1. A LAN has a data rate of 4 Mbps and a propagation delaybetween two stations at opposite ends of 20 s. For what range

1. A LAN has a data rate of 4 Mbps and a propagation delaybetween two stations at opposite ends of 20 µs. For what range ofPDU sizes does stop-and-wait give an efficiency of at least50%?

2. A disadvantage of the contention approach for LANs is thecapacity wasted due to multiple stations attempting to access thechannel at the same time. Suppose that time is divided intodiscrete slots, with each stations attempting to transmit withprobability p during each slot. What fraction of slots are wasteddue to multiple simultaneous transmission attempts?

3. A simple medium access control protocol would be to use afixed assignment time division multiplexing (TDM) scheme. Eachstation is assigned one time slot per cycle for transmission. Forthe bus, the length of each slot is the time to transmit 100 bitsplus the ene-to-end propagation delay. For the ring, assume a delayof 1 bit time per station, and assume that a round-robin assignmentis used. Stations monitor all time slots for reception. Assume apropagation time of 2×108 m/s. For N stations, what is thethroughput per station for

a. A 1-Km, 10 Mbps baseband bus

b. A 10-Mbps ring with a total length of 1Km

4. Consider two stations on a baseband bus at a distance of 1Kmfrom each other. Let the data rate be 1 Mbps, the frame length be100 bits, and the propagation velocity be 2 ×108 m/s. Assume thateach station generates frames at an average rate of 104 frames persecond. For the ALOHA protocol, if one station begins to transmit aframe at time t, what is the probability of collision? Repeat forslotted ALOHA.