Congestion control is a key issue in MANET. MANET has some special properties, such as large interference of wireless signal, heavy fading channel, multiple hops, unsymmetry links and node mobility, which may cause high packet loss rate, acknowledgement packets cumulating in intermediate nodes, lots of out-of-order packets and large jitter of round trip time. Consequently, improper congestion controls (e.g., unnecessary retransmission and mistakenly reducing the size of send window) are made and the throughput is very poor in MANET with traditional TCP congestion control mechanism. Many typical improved approaches proposed to overcome these difficulties in MANET were verified in this survey. In addition, the features and performances of these approaches were compared and concluded. According to this survey, real-time state information of the whole network obtained by cross-layer design is helpful to congestion control in MANET and this is the mainstream mechanism adopted by these proposed approaches.%拥塞控制是MANET(mobile Ad-hoc NETwork)中的关键问题.MANET具有无线信号干扰大、信道衰落严重、多跳路由、链路不对称和网络拓扑动态扩展等特性,这些特性会使传统TCP(transmission control protocol)在发送数据过程中经历丢包率高、应答包在中间节点累计、乱序包多和往返时间抖动大等问题,容易触发TCP作出错误的拥塞控制,进行不必要的超时重传、丢包重传和减小发送窗口大小,最终严重降低端到端的吞吐量.本文调研了近年来针对MANET提出的各种拥塞控制改进方法,按照拥塞产生的原因进行分类总结,详细介绍各个算法的工作原理并比较这些方法的技术特点.发现通过跨层设计获取网络实时状态信息,进而用来辅助拥塞控制,是改进方法的主流实现方式.
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