rah@sppy00.UUCP (MOORE ROBIN) (02/16/91)
Can anyone help me understand this problem, and hopefully correct it?
We have an application running on an IBM 3090, which is accessed via
IBM's Telnet server software. The application typically outputs an
entire 24 x 80 screen of data at a time. Occasionally, a line of text
towards the bottom of the screen will write over the previous line.
The problem has been experienced running a Telnet client from both
Pyramid and Sun 3 systems.
Placing a LAN analyzer on the net, we have determined two things;
I'm not sure if both of them pertain to the problem, or just the
second one.
1) It appears that the IBM Telnet software is changing every
occurance of CR LF in the output into the sequence CR NUL CR LF.
Reading over RFC 854, it sounds like it would not be unusual to
convert CR LF to CR NUL, but including both seems strange.
Perhaps this is because the IBM typically negotiates the terminal
type of the connection down to the simplest, line-by-line type
terminal available?
2) The problem of the overwritten line is seen when segmentation of
the message occurs between the 2nd CR and the LF. In other words:
First packet: ... Text_of_line_x CR NUL CR
Second packet: LF Text_of_line_y CR NUL CR LF ...
Line y is overwritten by line x.
Should IBM's software be refusing to split the message between these
characters? This seems unlikely, since I would expect the act of
segmentation to be done in the Transport layer by TCP.
On the other hand, are the Pyramid and Sun Telnet clients both faulty
in their handling of the CR LF when it crosses message boundaries?
Thanks in advance for your assistance, Robin
--
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