exam ID$.$

SUBJECT $1(30\%)$ Answer in detail the following questions selecting only $4$ out of the $8$ of them according to the following schedule taking into account your STUDENT'S EXAM ID associated numbers.

Take the MAXIMUM number out of the $5$ numbers your student exam $D$ has been transformed into, let's say MAXIMUM number $=14($transformed from the letter $N$ or $n$ of the Latin alphabet$).$ Divide this MAXIMUM number by $8$ and take the remainder, which is $6$

With numbering of the questions $q0,q1,q2,q3,q4,q5,q6,q7$ the above student with remainder $=6$ will start from the question$=$q$6$ and cyclically will choose $4$ questions, the following: $q6,q7,q0,q1$ and so forth.

q$0.$ Give a simple heuristic for finding two paths through a network from a given source to a given destination that can survive the loss of any communication line $($assuming two such paths exist$).$ The routers are considered reliable enough, so it is not necessary to worry about the possibility of router crashes.

q$1.$ If costs are recorded as $8-$bit numbers in a $50-$router network, and distance vectors are exchanged twice a second, how much bandwidth per $($full$-$duplex$)$ line is chewed up by the distributed routing algorithm? Assume that each router has three lines to other routers.

q$2.$ As a possible congestion control mechanism in a network using virtual circuits internally, a router could refrain from acknowledging a received packet until $(1)$ it knows its last transmission along the virtual circuit was received successfully and $(2)$ it has a free buffer. For simplicity, assume that the routers use a stop$-$and$-$wait protocol and that each virtual circuit has one buffer dedicated to it for each direction of traffic. If it takes $T$ sec to transmit a packet $($data or acknowledgement$)$ and there are $n$ routers on the path, what is the rate at which packets are delivered to the destination host? Assume that transmission errors are rare and that the host$-$router connection is infinitely fast so it is not a bottleneck.

q$3.$ Describe in detail with an example a way to reassemble IP fragments at the destination.