Question $1$

$($a$)$ A client$-$server network is served by a satellite link which connects a server based in

California with a client in Hawaii. The satellite is positioned on a geosynchronous orbit at

a fixed distance of $36,000km$ from the server and the client. The client uses a TCP

connection service for data transfer. Assume that the speed of signal is $300,000k\frac{m}{s}.$

$($i$)$ Estimate the minimum latency of the satellite reliable transmission link between the

server and the client.

$($ii$)$ If the online gaming standard requires latency below $100ms,$ do you think that this

satellite link is suitable for online gaming? Explain why. Will this change if instead

of a TCP a UDP service is used?

$($iii$)$ What are the main advantages and disadvantages of a client$-$server networking?

$($iv$)$ If the server transmits a $10-$Mbyte data packet at a speed of $1G\frac{b}{s},$ what is an

upper bound of the satellite link efficiency $(L{E}_{UB})?$ Which effect is more important

in this link: that of propagation delay, or that of limited bandwidth? Or do you

think they are equally important?

$($v$)$ Explain what the upper bound of the link efficiency $L{E}_{UB}$ represents.

$($b$)$ Consider designing a CSMA$/$CD Fast Ethernet which transmits at $100M\frac{b}{s}$ over a $2-$km

bus cable with two repeaters. The one$-$way delay in each repeater is $2\mathrm{.}5s.$ The signal

speed in the cable is $200,000k\frac{m}{s}.$ The Ethernet MAC frame is shown in Figure $1\mathrm{.}1.$

Figure $1\mathrm{.}1$

$($i$)$ Give a brief explanation how the CSMA$/$CD protocol works.

$($ii$)$ Calculate the minimum frame size which is required by the CSMA$/$CD protocol.

$($iii$)$ Calculate the amount of padding $($in bytes$)$ which is needed if the MAC sub$-$layer

receives $340$ bytes of data for transmission over the Fast Ethernet.

Question $1($continued$)$

$($c$)$ Data Link Layer is divided into two sub$-$layers $-$ the Logical Link Control $($LLC$)$ and the

Medium Access Control $($MAC$)$ sub$-$layers.

$($i$)$ The LLC sub$-$layer carries out the error control using an ARQ $($Automatic Repeat

Request$)$ algorithm. Similar error control algorithm is used in the TCP

$($Transmission Control Protocol$)$ of the Transport Layer. Discuss why the same

error control algorithm is used in two layers, and what is a difference in its

operation in these layers.

$($ii$)$ Consider the LLC which uses the flag bytes with byte stuffing method for data

framing. The fragment shown in Figure $1\mathrm{.}2$ occurs in the middle of a data stream.

Explain, why this fragment requires byte stuffing, and write down the data as they

appear on the line after the stuffing.

A B ESC ESC C ESC FLAG FLAG FLAG D ESC

Figure $1\mathrm{.}2$