Proxy-based Distribution of Streaming Video over Unicast/Multicast Connections

B. Wang, S. Sen, M. Adler and D. Towsley

University of Massachusetts

Presented by Nera Liu

Agenda Introduction Problem Setting and Model Optimal Proxy Cache Allocation Proxy-Assisted Transmission Schemes Performance Evaluation Conclusion

Introduction With the emergence of broadband network, streaming

video over the Internet becomes feasible nowadays. However, due to its high bandwidth and large client

requirement, it is inefficient in traditional VoD system i.e. unicast-based system.

Introduction In designing scalable and cost effective VoD system,

researchers mainly focused on two different approaches Open-loop architectures

System performance is independent of system load It achieves better performance under heavy system load

Closed-loop architectures System performance is dependent of system load It achieves better performance under light system load.

Introduction Assumption of previous works

It is designed based on a multicast-enabled network. However, IP multicast deployment in the Internet is

slow.

Introduction The use of proxy cache is an orthogonal technique for

reducing This technique is proved to be efficient for delivering

Web objects. Similar works have been proposed in which a certain

portion of video file is stored in either client side and proxy server

Introduction S. Sen, J. Rexford, and D. Towsley, “Proxy prefix

caching for multimedia streams,” in Proc. IEEE INFOCOM, Apr 1999.

J. Almedia, D. Eager, and M. Vernon, “A hybrid caching strategy for streaming media files,” in Proc. SPIE/ACM Conference on Multimedia Computing and Networking, Jan 2001

Y. Wang, Z.-L. Zhang, D. Du and D. Su, “A network conscious approach to end-to-end video delivery over wide area networks using proxy servers,” in Proc. IEEE INFOCOM, Apr 1998.

Introduction What are suitable proxy-assisted closed-loop

transmission schedules? For a given transmission schedules, what is the optimal

proxy prefix caching scheme that minimizes the transmission cost?

What are the resources tradeoffs (proxy cache space and transmission bandwidth etc.) for the different transmission schedules?

Problem Setting

The server-proxy path is unicast-enabled.

The proxy-client path is multicast-enabled.

Problem Setting

N CBR-encode video with different popularity fi Video i has a video bit rate bi, and length Li seconds and

size ni unit

Design Goal Ci(vi) is the transmission cost per unit time for video i

when a prefix of length vi of video i is cached in the proxy.

Goal: Minimize the value of Ci(vi).

Optimal Proxy Cache Allocation Determine the storage vector (v1, v2 ….) that minimizes

the aggregate transmission cost for a given proxy-assisted transmission scheme.

In this paper, it proposes two different schemes Optimal 0-1 caching Optimal prefix caching

Optimal Proxy Cache Allocation Optimal 0-1 caching

Video is either store entirely or not Saving = Ci(0) – Ci(L)

Optimal prefix caching Only a prefix of video is stored in the proxy Saving (mi) = Ci(0) – Ci(mi), where mi represents a

vector of possible prefix of video i storing in the proxy.

Optimal Proxy Cache Allocation The optimal problem

where S is the storage size of the proxy

Proxy-Assisted Transmission Scheme The next step is how to determine Ci(vi) ?

Unicast suffix batching (SBatch) Unicast patching with prefix caching (UPatch) Multicast patching with prefix caching (MPatch) Multicast merging with prefix caching (MMerge)

Unicast patching with prefix caching (UPatch)

Multicast patching with prefix caching (MPatch)

Performance Evaluation

Performance Evaluation

Performance Evaluation

Performance Evaluation Optimal caching > Priority Prefix caching > Optimal 0-1

caching

MMerge > MPatch > UPatch > SBatch

Conclusion Under optimal proxy caching, even a small cache is

sufficient to realize the transmission cost saving. The selection of closed-loop transmission scheme

coupled with optimal proxy caching can produce significant cost saving.