traffic Delivery
 To receivers only Tracking Joins/PrunesBandwidth Usage Minimize number of copies

3

Traffic Delivery Optimization


IGMP/PIM snooping

Snooping on ACs not an issue
 Amount of (S,G) state to be maintained is boundedCan be performed at different points of the ACs
 E.g. PE, MTU, DSLAM, CPE

Snooping on core PWs can lead to a large amount of state to bemaintained per PE
 Processor load for snooping Memory to maintain (S,G)

IGMP Snooping Defined in draft-ietf-magma-snoop

 PIM Snooping Defined in draft-hemige-serbest-l2vpn-vpls-pim-snooping

4Multicast Options

Trade-off between:

L3 Multicast solutions aim to optimize b/w usage

draft-rosen-vpn-mcast

L2 Multicast solutions aim to keep the corestatelessState maintained in the core
Optimization of bandwidth usage
Optimality of multicast routes

draft-hemige-serbest-l2vpn-vpls-pim-snooping
draft-ietf-magma-snoopHybrid modeldraft-raggarwa-l2vpn-vpls-mcast
5

VPLS Multicast

MTUMTUPEMTUPEMTUPEMTUMTUPEMTU

6

Replication Limitations
Ingress replication as defined in current VPLS drafts
can lead to inefficient bandwidth usage in VPLS
core
Multiple copies of the same multicast frame sentOver shared physical paths

Number of replications performed in h/w

Introduces latency & jitter
Limits the maximum number of VPN members that canefficiently receive multicast

7Bandwidth Optimization
So far, replication within metro networks has notbeen an issue
 Simple topologies (rings or very few P routers between PEs)
 Average number of sites per VPN typically small (between5 and 20)
 Hierarchical VPLS constructs distribute replication acrossmultiple nodesWith more complex topologies, multicast applications,use of p2mp LSPs leads to better bandwidthutilization

8

VPLS Multicast Drivers


Broadcast video/radio deliveryCarrier based services
E.g. regular TV channels

Dedicated multicast streams
Business based services
Customer video feeds

Financial informationE.g. Bank video advertisements in branch offices
E.g Reuters, TIBCO

Video conferencing
E.g. NetMeeting

9

VPLS Multicast Enhancements

10Broadcast Trees
Shared Broadcast Tree

One broadcast tree across VPLS
instances

Dedicated Broadcast Tree

One broadcast tree per VPLS
instanceRooted at each VPLS PE

Rooted at each VSIUsed to carry all customers’
bcast & mcast trafficUsed to carry one customer’s
bcast & mcast trafficApplicable to both L2
bcast/mcast and L3 mcast
Minimizes amount of multicast
state in the coreVPLS/VC agnostic
Requires support of draft-ietfmpls-rsvp-te-p2mp

Applicable to both L2bcast/mcast and L3 mcast
Minimizes amount of multicast
state in the core
VPLS/VC agnostic
Requires support of draft-ietfmpls-rsvp-te-p2mp

Ideally suited for residential
Broadcast Video/Radio delivery

Ideally suited for BusinessBroadcast Video delivery
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Multicast Trees
Dedicated Multicast Trees

Several trees per VPLS instance






Rooted at each source

Used to carry efficiently
customer’s specific mcast traffic
Applicable to IP mcast onlyRequires support of draft-ietfmpls-rsvp-te-p2mp
Requires a discovery procedureof multicast membership in core

Aggregate Multicast Trees

To map (S,G) to correct
multicast tree

Suited to business customers
with multiple multicast streams
with high b/w requirements

Use of p2mp trees to a defined set ofPEs across VPLS instances
Requires label coordination(upstream allocation)Per mcast group VC label for
demultiplexing

Only applicable to IP traffic
Requires a discovery procedure ofmulticast membership in core

PIM/IGMP snooping“signaling” protocol to advertize
membership (LDP or BGP)

Suited to business customers thatneed to exchange multicast
streams
12

Discovery Protocolfor Multicast Trees Several options available Use of IGMP/PIM snooping on core PWs
 Use of LDP extensions to carry mcast membership

information
 draft-qiu-serbest-l2vpn-vpls-mcast-ldp

 Use of BGP or PIM as defined in draft-raggarwa-l2vpn-vpls-mcast

13

VPLS Dataplane Changes
Use of default p2mp tree instead of ingress
replication for:All customer broadcast and multicast data traffic

Non-Use of default p2mp tree forAll customer broadcast & mcast control traffic

Use of multicast FECs to map customer mcast
traffic to appropriate mcast data trees (Options 3& 4 only) Encoding of mcast VC label for aggregate trees
 PHP turned off except for aggregate trees
14

VPLS Control Plane Changes
IGMP/PIM snooping on ACs
 RSVP-TE mcast extensions
 IGMP/PIM snooping on PWEs for multicast trees

Optional if use of “signaling” protocol

PIM refresh reduction turned off for multicasttrees
 PIM support in Ps for multicast trees
 BGP/PIM/LDP mcast state signaling over PWEs
for aggregated trees15Issues to be resolvedAdditional complexity for multicast trees
Aggregate trees have add’l requirements:Protocols for discovery and upstream allocation
 Current PWE/VPLS use downstream unsolicited label advertisementComplex heuristics and/or knobs to decide when to set up newaggregate trees

Which discovery protocol is best suited?


Snooping, PIM, BGP, LDP?
Subject for future discussion

16

Q&A

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