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