Receiver rdt_row(revpkt) && notcorrupt(revpkt) &&has_segrevpkt) extract(rovpkt, data) deliver_data(data) sndpkt = make_pkt(ACK, 0, chiksum) udt_send(sndpkt) rdt 3.0 Sender rdt_send(data) sndpkt -make_pkt(0, data, checksum) [dt_rev(revpkt) && udt_send(sndpkt) corrupt(cupkt) || iSACKircrpkt. 1)) rdt roverevpkt) start_timer Wait for Wait timeout for call ofron above ACKO udt_send(sndpkt) rdt_rev[revpkt) start_timer && notoorruptirovpkt) rdt_revrovpkt) && isACKircpkt. 1) && notoorrupt/rcvpkt) stop_timer && isACK/rcvpkt,0) stop_timer Wait timeout Wait for for cal 1 from udt_send(sndpkt) ACK1 above start_timer rdt_rorovpkt) rdt_send(data) rdt_revrevpkt) && sndpkt = make_pkt(1, data, checksum) (corrupt(revpkt) || isACK (revpkt,0)) udt_send(sndpkt) A start_timer rdt_rev(revpkt) && (corruptircupkt) II has_seq f(revpkt)) sndpkt = make_pkt(ACK, 1. chksum) udt_sendandpkt) Wait for O from below Wait for 1 from below rdt_revrcvpkt) && (corrupt(revpkt) has_seofreypkt) sndpkt - make_pkt(ACK, O. chksum) udt_send(sndpkt) rdt_rcv(revpkt) && notcorruptcypkt) &&has_set(revpkt) extractiepkt.data) deliver_data(data) sndpkt = make_pkt(ACK, 1, chksum) udt_send(sndpkt) Fig 2. Finite State Machines (FSMS) of rdt3.0 sender and receiver. Consider the FSM of rdt3.0 shown in Fig. 2. Recall that rdt3.0 is designed for a channel that can corrupt and lose packets. Note that the receiver of rdt3.0 is the same as the receiver for rdt2.2, which does not use NAK, rather only uses ACK with sequence numbers. Consider the scenario the sender is in the state of wait for call 1 from above and sends pkt1 to the receiver when receiving a packet from above (i.e., from the application layer). Suppose pkt1 is not lost or corrupted. The receiver is in the state of "wait for 1 from below" and sends an ACK, 1 after receiving pkt1. Suppose that the ACK is not corrupted or lost by the channel. But the sender has a premature timeout, i.e., it resends pkt1 before receiving ACK, 1. Suppose none of the packets is lost or corrupted, and there is no premature timeout afterwards and that the channel can also make packets to be out of order (i.e., reorder packets). Use a time sequence graph to show that in that scenario, rdt3.0 will NOT provide reliable data transfer. Receiver rdt_row(revpkt) && notcorrupt(revpkt) &&has_segrevpkt) extract(rovpkt, data) deliver_data(data) sndpkt = make_pkt(ACK, 0, chiksum) udt_send(sndpkt) rdt 3.0 Sender rdt_send(data) sndpkt -make_pkt(0, data, checksum) [dt_rev(revpkt) && udt_send(sndpkt) corrupt(cupkt) || iSACKircrpkt. 1)) rdt roverevpkt) start_timer Wait for Wait timeout for call ofron above ACKO udt_send(sndpkt) rdt_rev[revpkt) start_timer && notoorruptirovpkt) rdt_revrovpkt) && isACKircpkt. 1) && notoorrupt/rcvpkt) stop_timer && isACK/rcvpkt,0) stop_timer Wait timeout Wait for for cal 1 from udt_send(sndpkt) ACK1 above start_timer rdt_rorovpkt) rdt_send(data) rdt_revrevpkt) && sndpkt = make_pkt(1, data, checksum) (corrupt(revpkt) || isACK (revpkt,0)) udt_send(sndpkt) A start_timer rdt_rev(revpkt) && (corruptircupkt) II has_seq f(revpkt)) sndpkt = make_pkt(ACK, 1. chksum) udt_sendandpkt) Wait for O from below Wait for 1 from below rdt_revrcvpkt) && (corrupt(revpkt) has_seofreypkt) sndpkt - make_pkt(ACK, O. chksum) udt_send(sndpkt) rdt_rcv(revpkt) && notcorruptcypkt) &&has_set(revpkt) extractiepkt.data) deliver_data(data) sndpkt = make_pkt(ACK, 1, chksum) udt_send(sndpkt) Fig 2. Finite State Machines (FSMS) of rdt3.0 sender and receiver. Consider the FSM of rdt3.0 shown in Fig. 2. Recall that rdt3.0 is designed for a channel that can corrupt and lose packets. Note that the receiver of rdt3.0 is the same as the receiver for rdt2.2, which does not use NAK, rather only uses ACK with sequence numbers. Consider the scenario the sender is in the state of wait for call 1 from above and sends pkt1 to the receiver when receiving a packet from above (i.e., from the application layer). Suppose pkt1 is not lost or corrupted. The receiver is in the state of "wait for 1 from below" and sends an ACK, 1 after receiving pkt1. Suppose that the ACK is not corrupted or lost by the channel. But the sender has a premature timeout, i.e., it resends pkt1 before receiving ACK, 1. Suppose none of the packets is lost or corrupted, and there is no premature timeout afterwards and that the channel can also make packets to be out of order (i.e., reorder packets). Use a time sequence graph to show that in that scenario, rdt3.0 will NOT provide reliable data transfer
