滑动窗口实验报告

滑动窗口实验报告（含源码）一、实验目的1.实现一个数据链路层协议的数据传送部分。

2.更好地理解数据链路层协议中的“滑动窗口”技术的基本工作原理。

3.掌握计算机网络协议的基本实现技术。

二、实验要求在一个数据链路层的模拟实现环境中，用C语言实现下两个数据链路层协议。

1.1比特滑动窗口协议2.回退N帧滑动窗口协议三、实验内容充分理解滑动窗口协议，根据滑动窗口协议，模拟滑动窗口协议中发送端的功能，对系统发送的帧进行缓存并加入窗口等待确认，并在超时或者错误时对部分帧进行重传。

编写停等及退回N滑动窗口协议函数，响应系统的发送请求、接收帧消息以及超时消息，并根据滑动窗口协议进行相应处理。

四、源代码及注释#include "sysinclude.h"#include <iostream>using namespace std;extern void SendFRAMEPacket(unsigned char* pData, unsigned int len);//1比特滑动窗口#define WINDOW_SIZE_STOP_WAIT 1//回退N帧协议#define WINDOW_SIZE_BACK_N_FRAME 4//缓存区大小#define BUFFER_SIZE 50typedef enum {DATA,ACK,NAK} Frame_kind;//帧头typedef struct Frame_head{Frame_kind kind;unsigned int seq;unsigned int ack;unsigned char data[100];};//帧typedef struct Frame{Frame_head head;unsigned int size;};//缓存区Frame buffer[BUFFER_SIZE];//当前希望确认的帧，最近缓存的帧，下一次要发送的帧unsigned int expect_frame = 0, last_buffered_frame = 0, next_frame = 0;/** 停等协议测试函数*/int stud_slide_window_stop_and_wait(char *pBuffer, int bufferSize, UINT8 messageType){Frame_head* p = (Frame_head*)pBuffer;//unsigned int frameNum = ntohl(*(unsigned int*)pBuffer);switch (messageType){//网络层要发送一帧数据时case MSG_TYPE_SEND : {//缓存当前要发送的帧buffer[last_buffered_frame % BUFFER_SIZE].head = *p;buffer[last_buffered_frame % BUFFER_SIZE].size = bufferSize;//更新下次缓存的位置++ last_buffered_frame;//如果当前有空闲的窗口可以用if (last_buffered_frame - expect_frame <= WINDOW_SIZE_STOP_WAIT){//发送缓存帧SendFRAMEPacket((unsigned char*)pBuffer, (unsignedint)bufferSize);//窗口上界加1++ next_frame;}return 0;}//物理层收到一帧数据时case MSG_TYPE_RECEIVE : {//解码确认信号unsigned int ack = ntohl(p->ack);//试探for (int i = expect_frame; i < next_frame; ++ i){unsigned int exp_ack = ntohl(buffer[i % BUFFER_SIZE].head.seq);//如果确认消息大于等于期望消息，则说明期望帧已经被确认过了if (ack >= exp_ack){//期望帧+1++ expect_frame;//如果有缓存帧没发出if (next_frame < last_buffered_frame){//发出一个缓存帧SendFRAMEPacket((unsigned char*)(&buffer[next_frame % BUFFER_SIZE]), buffer[next_frame % BUFFER_SIZE].size);//窗口上界+1++ next_frame;}//否则，无法继续发送帧，退出。

等待下次再更新期望确认帧else break;}}return 0;}//超时case MSG_TYPE_TIMEOUT : {//超时重发，把当前窗口内未确认的帧重发一遍for (int i = expect_frame; i < next_frame; ++ i){//if (frameNum > ntohl(buffer[i % BUFFER_SIZE].head.seq)) continue;SendFRAMEPacket((unsigned char*)(&buffer[i % BUFFER_SIZE]), buffer[i % BUFFER_SIZE].size);}return 0;}default : break;}return -1;}/** 回退n帧测试函数*/int stud_slide_window_back_n_frame(char *pBuffer, int bufferSize, UINT8 messageType){Frame_head* p = (Frame_head*)pBuffer;unsigned int timeoutNum = *(unsigned int*)pBuffer;switch (messageType){//网络层要发送一帧数据时case MSG_TYPE_SEND : {buffer[last_buffered_frame % BUFFER_SIZE].head = *p;buffer[last_buffered_frame % BUFFER_SIZE].size = bufferSize;++ last_buffered_frame;//窗口数未达上限，则发送当前缓存帧，更新窗口上界if (last_buffered_frame - expect_frame <=WINDOW_SIZE_BACK_N_FRAME){SendFRAMEPacket((unsigned char*)z, (unsigned int)bufferSize);++ next_frame;}return 0;}//物理层接收到一帧数据时case MSG_TYPE_RECEIVE : {unsigned int ack = ntohl(p->ack);cout << "receive ack : " << ack << endl;for (int i = expect_frame; i < next_frame; ++ i){unsigned int exp_ack = ntohl(buffer[i % BUFFER_SIZE].head.seq);cout << "exp_ack : " << exp_ack << endl;if (ack >= exp_ack){++ expect_frame;if (next_frame < last_buffered_frame){SendFRAMEPacket((unsigned char*)(&buffer[next_frame % BUFFER_SIZE]), buffer[next_frame % BUFFER_SIZE].size);++ next_frame;}}else break;}return 0;}//超时case MSG_TYPE_TIMEOUT : {cout << "time out : " << timeoutNum << endl;//超时重发for (int i = expect_frame; i < next_frame; ++ i){unsigned int frameNum = ntohl(buffer[i % BUFFER_SIZE].head.seq);//if (timeoutNum > frameNum) continue;cout << frameNum << endl;SendFRAMEPacket((unsigned char*)(&buffer[i % BUFFER_SIZE]), buffer[i % BUFFER_SIZE].size);}return 0;}default : break;}return -1;}/** 选择性重传测试函数*/int stud_slide_window_choice_frame_resend(char *pBuffer, int bufferSize, UINT8messageType){return 0;}五、思考题1.退回N 帧协议不必像1bit 滑动窗口协议一样，允许发送完一帧后不等确认帧而继续发送，提高了发送效率。

2.缺点是在重传时可能重新传送已经正确发送的数据帧。