Subject: (usr-tc) USR vs Ascend (3com vs Lucent?)

From: Aaron Nabil <[email-masked]>
Date: Thu, 07 Oct 1999 13:55:16 +0000

One of my client ISP's has both USR hiperdsp's and Ascend
MAX's.  I've noticed that the Max's seem to perform better
(ratio of successful connects, number of dropped connections)
than the USR's, even when connecting to USR modems.

About 2am this morning I had a flash of insight and drove
into my office (I have a well-equipped home lab, but needed
access to a 4-wire interface.  Not much traffic at 2am, and
no trouble finding a parking space downtown.)  It was worth
the trip, I think I hit pay dirt.

What I tested was the level the server (ISP) modem was 
transmitting at.  I was surprised to see that is was at -10dbm,
which is quite hot.  Beacuse of the way digital lines are
coded, higher power levels have worse s/n ratios, there 
aren't at many quantitization bits available at higher powers.

I plugged in my laptop, fired up tcm, and looked at the hiperdsp
config.  It was set for -11dbm.  Hmmm.  I set it for -15, and yup,
I get -14 when I measure it.  An off by one error someplace, no
doubt.  But it gets better.

I call into our Max's and measured the level they were sending.  Only
-14dbm, much lower power, more what I was expecting.  Telnet in 
and check to see what they are set to, -13dbm, another off by one, but
this time in the opposite direction!

Here's a summary:
			Configured for		Actually sends
USR HiperDSP		-11dbm			-10dbm
Ascend Max		-13dbm			-14dbm

I don't have any scripts in place that monitor failure ratios, but
if someone does I'd be interested if they could set half their modems
to -15dbm (for an output of -14dbm) and see what effect that has.

-- 
Aaron Nabil

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From: Aaron Nabil <[email-masked]>
Date: Thu, 07 Oct 1999 14:48:33 +0000

Aaron Nabil writes...
>USR HiperDSP		-11dbm			-10dbm

One more entry for the above table:
USR HiperDSP		-15dbm			-14dbm

And some even more interesting results!

The above tests were made with 14.4k connections, I figured
that would be an old enough protocol not to have any power
negotiation sequences.  I retested with 33.6k, and here's
what I got.  Note that I'm listing the _median_ power,
occasionally it would pick a notch higher or lower.

33.6k connections:

			Configured for		Median power
USR HiperDSP		-11dbm			-12dbm
USR HiperDSP		-15dbm			-16dbm
Ascend Max		-13dbm			-16dbm

This seems like even more evidence that setting the USR 
to -15dbm might be worth a try. 

I'll be looking at 56k next, but the results aren't as meaningful,
there isn't a direct correllation between power and s/n in v.90.

-- 
Aaron Nabil

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From: Aaron Nabil <[email-masked]>
Date: Thu, 07 Oct 1999 15:44:23 +0000

Aaron Nabil writes...
> . . .

I tested V.90, it always gets about -16.5dbm independant of the
settings or box, which is both expected and reasonable.

-- 
Aaron Nabil

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From: Aaron Nabil <[email-masked]>
Date: Thu, 07 Oct 1999 15:44:24 +0000

Considering the number of requests I've gotten in the last two hours,
I think the'll be plenty of guinia pigs, er, helpful 3com owners
testing the -15dbm setting for me.

Here's the instructions (at least this works on my TCS 3.6)
>
>>Where in TCM do you change these levels.  I will change them on a couple of
>>DSPs and see what happens.
>
>Select the modems.  Configure/Programmed settings.  Select the
>modems you want to change.  Under Line Interface Options,
>change Transmit Level.

-- 
Aaron Nabil

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From: Richard Lorbieski <[email-masked]>
Date: Thu, 07 Oct 1999 17:40:21 +0000

Where in the TCM do you set the dbm levels? I looked everwhere on the
DSP config settings.

-- 

Richard Lorbieski - [email-masked]
Chief Technical Officer - Senior System Administrator
Alpha1 Internet  http://www.alpha1.net
409.731.8236  - 877.4.alpha1 (877.425.7421)

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From: Kevin Benton <[email-masked]>
Date: Thu, 07 Oct 1999 19:47:52 +0000

> Where in the TCM do you set the dbm levels? I looked everwhere on the

Same place as on the quads - at the modem level.  Click on the modem
status lights, configure, programmed settings, and poke around.  Most
people don't even know you can change settings for the modems on a DSP
card...

Kevin

> > to -15dbm (for an output of -14dbm) and see what effect that has.

E-Mail:  [email-masked]
Web:     http://users.sota-oh.com/~s1kevin/
Unsolicited advertisements processing fee: $50 subject to change without notice

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From: Mike Andrews <[email-masked]>
Date: Thu, 07 Oct 1999 21:20:12 +0000

There was some discussion on transmit levels a while back -- check the
archives.  If I remember right, David Bolen said that ANS made a habit of
setting all their modem pools (for AOL mostly) to -13dBm.

We had a few people have problems when we tried backing ours down, so for
now I've left it alone until I can get a better idea.

Complicating things more is that we have both Quads and DSP's, and the
Quads default to -11, but the DSP's default (or at least used to default)
to -12.  The Courier I-Modem I have at home defaults to -12.  What the
actual transmit power works out to in all these cases at each modulation
is anyone's guess...

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
"With sufficient thrust, pigs fly just fine." -- RFC 1925

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From: Brian <[email-masked]>
Date: Fri, 08 Oct 1999 03:50:38 +0000

> setting all their modem pools (for AOL mostly) to -13dBm.

nod, I have those emails.  The thing is, that was on the Quads.  The quads
could do analog or digital.  The default modem templates were optimized
for analog calls not digital.  So you would have to make some changes to
the Quads to optimize for CT1/PRI.

David did clarify however that the HDM's didn't have this problem.  But
that was when they first came out, who knows whats what since then.

>  "help" to the same address.  Do not use quotes in your message.

-----------------------------------------------------
Brian Feeny (BF304)     [email-masked]   
318-222-2638 x 109	http://www.shreve.net/~signal      
Network Administrator   ShreveNet Inc. (ASN 11881) 	      

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From: Mike Andrews <[email-masked]>
Date: Fri, 08 Oct 1999 05:45:34 +0000

> that was when they first came out, who knows whats what since then.

FWIW...  I just blew a 2.0.81 DSP back to factory defaults and it comes up
set to -11 now, instead of -12 like it used to.  So it looks like both
Quads and DSPs default to -11 now.

(Courier I-Modem still does -12 on my BRI at home...  that would be
interesting to experiment on...)

Anyway.  Given that the measured level and the programmed level tend to
vary on both 3Com and Ass^Hcend stuff...  anyone have a new consensus as
to what we should be using instead of 11?  13?  15?

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From: Greg Coffey <[email-masked]>
Date: Wed, 20 Oct 1999 16:38:34 +0000

Do you have a conclusion on this yet?  Does changing these settings have 
any impact?

>to -15dbm (for an output of -14dbm) and see what effect that has.

Thanks, Greg Coffey                     <[email-masked]>
Visionary Communications V 307-234-5443 F 307-234-5446
100 N. Center, Casper, WY  82601         www.vcn.com

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From: Aaron Nabil <[email-masked]>
Date: Wed, 20 Oct 1999 23:07:29 +0000

Greg Coffey writes...
>Do you have a conclusion on this yet?  Does changing these settings have 

I haven't tried it yet, haven't been around the office much.  

-a

-- 
Aaron Nabil

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From: [email-masked]
Date: Wed, 20 Oct 1999 23:41:13 +0000

We set a couple of HUBS to -13db and did not notice much of a
difference  our call fail rate is between 3% and 4%  For example out of
235 calls taken 7 would fail....

 This was about the same whether it was -11db/-12db/or -13db

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