Tips on Programming Assignment 2: Reliable Data Transfer

• For the rdt3.0, refer its FSM for programming:• Define five states for host A (sender)

enum Astate_type {waitAck0, waitAck1, waitData0, waitData1} Astate;

• Define two states for host B (receiver) enum Bstate_type {waitSeq0, waitSeq1} Bstate;

• Define subfunction for checksum– ComputChecksum(), CheckCorrupted()

rdt3.0: receiver FSM

Wait for 0 from below

udt_rcv(rcvpkt) && (corrupt(rcvpkt) || has_seq1(rcvpkt))

udt_send(sndpkt)

receiver FSM

udt_rcv(rcvpkt) && notcorrupt(rcvpkt) && has_seq1(rcvpkt)

extract(rcvpkt,data)deliver_data(data)sndpkt = make_pkt(ACK1, chksum)udt_send(sndpkt)

udt_rcv(rcvpkt) && (corrupt(rcvpkt) || has_seq0(rcvpkt))

udt_send(sndpkt)

Wait for 1 from below

udt_rcv(rcvpkt) && notcorrupt(rcvpkt) && has_seq0(rcvpkt)

extract(rcvpkt,data)deliver_data(data)sndpkt = make_pkt(ACK0, chksum)udt_send(sndpkt)

rdt3.0 sender FSM

sndpkt = make_pkt(0, data, checksum)udt_send(sndpkt)start_timer

rdt_send(data)

Wait for

ACK0

udt_rcv(rcvpkt) && ( corrupt(rcvpkt) ||isACK(rcvpkt,1) )

Wait for call 1 from

above

sndpkt = make_pkt(1, data, checksum)udt_send(sndpkt)start_timer

rdt_send(data)

udt_rcv(rcvpkt) && notcorrupt(rcvpkt) && isACK(rcvpkt,0)

udt_rcv(rcvpkt) && ( corrupt(rcvpkt) ||isACK(rcvpkt,0) )

udt_rcv(rcvpkt) && notcorrupt(rcvpkt) && isACK(rcvpkt,1)

stop_timerstop_timer

udt_send(sndpkt)start_timer

timeout

udt_send(sndpkt)start_timer

timeout

udt_rcv(rcvpkt)

Wait for call 0from

above

Wait for

ACK1

udt_rcv(rcvpkt)

• Program each state transition in FSM– If state changes, remember to change Astate, Bstate accordingly

• Some FSMcode mappings:– timeout A_timerinterrupt() is called

– udt_rcv(rcvpkt) A_input(packet), B_input(packet) is called

– udt_send(sndpkt) tolayer3(0/1, packet)– rdt_send(data) A_output(message) is called – deliver_data(data) tolayer5(message) is called in host B– extract(rcvpkt,data) copy packet.payload[] to message.data[] (do nothing) exit a function immediately

(e.g., return -1;)

Programming Tips• Some definition for easy naming:

– #define host_A 0 #define host_B 1– #define TRUE 100 #define FALSE 200– #define NOTUSED 300 #define TIMEOUT 15 (20)

• Program the simplest scenario first:– No loss, no error scenario

• Add your own “printf(“ #### …..\n”);” in all (or most) state transitions for debugging

– The printf text should show the detail of each action.– This is the most important “run-time” debugging method!!! Don’t be lazy here!

• Add “getchar();” in places where you want to stop the code temporally to see output results

– Your code will enter infinite loop if it has some errors

• tolayer5(hostB, message);

BreceivedMsgNum ++;

printf(" #### B correctly received the No. %d message\n", BreceivedMsgNum);