Anewfastfriendlywindo_省略_mingmediatransm

Science in China Ser. F Information Sciences 2005 V ol.48No.3273—284 273 A new fast friendly window-based congestion

control for real-time streaming media

transmission

LI Yongli1, 2, LIU Guizhong1, ZHANG Zhongwei1 & WU Chenggui1

1. Department of Electronic and Information Engineering, Xi’an Jiaotong University, Xi’an 710049, China;

2. Beijing ZhongChuang Telecom Test Co., Ltd, Beijing 100081, China

Correspondence should be addressed to Li Yongli (email: ylli@c58c851da58da0116d17496f; liyongli@c58c851da58da0116d17496f)

Received September 5, 2004

Abstract Real-time streaming media over the Internet is an important component of

multimedia applications. For the sake of quality of service (QoS), they make rigid

demands on bandwidth, delay and packet loss. However, the current Internet does not

offer any QoS guarantees to real-time streaming media over it. How to maximize the

transmission quality of real-time streaming applications in a best-effort network while

friendly sharing bandwidth with non-real time applications like TCP has become an

important issue. But now, many real-time streaming applications based on UDP rarely

perform congestion control in a TCP-friendly manner, and they do not share the available

bandwidth fairly with applications built on TCP. The Internet communication strongly fears

that the current evolution could lead to congestion collapse and starvation of TCP traffic.

For this reason, TCP-friendly protocols are being developed to behave fairly with respect

to coexistent TCP flows. In this paper we present a new window-based congestion control

method—fast fair binomial congestion control (FFBCC) for real-time applications. It

provides a good performance of bandwidth distribution and TCP-friendliness for real-time

streaming transmission while competing bandwidth with TCP flows.

Keywords: TCP-friendly, streaming media, congestion control, fairness.

DOI: 10.1360/03yf0108

1 Introduction

In the current Internet, not all applications use TCP and they do not follow the same

concept of fairly sharing the available bandwidth. The rapid growing of real-time

streaming media applications will bring much UDP traffic without integrating TCP

compatible congestion control mechanism into Internet. It threats the quality of service

(QoS) of real-time applications and the stability of the current Internet. For this reason, it

is desirable to define appropriate rate rules and mechanisms for real-time streaming me-

dia applications that are compatible with the rate adaptation mechanism of TCP. These

Copyright by Science in China Press 2005

274 Science in China Ser. F Information Sciences 2005 V ol.48 No.3 273—284 Copyright by Science in China Press 2005 adaptation rules should make real-time media applications TCP-friendly, and lead to a fair distribution of bandwidth.

In order to guarantee the fair distribution of bandwidth, the lower layer protocol must provide good congestion control performance to reduce the high variation of transmis-sion rate. High variations heavily affect the network utilization. Especially to the real-time applications, it is hard to guarantee the requirements of delay and jitter. Re-

cently proposed congestion control mechanisms include the equation-based schemes [1—3],

and the TCP-like window-based schemes [4]. For the equation-based schemes, computa-tion complexity and estimation error of the parameters heavily affect their performance. Window-based schemes, also called binomial method, have provided a simple avenue to get smooth rate control and TCP-friendliness by using TCP-like congestion control al-gorithm. But these methods cannot offer a fast fair bandwidth sharing among competing flows during congestion control.

TCP-friendliness [5] means that a flow does not reduce the long-term throughput of any coexistent TCP flow more than another flow on the same path would under the same network condition. Many researchers proposed different congestion control methods to realize TCP-friendly transmission. These TCP-friendly congestion control methods also can be categorized into two groups. One is equation-based such as classic method, TFRC [6], proposed by IETF; the other is window-based such as IIAD and SQRT [7,8]. Lower layer protocols of both groups are UDP. Equation-based mechanisms calculate the sending rate using an experimental rate equation. The main question about them is how to control the time steps of rate updating which heavily affects their performance. Although the window based methods can provide TCP-friendliness, the fairness of bandwidth distribution and its convergence speed cannot be improved much. In this pa-per a new window-based TCP-friendly congestion control algorithm is proposed. It pro-vides a fast fair binomial congestion control (FFBCC) mechanism which uses a small number of feedback messages to achieve a fast convergence speed and a good fairness. And then, a new UDP-based real-time streaming media transmission protocol using FFBCC as its sending window control mechanism is proposed. Compared with TFRC, the new protocol exhibits good TCP-friendliness and smooth transmission rate. 2 Window-based congestion control

TCP-AIMD (additive increase and multiplicative decrease) is a classic binomial win-dow-based congestion control algorithm. It increases the congestion window as a result of the successful transmission of a window of packets, and decreases the congestion window upon the detection of a packet loss event. Its control rules can be expressed as follows:

Increase: / (0),k t R t t w w w αα+=+> (1)

Decrease: (01),l t t t w w w τββ+=?<< (2)

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