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Media-Friendliness of a Slowly-Responsive Congestion

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Media-Friendliness of A Slowly-Responsive Congestion

Control Protocol

Zhiheng Wang

Dept. of EECS

University of Michigan

Ann Arbor, MI 48109

Sujata Banerjee

Internet Systems & Storage Lab

Hewlett-Packard Laboratories

Palo Alto, CA 94304

Sugih Jamin

Dept. of EECS

University of Michigan

Ann Arbor, MI 48109


Streaming media transfers over the Internet are expected to behave

in a TCP-friendly manner while reacting slower to congestion than

TCP. For this purpose, a number of slowly-responsive congestion

control protocols have been developed. In this paper, we present

our study on the media-friendliness of TFRC, one of the recently

developed slowly-responsive congestion control mechanisms. With

both simulation and Internet experiments, we show that TFRC is

not necessarily smooth enough to be "media-friendly". We also

discuss our approach to improve a congestion control mechanism's


Categories and Subject Descriptors

C.2.2 [Computer-Communication Networks]: Network Protocols

--Protocol Verification

General Terms

Performance, Design


TCP-Friendly congestion control, performance evaluation


With emerging advanced technologies on both end hosts and network

connections, the deployment of multi-media applications over

the Internet has increased rapidly in recent years [1, 2, 3]. Media

content can be disseminated over the Internet through bulk data

transfer or streaming. In this paper we concentrate on streaming

media transfers.

The implication of streaming is that network sending rate must

be closely matched to the data generation rate and the rate at which

the data is consumed by the client application. If these rates do not

match, receiver buffers can overflow or underflow and the end user

perceived media quality can suffer. Most applications have a small

startup buffer at the receiver which is filled before media playout

can begin. This is done to absorb variable network delays to ensure

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continuous playback. For interactive applications, the size of this

buffer must be small to reduce interaction latency.

Currently, wide-spread deployment of high fidelity streaming

media on the Internet is hindered by the best-effort nature of the

networks. Streaming applications using UDP or TCP for data transfer

are under the risk of either overloading network resources or

receiving lower perceived quality [4, 1]. TCP congestion control

interferes with streaming media throughput requirements by introducing

sudden drops in the sending rate when congestion occurs.

A number of slowly-responsive congestion control protocols [5,

6, 7, 8] have been introduced to reduce these sudden fluctuations,

while complying with TCP congestion control principle of avoiding

overloading network resources.Subsequent to these efforts, the

concept of TCP-friendliness [5] was introduced. TCP-friendliness

ensures the compatibility between a proposed protocol and existing

TCP. "A congestion control mechanism is TCP-friendly if it

displays congestion control behavior that, on time scales of several

round-trip times (RTTs), obtains roughly the same throughput

as a TCP connection in steady-state when the available bandwidth

does not change with time" [6]. However, very few previous efforts

on developing TCP friendly protocols have examined whether

they are media-friendly. A congestion control protocol is mediafriendly

if its congestion control behaviors 1) consider the characteristics

of streaming media and 2) provide streaming media with

uninterrupted transport services.




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