Question $2)$

a$)$ A number of medium access protocols have been proposed that can be used to determine

the access to the medium for a set of stations.

i$)$ Assume that the wired network of your company currently uses a Time$-$Division

Multiple Access $($TDMA$)$ approach that is configured to accommodate $6$ stations.

Explain how stations in this network gain access to the medium and the advantages

and disadvantages of this approach. Your explanation should be accompanied by

diagrams that visualise the behaviour of the protocol and its limitations$.$

ii$)$ Assume that your manager asks you to propose a protocol that could be used instead

of TDMA in i$)$ and that would be suitable to accommodate a varying number of

stations. Suggest a suitable protocol, explain the procedure by which stations would

gain access to the medium by competing with each other and discuss the advantages

and disadvantages of this protocol. Your explanation should be accompanied by

diagrams that visualise the behaviour of the protocol and its limitations$.$

b$)$ IEEE $802\mathrm{.}11$ defines two methods for medium access control, the Distributed Coordination

Function $($DCF$)$ and the Point Coordination Function $($PCF$).$

i$)$ Assume that six stations S $1$ to S $6$ use $802\mathrm{.}11$ radios and are within each other coverage

area. Station S$2$ intends to transmit to station S$4$ and station S$6$ intends to transmit to

station S$1.$ The stations will use $802\mathrm{.}11$ DCF to get access to the medium. Describe the

frames that will be exchanged by the stations and the inter frame spaces that are

involved in these exchanges. Use diagrams to visualise the chronological exchange of

the frames and the inter$-$frame spaces that are involved in these exchanges.

ii$)$ Assume that the communication laid out in i$)$ would use $802\mathrm{.}11$ PCF instead of $802\mathrm{.}11$

DCF and that an access point AP is present as point coordinator. Describe the frames

that will be exchanged by the stations and the inter frame spaces that are involved in

these exchanges. Use diagrams to visualise the chronological exchange of the frames

and the inter$-$frame spaces that are involved in these exchanges.