三种ARQ算法C语言.docx
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三种ARQ算法C语言
三种ARQ协议的C语言算法
一、停止等待ARQ（stop-and-waitARQ）
文件名p2.c
/*Protocol2（stop-and-wait）alsoprovidesforaone-directionalflowofdatafrom
sendertoreceiver.Thecommunicationchannelisonceagainassumedtobeerror
free,asinprotocol1.However,thistime,thereceiverhasonlyafinitebuffer
capacityandafiniteprocesingspeed,sotheprotocolmustexplicitlyprevent
thesenderfromfloodingthereceiverwithdatafasterthanitcanbehandled.*/
typedefenum{frame_arrival}event_type;
#include"protocol.h"
voidsender2（void）
{
frames;/*bufferforanoutboundframe*/
packetbuffer;/*bufferforanoutboundpacket*/
event_typeevent;/*frame_arrivalistheonlypossibility*/
while（true）{
from_network_layer（&buffer）;/*gogetsomethingtosend*/
s.info=buffer;/*copyitintosfortransmission*/
to_physical_layer（&s）;/*byebyelittleframe*/
wait_for_event（&event）;/*donotproceeduntilgiventhegoahead*/
}
}
voidreceiver2（void）
{
framer,s;/*buffersforframes*/
event_typeevent;/*frame_arrivalistheonlypossibility*/
while（true）{
wait_for_event（&event）;/*onlypossibilityisframe_arrival*/
from_physical_layer（&r）;/*gogettheinboundframe*/
to_network_layer（&r.info）;/*passthedatatothenetworklayer*/
to_physical_layer（&s）;/*sendadummyframetoawakensender*/
}
}
二、
回退N帧ARQ（go-back-nARQ）
文件名p5.c
/*Protocol5（pipelining）allowsmultipleoutstandingframes.Thesendermaytransmitup
toMAX_SEQframeswithoutwaitingforanack.Inaddition,unlikethepreviousprotocols,
thenetworklayerisnotassumedtohaveanewpacketallthetime.Instead,the
networklayercausesanetwork_layer_readyeventwhenthereisapackettosend.*/
#defineMAX_SEQ7/*shouldbe2^n-1*/
typedefenum{frame_arrival,cksum_err,timeout,network_layer_ready}event_type;
#include"protocol.h"
staticbooleanbetween（seq_nra,seq_nrb,seq_nrc）
{
/*Returntrueif（a<=bif（（（a<=b）&&（breturn（true）;
else
return（false）;
}
staticvoidsend_data（seq_nrframe_nr,seq_nrframe_expected,packetbuffer[]）
{
/*Constructandsendadataframe.*/
frames;/*scratchvariable*/
s.info=buffer[frame_nr];/*insertpacketintoframe*/
s.seq=frame_nr;/*insertsequencenumberintoframe*/
s.ack=（frame_expected+MAX_SEQ）%（MAX_SEQ+1）;/*piggybackack*/
to_physical_layer（&s）;/*transmittheframe*/
start_timer（frame_nr）;/*startthetimerrunning*/
}
voidprotocol5（void）
{
seq_nrnext_frame_to_send;/*MAX_SEQ>1;usedforoutboundstream*/
seq_nrack_expected;/*oldestframeasyetunacknowledged*/
seq_nrframe_expected;/*nextframeexpectedoninboundstream*/
framer;/*scratchvariable*/
packetbuffer[MAX_SEQ+1];/*buffersfortheoutboundstream*/
seq_nrnbuffered;/*#outputbufferscurrentlyinuse*/
seq_nri;/*usedtoindexintothebufferarray*/
event_typeevent;
enable_network_layer（）;/*allownetwork_layer_readyevents*/
ack_expected=0;/*nextackexpectedinbound*/
next_frame_to_send=0;/*nextframegoingout*/
frame_expected=0;/*numberofframeexpectedinbound*/
nbuffered=0;/*initiallynopacketsarebuffered*/
while（true）{
wait_for_event（&event）;/*fourpossibilities:
seeevent_typeabove*/
switch（event）{
casenetwork_layer_ready:
/*thenetworklayerhasapackettosend*/
/*Accept,save,andtransmitanewframe.*/
from_network_layer（&buffer[next_frame_to_send]）;/*fetchnewpacket*/
nbuffered=nbuffered+1;/*expandthesender'swindow*/
send_data（next_frame_to_send,frame_expected,buffer）;/*transmittheframe*/
inc（next_frame_to_send）;/*advancesender'supperwindowedge*/
break;
caseframe_arrival:
/*adataorcontrolframehasarrived*/
from_physical_layer（&r）;/*getincomingframefromphysicallayer*/
if（r.seq==frame_expected）{
/*Framesareacceptedonlyinorder.*/
to_network_layer（&r.info）;/*passpackettonetworklayer*/
inc（frame_expected）;/*advanceloweredgeofreceiver'swindow*/
}
/*Acknimpliesn-1,n-2,etc.Checkforthis.*/
while（between（ack_expected,r.ack,next_frame_to_send））{
/*Handlepiggybackedack.*/
nbuffered=nbuffered-1;/*oneframefewerbuffered*/
stop_timer（ack_expected）;/*framearrivedintact;stoptimer*/
inc（ack_expected）;/*contractsender'swindow*/
}
break;
casecksum_err:
;/*justignorebadframes*/
break;
casetimeout:
/*trouble;retransmitalloutstandingframes*/
next_frame_to_send=ack_expected;/*startretransmittinghere*/
for（i=1;i<=nbuffered;i++）{
send_data（next_frame_to_send,frame_expected,buffer）;/*resend1frame*/
inc（next_frame_to_send）;/*preparetosendthenextone*/
}
}
if（nbufferedenable_network_layer（）;
else
disable_network_layer（）;
}
}
三、选择拒绝ARQ（selective-rejectARQ）
文件名p6.c
/*Protocol6（nonsequentialreceive）acceptsframesoutoforder,butpassespacketstothe
networklayerinorder.Associatedwitheachoutstandingframeisatimer.Whenthetimer
goesoff,onlythatframeisretransmitted,notalltheoutstandingframes,asinprotocol5.*/
#defineMAX_SEQ7/*shouldbe2^n-1*/
#defineNR_BUFS（（MAX_SEQ+1）/2）
typedefenum{frame_arrival,cksum_err,timeout,network_layer_ready,ack_timeout}event_type;
#include"protocol.h"
booleanno_nak=true;/*nonakhasbeensentyet*/
seq_nroldest_frame=MAX_SEQ+1;/*initvalueisforthesimulator*/
staticbooleanbetween（seq_nra,seq_nrb,seq_nrc）
{
/*Sameasbetweeninprotocol5,butshorterandmoreobscure.*/
return（（a<=b）&&（b}
staticvoidsend_frame（frame_kindfk,seq_nrframe_nr,seq_nrframe_expected,packetbuffer[]）
{
/*Constructandsendadata,ack,ornakframe.*/
frames;/*scratchvariable*/
s.kind=fk;/*kind==data,ack,ornak*/
if（fk==data）s.info=buffer[frame_nr%NR_BUFS];
s.seq=frame_nr;/*onlymeaningfulfordataframes*/
s.ack=（frame_expected+MAX_SEQ）%（MAX_SEQ+1）;
if（fk==nak）no_nak=false;/*onenakperframe,please*/
to_physical_layer（&s）;/*transmittheframe*/
if（fk==data）start_timer（frame_nr%NR_BUFS）;
stop_ack_timer（）;/*noneedforseparateackframe*/
}
voidprotocol6（void）
{
seq_nrack_expected;/*loweredgeofsender'swindow*/
seq_nrnext_frame_to_send;/*upperedgeofsender'swindow+1*/
seq_nrframe_expected;/*loweredgeofreceiver'swindow*/
seq_nrtoo_far;/*upperedgeofreceiver'swindow+1*/
inti;/*indexintobufferpool*/
framer;/*scratchvariable*/
packetout_buf[NR_BUFS];/*buffersfortheoutboundstream*/
packetin_buf[NR_BUFS];/*buffersfortheinboundstream*/
booleanarrived[NR_BUFS];/*inboundbitmap*/
seq_nrnbuffered;/*howmanyoutputbufferscurrentlyused*/
event_typeevent;
enable_network_layer（）;/*initialize*/
ack_expected=0;/*nextackexpectedontheinboundstream*/
next_frame_to_send=0;/*numberofnextoutgoingframe*/
frame_expected=0;/*framenumberexpected*/
too_far=NR_BUFS;/*receiver'supperwindow+1*/
nbuffered=0;/*initiallynopacketsarebuffered*/
for（i=0;iwhile（true）{
wait_for_event（&event）;/*fivepossibilities:
seeevent_typeabove*/
switch（event）{
casenetwork_layer_ready:
/*accept,save,andtransmitanewframe*/
nbuffered=nbuffered+1;/*expandthewindow*/
from_network_layer（&out_buf[next_frame_to_send%NR_BUFS]）;/*fetchnewpacket*/
send_frame（data,next_frame_to_send,frame_expected,out_buf）;/*transmittheframe*/
inc（next_frame_to_send）;/*advanceupperwindowedge*/
break;
caseframe_arrival:
/*adataorcontrolframehasarrived*/
from_physical_layer（&r）;/*fetchincomingframefromphysicallayer*/
if（r.kind==data）{
/*Anundamagedframehasarrived.*/
if（（r.seq!
=frame_expected）&&no_nak）
send_frame（nak,0,frame_expected,out_buf）;elsestart_ack_timer（）;
if（between（frame_expected,r.seq,too_far）&&（arrived[r.seq%NR_BUFS]==false））{
/*Framesmaybeacceptedinanyorder.*/
arrived[r.seq%NR_BUFS]=true;/*markbufferasfull*/
in_buf[r.seq%NR_BUFS]=r.info;/*insertdataintobuffer*/
while（arrived[frame_expected%NR_BUFS]）{
/*Passframesandadvancewindow.*/
to_network_layer（&in_buf[frame_expected%NR_BUFS]）;
no_nak=true;
arrived[frame_expected%NR_BUFS]=false;
inc（frame_expected）;/*advanceloweredgeofreceiver'swindow*/
inc（too_far）;/*advanceupperedgeofreceiver'swindow*/
start_ack_timer（）;/*toseeif（aseparateackisneeded*/
}
}
}
if（（r.kind==nak）&&between（ack_expected,（r.ack+1）%（MAX_SEQ+1）,next_frame_to_send））
send_frame（data,（r.ack+1）%（MAX_SEQ+1）,frame_expected,out_buf）;
while（between（ack_expected,r.ack,next_frame_to_send））{
nbuffered=nbuffered-1;/*handlepiggybackedack*/
stop_timer（ack_expected%NR_BUFS）;/*framearrivedintact*/
inc（ack_expected）;/*advanceloweredgeofsender'swindow*/
}
break;
casecksum_err:
if（no_nak）send_frame（nak,0,frame_expected,out_buf）;break;/*damagedframe*/
casetimeout:
send_frame（data,oldest_frame,frame_expected,out_buf）;break;/*wetimedout*/
caseack_timeout:
send_frame（ack,0,frame_expected,out_buf）;/*acktimerexpired;sendack*/
}
if（nbuffered}
}
四、协议中用到的H文件
文件名protocol.h
#defineMAX_PKT4/*determinespacketsizeinbytes*/
typedefenum{false,true}boolean;/*booleantype*/
t
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