/* called from layer 3, when a packet arrives for layer 4 */
void A_input(struct pkt packet)
{
printf("CCH> A_input> Got packet\n");
// isChecksumValid
if(pkt_checksum_valid(&packet)) {
printf("CCH> A_input> Valid checksum\n");
// isACK
if(strncmp(packet.payload, ACK, strlen(ACK)) == 0) {
if(packet.acknum == last_pkt->seqnum) {
printf("CCH> A_input> Received valid ACK\n");
last_ack = &packet;
stoptimer(A);
} else {
// We received an ACK we don't care about
printf("CCH> A_input> Received invalid ACK (ignoring)\n");
}
// isNACK
} else if (strncmp(packet.payload, NACK, strlen(ACK)) == 0) {
printf("CCH> A_input> Received NACK\n");
send_pkt(A, last_pkt);
} else {
// Message
stoptimer(A);
tolayer5(A, packet.payload);
}
} else {
printf("CCH> A_input> Invalid checksum\n");
send_nack(A, &packet);
stoptimer(A);
starttimer(A, TIMEOUT);
return;
}
}
/* called from layer 3, when a packet arrives for layer 4 at B*/
void B_input(struct pkt packet)
{
printf("CCH> B_input> Got packet\n");
// Send ACK
send_ack(B, &packet);
// Pass message to layer 5
tolayer5(B, packet.payload);
}
void B_input(struct pkt packet)
{
//struct pkt new_packet_b;
int my_checksum=0;
B_transport++;
my_checksum=packet.seqnum+packet.acknum;
for(int i=0;i<20;i++)
my_checksum+=packet.payload[i];
memset(new_packet_b.payload,'\0',20);
if(expectedseqno==0)
{
new_packet_b.seqnum=-1;
new_packet_b.acknum=1;
new_packet_b.checksum=new_packet_b.acknum+new_packet_b.seqnum;
for(int i=0;i<20;i++)
new_packet_b.checksum+=new_packet_b.payload[i];
}
if((my_checksum==packet.checksum )&& (packet.seqnum ==expectedseqno))//reject out of order packets
{
tolayer5(1,packet.payload);
B_application++;
new_packet_b.acknum=1;
new_packet_b.seqnum=expectedseqno;
new_packet_b.checksum=new_packet_b.acknum+new_packet_b.seqnum;
for(int i=0;i<20;i++)
new_packet_b.checksum+=new_packet_b.payload[i];
tolayer3(1,new_packet_b);
expectedseqno++;
}
else
{
tolayer3(1,new_packet_b);//to tell sender which packet is needed
}
}
/*
* B_input(packet),where packet is a structure of type pkt. This routine
* will be called whenever a packet sent from the A-side (i.e., as a result
* of a tolayer3() being done by a A-side procedure) arrives at the B-side.
* packet is the (possibly corrupted) packet sent from the A-side.
*/
void B_input(struct pkt packet) {
struct pkt ack;
if (iscorrupt(packet)) {
return;
}
if (packet.acknum == DATAACK) {
if (!iscorrupt(packet) && packet.seqnum != Bexpectedseqnum) { //wrong seq num
ack = Bpastack;
tolayer3(BEntity,ack);
return;
}
if (!iscorrupt(packet) && packet.seqnum == Bexpectedseqnum) { //right seqnum
ack.checksum = 0;
ack.seqnum = packet.seqnum;
ack.acknum = ACK;
memcpy(ack.payload,packet.payload,MESSAGE_LENGTH);
ack.checksum = genchecksum(ack);
Bpastack = ack;
tolayer3(BEntity,ack);
struct msg message;
memcpy(message.data,packet.payload,MESSAGE_LENGTH);
tolayer5(BEntity,message);
Bexpectedseqnum++;
return;
}
}
////new stuff
if (packet.acknum == ACK) {
if (Bbase >= (packet.seqnum + 1)) {
if (packet.seqnum + 1 == Bnextseqnum) {
stopTimer(BEntity);
}
return;
}
Bbase = packet.seqnum + 1;
if (Bbase == Bnextseqnum) {
stopTimer(BEntity);
}
else {
stopTimer(BEntity);
startTimer(BEntity,TIMERAMT);
}
}
////old stuff
}
/*Initial state of receiver side*/
void B_Initial_State(struct pkt packet)
{
struct msg message;
createMessageforLayer5(&packet,&message);
bool corrupt = isPacketCorrupt(packet.checksum,packet.seqnum,packet.acknum,message.data);
int seqnum = packet.seqnum;
struct pkt datapacket; //creating packet containing acknowledgment
int checksum=0;
if(!corrupt && seqnum==expectedSeqNum)
{
int ack=expectedSeqNum; //send ack for received packet
createDataPacket(&datapacket,0,ack,checksum,"");
createCheckSum(&datapacket); //set checksum
datapacket.acknum = expectedSeqNum; //re assigning value for correctness
tolayer3(B,datapacket);
tolayer5(B,message.data);
int i;
for(i=0;i<20;i++)
{
printf("%c",message.data[i]);
}
printf("\n");
//printf("\nB SIDE : Printing Packet payload Sent Above %s\n",message.data);
//printf("\nB SIDE : Printing Acknum %d sent from B to A \n",datapacket.acknum);
//incrementing the expected sequence number
expectedSeqNum++;
}
else //send previous acknowledgment
{
int ack =expectedSeqNum-1;
createDataPacket(&datapacket,0,ack,checksum,"");
createCheckSum(&datapacket); //set checksum
datapacket.acknum = expectedSeqNum-1; //reassign for correctness
tolayer3(B,datapacket);
}
}
/* called from layer 3, when a packet arrives for layer 4 at B*/
void B_input(struct pkt packet)
{
struct pkt sendpkt;
int i;
/* if not corrupted and received packet is in order */
if ( (!IsCorrupted(packet)) && (packet.seqnum == expectedseqnum) ) {
if (TRACE > 0)
printf("----B: packet %d is correctly received, send ACK!\n",packet.seqnum);
packets_received++;
/* deliver to receiving application */
tolayer5(B, packet.payload);
/* send an ACK for the received packet */
sendpkt.acknum = expectedseqnum;
/* update state variables */
expectedseqnum = (expectedseqnum + 1) % SEQSPACE;
}
else {
/* packet is corrupted or out of order resend last ACK */
if (TRACE > 0)
printf("----B: packet corrupted or not expected sequence number, resend ACK!\n");
if (expectedseqnum == 0)
sendpkt.acknum = SEQSPACE - 1;
else
sendpkt.acknum = expectedseqnum - 1;
}
/* create packet */
sendpkt.seqnum = B_nextseqnum;
B_nextseqnum = (B_nextseqnum + 1) % 2;
/* we don't have any data to send. fill payload with 0's */
for ( i=0; i<20 ; i++ )
sendpkt.payload[i] = '0';
/* computer checksum */
sendpkt.checksum = ComputeChecksum(sendpkt);
/* send out packet */
tolayer3 (B, sendpkt);
}
/*
* B_input(packet),where packet is a structure of type pkt. This routine
* will be called whenever a packet sent from the A-side (i.e., as a result
* of a tolayer3() being done by a A-side procedure) arrives at the B-side.
* packet is the (possibly corrupted) packet sent from the A-side.
*/
void B_input(struct pkt packet) {
struct msg message; // Store message retrived from network
struct pkt ack; // Store ack packet
// Pass message to layer 5 when it not corrupted and when it has expected seqnum
if (not_corrupted(packet) && (packet.seqnum == rev_seqnum)) {
strncpy(message.data, packet.payload, MESSAGE_LENGTH);
tolayer5(BEntity, message);
// Make ack message
ack = prepare_pkt(1, rev_seqnum, NULL);
// flip expected sequence number of packet
rev_seqnum = !rev_seqnum;
} else {
// Make ack message
ack = prepare_pkt(1, !rev_seqnum, NULL);
}
// Send ack message
tolayer3(BEntity, ack);
}
/*Function send packets to layer5, using the value returned by function returnNextMaximumContiguousSequenceAcknowledged()*/
void sendMessagestoLayer5(int tillThisPacket) {
int startOfWindow = receiverBase;
while (startOfWindow <= tillThisPacket) {
if (ackSent[startOfWindow] != 2) {
tolayer5(B, receiverBuffer[startOfWindow].data);
//printf("#B SIDE : Printing Packet payload Sent Above %s with a size of %zu\n",
// receiverBuffer[startOfWindow].data,sizeof(receiverBuffer[startOfWindow].data));
//printf("Previous Receiver Base value is : %d and New receiver base value is %d\n",receiverBase,receiverBase+1);
receiverBase++; //every time you send a message, increment receiver base
ackSent[startOfWindow] = 2;
}
startOfWindow++;
}
}
