In protocol rdt$3\mathrm{.}0,$ the ACK packets flowing from the receiver to the

sender do not have sequence numbers $($although they do have an ACK field

that contains the sequence number of the packet they are acknowledging$).$

Why is it that our ACK packets do not require sequence numbers?

Wait for

$0$ from

below

rdt$\_$rcv$($rcvpkt$)$ &&

$($corrupt$($rcvpkt$)||$

has$\_$seq$0($rcvpkt$)))$

compute chksum

make$\_$pkt$($sndpkt$,$NAK,chksum$)$

udt$\_$send$($sndpkt$)$

rdt$\_$rcv$($rcvpkt$)$ &&

$($corrupt$($rcvpkt$)||$

has$\_$seq$1($rcvpkt$)))$

compute chksum

make$\_$pkt$($sndpkt$,$NAK,chksum$)$

udt$\_$send$($sndpkt$)$ rdt$\_$rcv$($rcvpkt$)$ && notcorrupt$($rcvpkt$)$

&& has$\_$seq$1($rcvpkt$)$

extract$($rcvpkt$,$data$)$

deliver$\_$data$($data$)$

compute chksum

make$\_$pkt$($sendpkt$,$ACK,chksum$)$

udt$\_$send$($sndpkt$)$

rdt$\_$rcv$($rcvpkt$)$ && notcorrupt$($rcvpkt$)$

&& has$\_$seq$0($rcvpkt$)$

extract$($rcvpkt$,$data$)$

deliver$\_$data$($data$)$

compute chksum

make$\_$pkt$($sendpkt$,$ACK,chksum$)$

udt$\_$send$($sndpkt$)$

Wait for

$1$ from

below

Figure $3\mathrm{.}60$ An incorrect receiver for protocol rdt $2\mathrm{.}1$