计算机与通信网络实验报告
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0 戴妍
实验一隐终端和暴露终端问题分析
一、实验设定:
基本参数配置:仿真时长100s;随机数种子1;仿真区域2000x2000;节点数4。
节点位置配置:本实验用[1] 、[2]、[3] 、[4]共两对节点验证隐终端问题。节点[1]、[2]距离为200m,节点[3]、[4]距离为200m,节点[2]、[3]距离为370m。
业务流配置:业务类型为恒定比特流CBR。[1]给[2]发,发包间隔为,发包大小为512bytes;
[3]给[4]发,发包间隔为,发包大小为512bytes。
二、实验结果:
Node: 1, Layer: AppCbrClient, (0) Server address: 2
Node: 1, Layer: AppCbrClient, (0) First packet sent at [s]:
Node: 1, Layer: AppCbrClient, (0) Last packet sent at [s]:
Node: 1, Layer: AppCbrClient, (0) Session status: Not closed
Node: 1, Layer: AppCbrClient, (0) Total number of bytes sent: 5120000
Node: 1, Layer: AppCbrClient, (0) Total number of packets sent: 10000
Node: 1, Layer: AppCbrClient, (0) Throughput (bits per second): 409600
Node: 2, Layer: AppCbrServer, (0) Client address: 1
Node: 2, Layer: AppCbrServer, (0) First packet received at [s]:
Node: 2, Layer: AppCbrServer, (0) Last packet received at [s]:
Node: 2, Layer: AppCbrServer, (0) Average end-to-end delay [s]:
Node: 2, Layer: AppCbrServer, (0) Session status: Not closed
Node: 2, Layer: AppCbrServer, (0) Total number of bytes received: 4975616
Node: 2, Layer: AppCbrServer, (0) Total number of packets received: 9718
Node: 2, Layer: AppCbrServer, (0) Throughput (bits per second): 398078
Node: 3, Layer: AppCbrClient, (0) Server address: 4
Node: 3, Layer: AppCbrClient, (0) First packet sent at [s]:
Node: 3, Layer: AppCbrClient, (0) Last packet sent at [s]:
Node: 3, Layer: AppCbrClient, (0) Session status: Not closed
Node: 3, Layer: AppCbrClient, (0) Total number of bytes sent: 5120000 Node: 3, Layer: AppCbrClient, (0) Total number of packets sent: 10000 Node: 3, Layer: AppCbrClient, (0) Throughput (bits per second): 409600 Node: 4, Layer: AppCbrServer, (0) Client address: 3
Node: 4, Layer: AppCbrServer, (0) First packet received at [s]:
Node: 4, Layer: AppCbrServer, (0) Last packet received at [s]:
Node: 4, Layer: AppCbrServer, (0) Average end-to-end delay [s]:
Node: 4, Layer: AppCbrServer, (0) Session status: Not closed
Node: 4, Layer: AppCbrServer, (0) Total number of bytes received: 5120000 Node: 4, Layer: AppCbrServer, (0) Total number of packets received: 10000 Node: 4, Layer: AppCbrServer, (0) Throughput (bits per second): 409612
通过仿真结果可以看出,节点[2]无法收到数据。由于节点[3]是节点[1]的一个隐终端,节点[1]无法通过物理载波检测侦听到节点[3]的发送,且节点[3]在节点[2]的传输范围外,节点[3]无法通过虚拟载波检测延迟发送,所以在节点[1]传输数据的过程中,节点[3]完成退避发送时将引起冲突。
三、课后思考
1、RTS/CTS能完全解决隐终端问题吗如果不能,请说明理由。
答:能。对于隐发送终端问题,[2]和[3]使用控制报文进行握手(RTS-CTS),听到回应握手信号的[3]知道自己是隐终端,便能延迟发送;对于隐接受终端问题,在多信道的情况下,[3]给[4]回送CTS告诉[4]它是隐终端,现在不能发送报文,以避免[4]收不到[3]的应答而超时重发浪费带宽。
2、如何设计仿真场景来验证暴露终端问题
答:只需更改业务流配置:业务类型为恒定比特流CBR。[2]给[1]发,发包间隔为,发包大小为512bytes;[3]给[4]发,发包间隔为,发包大小为512bytes。观察在[2]给[1]发送数据的同时,[3]给[4] 发送数据会不会被影响。
3、如何设计协议使暴露终端场景下的流实现并发