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Tips on Programming Assignment 2: Reliable Data Transfer

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 Astat e _type {waitAck0, waitAck1, waitData0, waitData1} Astat e ; Define two states for host B (receiver)

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Tips on Programming Assignment 2: Reliable Data Transfer

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  1. 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()

  2. Wait for 0 from below Wait for 1 from below rdt3.0: receiver FSM udt_rcv(rcvpkt) && notcorrupt(rcvpkt) && has_seq0(rcvpkt) extract(rcvpkt,data) deliver_data(data) sndpkt = make_pkt(ACK0, chksum) udt_send(sndpkt) udt_rcv(rcvpkt) && (corrupt(rcvpkt) || has_seq0(rcvpkt)) udt_rcv(rcvpkt) && (corrupt(rcvpkt) || has_seq1(rcvpkt)) receiver FSM udt_send(sndpkt) udt_send(sndpkt) udt_rcv(rcvpkt) && notcorrupt(rcvpkt) && has_seq1(rcvpkt) extract(rcvpkt,data) deliver_data(data) sndpkt = make_pkt(ACK1, chksum) udt_send(sndpkt)

  3. Wait for ACK0 Wait for ACK1 Wait for call 1 from above Wait for call 0from above rdt3.0 sender FSM rdt_send(data) udt_rcv(rcvpkt) && ( corrupt(rcvpkt) || isACK(rcvpkt,1) ) sndpkt = make_pkt(0, data, checksum) udt_send(sndpkt) start_timer L udt_rcv(rcvpkt) L timeout udt_send(sndpkt) start_timer udt_rcv(rcvpkt) && notcorrupt(rcvpkt) && isACK(rcvpkt,1) udt_rcv(rcvpkt) && notcorrupt(rcvpkt) && isACK(rcvpkt,0) stop_timer stop_timer timeout udt_send(sndpkt) start_timer udt_rcv(rcvpkt) L rdt_send(data) udt_rcv(rcvpkt) && ( corrupt(rcvpkt) || isACK(rcvpkt,0) ) sndpkt = make_pkt(1, data, checksum) udt_send(sndpkt) start_timer L

  4. Program each state transition in FSM • If state changes, remember to change Astate, Bstate accordingly • Some FSMcode 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;)

  5. 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);

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