Second thoughts in defense of the Telnet Go-Ahead (RFC0595)

Publishing Venue

Internet Society Requests For Comment (RFCs)

Related People

W. Hathaway: AUTHOR

Abstract

This note is a reply to Edward Taft's "Second Thoughts on TELNET Go- Ahead" (NIC #20812). Specifically, I will attempt to show the following about the three main directions of his objections:

Network Working Group Wayne Hathaway

Request for Comments # 595 AMES-67

NIC # 20617 12 Dec 1973

References: NIC # 20812

Some Thoughts in Defense of the TELNET Go-Ahead

This note is a reply to Edward Taft's "Second Thoughts on TELNET Go-

Ahead" (NIC #20812). Specifically, I will attempt to show the

following about the three main directions of his objections:

1. It is the idea of line-at-a-time systems which are esthetically

unappealing, not the GA mechanism. This may be a valid point, but

given the large number of such systems on the net, it would seem a

rather academic one.

2. The specified GA mechanism will in fact work very well between

(reasonably implemented) line-at-a-time systems, and should provide

significant help elsewhere.

3. While the GA mechanism may not be correct in all cases, it can

provide significant advantages fro the line-at-a-time systems and

users.

My comments will be arranged under the original headings from the

subject RFC (NIC #20812).

"TECHNOLOGY"

The definitions of "half-duplex" and "reverse break" are

satisfactory. Two points should be made regarding "reverse break",

however. First: having reverse break on the terminal is of course not

sufficient; the operating system must support it. As "support" is

equivalent to "require" in this context, it is not too surprising

that some systems do not in fact do this. That is, there are systems

which will not type through an unlocked keyboard until the user

manually turns the line around, and the operational problems with

such systems are much less than might be assumed. Second, at least on

IBM 2741's and equivalent, the line turnaround takes a significant

amount of time, during which user-typed characters may be missed or

garbled. In fact, a fairly standard mode of operation with systems

that use reverse break (including TIP's) is to automatically enter

a "line delete" character and start over every time the reverse break

is used while typing, which can hardly be called esthetic. One

solution to this problem would be for the system to not use reverse

break once the user has begun typing (as suggested near the end of

NIC #20812), but most systems (including TIP's) do not do this.

Some discussion is also warranted at this point about line-at-a-time

systems (hereafter abbreviated as LAAT systems). One prime reason for

LAAT operation is to avoid the overhead of interrupting the CPU (and

possibly the user process) for every character ...