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Subject: TCP-Group Digest 96/170A
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TCP-Group Digest Sat, 24 Aug 96 Volume 96 : Issue 170
Today's Topics:
PPP/SLIP in connected AX25? (6 msgs)
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----------------------------------------------------------------------
Date: Fri, 23 Aug 1996 20:03:24 +1000
From: Terry Dawson <terry@perf.no.itg.telstra.com.au>
Subject: PPP/SLIP in connected AX25?
Phil Karn wrote:
> The over-the-air interface would then be PPP or SLIP in connected-mode
> AX25 with PID F0. To distinguish this mode from conventional "dumb
> terminal" (e.g., BBS) mode, the NOS router could either set aside a
> separate AX25 SSID. Or it could get clever and look for the
> distinguishing characteristics of a SLIP or PPP frame in the incoming
> data, e.g., the leading C0 or 7E flag character. I understand that
> some dialup IP routers/terminal servers already do this.
Most NOS derivatives already wait for a carriage return on input before
entering the BBS now, so testing the first character for either a
newline, or a C0 would be simple enough.
Thinking about the mtu/paclen relationship. I suppose you could get
away with setting setting mtu == AX.25 Window * PacLen ok. Finding
the optimum balance between IP overhead and Too Large Window could
be a fun experiment.
You could get away with using very short 'wait for next key before
sending' paramaters in transparent mode, since they'll be computer
generated anyway.
Ironically it would appear there is actually some advantage to be
gained from using this system. That being that is will be possible,
even likely at times, for more than one datagram to be carried in the
same AX.25 frame, helping minimise AX.25 overhead.
Terry
------------------------------
Date: Fri, 23 Aug 1996 19:51:51 +1000
From: Terry Dawson <terry@perf.no.itg.telstra.com.au>
Subject: PPP/SLIP in connected AX25?
Phil Karn wrote:
> What about plugging a standard Winsock stack that supports PPP or SLIP
> (like the one that built into Windows 95) into a conventional (not
> KISS) AX25 TNC and connecting it to a suitably configured NOS gateway?
>
> The over-the-air interface would then be PPP or SLIP in connected-mode
> AX25 with PID F0. To distinguish this mode from conventional "dumb
> terminal" (e.g., BBS) mode, the NOS router could either set aside a
> separate AX25 SSID. Or it could get clever and look for the
> distinguishing characteristics of a SLIP or PPP frame in the incoming
> data, e.g., the leading C0 or 7E flag character. I understand that
> some dialup IP routers/terminal servers already do this.
You'd use SLIP, less overhead than PPP, and PPP would be overkill on
a 'reliable' AX.25 connection in any case.
Do you mean that at the NOS end you would build receive slip
encapsulated
IP that you would unwrap and then pass to the IP code ? It doesn't sound
terribly difficult. It sounds kinda fun too. There is a certain elegance
to the otehr end of the link, just dirve the tnc with the usual modem
expect/send sequences to establish the link and treat it like any other,
slow, serial link. If the mtu's were dropped low enough, and the tnc
were set for transparent mode, which it would have to be for SLIP, then
you might manage one datagram/packet easily enough.
Do you really want to support that style of connection ? :)
Terry
------------------------------
Date: Fri, 23 Aug 96 17:15:00 -0000
From: mikebw@bilow.bilow.uu.ids.net (Mike Bilow)
Subject: PPP/SLIP in connected AX25?
To be continued in digest: tcp_96_170B
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