$1.$ Consider the figure below. The IP and MAC addresses are shown for nodes $\backslash ($ A$,$ B$,$ C $\backslash )$ and $\backslash ($ D $\backslash ),$ as well as for the router's interfaces. Consider an IP datagram being sent from node $\backslash ($ C $\backslash )$ to node D $.(1$ points per question$)$

a$.$ What is the source mac address at point $6?$

b$.$ What is the destination mac address at point $6?$

c$.$ What is the source IP address at point $6?$

d$.$ What is the destination IP address at point $6?$

e$.$ Do the source and destination mac addresses change at point $5?$ Answer with yes or no$.$

$2.$ Consider the figure below, which shows the arrival of $7$ messages $($numbered message $1,2,3..\mathrm{.}7)$ for transmission at different multiple access wireless nodes at times $\backslash (\backslash$mathrm$\{$t$\}=\backslash \{0\mathrm{.}9,1\mathrm{.}2,2\mathrm{.}4,3\mathrm{.}7,3\mathrm{.}9,4\mathrm{.}2,4\mathrm{.}8\backslash \}\backslash )$ and each transmission requires exactly one time unit. $(2$ points per question$)$

a$.$ Suppose all nodes are implementing the Aloha protocol. For each message, indicate the time at which each transmission begins.

b$.$ Which messages transmit successfully? Write your answer as a comma separated list with no spaces using the messages' numbers. c$.$ Suppose all nodes are implementing the Slotted Aloha protocol. For each message, indicate the time at which each transmission begins.

d$.$ Which messages transmit successfully?

e$.$ Which protocol has better efficiency? $($Aloha$/$Slotted Aloha$)$

$3.$ Consider the $6-$node network shown below. with the given link costs:

a$.$ When the algorithm converges, what are the distance vectors from router $\text{'}\backslash ($ W $\backslash )\text{'}$ to all routers? Write your answer as $\backslash ($ u$,$ v$,$ w$,$ x$,$ y $\backslash ).[2$ pt$]$

b$.$ What are the initial distance vectors for router $\text{'}$ X $\text{'}?$ Write your answer as $\backslash (\backslash$mathrm$\{$u$\},\backslash$mathrm$\{$v$\},\backslash$mathrm$\{$w$\},\backslash$mathrm$\{$x$\},\backslash$mathrm$\{$y$\}\backslash )$ and if a distance is $\backslash (\backslash$infty $\backslash ),$ write $\text{'}\backslash ($ x $\backslash )\text{'}.[2$ pt$]$

c$.$ The phrase 'Good news travels fast' is very applicable to distance vector routing when link costs decrease; what is the name of the problem that can occur when link costs increase? $[1$ pt$]$