Subject: (usr-tc) V.42 selective reject

From: Antonio Querubin <[email-masked]>
Date: Sun, 26 Mar 2000 06:29:35 +0000

I've just loaded the Hi-Per DSP firmware version 2.0.51 into one of our
TCS hubs for testing.  In older versions of the firmware (I think 3 or so
versions prior to this one), the default setting for V.42 Selective Reject
was disabled.  However, newer versions of the firmware including this most
recent one have it enabled by default.  The docs indicate it benefits
modems and phone lines experiencing some packet loss.

However, up till now, we disabled V.42 Selective Reject explicitly just to
ensure the same behaviour on our TCS with previous versions of the
firmware.  We even disabled it on the quad-modem cards for the same
reason.  This time we're leaving the default setting alone (enabled) but
I'm wondering if this might be opening us up to increased problems with
customers running older modems.

I haven't yet noticed any mention of this feature on the lists or in the
archives so I thought I'd ask directly.  Has anyone run into problems with
using V.42 Selective Reject on the quad-modem cards (version 6.1.6) and/or
the HiPer DSP modem cards (version 2.0.81 or 2.0.51)?  If so, what
percentage of users were affected?  What kinds of modems were most
susceptible to problems, if any at all?

Antonio Querubin

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From: Mike Andrews <[email-masked]>
Date: Sun, 26 Mar 2000 07:58:32 +0000

As far as I know, Selective Reject is only supported by 3Com client modems
(err, USRobotics, or whatever little company it is that owns that product
now, sigh)...  but anyway it seems to be safe in every config combo we
have here (Quad, DSP 2.0.51, all client modems).

Short version of what it does is that it reduces the amount of data that's
retransmitted when a v.42 frame gets corrupted.  It's an optional part of
the v.42 spec and not many people bothered to implement it.  For client
modems that don't implement it, it doesn't make a bit of difference
whether you turn it on or off at the server end.

Mike Andrews (MA12) * [email-masked] * http://www.bit0.com/
VP, sysadmin, & network guy, Digital Crescent Inc, Frankfort KY
Internet services for Frankfort, Lawrenceburg, Owenton, Shelbyville
www.fark.com: If it's not news, it's Fark.  (Or something like that.)

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