摘要
考虑到 TCP直接应用于无线环境的局限性 ,人们提出了多种 TCP拥塞控制的改进机制 ,这些方案一般没有考虑误码丢包对数据发送速率的影响 .不过 ,链路误码率较高时 ,TCP发送端若不降低其数据发送速率 ,势必会引起更多的数据因误码而丢失 ,降低了数据发送的可靠性 ,从而增加了移动主机不必要的能源消耗和系统不必要的开销 .为此 ,该文详细讨论了 3种基于误码丢包的 TCP速率调节机制 .它们实现简单 ,系统额外开销小 ,既能有效提高数据发送的可靠性 ,又不会过多降低系统吞吐量和加大系统时延 ,并且 ,为进一步研究
Comparing to wire networks, there are many different characteristics in wireless environments, such as higher error rate, longer delay, lower bandwidth, frequent mobility and so on, which makes TCP congestion control mechanisms not directly suitable for wireless networks, and many improved TCP congestion control mechanisms have been presented. Generally, the influences to TCP sender's packet sending rate by link corruption are not considered in these improved schemes. However, unnecessary packet lost by corruption can be greatly avoided through the decrease of packet sending rate, which may lead to higher reliability, unnecessary energy consumption of mobile hosts, and less system overheads. For a given TCP connection, it is reasonable to assume that the possibility of packet lost by corruption can be obtained approximately from p e=m/n , where n is the number of total packets and m is the sum of packets lost by corruption during the period of time T . In this way, the possibility for n packets to be sent successfully to receiver is p=(1-p e) n , and TCP sender's maximum average packet sending rate is rate max =log a log( 1-p e ), where a is the lower limit of p . Based on the main idea, we obtain three TCP corruption based rate adjustment mechanisms, namely, two mechanisms driven by the event of packet loss in which TCP sender's packet sending rate is adjusted as soon as packet lost by corruption is detected, and one mechanism driven by TCP sender's sending period in which the rate is only adjusted while sending period expires. In terms of analysis, the mechanisms presented in this paper have the following characteristics: (1) TCP sender's packet sending rate is adjusted self adaptively by link corruption. (2) Unnecessary packets lost by corruption can be greatly avoided with light influences to throughput and delay through the choic of parameter a from (1-p e) rate 0×T/3 to (1-p e) rate 0×T/6 at the time of heavy packet loss by corruption. (3) The mechanisms can also be simply implemented with less overheads.
出处
《计算机学报》
EI
CSCD
北大核心
2002年第4期438-444,共7页
Chinese Journal of Computers
基金
重庆邮电学院青年教师科技基金项目 (A2 0 0 1-10 )资助
