计算机网络原理实验七实验报告.doc

实验七、传输层可靠传输协GBN编程实验报告序号： 姓名： 学号： 成绩 指导老师： 一、实验目的：1、通过编写实现一个简单可靠的数据传输协议GBN的发送和接收代码，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传输协议的发送方和接收方两程序，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.附源代码及注释通过本次实验，了解了GBN传输协议的相关知识，因为实验代码是由三部分组成，所以用Studio做实验时，要建立3个文件，一个是头文件，存放gbn.h, 另外2个是源文件，分别存放gbn.c 和 gbn-cs.c，然后再启动调试。实验代码通过查阅资料很容易理解，但是怎么实现这个程序对我来说是个问题。后来我把程序分了3部分，一个头文件和两个源文件，通过visual studio可以良好的运行，以下为老师附带代码的运行结果一、 GBN.h#pragma once#include /基础功能模块的数据结构声明#define BIDIRECTIONAL 1 /* change to 1 if youre doing extra credit and write a routine called B_output */* 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 char data20;/* 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. */struct pktint seqnum;int acknum;int checksum;char payload20;#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 1/网络仿真部分数据结构声明*struct eventfloat evtime; /* event time */int evtype; /* event type code */int eventity; /* entity where event occurs */struct pkt *pktptr; /* ptr to packet (if any) assoc w/ this event */struct event *prev;struct event *next; ;/* possible events: */#define TIMER_INTERRUPT 0 #define FROM_LAYER5 1#define FROM_LAYER3 2#define OFF 0#define ON 1/基础功能模块的函数声明*void ComputeChecksum(struct pkt *packet);/计算校验和int CheckCorrupted(struct pkt packet);/检查数据是否出错void A_output( struct msg message);/A端向外发送数据void A_input(struct pkt packet);/A端接收数据void A_timerinterrupt();/A计时器超时void A_init();/A端初始化void B_output(struct msg message); void B_input(struct pkt packet);void B_timerinterrupt();void B_init();/网络仿真部分的函数声明*void init(); /初始化仿真器float jimsrand();/随机数发生器0,1/处理事件列表部分的函数声明*void generate_next_arrival();/产生下一个到达的分组void insertevent(struct event *p);/向事件列表中插入一条新的事件void printevlist();/打印事件列表/*/*计时器模块*void stoptimer(int);/停止计时器void starttimer(int,float);/启动计时器/*/*网络各层之间传送模块*void tolayer3(int AorB,struct pkt packet);/向第3层发送信息void tolayer5(int AorB,char datasent20);/向第5层发送信息二、 GBN.c#include GBN.h#include #include #include extern int TRACE = 1; /* for my debugging */extern int nsim = 0; /* number of messages from 5 to 4 so far */ extern int nsimmax = 0; /* number of msgs to generate, then stop */extern float time = 0.000;float lossprob; /* probability that a packet is dropped */float corruptprob; /* probability that one bit is packet is flipped */float lambda; /* arrival rate of messages from layer 5 */ int ntolayer3; /* number sent into layer 3 */static int nlost = 0; /* number lost in media */static int ncorrupt = 0; /* number corrupted by media*/static int expectedseqnum = 0; /* expected sequence number at receiver side */static int nextseqnum; /* next sequence number to use in sender side */static int base; /* the head of sender window */struct pkt winbufWINDOWSIZE; /* window packets buffer */static int winfront,winrear; /* front and rear points of window buffer */static int pktnum;/* packet number of window buffer */struct msg bufferMAXBUFSIZE; /* sender message buffer */int buffront,bufrear; /* front and rear pointers of buffer */static int msgnum;/* message number of buffer */int packet_lost =0; int packet_corrupt=0;int packet_sent =0;extern int packet_correct=0;extern int packet_resent =0;int packet_timeout=0;extern struct event *evlist = NULL; /* the event list */计算校验和void ComputeChecksum( struct pkt *packet) int checksum;int i;checksum = packet-seqnum;checksum = checksum + packet-acknum;for ( i=0; ipayloadi);checksum = 0-checksum;packet-checksum = checksum;/检查是否出错int CheckCorrupted(struct pkt packet)int checksum;int i;checksum = packet.seqnum;checksum = checksum + packet.acknum;for ( i=0; i20; i+ ) checksum = checksum + (int)(packet.payloadi);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 */void A_output(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 */sendpkt.seqnum = nextseqnum;sendpkt.acknum = NOTUSED;for ( i=0; i20 ; i+ ) sendpkt.payloadi = message.datai;/* computer checksum */ComputeChecksum (&sendpkt); /* send out packet */ tolayer3 (A, sendpkt); /* copy the packet to window packet buffer */ winrear = (winrear+1)%WINDOWSIZE; pktnum +; winbufwinrear = sendpkt; for (i=0; i20; i+) winbufwinrear.payloadi= sendpkt.payloadi; /* update state variables */ nextseqnum = nextseqnum+1; starttimer(A,RTT); B_input(sendpkt); A_input(sendpkt);/* if window is full */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 */ else printf(buffer new message!n); bufrear = (bufrear+1) % MAXBUFSIZE; for (i=0; i20; i+) bufferbufrear.datai = message.datai; msgnum +; /B端向外发送数据/* called from layer 5, passed the data to be sent to other side */void B_output(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 */sendpkt.seqnum = nextseqnum;sendpkt.acknum = NOTUSED;for ( i=0; i20 ; i+ ) sendpkt.payloadi = message.datai;/* computer checksum */ComputeChecksum (&sendpkt); /* send out packet */ tolayer3 (A, sendpkt);A_input(sendpkt); /* copy the packet to window packet buffer */ winrear = (winrear+1)%WINDOWSIZE; pktnum +; winbufwinrear = sendpkt; for (i=0; i20; i+) winbufwinrear.payloadi= sendpkt.payloadi; /* if it is the first packet in window, start timeout */ /if ( base = nextseqnum ) / /starttimer(A,RTT); /printf(-A: start a new timer!n); / /* update state variables */ nextseqnum = nextseqnum+1;/* if window is full */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 */ else printf(buffer new message!n); bufrear = (bufrear+1) % MAXBUFSIZE; for (i=0; i20; i+) bufferbufrear.datai = message.datai; msgnum +; /A端接收数据void A_input(struct pkt packet)struct pkt sendpkt;int i;/* if received packet is not corrupted and ACK is received */ 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 */ winfront = (winfront+(packet.acknum+1-base) % WINDOWSIZE; pktnum = pktnum - (packet.acknum+1-base); /* move window base */ base = packet.acknum+1; stoptimer(A); if ( base nextseqnum) /starttimer(A,RTT); printf (nnnsend new packets!); /* if buffer is not empty, send new packets */ while ( (msgnum!=0) & (nextseqnumbase+WINDOWSIZE) )/* create packet */ sendpkt.seqnum = nextseqnum; sendpkt.acknum = NOTUSED; buffront = (buffront+1) % MAXBUFSIZE; for ( i=0; i20 ; i+ ) sendpkt.payloadi = bufferbuffront.datai; /* computer checksum */ ComputeChecksum (&sendpkt); /* if it is the first packet in window, start timeout */ if ( base = nextseqnum )/starttimer(A,RTT);printf (send new packets!n); /* send out packet */ tolayer3 (A, sendpkt); /* copy the packet to window packet buffer */ winrear = (winrear+1)%WINDOWSIZE; winbufwinrear = sendpkt; pktnum +; /* update state variables */nextseqnum = nextseqnum+1; /* delete message from buffer */msgnum -;else printf (-A: NACK is received, do nothing!n);/B端接收数据*一定要调用这个/* 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*/void B_input(struct pkt packet) struct pkt sendpkt;int i;/* if not corrupted and received packet is in order */if ( (CheckCorrupted(packet) = FALSE) & (packet.seqnum = expectedseqnum)printf(n-B: packet %d is correctly received, send ACK!n,packet.seqnum);/* send an ACK for the received packet */ /* create packet */ sendpkt.seqnum = NOTUSED; sendpkt.acknum = expectedseqnum; for ( i=0; i20 ; i+ )sendpkt.payloadi = 0; /* computer checksum */ ComputeChecksum (&sendpkt); /* send out packet */tolayer3 (B, sendpkt);/* update state variables */expectedseqnum = expectedseqnum+1; printf(-B:expectedseqnum = %dn,expectedseqnum); /* deliver received packet to layer 5 */ /tolayer5(B,packet.payload); /* otherwise, discard the packet and send a NACK */ elseprintf(-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; i20 ; i+ ) sendpkt.payloadi = 0; /* computer checksum */ ComputeChecksum (&sendpkt); /* send out packet */ tolayer3 (B, sendpkt); /A计时器超时/* called when As timer goes off */void A_timerinterrupt()int i;printf(-A: time out,resend packets!n);/* start timer */starttimer(A,RTT);/* resend all packets not acked */for ( i=1; i=pktnum; i+ )packet_resent+; tolayer3(A,winbuf(winfront+i)%WINDOWSIZE); /B计时器超时/* called when Bs timer goes off */void B_timerinterrupt()int i;printf(-B: time out,resend packets!n);/* start timer */starttimer(B,RTT);/* resend all packets not acked */for ( i=1; i 0.0: ); /fscanf(fp,%f,&lambda);scanf(%f,&lambda); printf(nEnter TRACE: );/fscanf(fp,%d,&TRACE);scanf(%d,&TRACE);printf(nn);srand(9999); /* init random number generator */sum = 0.0; /* test random number generator for students */for (i=0; i1000; i+)sum=sum+jimsrand(); /* jimsrand() should be uniform in 0,1 */avg = sum/1000.0; /*if(avg 0.75) printf(It is likely that random number generation on your machinen ); printf(is different from what this emulator expects. Please taken); printf(a look at the routine jimsrand() in the emulator code. Sorry. n); exit(0); */ printf(%f,avg);ntolayer3 = 0;nlost = 0;ncorrupt = 0;time=0.0; /* initialize time to 0.0 */ generate_next_arrival(); /* initialize event list */随机数发生器float jimsrand() double mmm = 2147483647; /* largest int - MACHINE DEPENDENT! */float x; /* individual students may need to change mmm */ x = rand()/mmm; /* x should be uniform in 0,1 */return(x); /*/*事件处理部分*void generate_next_arrival()double x,log(),ceil();struct event *evptr;float ttime;int tempint;/if (TRACE2)/printf(-GENERATE NEXT ARRIVAL: creating new arrivaln);x = lambda*jimsrand()*2; /* x is uniform on 0,2*lambda */ /* having mean of lambda */evptr = (struct event *)malloc(sizeof(struct event);evptr-evtime = time + x; evptr-evtype = FROM_LAYER5;if (jimsrand()eventity = A;elseevptr-eventity = B;insertevent(evptr);/向事件列表中插入一条新的事件void insertevent(struct event *p) struct event *q,*qold;if (TRACE2)/printf( INSERTEVENT: time is %lfn,time);/printf( INSERTEVENT: future time will be %lfn,p-evtime); q = evlist; /* q points to front of list in which p struct inserted */if (q=NULL)/* list is empty */ 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 */ qold-next = p; p-prev = qold; p-next = NULL;else if (q=evlist)/* front of list */ p-next=evlist; p-prev=NULL; p-next-prev=p; evlist = p;else /* middle of list */ p-next=q; p-prev=q-prev; q-prev-next=p; q-prev=p;/打印事件列表void 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: %dn,q-evtime,q-evtype,q-eventity); printf(-n);/启动计时器void starttimer(int AorB,float increment)struct event *q;struct event *evptr;if (TRACE2)printf(n-A: START TIMER: starting timer at %fn,time);/* be nice: check to see if timer is already started, if so, then warn */* 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 startedn);return;/* create future event for when timer goes off */evptr = (struct event *)malloc(sizeof(struct event);evptr-evtime = time + increment;evptr-evtype = TIMER_INTERRUPT;evptr-eventity = AorB;insertevent(evptr); /停止计时器/* called by students routine to cancel a previously-started timer */void stoptimer(int AorB) /* A or B is trying to stop timer */struct event *q,*qold;if (T