计算机网络原理.实验五

实验五、传输层可靠传输协议GBN编程实验报告序号：姓名：学号：成绩一、实验目的：1、编程实现简单可靠的数据传输GBN协议，模拟可靠数据传输2、理解TCP协议可靠传输的差错检测、重传、累计确认、定时器的可靠传输策略。

二、实验指导：参考教材。

三、实验要求：编程实现一个GBN传输协议，采用编程语言不限，要求能将发送――接收流程以及处理方法表现出来.附源代码及注释并附上实验结果截图。

#include <stdio.h>#define BIDIRECTIONAL 0 /* change to 1 if you're doing extra credit *//* and write a routine called B_output */ 如果你想做酷文解码和写一个程序叫B_output就改变值为0/* a "msg" is the data unit passed from layer 5 (teachers code) to layer */ /* 4 (students' code). It contains the data (characters) to be delivered */ /* to layer 5 via the students transport level protocol entities. */ struct msg是从第五层传送到第四层的数据单元，它包含了通过传送层协议被传送到第五层的数据{char data[20];};/* a packet is the data unit passed from layer 4 (students code) to layer */ /* 3 (teachers code). Note the pre-defined packet structure, which all */ /* students must follow. */ 一个数据包从第四层传送到第三层的数据单元，声明提前定义的学生必须遵守的数据包结构struct pkt/*定义结构体*/ {int seqnum;int acknum;int checksum;char payload[20];};/********* STUDENTS WRITE THE NEXT SEVEN ROUTINES *********/#define WINDOWSIZE 8#define MAXBUFSIZE 50#define RTT 15.0#define NOTUSED 0#define NACK -1#define TRUE 1#define FALSE 0#define A 0#define B 1int expectedseqnum; /* expected sequence number at receiver side */ 在接收端预期序列号int nextseqnum; /* next sequence number to use in sender side */ 下一个序号在发送方使用int base; /* the head of sender window */发送方窗口的负责人struct pkt winbuf[WINDOWSIZE]; /* window packets buffer */窗口包缓冲区int winfront,winrear; /* front and rear points of window buffer */ 前后点的窗口缓冲区int pktnum; /* packet number of window buffer */包数量的窗口缓冲区struct msg buffer[MAXBUFSIZE]; /* sender message buffer */发送消息缓冲区int buffront,bufrear; /* front and rear pointers of buffer */前方和后方的缓冲区的指针int msgnum; /* message number of buffer */消息数量的缓冲int packet_lost =0;int packet_corrupt=0;int packet_sent =0;int packet_correct=0;int packet_resent =0;int packet_timeout=0;void ComputeChecksum(packet)//计算校验和struct pkt *packet;{int checksum;int i;checksum = packet->seqnum;checksum = checksum + packet->acknum;for ( i=0; i<20; i++ )checksum = checksum + (int)(packet->payload[i]);checksum = 0-checksum;packet->checksum = checksum;}//检查是否出错int CheckCorrupted(packet)struct pkt packet;{int checksum;int i;checksum = packet.seqnum;checksum = checksum + packet.acknum;for ( i=0; i<20; i++ )checksum = checksum + (int)(packet.payload[i]);if ( (packet.checksum+checksum) == 0 )return (FALSE);elsereturn (TRUE);}//A端向外发送数据/* called from layer 5, passed the data to be sent to other side */A_output(message)来自第五层，通过数据派往另一边struct msg message;{int i;struct pkt sendpkt;/* if window is not full */if ( nextseqnum < base+WINDOWSIZE ) {printf("----A: New message arrives, send window is not full, send new messge to layer3!\n");/* create packet */如果窗口没有满sendpkt.seqnum = nextseqnum;sendpkt.acknum = NOTUSED;for ( i=0; i<20 ; i++ )sendpkt.payload[i] = message.data[i];/* computer checksum */计算机校验和ComputeChecksum (&sendpkt);/* send out packet */发送数据包tolayer3 (A, sendpkt);/* copy the packet to window packet buffer */复制包窗口包缓冲区winrear = (winrear+1)%WINDOWSIZE;pktnum ++;winbuf[winrear] = sendpkt;for (i=0; i<20; i++)winbuf[winrear].payload[i]= sendpkt.payload[i];/* if it is the first packet in window, start timeout */如果第一个包在窗口,开始超时if ( base == nextseqnum ) {starttimer(A,RTT);printf("----A: start a new timer!\n");}/* update state variables */更新状态变量nextseqnum = nextseqnum+1;}/* if window is full */如果窗口已满else {printf("----A: New message arrives, send window is full,");/* if buffer full, give up and exit*/if ( msgnum == MAXBUFSIZE) {printf (" Error: Sender buffer is full! \n");exit (1);}/* otherwise, buffer the message */ 否则,缓冲消息else {printf("buffer new message!\n");bufrear = (bufrear+1) % MAXBUFSIZE;for (i=0; i<20; i++)buffer[bufrear].data[i] = message.data[i];msgnum ++;}}}//B端向外发送数据B_output(message) /* need be completed only for extra credit */struct msg message;{}/* called from layer 3, when a packet arrives for layer 4 */A_input(packet)struct pkt packet;{struct pkt sendpkt;int i;/* if received packet is not corrupted and ACK is received */ 如果收到的数据包并没有破坏和收到ACK应答if ( (CheckCorrupted(packet) == FALSE) && (packet.acknum != NACK) ) {printf("----A: ACK %d is correctly received,",packet.acknum);packet_correct++;/* delete the acked packets from window buffer */删除ack数据包从窗口缓冲区winfront = (winfront+(packet.acknum+1-base)) % WINDOWSIZE;pktnum = pktnum - (packet.acknum+1-base);/* move window base */ 移动窗口base = packet.acknum+1;stoptimer(A);if ( base < nextseqnum) {starttimer(A,RTT);printf ("send new packets!\n");}/* if buffer is not empty, send new packets */ 如果缓冲区不是空的,发送新的包while ( (msgnum!=0) && (nextseqnum<base+WINDOWSIZE) ) {/* create packet */创建包sendpkt.seqnum = nextseqnum;sendpkt.acknum = NOTUSED;buffront = (buffront+1) % MAXBUFSIZE;for ( i=0; i<20 ; i++ )sendpkt.payload[i] = buffer[buffront].data[i];/* computer checksum */计算机校验和ComputeChecksum (&sendpkt);/* if it is the first packet in window, start timeout */如果它是第一个包在窗口,开始超时if ( base == nextseqnum ){starttimer(A,RTT);printf ("send new packets!\n");}/* send out packet */发送数据包tolayer3 (A, sendpkt);/* copy the packet to window packet buffer */复制包窗口包缓冲区winrear = (winrear+1)%WINDOWSIZE;winbuf[winrear] = sendpkt;pktnum ++;/* update state variables */更新状态变量nextseqnum = nextseqnum+1;/* delete message from buffer */删除消息从缓冲区msgnum --;}}elseprintf ("----A: NACK is received, do nothing!\n");}/* called when A's timer goes off */称当一个的计时器响起A_timerinterrupt(){int i;printf("----A: time out,resend packets!\n");/* start timer */开始按时器starttimer(A,RTT);/* resend all packets not acked */for ( i=1; i<=pktnum; i++ ) {packet_resent++;tolayer3(A,winbuf[(winfront+i)%WINDOWSIZE]);}}/* the following routine will be called once (only) before any other *//* entity A routines are called. You can use it to do any initialization */A_init(){base = 0;nextseqnum = 0;buffront = 0;bufrear = 0;msgnum = 0;winfront = 0;winrear = 0;pktnum = 0;}/* Note that with simplex transfer from a-to-B, there is no B_output() *//* called from layer 3, when a packet arrives for layer 4 at B*/B_input(packet)//B接收数据包struct pkt packet;{struct pkt sendpkt;int i;/* if not corrupted and received packet is in order */如果没有破坏和接收数据包 if ( (CheckCorrupted(packet) == FALSE) && (packet.seqnum == expectedseqnum)){ printf("----B: packet %d is correctly received, send ACK!\n",packet.seqnum);/* send an ACK for the received packet */发送ACK数据包的响应/* create packet */创建包sendpkt.seqnum = NOTUSED;sendpkt.acknum = expectedseqnum;for ( i=0; i<20 ; i++ )sendpkt.payload[i] = '0';/* computer checksum */计算机校验和ComputeChecksum (&sendpkt);/* send out packet */发送数据包tolayer3 (B, sendpkt);/* update state variables */更新状态变量expectedseqnum = expectedseqnum+1;/* deliver received packet to layer 5 */收到第5层的包tolayer5(B,packet.payload);}/* otherwise, discard the packet and send a NACK */否则,丢弃封包和发送NACKelse {printf("----B: packet %d is corrupted or not I expects, send NACK!\n",packet.seqnum);/* create packet */sendpkt.seqnum = NOTUSED;sendpkt.acknum = NACK;for ( i=0; i<20 ; i++ )sendpkt.payload[i] = '0';/* computer checksum */ComputeChecksum (&sendpkt);/* send out packet */tolayer3 (B, sendpkt);}}/* called when B's timer goes off */B时调用计时器响起B_timerinterrupt(){}/* the following rouytine will be called once (only) before any other *//* entity B routines are called. You can use it to do any initialization */B_init(){expectedseqnum = 0;}/********************************************************************************** NETWORK EMULATION CODE STARTS BELOW ***********The code below emulates the layer 3 and below network environment:- emulates the tranmission and delivery (possibly with bit-level corruption and packet loss) of packets across the layer 3/4 interface- handles the starting/stopping of a timer, and generates timerinterrupts (resulting in calling students timer handler).- generates message to be sent (passed from later 5 to 4)THERE IS NOT REASON THAT ANY STUDENT SHOULD HAVE TO READ OR UNDERSTANDTHE CODE BELOW. YOU SHOLD NOT TOUCH, OR REFERENCE (in your code) ANYOF THE DATA STRUCTURES BELOW. If you're interested in how I designedthe emulator, you're welcome to look at the code - but again, you should have to, and you defeinitely should not have to modify******************************************************************/struct event {float evtime; /* event time */事件时间int evtype; /* event type code */事件类型的代码int eventity; /* entity where event occurs */实体在事件发生struct pkt *pktptr; /* ptr to packet (if any) assoc w/ this event */struct event *prev;struct event *next;};struct event *evlist = NULL; /* the event list */事件列表/* possible events: */#define TIMER_INTERRUPT 0#define FROM_LAYER5 1#define FROM_LAYER3 2#define OFF 0#define ON 1#define A 0#define B 1int TRACE = 1; /* for my debugging */int nsim = 0; /* number of messages from 5 to 4 so far */消息数量从5到4到目前为止int nsimmax = 0; /* number of msgs to generate, then stop */数量的短信息来生成,然后停止float time = 0.000;float lossprob; /* probability that a packet is dropped */一个包被删除的概率float corruptprob; /* probability that one bit is packet is flipped */ 这一点是包翻转的概率float lambda; /* arrival rate of messages from layer 5 */消息从第5层的到达率int ntolayer3; /* number sent into layer 3 */号码发送到第三层int nlost; /* number lost in media */号码丢失int ncorrupt; /* number corrupted by media*/号码败坏main(){struct event *eventptr;struct msg msg2give;struct pkt pkt2give;int i,j;char c;init();A_init();B_init();while (1){eventptr = evlist; /* get next event to simulate */获得下一个事件来模拟if (eventptr==NULL)goto terminate;evlist = evlist->next; /* remove this event from event list */获得下一个事件来模拟if (evlist!=NULL)evlist->prev=NULL;if (TRACE>=2){printf("\nEVENT time: %f,",eventptr->evtime);printf(" type: %d",eventptr->evtype);if (eventptr->evtype==0)printf(", timerinterrupt ");else if (eventptr->evtype==1)printf(", fromlayer5 ");elseprintf(", fromlayer3 ");printf(" entity: %d\n",eventptr->eventity);}time = eventptr->evtime; /* update time to next event time */更新时间下一个事件的时间if (nsim==nsimmax)break; /* all done with simulation */所有完成模拟if (eventptr->evtype == FROM_LAYER5 ){generate_next_arrival(); /* set up future arrival */建立未来响应/* fill in msg to give with string of same letter */ 填写msg给一系列相同的字母j = nsim % 26;for (i=0; i<20; i++)msg2give.data[i] = 97 + j;if (TRACE>2) {printf(" MAINLOOP: data given to student: ");for (i=0; i<20; i++)printf("%c", msg2give.data[i]);printf("\n");}nsim++;if (eventptr->eventity == A)A_output(msg2give);elseB_output(msg2give);}else if (eventptr->evtype == FROM_LAYER3){pkt2give.seqnum = eventptr->pktptr->seqnum;pkt2give.acknum = eventptr->pktptr->acknum;pkt2give.checksum = eventptr->pktptr->checksum;for (i=0; i<20; i++)pkt2give.payload[i] = eventptr->pktptr->payload[i];if (eventptr->eventity ==A) /* deliver packet by calling */交付数据包通过调用A_input(pkt2give); /* appropriate entity */适当的实体elseB_input(pkt2give);free(eventptr->pktptr); /* free the memory for packet */释放包}else if (eventptr->evtype == TIMER_INTERRUPT){if (eventptr->eventity == A)A_timerinterrupt();elseB_timerinterrupt();}else{printf("INTERNAL PANIC: unknown event type \n");}free(eventptr);}terminate:printf(" Simulator terminated at time %f\n after sending %d msgs from layer5\n",time,nsim);printf(" correctly sent pkts: %d \n", packet_correct);printf(" resent pkts: %d \n", packet_resent);}init() /* initialize the simulator */初始化模拟器{int i;float sum, avg;float jimsrand();FILE *fp;fp = fopen ("parameter.txt","r");printf("----- Stop and Wait Network Simulator Version 1.1 -------- \n\n"); printf("Enter the number of messages to simulate: ");fscanf(fp,"%d",&nsimmax);//scanf("%d",&nsimmax);printf("Enter packet loss probability [enter 0.0 for no loss]:");fscanf(fp, "%f",&lossprob);//scanf("%f",&lossprob);printf("Enter packet corruption probability [0.0 for no corruption]:");fscanf(fp,"%f",&corruptprob);//scanf("%f",&corruptprob);printf("Enter average time between messages from sender's layer5 [ > 0.0]:"); fscanf(fp,"%f",&lambda);//scanf("%f",&lambda);printf("Enter TRACE:");fscanf(fp,"%d",&TRACE);//scanf("%d",&TRACE);srand(9999); /* init random number generator */随机数发生器sum = 0.0; /* test random number generator for students */测试随机数字生成器for (i=0; i<1000; i++)sum=sum+jimsrand(); /* jimsrand() should be uniform in [0,1] */jimsrand()应该统一在[0,1]avg = sum/1000.0;if (avg < 0.25 || avg > 0.75) {printf("It is likely that random number generation on your machine\n" );printf("is different from what this emulator expects. Please take\n");printf("a look at the routine jimsrand() in the emulator code. Sorry. \n"); exit(1);}ntolayer3 = 0;nlost = 0;ncorrupt = 0;time=0.0; /* initialize time to 0.0 */初始化时间0.0generate_next_arrival(); /* initialize event list */初始化事件列表}/****************************************************************************//* jimsrand(): return a float in range [0,1]. The routine below is used to *//* isolate all random number generation in one location. We assume that the*//* system-supplied rand() function return an int in therange [0,mmm] *//****************************************************************************/ float jimsrand(){double mmm = 65535; /* largest int 2147483647 65535 - MACHINE DEPENDENT!!!!!!!! */最大的int 2147483647 65535 -依赖机器float x; /* individual students may need to change mmm */x = rand()/mmm; /* x should be uniform in [0,1] */x应该统一在[0,1] return(x);}/********************* EVENT HANDLINE ROUTINES ****2147483647***//* The next set of routines handle the event list *//*****************************************************/generate_next_arrival(){double x,log(),ceil();struct event *evptr;char *malloc();float ttime;int tempint;if (TRACE>2)printf(" GENERATE NEXT ARRIVAL: creating new arrival\n");x = lambda*jimsrand()*2; /* x is uniform on [0,2*lambda] */x应该统一在[0,1] /* having mean of lambda */平均lambdaevptr = (struct event *)malloc(sizeof(struct event));evptr->evtime = time + x;evptr->evtype = FROM_LAYER5;if (BIDIRECTIONAL && (jimsrand()>0.5) )evptr->eventity = B;elseevptr->eventity = A;insertevent(evptr);}insertevent(p)struct event *p;{struct event *q,*qold;if (TRACE>2){printf(" INSERTEVENT: time is %lf\n",time);printf(" INSERTEVENT: future time will be %lf\n",p->evtime);}q = evlist; /* q points to front of list in which p struct inserted */问点前的列表,在其中p struct插入if (q==NULL){ /* list is empty */清空列表evlist=p;p->next=NULL;p->prev=NULL;}else{for (qold = q; q !=NULL && p->evtime > q->evtime; q=q->next)qold=q;if (q==NULL){ /* end of list */结束列表qold->next = p;p->prev = qold;p->next = NULL;}else if (q==evlist){ /* front of list */前列表p->next=evlist;p->prev=NULL;p->next->prev=p;evlist = p;}else{ /* middle of list */中列表p->next=q;p->prev=q->prev;q->prev->next=p;q->prev=p;}}}printevlist(){struct event *q;int i;printf("--------------\nEvent List Follows:\n");for(q = evlist; q!=NULL; q=q->next) {printf("Event time: %f, type: %d entity: %d\n",q->evtime,q->evtype,q->eventity);}printf("--------------\n");}/********************** Student-callable ROUTINES ***********************//* called by students routine to cancel a previously-started timer */stoptimer(AorB)int AorB; /* A or B is trying to stop timer */阻止定时器{struct event *q,*qold;if (TRACE>2)printf(" STOP TIMER: stopping timer at %f\n",time);/* for (q=evlist; q!=NULL && q->next!=NULL; q = q->next) */for (q=evlist; q!=NULL ; q = q->next)if ( (q->evtype==TIMER_INTERRUPT && q->eventity==AorB) ) {/* remove this event */删除此事件if (q->next==NULL && q->prev==NULL)evlist=NULL; /* remove first and only event on list */删除第一个也是唯一的活动列表else if (q->next==NULL) /* end of list - there is one in front */后的列表q->prev->next = NULL;else if (q==evlist) { /* front of list - there must be event after */前列表q->next->prev=NULL;evlist = q->next;}else { /* middle of list */中列表q->next->prev = q->prev;q->prev->next = q->next;}free(q);return;}printf("Warning: unable to cancel your timer. It wasn't running.\n");}starttimer(AorB,increment)int AorB; /* A or B is trying to stop timer */时间停止器float increment;{struct event *q;struct event *evptr;char *malloc();if (TRACE>2)printf(" START TIMER: starting timer at %f\n",time);/* be nice: check to see if timer is already started, if so, then warn */如果计时器已经启动,那么警告/* for (q=evlist; q!=NULL && q->next!=NULL; q = q->next) */for (q=evlist; q!=NULL ; q = q->next)if ( (q->evtype==TIMER_INTERRUPT && q->eventity==AorB) ) {printf("Warning: attempt to start a timer that is already started\n");return;}/* create future event for when timer goes off */创造未来的事件,当计时器响起evptr = (struct event *)malloc(sizeof(struct event));evptr->evtime = time + increment;evptr->evtype = TIMER_INTERRUPT;evptr->eventity = AorB;insertevent(evptr);}/************************** TOLAYER3 ***************/tolayer3(AorB,packet)int AorB; /* A or B is trying to stop timer */A或B是试图阻止定时器struct pkt packet;{struct pkt *mypktptr;struct event *evptr,*q;char *malloc();float lastime, x, jimsrand();int i;ntolayer3++;/* simulate losses: */if (jimsrand() < lossprob){nlost++;if (TRACE>0)printf(" TOLAYER3: packet being lost\n");return;}/* make a copy of the packet student just gave me since he/she may decide */ /* to do something with the packet after we return back to him/her */mypktptr = (struct pkt *)malloc(sizeof(struct pkt));mypktptr->seqnum = packet.seqnum;mypktptr->acknum = packet.acknum;mypktptr->checksum = packet.checksum;for (i=0; i<20; i++)mypktptr->payload[i] = packet.payload[i];if (TRACE>2){printf(" TOLAYER3: seq: %d, ack %d, check: %d ", mypktptr->seqnum, mypktptr->acknum, mypktptr->checksum);for (i=0; i<20; i++)printf("%c",mypktptr->payload[i]);printf("\n");}/* create future event for arrival of packet at the other side */创建未来事件evptr = (struct event *)malloc(sizeof(struct event));evptr->evtype = FROM_LAYER3; /* packet will pop out from layer3 */从layer3数据包将弹出evptr->eventity = (AorB+1) % 2; /* event occurs at other entity */事件发生在其他实体evptr->pktptr = mypktptr; /* save ptr to my copy of packet */复制ptr /* finally, compute the arrival time of packet at the other end.最后,计算到达时间的包在另一端。