#include?
#include?

#include?“protocol.h“

#define?MAX_SEQ?15
#define?NR_BUFS?（（MAX_SEQ+1）/2）

#define?DATA_TIMER??3000???????//幀超時時間間隔
#define?ACK_TIMER?240??????????//ack的超時間隔

struct?frame?{?
????unsigned?char?kind;
????unsigned?char?ack;
????unsigned?char?seq;
????unsigned?char?data[PKT_LEN];?
????unsigned?int??padding;
};

int?no_nak=1;????????????????????????//標志是否已經發送過nak
static?int?phl_ready?=?0;
unsigned?char?oldest_frame=MAX_SEQ+1;

static?int?between（unsigned?char?aunsigned?char?bunsigned?char?c）??
//窗口函數，判斷幀號（ack號）是否在窗口內
{
???if（（（a<=b）&&（b		return?1;
	else
		return?0;

}

static?void?put_frame（unsigned?char?*frame?int?len）//加入校驗和crc
{
????*（unsigned?int?*）（frame?+?len）?=?crc32（frame?len）;
????send_frame（frame?len?+?4）;
????phl_ready?=?0;
}

static?void?send_data_frame（unsigned?char?fkunsigned?char?frame_nrunsigned?char?frame_expectedunsigned?char?buffer[NR_BUFS][PKT_LEN]）
{//發送數據幀，或ack，或nak
????struct?frame?s;
????
????s.kind?=?fk;
????s.seq?=?frame_nr;
????s.ack?=?（frame_expected?+?MAX_SEQ）?%?（MAX_SEQ?+?1）;

	if（fk==frame_DATA）
	{
		memcpy（s.data?buffer[frame_nr?%?NR_BUFS]?PKT_LEN）;//復制分組到幀內
		dbg_frame（“Send?DATA?%d?%d?ID?%d\n“?s.seq?s.ack?*（short?*）s.data）;
????????put_frame（（unsigned?char?*）&s?3?+?PKT_LEN）;???//加入校驗和
		start_timer（frame_nr%NR_BUFS?DATA_TIMER）;?????//啟動定時器
	}
	else?if（fk?==?frame_NAK）
	{
		no_nak=0;?????????????????????????????????????//下一次不再發送nak
	????put_frame（（unsigned?char?*）&s?3）;????????????
	}
	else?if（fk?==?frame_ACK）
	{
		dbg_frame（“Send?ACK??%d\n“?s.ack）;
????????put_frame（（unsigned?char?*）&s?3）;
	}
	phl_ready?=?0;
	stop_ack_timer（）;??????????????????????????//沒有必要啟動ack定時器
}

void?main（int?argc?char?**argv）
{
	int?event?arg;
????struct?frame?f;
????int?len?=?0;
????int?i;
	static?unsigned?char?ack_expected=0?next_frame_to_send=0;
	static?unsigned?char?frame_expected=0?too_far=NR_BUFS;
????static?unsigned?char?nbuffered;
	int?arrived[NR_BUFS];
	static?unsigned?char?out_buf[NR_BUFS][PKT_LEN]?in_buf[NR_BUFS][PKT_LEN];

????protocol_init（argc?argv）;?
????lprintf（“Designed?by?成賀睿&魏娜?build:?“?__DATE__“??“__TIME__“\n“）;

	for（i?=?0;?i?		arrived[i]=0;

????enable_network_layer（）;

	while（1）
	{
		event?=?wait_for_event（&arg）;
		switch?（event）
		{
			case?NETWORK_layer_READY:
				nbuffered++;?????????????????????//發送卻未被確認的幀數目++
				get_packet（out_buf[next_frame_to_send?%?NR_BUFS]）;//得到分組存入緩沖區內
				send_data_frame（frame_DATAnext_frame_to_sendframe_expectedout_buf）;
				next_frame_to_send=（next_frame_to_send?+?1）?%?（?MAX_SEQ?+?1）;
				break;

			case?PHYSICAL_layer_READY:
				phl_ready?=?1;
				break;

			case?frame_RECEIVED:
				len?=?recv_frame（（unsigned?char?*）&f?sizeof?f）;
????????????????if?（len?				{	//校驗和出錯，就發送nak請求重傳
				???	if（no_nak=