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Modem trouble (analogue and digital)

Modem trouble (analogue and digital)

Modem trouble (analogue and digital)

I am struggling to connect any form of modem through my ProLogix switch. We moved to a new building about 2 years ago with a set of analogue modems that used to connect direct to Telco copper lines. These are now connected into an analogue card on the switch and the switch has a PRI line to the Telco (British Telecom). The connections we were achieving were much worse than previously on the direct lines.

The problems are several, firstly the modems take many attempts to connect (10 tries is not uncommon), secondly we get lots of data errors, causing many re-transmissions (the lines are running PPP). Consequently, data rates are very poor (1kb/s is about the maximum).
Finally, the lines regularly drop out. Keeping the connection open for more than 15 minutes is sometimes impossible.

To try to solve the problem I have replaced the analogue modems with Eicon digital modem cards (4BRI Diva Server card) connected to a BRI card in the switch.

To my utter amazement, this was no different. Exactly the same problems (poor connection, low connection speeds and low data rates) occur with the digital modems as with the analogue modems.

I would welcome any suggestions of what to try. I have tried connecting to the digital modems as an internal call and always get very good connection (upwards of 52k connection, data transfer rates >4kb/s). I can only think that the problem is with the setup of the PRI line, or with BT. I have heard mention of "bit slip", but I don't really know what this is or what I can do about it.

Tim Wright

RE: Modem trouble (analogue and digital)

First of all check if the DEFINITY has the E1 from the ISDN PRI set as the synchronization source.
(check this with the display sync command, and chanch it with set sync command)

If the sync is set at the DS1 you could try setting SLIP to yes on the DS1 form

Please let me know if the information that was provided is helpfull.
Edwin Plat
A.K.A. Europe

RE: Modem trouble (analogue and digital)

I have checked and the sync is set to the DS1, I have changed the sync to yes and will try the modem performance now.

RE: Modem trouble (analogue and digital)

As ana idea what Companding Law in system country-options you have? It could be a problem for modems if you will have several companding reverse in call path. Compare your switch Companding, DS1 form Companding and modems Companding setting if they have.
What about local modem connection (from extension to extension) did you check it?

RE: Modem trouble (analogue and digital)

All companding modes are set to a-law, which I believe to be correct for the UK. I think the modem connections are good, they are all short (less than 3m from modem to switch) and besides, I have 6 analogue modems and 10 digital modems, all of which exhibit the same problems.


             Companding Mode: A-Law             Base Tone Generator Set: 10
         440Hz PBX-dial Tone? n               440Hz Secondary-dial Tone? n
           Digital Loss Plan: 10           Version of Digital Loss Plan: B
      Analog Ringing Cadence: 10     Set Layer 1 timer T1 to 30 seconds? n
    Analog Line Transmission: 10 Enhanced 64/84xx Display Character Set? n

         Tone Detection Mode: 6
            Interdigit Pause: short

RE: Modem trouble (analogue and digital)

The solution seems to be setting the following parameter on the DS1 page to 3.1kHz from voice. I will continue testing, but initial results look good

            DCP/Analog Bearer Capability: 3.1kHz

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