QUESTION $1$

$[$TOTAL MARKS: $25]$

Q$1($a$)$

$[10$ Marks$]$

For the following applications, state whether they run over TCP or UDP and give a reason for the choice of transport layer protocol.

i$)$ File Transfer Protocol $($FTP$)(2$ marks$)$

ii$)$ Telnet $(2$ marks$)$

iii$)$ Domain Name System $($DNS$)(2$ marks$)$

iv$)$ Streaming stored video $(4$ marks$)$

Q $1($b$)$

$[15$ Marks$]$

Consider The DNS protocol.

i$)$ In $50$ words or less, describe the steps a local DNS server uses to get the IP address for a given URL assuming that no caching is used. $(3$ marks$)$

ii$)$ As outlined in i$)$ consider a client trying to find the IP address associated with a given URL where the local DNS has caching facilities.

Assume that the local network and institutional access link do not impose significant delay relative to the internet Round Trip Time of $4$ seconds.

a$.$ What is the maximum delay the client will experience? State under what conditions this delay would occur.

$(3$ marks$)$

b$.$ What is the minimum delay the client might experience? State under what conditions this delay would occur.

$(3$ marks$)$

c$.$ What is the average delay a client seeking an IP address might experience? Derive a formula and state any assumptions you make for this calculation.

$(6$ marks$)$