#include?
#include?
#include?

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

void?printData（char?*p?int?size）;

typedef?unsigned?char?seq_nr;
typedef?unsigned?char?frame_kind;
typedef?struct{unsigned?char?data[PKT_LEN];}?packet;
typedef?enum{network_layer_ready?physical_layer_ready?frame_arrive?data_timout?ack_timeout?chksum_error}?event_type;
typedef?enum{F?T}?mybool;

typedef?struct
{
????frame_kind?kind;?/*?frame_DATA?*/
????seq_nr?ack;
????seq_nr?seq;
????packet?info;	/*?packet?*/
	unsigned?char?padding[4];	/*?memory?space?used?for?crc?code?32?bit?*/
}?frame;

mybool?no_nak?=?T;?/*?no?nak?has?beem?yet?*/


static?void?Inc（seq_nr?*seq）
{
	*seq?=?（*seq?+?1）?%?（MAX_SEQ?+?1）;
}


static?mybool?between（seq_nr?a?seq_nr?b?seq_nr?c）
{
????/*return?T?if?a?<=?b?circulaly;?F?otherwise*/
????return?（（a?<=?b）?&&?（b?}


static?void?send（frame_kind?fk?seq_nr?frame_nr?seq_nr?frame_expected?packet?buf[]）
{
????/*?construct?frame?and?send?*/
????frame?s;?/*?tmp?variable?*/
????s.kind?=?fk;?/*?s.kind??=?data/ack/nak?*/

	if?（fk?==?frame_DATA）
		memcpy（（char*）&s.info?（char*）&buf[frame_nr?%?NR_BUFS]?PKT_LEN）;	/*?store?the?packet?*/
	
????s.seq?=?frame_nr;?/*?only?meaning?for?data?*/
????s.ack?=?（frame_expected?+?MAX_SEQ）?%?（MAX_SEQ?+?1）;

	if?（fk?==?frame_NAK）
????????no_nak?=?F;

	/*?compute?the?crc?code?the?crc?code?is?in?the?padding?memory?*/
	*（unsigned?int*）?（（unsigned?char*）&s?+?PKT_LEN?+?3）?=?crc32（（unsigned?char*）&s?PKT_LEN?+?3）;

	/*?send?the?frame?to?the?physical?layer?*/
	send_frame（（unsigned?char*）&s?sizeof（s））;

	dbg_event（“組裝之后的?!!\n“）;
	printData（（char*）&s?sizeof（s））;

	//printf（“CRC?send“）;
	//printData（s.padding4）;
	/*?warning:?short?may?not?be?2?bytes?according?to?the?computer?*/
	if?（fk?==?frame_DATA）
		dbg_frame（“Send?DATA?seq:%d?ack:%d?ID?%d\n“?s.seq?s.ack?*（short?*）（&s.info））;
	else?if?（fk?==?frame_ACK）
		dbg_frame（“Send?ACK?seq:%d\n“?s.seq）;
	else?if?（fk?==?frame_NAK）
		dbg_frame（“Send?NAK?seq:%d\n“?s.seq）;

	if?（fk?==?frame_DATA）	/*?start?the?timeout?if?timeout??repeat?transmit?*/
		start_timer（frame_nr?%?NR_BUFS?DATA_TIMER）;

????stop_ack_timer（）;?/*?no?need?for?separate?ack?frame?*/
}


void?protocol6（）
{
	int?midstop=0;
????seq_nr?ack_expected?=?0;	/*?lower?edge?of?sender‘s?window?*/
????seq_nr?next_frame_to_send?=?0;	/*?upper?edge?of?sender‘s?window?*/
????seq_nr?frame_expected?=?0;	/*?lower?edge?of?receiver‘s?window?*/
	seq_nr?too_far?=?NR_BUFS;	/*?uppder?edge?receiver‘s?window?+?1*/
????
????packet?out_buf[NR_BUFS];????/*?buffers?for?the?outbound?stream*/
????packet?in_buf[NR_BUFS];????/*?buffers?for?the?inbound?stream*/
	mybool?arrived[NR_BUFS]?=?{F};	/*?inbound?bit?map?intial?to?all?F?*/
????seq_nr?nbuffered?=?0;	/*?the?size?of?buffered?*/

	frame?r;	/*?tmp?variable?*/
????int?arg?=?MAX_SEQ?+?1;?/*?para?*/
????int?len?=?0;?/*?the?length?of?received?packet*/
	unsigned?crc_ret?=?0;
	event_type?even