#include?
#include?

#include?“protocol.h“
#include?“datalink.h“

typedef?struct{????????//frames結構定義?由5個域kind、seq、ack和info??padding
????unsigned?char?kind;???/*?frame_DATA?*/
????unsigned?char?ack;
????unsigned?char?seq;
????unsigned?char?info[PKT_LEN];?
	unsigned?int??padding;
}?frame?;??

static?int?phl_ready?=?0;????//對物理層狀態記錄
bool?no_nak?=?true;??/*?no?nak?has?been?sent?yet?*/

static?bool?between?（seq_nr?a?seq_nr?b?seq_nr?c）??/*已接受的確認應答號應該小于下一個要發送的序列號*/
{
	/*return?true?if?a?<=b?	if?（（（a?<=?b）&&（b?		return?（true）;
	else
		return?（false）;
}

static?void?put_frame（unsigned?char?*frame?int?len）?????//生成CRC-32?校驗和，并且把這32?比特校驗和附其后?
{
????*（unsigned?int?*）（frame?+?len）?=?crc32（frame?len）;??
????send_frame（frame?len?+?4）;??//函數send_frame?（）用于將內存frame?處長度為len的緩沖區塊向物理層發送為一幀
????phl_ready?=?0;??
}

static?void?send_data（seq_nr?frame_nrseq_nr?frame_expectedpacket?buffer[]）
{
????/*Construct?and?send?a?data?frame.?*/
????frame?s;

????s.kind?=?frame_DATA;
????s.seq?=?frame_nr;
????s.ack?=?（frame_expected?+?MAX_SEQ）?%（MAX_SEQ?+?1）;??/*將frame_expected-1，期望接受的是frame_expected，
	???????????????????????????????????而現在已經接收到的幀序號是frame_expected，所以捎帶確認的ACK應該是frame_expected-1?*/
???
????memcpy（s.info?&buffer[frame_nr].info?PKT_LEN）;?
????dbg_frame（“Send?DATA?%d?%d?ID?%d\n“?s.seq?s.ack?*（short?*）s.info）;

????put_frame（（unsigned?char?*）&s?3?+?PKT_LEN）;??????
????start_timer（frame_nr?DATA_TIMER）;????//啟動frame_nr號寄存器??時限DATA_TIMER
	stop_ack_timer（）;
}

static?void?send_nak_frame（seq_nr?frame_expected）??/*發送NAK*/
{
????frame?s;

????s.kind?=?frame_NAK;?????
????s.ack?=?frame_expected;????/*發送NAK?攜帶的ACK應該就是當前frame_expected幀*/???//pay?attention!
	no_nak?=?false;

????dbg_frame（“Send?NAK??%d\n“?s.ack）;
????put_frame（（unsigned?char?*）&s?2）;
	stop_ack_timer（）;
}

int?main（int?argc?char?**argv）
{
	int?len=0?arg?event;

????seq_nr?next_frame_to_send;			/*?MAX_SEQ?>?1;?used?for?outbound?stream?*/
	seq_nr?ack_expected;				/*?oldest?frame?as?yet?unacknowledged?*/
	seq_nr?frame_expected;				/*?next?frame?expected?on?inbound?stream?*/
	frame?r;							/*?scratch?variable?*/
	packet?buffer[MAX_SEQ+1];			/*?buffers?for?the?outbound?stream?*/
	seq_nr?nbuffered;					/*?#?output?buffers?currently?in?use?*/
	seq_nr?i;							/*?used?to?index?into?the?buffer?array?*/

	ack_expected?=?0;					/*?next?ack?expected?inbound?*/
	next_frame_to_send?=?0;				/*?next?frame?going?out?*/
????frame_expected?=?0;					/*?number?of?frame?expected?inbound?*/
	nbuffered?=?0;						/*?initially?no?packets?are?buffered?*/
???
	protocol_init（argc?argv）;
????disable_network_layer（）;??/*數據鏈路層在緩沖區滿等條件下無法發送分組時通過disable_network_layer（）?通知網絡層；*/?
	lprintf（“Designed?by?計科4班2組（楊培軍、吳科橋、宋瑞）程序1：GoBackNbuild:?“?__DATE__“??“__TIME__“\n“）;

	for（;;）{
		event?=?wait_for_event（&arg）;	/*?four?possibilities:?see?event_t

?屬性????????????大小?????日期????時間???名稱
-----------?---------??----------?-----??----
?????目錄???????????0??2012-03-18?22:38??GoBackN\
?????文件?????????518??2010-11-30?19:02??GoBackN\datalink.h
?????文件???????10752??2010-12-08?23:16??GoBackN\datalink.suo
?????目錄???????????0??2012-03-18?22:38??GoBackN\Debug\
?????文件????????3581??2010-12-12?19:29??GoBackN\Debug\GoBackN-A.log
?????文件????????3621??2010-12-12?19:29??GoBackN\Debug\GoBackN-B.log
?????文件??????172108??2010-12-07?13:21??GoBackN\Debug\GoBackN.exe
?????文件??????197556??2010-12-07?13:21??GoBackN\Debug\GoBackN.ilk
?????文件???????10644??2010-12-07?13:21??GoBackN\Debug\GoBackN.obj
?????文件??????220580??2010-12-07?12:58??GoBackN\Debug\GoBackN.pch
?????文件??????443392??2010-12-07?13:21??GoBackN\Debug\GoBackN.pdb
?????文件???????94208??2010-11-30?14:11??GoBackN\Debug\Protocol.dll
?????文件?????1550624??2010-12-11?00:33??GoBackN\Debug\test5a.log
?????文件?????1547472??2010-12-11?00:33??GoBackN\Debug\test5b.log
?????文件???????41984??2010-12-12?19:28??GoBackN\Debug\vc60.idb
?????文件???????53248??2010-12-07?13:21??GoBackN\Debug\vc60.pdb
?????文件????????7260??2010-12-07?13:21??GoBackN\GoBackN.cpp
?????文件????????3604??2010-12-01?13:00??GoBackN\GoBackN.dsp
?????文件?????????522??2010-12-01?12:59??GoBackN\GoBackN.dsw
?????文件???????58368??2011-10-23?21:01??GoBackN\GoBackN.ncb
?????文件???????53760??2011-10-23?21:01??GoBackN\GoBackN.opt
?????文件????????1165??2010-12-07?13:21??GoBackN\GoBackN.plg
?????文件???????13312??2010-12-08?23:16??GoBackN\GoBackN.suo
?????文件???????94208??2010-11-30?14:11??GoBackN\Protocol.dll
?????文件????????2344??2010-12-12?19:28??GoBackN\protocol.h
?????文件????????5932??2010-11-30?14:12??GoBackN\Protocol.lib