Performance Analysis of the SNA Virtual Route Pacing Control

In this paper the authors provide a model and analysis of the IBM SNA virtual route pacing control used to control congestion in SNA networks. The model is appropriate to single virtual routes only. The analysis uses a Norton equivalent of the virtual route queueing model. Similar analyses of two other end-to-end window control mechanisms are carried out; one a sliding window with each message individually acknowledged, the other a fixed window control with the final message in the window only producing an acknowledgement, enabling comparisons to be made between all three. The SNA pacing control procedure, in which the first message in a given window induces an acknowledgement, is found to perform within 4 percent of the sliding window mechanism. Simulation results validate the analysis and performance curves obtained. The third window scheme, with the final message in the window generating an acknowledgement, is found to result in considerable reduction in throughput, as expected.