Solution to Exercise 4: Communication Protocol

1. A simple network consisting of two nodes, X and Z is shown in Fig 1. The nodes are separated by a distance of L = 800 m, and each node has a single frame of F = 1500 bits (including all headers and preambles) to send to each other. Both nodes attempt to transmit at time t = 0. In case that a node detects a collision, the node executes the exponential back-off algorithm. In the exponential back-off algorithm, a node experiencing the n collision in a row for a given frame, randomly chooses a value for K from {1 · · · 2}, where m =min(n, 10). The node then waits for a time K × tw before attempting to re-transmit the frame. tw is the latest time at which all nodes detect collision. The propagation speed of the signal over the network is σ = 2× 10m/s. It is given that X and Y have data-rate of 150 Mbps.