Optimal HDLC I-Frame Structure in a Two-Way File Transfer and IIASA Data Communication Network

Masunaga, Y. (1976). Optimal HDLC I-Frame Structure in a Two-Way File Transfer and IIASA Data Communication Network. IIASA Research Memorandum. IIASA, Laxenburg, Austria: RM-76-031

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Abstract

This memorandum discusses the optimization problem that arises from adopting the HDLC procedure as the link protocol for the IIASA data communication network. In particular, the problem of identifying the optimal length of the information part of a HDLC information frame (I-frame) is solved by using a "two-way" file transfer in the network. The results show that the optimal length of the information part of a HDLC I-frame is 5, 13, 47, 160, 500 and 1,460 bytes, corresponding to the communication line error probabilities of 10^(-2), 10^(-3), 10^(-4), 10^(-5), 10^(-6), and 10^(-7) in one bit, respectively, so that the throughput is maximized, where the modem polarity switching time is set at 250 ms. The author suggests that the results of the two-way file transfer be compared with those of a "one-way" file transfer presented in [6]; the optimal length in a two-way file transfer is about 20% less than that in a one-way file transfer. It is suggested that the network designer choose the length of the information part that lies between two values corresponding to the line quality. This is because the two-way and one-way file transfers cover two extreme cases where the load (i.e. files to be transmitted) is equally distributed among network stations, and the one-way file transfer represents the case where the load is only partially distributed. The author also discusses the effects of the change in the modem polarity switching time on the optimal length of the information part. When the switching time is changed. from 250 to 100 ms, the optimal length is about 13% less.

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