《视频处理与传输》实验报告材料

西南科技大学《视频处理与传输》实验报告

题目：实验三

设计者：

专业班级：

学号：

指导教师：

2014年12月23日

一、实验目的

1．了解和认识TCP的相关内容；

2．学习和掌握TCP模块的C语言编程；

3．尝试用C语言写出TCP有限状态机的实现函数

二、实验内容

TCP（Transmission Control Protocol 传输控制协议）是一种面向连接（连接导向）的、可靠的、基于IP的传输层协议，由IETF的RFC 793说明（specified）。TCP在IP报文的协议号是6。

设计一个C程序实现TCP。

三、实验过程

1、创建一头文件，包括C语言实现TCP的所有常量。

2、完成struct语句，它是TCP首部的说明语句。

3、完成struct语句，它是TCP报文的说明语句。

4、用C语言写出TCP有限状态机的函数。

四、实验结果及分析

1、头文件

#ifndef _TCP_H

#define _TCP_H

#include

#include

#include

#include

#include

#include

#include

#include

#define SERVERPORT 3333 /*服务器监听端口号*/

#define BACKLOG 10 /*最大同时连接请求数*/

#endif

2、TCP首部：

struct TCP_Header{

u_char byte1;

u_char byte2;

u_char byte3;

u_char byte4;

}ip_address; /* IPv4 首部 */

struct TCP_header{

unsigned short SPortAddr

u_char ver_ihl; // 版本 (4 bits) + 首部长度 (4 bits) == 8 u_char tos; // 服务类型(Type of service)

u_short tlen; // 总长(Total length)

u_short identification; // 标识(Identification)

u_short flags_fo;

// 标志位(Flags) (3 bits) + 段偏移量(Fragment offset) (13 bits)

u_char ttl; // 存活时间(Time to live)

u_char proto; // 协议(Protocol)

u_short crc; // 首部校验和(Header checksum)

ip_address saddr; // 源地址(Source address)

ip_address daddr; // 目的地址(Destination address)

u_int op_pad; // 选项与填充(Option + Padding)

}ip_header;

3、struct TCP Packet

{

struct TCP_Header tcpHeader;

uint16 source; /* Source port */

uint16 dest; /* Destination port */

int32 seq; /* Sequence number */

int32 ack; /* Acknowledgment number */

uint16 wnd; /* Receiver flow control window */

uint16 checksum; /* Checksum */

uint16 up; /* Urgent pointer */

uint16 mss; /* Optional max seg size */

uint8 wsopt; /* Optional window scale factor */

uint32 tsval; /* Outbound timestamp */

uint32 tsecr; /* Timestamp echo field */

struct {

unsigned int congest:1; /* Echoed IP congestion experienced bit */ unsigned int urg:1;

unsigned int ack:1;

unsigned int psh:1;

unsigned int rst:1;

unsigned int syn:1;

unsigned int fin:1;

unsigned int mss:1; /* MSS option present */

unsigned int wscale:1; /* Window scale option present */

unsigned int tstamp:1; /* Timestamp option present */

tcpData; } };

4、TCP有限状态机

#include "global.h"

#include "timer.h"

#include "mbuf.h"

#include "netuser.h"

#include "internet.h"

#include "tcp.h"

#include "ip.h"

void

tcp_output(tcb)

register struct tcb *tcb;

{

struct mbuf *dbp; /* Header and data buffer pointers */

struct tcp seg; /* Local working copy of header */

uint16 ssize; /* Size of current segment being sent, * including SYN and FIN flags */

uint16 dsize; /* Size of segment less SYN and FIN */

int32 usable; /* Usable window */

int32 sent; /* Sequence count (incl SYN/FIN) already * in the pipe but not yet acked */

int32 rto; /* Retransmit timeout setting */

if(tcb == NULL)

return;

switch(tcb->state){

case TCP_LISTEN: case TCP_CLOSED:

return; /* Don't send anything */

}

for(;;){

memset(&seg,0,sizeof(seg)); /* Compute data already in flight */ sent = tcb->snd.ptr - tcb->snd.una;

usable = min(tcb->snd.wnd,tcb->cwind);

if(usable > sent)

usable -= sent; /* Most common case */

else if(usable == 0 && sent == 0)

usable = 1; /* Closed window probe */

else usable = 0; /* Window closed or shrunken */

ssize = min(tcb->sndcnt - sent,usable);

ssize = min(ssize,tcb->mss);

if(!tcb->flags.force && sent != 0 && ssize < tcb->mss && !(tcb->state == TCP_FINWAIT1 && ssize == tcb->sndcnt-sent))

{ ssize = 0; }

if(!tcb->flags.synack && !Tcp_syndata){

if(tcb->snd.ptr == tcb->iss)

ssize = min(1,ssize); /* Send only SYN */

else ssize = 0; /* Don't send anything */ }

if(tcb->flags.force && tcb->snd.ptr != tcb->snd.nxt)

ssize = 0;

if(ssize == 0 && !tcb->flags.force)

break; /* No need to send anything */

tcb->flags.force = 0;/* Only one forced segment! */

seg.source = tcb->conn.local.port;

seg.dest = tcb->conn.remote.port;

seg.flags.ack = 1; /* Every state except TCP_SYN_SENT */

seg.flags.congest = tcb->flags.congest;

if(tcb->state == TCP_SYN_SENT)

seg.flags.ack = 0; /* Haven't seen anything yet */

dsize = ssize;

if(!tcb->flags.synack && tcb->snd.ptr == tcb->iss){ /* Send SYN

*/ seg.flags.syn = 1;

dsize--; /* SYN isn't really in snd queue */ /* Also send MSS,

wscale and tstamp (if OK) */

seg.mss = Tcp_mss;

seg.flags.mss = 1;

seg.wsopt = DEF_WSCALE;

seg.flags.wscale = 1;

if(Tcp_tstamps){

seg.flags.tstamp = 1;

seg.tsval = msclock(); } }

if(ssize == 0)

seg.seq = tcb->snd.nxt;

else seg.seq = tcb->snd.ptr;

tcb->last_ack_sent = seg.ack = tcb->rcv.nxt;

if(seg.flags.syn || !tcb->flags.ws_ok)

seg.wnd = tcb->rcv.wnd;

else seg.wnd = tcb->rcv.wnd >> tcb->rcv.wind_scale;

dbp = ambufw(TCP_HDR_PAD+dsize);

dbp->data += TCP_HDR_PAD; /* Allow room for other hdrs */ If(dsize != 0){

int32 offset;

offset = sent;

if(!tcb->flags.synack && sent != 0)

offset--;

dbp->cnt = extract(tcb->sndq,(uint16)offset,dbp->data,dsize);

if(dbp->cnt != dsize){ /* We ran past the end of the send queue;

* send a FIN */

seg.flags.fin = 1;

dsize--; } }

if(dsize != 0 && sent + ssize == tcb->sndcnt)

seg.flags.psh = 1;

if(tcb->snd.ptr < tcb->snd.nxt)

tcb->resent += min(tcb->snd.nxt - tcb->snd.ptr,ssize);

tcb->snd.ptr += ssize;

if(seq_gt(tcb->snd.ptr,tcb->snd.nxt))

tcb->snd.nxt = tcb->snd.ptr;

if(tcb->flags.ts_ok && seg.flags.ack){

seg.flags.tstamp = 1;

seg.tsval = msclock();

seg.tsecr = tcb->ts_recent; } /* Generate TCP header, compute checksum, and link in data */ htontcp(&seg,&dbp,tcb->conn.local.address,

tcb->conn.remote.address)

if(ssize != 0){ /* Set round trip timer. */

rto = backoff(tcb->backoff) * (4 * tcb->mdev + tcb->srtt);

set_timer(&tcb->timer,max(MIN_RTO,rto));

if(!run_timer(&tcb->timer))

start_timer(&tcb->timer); /* If round trip timer isn't running, start it */

if(tcb->flags.ts_ok|| !tcb->flags.rtt_run){

tcb->flags.rtt_run = 1;

tcb->rtt_time = msclock();

tcb->rttseq = tcb->snd.ptr;

tcb->rttack = tcb->snd.una; } } if(tcb->flags.retran)

tcpRetransSegs++;

else

tcpOutSegs++;

ip_send(tcb->conn.local.address,tcb->conn.remote.address,

TCP_PTCL,tcb->tos,0,&dbp,len_p(dbp),0,0); } }

五、实验存在的问题及思考

本次实验的主要内容是了解TCP协议，并通过实验编写C程序语言实现对tcp

协议的检验。实验过程中对于TCP协议的内容了解不全面，对于它的程序编写不

熟悉，许多问题不能得到解决。本次实验让我们了解到自己对于理论知识学习的不足以及实践能力的不足，所以在以后的学习生活中我需要更努力地读书和实践。还有的就是采纳那些积极有利的知识或信息这对即将踏入社会的我们来说是宝贵的经验。

六、参考文献及出处

1．冯先成，李德骏主编. 计算机网络及应用. 武汉市：华中科技大学出版社, 2011.07.