Ten devices are connected at different points along a cable of length $600$ m$.$ The physical layer operates at $10$ Mbit$/$s$,$ and signals travel on the cable at $2108$ m$/$s$.$ The devices transmit in turn, using a fixed TDMA system. A device is allowed to transmit one or more link layer frames in its timeslot. These could be data frames, addressed to different devices, and$/$or acknowledgement frames for data frames received earlier. Most of the devices transmit equal amounts of data, but devices $1$ and $4$ each transmit twice as much data as the others. a$)$ Propose a suitable guard time for this system. Then propose a suitable duration for each time slot and calculate the total duration of the TDMA frame. Give reasons for your proposals. $(30\%)$ b$)$ Assuming sensible time slots, the efficiency of the link layer protocol should be about $90\%.$ Estimate the total throughput that can be achieved in this system, assuming the devices always have data to send. $(30\%)$ c$)$ Propose one alternative method of sharing the channel in this system, which would give better overall throughput when devices had varying amounts of data to send. It is not necessary to calculate the throughput, but you should explain why you think your proposal would be better than fixed TDMA.