Omnet++停等式ARQ模型仿真实验.doc

实验二 Omnet+停等式ARQ模型仿真实验一实验目的1.熟悉omnet+软件使用。2.对停等式ARQ模型进行更形象的分析与学习，了解此协议的思想。二实验工具Omnet+软件三实验步骤1.用omnet+软件，创建一个arq.ned文件，编写代码，建立两个具有 收发功能的节点并连接，传输延迟设置为100ms。代码如下：simple sender parameters: display(i=block/process); gates: input in; output out;simple reciever parameters: display(i=block/process); gates: input in; output out;network Arq submodules: sender: sender parameters: display(i=,cyan); reciever: reciever parameters: display(i=,gold); connections: sender.out - delay = 100ms; - reciever.in; sender.in - delay = 100ms; - reciever.out;图形如下图所示：2.对停等式ARQ协议进行编程实现。 在发送端设置定时器，当超出一定时间未收到接收端返回的ACK就认为 所发message丢失，再次发送相同message。按时接到相对应的ACK后， 定时器重启。 模块声明及初始化代码如下：class sender : public cSimpleModule private: simtime_t timeout; / timeout cMessage *timeoutEvent; / holds pointer to the timeout self-message int seq; / message sequence number cMessage *message; / message that has to be re-sent on timeout public: sender(); virtual sender(); protected: virtual cMessage *generateNewMessage(); virtual void sendCopyOf(cMessage *msg); virtual void initialize(); virtual void handleMessage(cMessage *msg);Define_Module(sender);sender:sender() timeoutEvent = message = NULL;sender:sender() cancelAndDelete(timeoutEvent); delete message;void sender:initialize() / Initialize variables. seq = 0; timeout = 1.0; timeoutEvent = new cMessage(timeoutEvent); / Generate and send initial message. EV Sending initial messagen; message = generateNewMessage(); sendCopyOf(message); scheduleAt(simTime()+timeout, timeoutEvent); 我们在设定发送端sender的时候，考虑到如果接收端reciever没有接到，sender的上一个message不能被清除，则规定接到相对应的ACK后， 将刚刚发送的message清除，否则重发。 发送端规则及对message编号的代码如下：void sender:handleMessage(cMessage *msg) if (msg=timeoutEvent) / If we receive the timeout event, that means the packet hasnt / arrived in time and we have to re-send it. EV Timeout expired, resending message and restarting timern; sendCopyOf(message); scheduleAt(simTime()+timeout, timeoutEvent); else / message arrived / Acknowledgement received! EV Received: getName() n; delete msg; / Also delete the stored message and cancel the timeout event. EV Timer cancelled.n; cancelEvent(timeoutEvent); delete message; / Ready to send another one. message = generateNewMessage(); sendCopyOf(message); scheduleAt(simTime()+timeout, timeoutEvent); cMessage *sender:generateNewMessage() / Generate a message with a different name every time. char msgname20; sprintf(msgname, send-%d, +seq); cMessage *msg = new cMessage(msgname); return msg; 在接收端我们需要做的就是将丢包情况考虑进去，设置随机丢包的情况。如果message丢失，那么打印出丢失的字样，收到message，就返回一个相同编号的ACK。 代码如下：class reciever : public cSimpleModule protected: virtual void handleMessage(cMessage *msg);Define_Module(reciever);void reciever:handleMessage(cMessage *msg) if (uniform(0,1) 0.1) EV Losing message msg endl; bubble(message lost); delete msg; else EV msg received, sending back an acknowledgement.n; delete msg; send(new cMessage(ack), out); 3.运行仿真程序并记录结果。 4.对实验结果进行分析总结。 实验结果及分析这是13号message发送的全过程，包被接收端接收后，将接到一个ACK， 然后定时器重启。如果包丢失，则会出现如下图的情况：发送端收到ACK时间超时，认为数据丢失，再次发送send16，直到收到 ACK为止。在停等式ARQ中，数据报文发送完成之后，发