计算机与通信网络实验报告

计算机与通信网络实验报告

041220111 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0.01s，发包大小为512bytes；

[3]给[4]发，发包间隔为0.01s，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]: 0.000000000

Node: 1, Layer: AppCbrClient, (0) Last packet sent at [s]: 99.990000000

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]: 0.007438001

Node: 2, Layer: AppCbrServer, (0) Last packet received at [s]: 99.999922073

Node: 2, Layer: AppCbrServer, (0) Average end-to-end delay [s]: 0.739902205

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]: 0.000000000

Node: 3, Layer: AppCbrClient, (0) Last packet sent at [s]: 99.990000000

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]: 0.003058001

Node: 4, Layer: AppCbrServer, (0) Last packet received at [s]: 99.993058001

Node: 4, Layer: AppCbrServer, (0) Average end-to-end delay [s]: 0.003119031

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0.01s，发