Problem A:

Consider the figure below in which a TCP sender and receiver communicate over a connection in which the segments can be lost. The TCP sender wants to send a total of $10$ segments to the receiver and sends an initial window of $5$ segments at t $=1,2,3,4,$ and $5,$ respectively. Suppose the initial value of the sequence number is $126$ and every segment sent to the receiver each contains $500$ bytes. The delay between the sender and receiver is $7$ time units, and so the first segment arrives at the receiver at t $=8,$ and an ACK for this segment arrives at t $=15.$ As shown in the figure, $2$ of the $5$ segments is lost between the sender and the receiver, but one of the ACKs is lost. Assume there are no timeouts and any out of order segments received are thrown out

$1.$ What is the sequence number of the segment sent at t$=1?$

$2.$ What is the sequence number of the segment sent at t$=2?$

$3.$ What is the sequence number of the segment sent at t$=3?$

$4.$ What is the sequence number of the segment sent at t$=4?$

$5.$ What is the sequence number of the segment sent at t$=5?$

$6.$ What is the value of the ACK sent at t$=8?($If segment lost, write $\text{'}$x$\text{'})$

$7.$ What is the value of the ACK sent at t$=9?($If segment lost, write $\text{'}$x$\text{'}).$

$8.$ What is the value of the ACK sent at t$=10?($If segment lost, write $\text{'}$x$\text{'})$

$9.$ What is the value of the ACK sent at t$=11?($If segment lost, write $\text{'}$x$\text{'})$

$10.$ What is the value of the ACK sent at t$=12?($If segment lost, write $\text{'}$x$\text{'})$

$11.$ What is the sequence number of the segment sent at t $=15?($If ACK never arrives,

write $\text{'}$x$\text{'})$

$12.$ What is the sequence number of the segment sent at t $=16?($If ACK never arrives, write $\text{'}$x$\text{'})$

$13.$ What is the sequence number of the segment sent at t $=17?($If ACK never arrives, write $\text{'}$x$\text{'})$

$14.$ What is the sequence number of the segment sent at t $=19?($If ACK never arrives,

write $\text{'}$x$\text{'})$

Problem B:

Suppose Client A initiates a Telnet session with Server S$.$ At about the same time, Client

B also initiates a Telnet session with Server S$.$ Provide possible source and destination

port numbers for. $[0\mathrm{.}5$ points per question$]$

a$.$ The segments sent from A to S$.$

b$.$ The segments sent from B to S$.$

c$.$ The segments sent from S to A$.$

d$.$ The segments sent from S to B$.$

e$.$ If A and B are different hosts, is it possible that the source port number in the

segments from A to S is the same as that from B to S$?$

f$.$ How about if they are the same host?