dlpsim: a teaching harness for data link protocols

Protocol test harnesses have been in use for a number of years to assist implementors in checking conformance of their implementations with reference implementations. The system described here is designed for teaching the principles of data link protocols. Students write protocol implementations in a high-level language and exercise them on a simulator. The simulator checks that data is not duplicated or lost by the protocol. On suitable terminals, visualization of the transmitting window and of the frames traversing the link can provide useful feedback to students. Simple estimates of throughput are also calculated.