RFC 508 (rfc508) - Page 2 of 10
Real-time data transmission on the ARPANET
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RFC 508 Real-Time Data Transmission On The Arpanet 7 May 1973 the number of hops), and conclusions were reached that with delay characteristics similar to a lightly loaded ARPA Network speech communications could be satisfactory from a human-factors standpoint. II. CONFIGURATION Data for this experiment originated in an SEL 810-B computer located in the Electrical Engineering Department at UCSB. This 70ns cycle time computer is the heart of an interactive signal processing system developed by Retz[3]. It has associated hardware such as a card reader, two IBM 1311 disk drives, a drum storage unit, A/D and D/A converters, Teletype, Tektronix 611 storage display unit, OLS keyboard, and a connection to an IBM 1800 computer. This system is linked to the UCSB IBM 360/75 via a 500 kilobit line for high speed data transfers. Software in both the SEL 810-B and the IBM 360 enables the SEL to communicate with the ARPA Network. The hardware configuration of the data path between the SEL 810-B and UCLA is shown in Figure 1. For simulating speech transmission, the SEL is thought of as a "speech processor", analyzing and encoding the one-way conversation of a person at UCSB talking to someone at UCLA. The fact that there was no "speech processor" at UCLA probably had little or no effect on the measurements that were made. This is substantiated by noting that the SEL was a dedicated processor that did not introduce delays and if a similar dedicated processor was attached to the host computer at UCLA it probably would not have caused delays either. However, the UCLA host merely discarded the data it received, thereby going through fewer steps than if an external processor was attached, and so our simulation was not exact. A configuration such as that of Figure 1 did yield information about host-to-host transmission, since the SEL was essentially a zero-delay data generator. If real-time processors are to access the ARPA Network through large-scale time-shared host computers then host-to- host transmission rate and delay are important measurements. In this configuration we can expect the host computers to be the primary bottlenecks in the data path. Pfeifer & MacAfee
