TOMA: A Viable Solution for Large-Scale Multicast Service

SupportLi Lao, Jun-Hong Cui, and Mario GerlaUCLA and University of Connecticut

Networking 2005

Presented by Kyungmin Cho2005/10/19

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Network Computing Laboratory

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Contents

• One Line Comment• Motivation• Problem• Solution Approach• Experiments• Conclusion• Critique

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One Line Comment

• This paper presents Two-tier Overlay Multicast Architecture (TOMA) to provide scalable and efficient multicast support for various group communication applications

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Motivation(1/2)• IP multicast

– the lack of a scalable inter-domain routing protocol– the state scalability issue with a large number of groups– the lack of support in access control– the requirement of global deployment of multicast-capable IP

routers– the lack of appropriate pricing models

• Application-layer multicast– generally not scalable to support large multicast groups

• relatively low bandwidth efficiency• heavy control overhead

– hard to have an effective service model for ISP• difficult to have efficient member access control• not easy to obtain the knowledge of the group bandwidth usage

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Motivation (2/2)

• Who care about a practical solution for large-scale multicast support?– Network service providers (or higher-tier ISPs) ?– Internet Service Providers (or lower-tier ISPs) ?– End users?

• ISPs in the middle want to use limited bandwidth purchased from network service providers to support as many users as possible

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Problem

• How to provide scalable, efficient, and practical multicast support for various group communication applications

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Solution Approach

• Two-tier Overlay Multicast Architecture (TOMA)– MSON (Multicast Service Overlay Network) node is deployed by MSON

provider (ISP)– end hosts (group members) subscribe to MSON by transparently

connecting to some special proxies

MSON Node

End hostst

0

g0

g0g1

g3

g3

Member proxy

Member proxy

Member proxy

g1

g0

g1

g0

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Issues

• Efficient management of MSON– How does an MSON provider efficiently establish and

manage numerous multicast trees?

• Cluster formation outside MSON – How should members select and subscribe to

appropriate member proxies?– How are efficient clusters formed among end users?

• MSON dimensioning– Where should the overlay proxies be placed?– How much bandwidth should be reserved on each link?

• Pricing– How to charge the users of MSON?

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OLAMP for Efficient MSON Management

• Aggregated Tree

MSON Node

End hosts

DNS Server(Group Registry

Server)

t0 (g0, g1)t1 (g3)

Host Proxy of g0

Host Proxy of g3

g0

g3

g3

g1

g1

g0

g1

g0

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OLAMP for Efficient MSON Management

• Member Join; Before selecting a member proxy

MSON Node

End hosts

DNS Server(Group Registry

Server)

TOMA://groupname.xyzmson.com/

t0 (g0, g1)t1 (g3)

Host Proxy of g0

Host Proxy of g3

g1

g0

g0

g1

g0

g3

g3

IP addresses ofmember proxies

g1

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OLAMP for Efficient MSON Management

• Member Join; After selecting a member proxy

host proxy

End hosts

t0 (g0, g1)t1 (g3)

t0

t1

g0

g1

g3

O-JOIN(g

1)

O-JOIN-ACK(g1, t0)

O-GRAFT(t

0)

g3

Group-tree matchingg1

g0

g1

g0

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• Member Leave

host proxy

End hosts

t0 (g0, g1)t1 (g3)

t0

t1

g0

g0g1

g3

g3

Tree Groups

t1 g3

Group-Tree Matching Table

O-LEAVE(g3)

X

O-LEAVE-ACK(t1)

O-PRUNE(t1) Leave

OLAMP for Efficient MSON Management

g1

g0

g1

g0

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• A trade-off between bandwidth waste and aggregation– the more bandwidth we are willing to sacrifice, the more groups c

an share one tree

• Dynamic Group-Tree Matching Algorithm– average percentage bandwidth overhead for tree t

– bth is a bandwidth overhead threshold– Algorithm

• if g is not new and the current tree t for group g is still appropriate (t can cover g, enough bandwidth, and bth is OK), t is used for g

• else, check if any existing tree is appropriate for g– If so, the one with the minimum cost is selected (O-SWITCH(g, t, t’))– else, the native tree to is used to cover g

OLAMP for Efficient MSON Management

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Cluster Formation Outside MSON

• Member Proxy Selection– An end user selects one proxy based on the criteria of low latency and lo

w workload– measure the RTT by sending ping requests– In the reply, the proxy piggybacks its workload information

• the total number of end users• the total amount of access bandwidth in use

• P2P Multicast in Access Networks– the member proxy stores the group membership information

• end users monitor its peers (delay, available bandwidth) and reports this information to its member proxy

– the member proxy computes P2P multicast delivery trees and disseminates the (parent, children) entries to the members

– end users connect with their children and transmit data packets via unicast

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Experiments

• Experiments in NS-2• compare TOMA with

– (1) NICE, (2) IP multicast, and (3) unicast• Simulation Settings

– Transit-Stub topologies• 50 transit domain routers and 500-2,000 stub domain router

s• End hosts are attached to stub routers uniformly at random

– topology abstracted from real network topology, AT&T backbone

• 54 routers• each router has a weight wi, end hosts are attached with a pr

obability proportional to wi

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Experiments

• Multicast Tree Performance– total number of links in a multicast tree

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Experiments

• Multicast Tree Performance– average link stress, average path length

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Experiments

• Control Overhead

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Experiments

• Effectiveness of MSON Management Protocol

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Conclusion

• A Two-tier Overlay Multicast Architecture (TOMA)– group communication applications– infrastructure-supported overlays

• facilitate the deployment of multicast server

– MSON as the backbone service domain and P2P multicast in the access domains

• efficient resource utilization with reduced control overhead

– OLAMP for MSON management• the control overhead for establishing and maintaining

multicast tress are significantly reduced• far less forwarding state

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Critiques

• Strong Points– address the issue of who is responsible for

deploying multicast service– supporting numerous groups having a large

number of members– Dynamic group tree matching algorithm

• Weak Points– messages which is required for a subset of

members are also delivered to all members through network

• fine grained-filtering should be performed at end hosts