Comments on the RCTE Telnet option
RFC - Unknown
(August 1973; No errata)
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RFC 563 (Unknown)
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Network Working Group J. Davidson
Request for Comments: 563 University of Hawaii
NIC: 18775 28 August 1973
References: RFC 357, RFC 560
Comments on the RCTE TELNET Option
RFC 560 describes a Remote Controlled Transmission and Echoing TELNET
option. Its authors provide a framework wherein a serving host may
control two aspects of TELNET communication over the (simplex) user-
Commands are introduced which govern
1. when (and which) characters shall be echoed by the user, and
2. when (and which) characters shall be transmitted by the
Motivation for the option was based on two considerations:
1. the latency between striking and printing of a character
which is to be echoed by a remote server is disconcerting to
the human typist, and
2. character-at-a-time transmission introduces processing
inefficiencies (for IMPS, for servers, for users) and
decreases effective channel thruputs over the net.
The author feels that the RCTE description is in error (or at least
unclear ) in its treatment of when characters are to be
transmitted. However, discussion of the subject in the RCTE
specification is incomplete, so it is difficult to point to a
statement which is "wrong." Rather, the present objections are based
on inferences drawn from the sample TENEX interaction
Perhaps there is some misunderstanding of the original issues to
which RCTE now addresses itself.
Original Motivation for Remote Controlled Echoing (RCE)
RFC 357 (An Echoing Strategy for Satellite Links) introduced a need
for RCE for users who are separated from a service host by a
satellite link. The motivation was to lessen human frustration and
confusion; no consideration was given to resulting processing
inefficiencies or channel thruputs.
(In the remainder of this RFC, we consider character transmission
apart from echoing considerations.)
Davidson [Page 1]
RFC 563 Comments on the RCTE TELNET Option 28 August 1973
It was recognized that the human's best interests could be served if
user-to-server transmission were performed on a character-by-
character basis, (the implicit assumption being that this insured
the most rapid server response possible). This scheme allowed for
the classic overlap of (network) I/O and computation, and was thus
efficient as far as the (human) user was concerned.
Concessions were made in the transmission strategy when it was
accepted that the serving process could not in fact do any
significant processing until a completed command was available.
Ideally then, users should be able to buffer characters until they
have a completed command and then fire off the entire command in a
single "packet," with the resultant savings in channel usage and a
greater per-packet data efficiency. The characters which delimited
commands were called wakeup characters, in 357, for their effect on
the serving process. RCTE calls them transmission characters for the
effect they have at the User TELNET.
The key here is that it is quite possible for a human, separated by
a satellite link from his remote host, to type several completed
commands - and to therefore initiate several packet transmissions-
all the while awaiting the server's response to his first command.
Again we see the overlap of I/O and computation, and again we
achieve maximum efficiency from the human's viewpoint.
The problem, however, is that wakeup (transmission) character sets
change. And there will always be a finite amount of time [the one-
way transmission time] during which the set definitions will differ
between server and user. This says that during such times the user
will be sending off packets which do not contain completed commands,
(or contain more than a single completed command), or he will be
buffering characters beyond the end of a completed command. (A
fourth alternative is that he may actually still be doing the right
thing by chance). Buffering beyond the end of a command is the only
case which lessens processing efficiency for the human, however.
Dissatisfaction With RCTE
Here is the author's complaint: RCTE [at least the sample
interaction which allowed transmission (by default) only at break
characters] would have the TELNET user wait until he knows exactly
the wakeup (transmission) character set being used by the server !
Ideal channel utilization might be achieved, since no "unnecessary"
packets are sent (and, strangely, no extra characters are allowed in
the current packet) but the overlap of I/O and computation has been
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