a$.$ Consider a network of two hosts connected by three routers, as depicted below. Each link has a propagation delay of

$50$ ms$.$ The H$1-$R$1$ and R$2-$R$3$ links, respectively, have a data rate of $10$ Mbps$.$ Each of the other two links has a date

rate of $12Mbps.$ The routing and$/$or queuing delays at each node are negligible.

Consider a $1MB$ message sent from $H1$ to $H2$ using virtual circuit packet switching with $10KB$ packets. Each packet has

a $50B$ header, which is a negligible fraction of the overall packet. Calculate the end$-$to$-$end delay, including teardown.

b$.$ An organization has a class C network with IP address $223\mathrm{.}0\mathrm{.}5\mathrm{.}0$ and wants to form respective subnets for three

departments. These departments are D$1,$ D$2,$ and D$3$; which require $99,63,$ and $35$ hosts, respectively.

Give a possible arrangement of subnet masks to make this possible. Your final answer should include one subnet mask

for each of the three departments, assigned such that any potential host address can be unambiguously associated

with only a single department. Use the fewest possible number of table entries. Show your work.