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Difference between CO Trunk and B1/POTs


   I am currently deploying Cisco VoIP to a number of sites.  Some of these sites currently have B1/POTs lines, some have DID & CO trunks. Is there a difference between a CO trunk and a regular land line/B1? Can you terminate a CO trunk directly on a analog device like a Fax machine?

The question is probably elementary but I cant find anything specific on the differences between them.               

2 Replies 2

paolo bevilacqua
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Some telco charge a premium for business grade lines and call them trunks, however these are the same as regular circuits.

On the other hand DID circuits have to be terminated on FXS, not FXO.

For a final answer you have to ask your telco what is what necause different people calls the same thing with different names.

In any case it is better to avoid analog anyway, and use T1 PRI instead.

Is there any difference in quality of the lines/trunk themselves?

I am having issues with Postage Machines at the sites.  We can get them to work fine on PRI sites, however if the Postage Machine is trying to connect over a CO trunk the handshake fails. It seems to come down to the input gain/outout attenuation/impedance settings on the voice-port connected to the CO trunk. I can get it to work occasionally but its not consistent. Its basically two modems connecting to each other, same as a fax session.

We also have some sites that have B1 lines instead of CO/DID trunks.  The B1 lines will be terminated on FXO ports on the router and be configured as a single trunk-group for all inbound/outbound calls. 

I am curious if the B1 lines will have the same amount of static/noise on them as the CO Trunks.  Is a B1/POTs line more clean than a CO Trunk, even if they are both terminated on FXO ports?

Thank you for the response

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