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Digital Padding at the Switch, was RE: (ASCEND) 56k and CT1



Just FYI -

On channelized T1's (not PRI), the digital-padding Kevin refereed to is
usually configurable at the Switch.  While I don't have specifics for
Lucent/AT&T switches, on NorTel the following info may be handy.

When ordering lines (trunk side) from DMS provisioned services, specify
to the provider that you wish to have your trunks data-filled with NIL
PAD GROUP.  This tells the DSP on the DMS switch to *not* alter the gain
or frequency response of the incoming DS0 channels.  Most Telco's still
apply standard "pads" to data circuits incorrectly, mainly because of
not understanding the issues.  (they use voice designed pads as a
default in many cases)

On a DMS switch, there are about 50 pad groups, the one you usually want
is "NPDGP" (NIL PAD GROUP)

In some cases, this change alone is worth 2 speed increases higher in
connect rates, and far less "phantom" discos for end users.

You mileage will vary and there are a few reasons why this is NOT
absolute advise for all instances, but it is a pointer for those who are
experiencing troubles.

Best regards,

Dave Van Allen - You Tools Corporation/FASTNET(tm)
dave@fast.net (610)289-1100 http://www.fast.net
FASTNET - PA/NJ/DE Business Internet Solutions


>-----Original Message-----
>From:	Kevin Smith [SMTP:kevin@ascend.com]
>Sent:	Thursday, May 22, 1997 9:21 PM
>To:	Matt Holdrege
>Cc:	ascend-users@bungi.com
>Subject:	Re: (ASCEND) 56k and CT1
>
>At 05:58 PM 5/22/97 -0700, Matt Holdrege wrote:
>>At 08:15 PM 5/22/97 -0400, Matthew S. Dwyer wrote:
>>>
>>>Hello,
>>>
>>>We are planning to order a number of Series56 modems for evaluation 
>>>on our CT1 circuits. Given that we have seen lower performance on CT1
>>>compared to PRI with 28.8k, what sort of performance should we
>>>expect with 56k? Can these modems adjust for the bandwidth limitations
>>>per channel on CT1? (200-3800hz)
>>
>>With channelized T1, you must have the telco provision trunk-side rather
>>than line-side to get the higher speeds. It's theoretically possible to get
>>56K on a trunk-side T1, but in practice that may be iffy.
>
>According to USR/Rockwell:
>
>As far as T1 lines are concerned, both Rockwell and USR claim to have 
>been able to avoid signal loss in T1 lines by detecting what they call 
>"digital-padding" in T1 switch. This digital pad can cause the modem signal 
>to drop as much as 6db. Once they detect this digital pad during the first 
>stage of negotiation, they boost their transmit level by 6db. They also have 
>algorithm to compensate for robbed-bit signaling.
>
>Kevin Smith                              Updated Service and Support
>Ascend Communications                    Resources are now at:
>                                         http://www.ascend.com/service
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