Browse Prior Art Database

Real-time data transmission on the ARPANET (RFC0508)

IP.com Disclosure Number: IPCOM000005906D
Original Publication Date: 1973-May-07
Included in the Prior Art Database: 2001-Nov-15
Document File: 11 page(s) / 25K

Publishing Venue

Internet Society Requests For Comment (RFCs)

Related People

L. Pfeifer: AUTHOR [+2]

Abstract

The ARPA Network is rapidly proving to be a useful tool in computer communications and resource sharing. It has been proposed that the same network might also be able to support real-time processes such as audio or video communications for conferencing purposes. The degree of support of these types of processes will largely be determined by transmission bit-rates and delays.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 15% of the total text.

Network Working Group                                         L. Pfeifer

Request for Comments: 508                                      J. McAfee

NIC: 16159                            Computer Systems Laboratory / UCSB

                                                              7 May 1973

               REAL-TIME DATA TRANSMISSION ON THE ARPANET

I. INTRODUCTION

   The ARPA Network is rapidly proving to be a useful tool in computer

   communications and resource sharing.  It has been proposed that the

   same network might also be able to support real-time processes such

   as audio or video communications for conferencing purposes.  The

   degree of support of these types of processes will largely be

   determined by transmission bit-rates and delays.

   The IMP subnetwork throughput rates (one way) average about 37

   kilobits[1], therefore an external process must operate at a bit-rate

   below that level.  This would imply some form of data compression for

   both audio and video transmission.  Research in these areas is still

   in progress so these processes must be simulated at the present time.

   In addition to bit-rate, system response time (system delay) is an

   important factor since this has direct influence on the amount of

   data which must be buffered in order to keep a real-time process

   running without discontinuities or gaps.  Such delays may be caused

   by network loading, host loading, or an excessive number of IMP-to-

   IMP hops in the transmission path.

   In order to get a feel for the ability of the network to support a

   real-time process an experiment was conducted with real-time data

   being sent from the UCSB SEL810-B computer, by way of the UCSB IBM

   360 host, onto the ARPA Network and into a host discard socket in the

   UCLA IBM 360 computer.  This particular data path very nearly

   duplicates the path which might be taken if real-time devices were

   attached to large scale host computers operating in their normal mode

   (usually timesharing).  The experiment consisted of measuring the

   duration of gaps incurred at various process bit-rates, and buffer

   sizes ranging from one to eight network packets.

   Earlier experiments at MIT[2] simulated vocoded speech transmission

   over the ARPA Network using the TX-2 computer and "Fake host 3" in a

   destination IMP.  Speech was sampled by the TX-2 and simulated speech

   data blocks were sent to a particular fake host.  Receipt of an

   acknowledgment by TX-2 indicated that the corresponding blocks of

   speech data could be reconstituted.  Experiments were conducted with

   bit-rates from 2400-17000 bps and varying block sizes (depending on

Pfeifer & MacAfee                                               [Page 1]

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 dri...