PART C: Multiple Access

$[15$ Points$]$ Question $3$: George wants to setup a wireless network in a reserved frequency band

for only the ICS$-343$ staff to use. The frequency band reserved for the staff is $500MHz$ wide, for which

Peter, Bruce, David, George, and Jacob will share. George, who did not pay attention during lecture, is

trying to figure out the best way to multiplex the channel such that each member can achieve the best

throughput in the network. The only method he can currently remember is time division multiple

access $($TDMA$).$ To test the network the staff will perform a $500$KB file transfer simultaneously. Ignore

propagation delay and handshaking, and assume each user has one transceiver that is tunable to any

frequency and can transmit data at a maximum rate of $2Mbps,$ using $100MHz$ of the channel. There

is a maximum packet size of $1000$ bytes, no header is used. Assume a noiseless channel $($no loss will

occur$),$ such that no ACKing or collision detection scheme is needed.

A$.$ In the TDMA protocol that George develops, each staff member is allowed to transmit a single

packet, to avoid interference $5ms$ of silence is required, followed by the next staff member's

packet transmission. Therefore, a single 'round' of transmissions looks like this, note the order:

George, $5ms,$ Bruce, $5ms,$ David, $5ms,$ Peter, $5ms,$ Jacob, $5ms.$ Using this protocol, how long will it

take George's $500$KB file transmission to finish?

B$.$ TDMA is not the optimal way to multiplex the given channel. There is a more efficient way which

allows all staff member's transmissions to finish faster. Name the technique and briefly describe

how it works. How fast can George's file transmission finish now

Hint: Break the times down in this problem, such as the time to transmit a packet and a total round

time $($e$.$g$.,$ the time it takes from the start of George's first packet to the start of George's second

packet$).$

Solution