Leased line modem communications

S

Thread Starter

Sam Kwok

My questions are:
1. Is there modem on the market that are dedicated for leased line communications?

2. Must I use these modems for PLC communication over leased line or any ordinary 56K dial up modems will do the job?

3. Does the setup, initialization strings, AT command used etc. between modem communicating over dial up line and leased line communication differ a lot?

Please give me some clue or idea on the above, any information are appreciated.

Sam
 
These answers are to the best of my experience with leased line communications, and may not be 100% accurate. It's been a long time since
I've used leased lines for serial comms. These days most customers I see are using frame relay or T1 and TCP/IP ethernet, not much serial. Going
back to my BBS days here...

1. Yes there are leased line modems. Check www.data-linc.com for a couple, I'm sure there are other ones out there.

2. Leased line modems and dial-up modems are a bit different, as there is no dialing on a leased line. A leased line modem is more like a CSU/DSU
unit, to control communications over the line. However most dial-up modems are capable of being configured to operate over a permanent connection.

3. Since a leased line is a permanent connection, there is no dialtone, dialing, or ringer and so no AT command set. These units are usually configured with a serial terminal program.

CK
 
V

Vedran Kosta

Hi,
I work for local Watersupply Company, as automation engineer.
For closer pump stations we have telephone cable laid along with pipeline.
We use this cable for star connections between PLC at pump stations and computer with SCADA software in control centre.
We have worries about signal attenuation and lightning strikes, but real problem shows construction workers, as they dig and cut these cables.
So actually we never had communications interruptions because of attenuation or lightning strikes, only because of construction workers.
Today we have 5 pump stations connected this way, all in range about 6 km from centre, and few more soon will come.
NOTE: For this topology you must obtain serial multiport card for control computer.

>1. Is there modem on the market that are dedicated for leased line
>communications?
>
USRobotics Curier. Modem itself isn't sealed, but we put it in sealed cabinets with heater at pump stations. One works since 1996 without
interruption 24h/day.

>2. Must I use these modems for PLC communication over leased line or any
>ordinary 56K dial up modems will do the job?
>
Dial-up modem won't automatically reconnect in case of disconnection.

>3. Does the setup, initialization strings, AT command used etc. between
>modem communicating over dial up line and leased line communication differ
>a lot?
>
Standard command set is widened with commands for leased line operation.

I hope that this information will help you.
Best regards,
Vedran Kosta,
"Vodovod Dubrovnik", Croatia
 
Sam,

Look for a Bell 202 type modem, such as the Data-Linc LLM1100, for dedicated leased-lines. This type of modem is not the same as your standard 56K modem you use to connect to the internet. check out http://www.data-linc.com/
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Don Best
[email protected]
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