ON DESIGING END-USER MULTICAST

FOR MULTIPLE VIDEO SOURCES

Y.Nakamura, H.Yamaguchi, A.Hiromori, K.Yasumoto†, T.Higashino and K.Taniguchi

Osaka University†Nara Institute of Science and Technology

ICME2003 2July/9/2003

Goal

Realizing Multi-party video conferencing systems Many-to-many multicast application which consists of

hundreds of users User hosts exchange multiple video streams in real-time

Efficient use of bandwidth is required

Internet

ICME2003 3July/9/2003

Application Layer Multicast (ALM)

ALM is multicast on overlay networks End users act as multicast routers Does not require special hardware such as IP multicast

enable routers Application-specific routing protocols can be designed More efficient than Unicast because a sender does not

need to send data to all receiversUnicast A

B

C

S

D

A

B

C

S

D

ALM

ICME2003 4July/9/2003

Design Issues Each video uses some amount of bandwidth on overlay

networks→In delivering multiple video streams, they compete for bandwidth on overlay links

Users may have priority requirements to video streamse.g. users may prefer the speaker’s video than audience’s

Internet

ICME2003 5July/9/2003

InternetOverlay Network

End-user Multicast for Multi-party Application (Emma)

New ALM protocol for multi-party communication systems Users construct overlay networks Each user host sends its own video continuously and receives some of other

user hosts’ video streams on overlay networks The sending and receiving video streams are controlled based on users’

priority requirement given to the video streams

Red

Red

ICME2003 6July/9/2003

Users’ Join When a new user wants to join a session, the user gets the current

users’ addresses from a central server The user measures delay with these users and establish overlay links

with the closest two or three users to construct mesh-like overlay networks

Existing routing trees are expanded so that they do not overlap each other as long as they can

E C A

BD

Routing tree can be expanded with•small delay from each source•less duplication

AddressManagementServer

A:133.1.xx.xxB:129.3.yy.yyC: …

ICME2003 7July/9/2003

Priority-based Video Delivery Each user specifies a priority requirement as a priority value

to each video stream. A request message with a priority value is forwarded to the

video source user But there is no enough bandwidth on the path

C A

BD

B: 5

A: 8

C: 6

D:15

ICME2003 8July/9/2003

Priority-based Video Delivery In forwarding the message, the followings are calculated step

by step how to stop existing video streams how to minimize the loss of priority values

If the loss of priority value < the gain of priority value by accepting the request The existing streams are stopped and the new stream is delivered

C A

BD

B: 5

A: 8

C: 6

D:15

The sum of the satisfied priority values

becomes larger than before

ICME2003 9July/9/2003

Users’ Leave and Failure Even if an user host leaves, trees can be recovered

When a user leaves, the simplest way to recover tree is to let child nodes connect with the parent of the leaving user

However, this may cause the concentration of overlay links to the parent user To prevent this, each user periodically collects the information of # of overlay links of its

descendant users When a user leaves, its parent can immediately suggest the children of the leaving user

where to connect again

C A

B

G

H F D

EUser E leaves

D,F,GC,D

Recovery can be done quickly without causing

unbalanced trees

ICME2003 10July/9/2003

Performance Evaluation

We have developed a simulator for evaluating performance of EmmaWritten in an object oriented scripting language

Ruby Network model

Hierarchical topology model based on tiers146 nodes, 66 usersUsers give priority values to video by Zipf’s law

ICME2003 11July/9/2003

Users’ Satisfaction

The variation of average of satisfied priority value per userCompared with First-Come-First-Serve (FCFS)

method which accepts user requests in a greedy manner

Simulation Scenario Until 5 units of time, 66 users joined After 21 units of time, 1 user joins or leaves at one time

ICME2003 12July/9/2003

Users’ Satisfaction Emma achieves 1.5 times higher values than FCFS Under the presence of users’ leave and join, priority values

are kept high

0

20

40

60

80

100

120

140

160

180

1 4 7 10 13 16 19 22 25 28 31 34 37 40 43

time

prio

rity

val

ue p

er u

ser

(ave

.)

40

50

60

70

# of

use

rs

# of users FCFS Emma

ICME2003 13July/9/2003

Routing Tree Duplication on Overlay Link

# of routing trees on an overlay linkLess duplication is desirable

Simple estimation of average duplication in the ideal case

# of users × (# of users -1) / # of total overlay links

= about 20

→Measure the # of routing trees on each overlay link

ICME2003 14July/9/2003

Routing Tree Duplication on Overlay Link

80% of overlay links have at most 10 routing trees

0

20

40

60

80

100

120

0 3 6 9 12 15 18 21 24 27 30 33

# of routing trees on overlay link

# of

ove

rlay

link

s

00.10.20.30.40.50.60.70.80.91

cum

ulat

ive

ratio

Emma cumulative

ICME2003 15July/9/2003

Conclusion We have proposed new ALM protocol called Emma

Avoiding resource competition

From the experimental results Higher satisfaction of users than a simple method Even though some users leave from or join to a session,

users’ satisfaction is kept high

We have designed and implemented Java middleware based on Emma

(http://www-tani.ist.osaka-u.ac.jp/software/s2.html)

ICME2003 16July/9/2003