Performance Analysis of the SNA Virtual Route Pacing Control

Abstract

In this paper we 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 acknowledgment, enabling comparisons to be made between all three. The SNA pacing control procedure, in which the first message in a given window induces an acknowledgment, 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 acknowledgment, is found to result in considerable reduction in throughput, as expected. As a by-product of the analysis the Norton equivalent is found to be a useful tool in obtaining approximate solutions to rather complex queueing networks. Copyright © 1982 by The Institute of Electrical and Electronics Engineers, Inc.