RFC 357 (rfc357) - Page 1 of 13

Echoing strategy for satellite links

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Network Working Group                                      John Davidson
Request for Comments: 357                           University of Hawaii
NIC: 10599                                                 Will Crowther
Categories: Remote Controlled Echoing, Satellite, TELNET             BBN
References: RFC's 346, 355, 358, 318                      John McConnell
                                                                  ILLIAC
                                                              Jon Postel
                                                                    UCLA
                                                           June 26, 1972


                An Echoing Strategy For Satellite Links

I. Introduction

   As mentioned in RFC 346 ("Satellite Considerations" by Jon Postel)
   those interactive systems which provide echoing for full-duplex
   terminals over the ARPANET become more awkward to use as transmission
   delays increase.  The reason, of course, is that a character's round
   trip time is added to the inherent echo delay of the server with the
   result that the terminal echoing appears extremely sluggish.

   For a terminal separated from its server by a single satellite link,
   the delay will be such that even if echoing at the server were
   instantaneous, the latency between keying and printing of an input
   character will be nearly half a second.  If, in addition, the
   character is routed thru a portion of the surface net, the delay will
   be of course increase.  It is estimated that echo delays of at least
   one second will not be uncommon.

   This document describes a strategy which will eliminate the delay
   associated with simple echoing and allow the transmission delay to be
   hidden in the cost of computation only.  This scheme is proposed as
   an optional addition to existing User TELNETs; its use requires the
   explicit support of a cooperating server process.

II.  Standard Echo Strategy

   Echoing for locally connected full-duplex terminals is normally
   provided at the server by a resident system task called the (e.g.)
   Terminal Handler.  The Terminal Handler echoes on a one-for-one or
   simple replacement basis and buffers all typed input on behalf of the
   user process.

   To let the user process operate most efficiently, the Terminal
   Handler should collect characters until a complete command or
   parameter (or whatever) has been typed.  Then, presumably, the
   process can do some significant computing.  Since the user process



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