RFC 508 (rfc508) - Page 2 of 10

Real-time data transmission on the ARPANET

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