BRI over E1 interface - possible (perhaps TDM? )

Unanswered Question
Jun 13th, 2007


we have two locations, which are connected to the central via an E1 line. On each of the three locations (2 subsidiaries and the central) we have an Cisco 2811 with VWIC2-1MFT on the subs and WIC2-2MFT on the central location.

For connecting the PBXs of the locations we need a dedicated leased line from our telco. My idea is to provide the leased line by ourselves via our E1 line.

Is this possible?

Can I install a BRI interface (which one) in the routers and cross connect the BRIs in the sub and the central?

How can this be done and how do I have to configure it?

At the moment we use the VWIC2-2MFT like this:

controller E1 0/0/0

channel-group 0 timeslots 1-31

My idea is to change channel-group 0 to timeslots 1-29 and use channel 30-31 for crossconnecting the BRIs.

How can this be done?

Thanks for your assistance and best regards

Florian Zahn

I have this problem too.
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Paolo Bevilacqua Wed, 06/13/2007 - 05:11

Hi Floran,

yes you can do this.

Howver you do not need to do TDM or statically allocate anything. It is just a regular VoIP that you will be doing. On the 2811 install VIC2-2BRI-NT/TE, each one has two BRI ports, for teh quantity you need. Also you will need PVDM2-xx where xx is the number of simultaneous calls you want to support, then multiply by two. that, if 4 calls, you will need pvdm2-8. You will be able to send compressed voice. Ask again for more details on the "general" forum of Voice.

Paolo Bevilacqua Wed, 06/13/2007 - 10:11

Partial correction to the above, actually you need a pvdm2-xx with xx just asm number of concurrent voice calls using uncompressed voice, for compressed, the exact pvdm2-xx required can be calculated.

Florian Zahn Wed, 06/13/2007 - 21:11

Hi Paolo,

thanks for your quick respone to my question.

I am not sure, if I can solve my problem with VoIP configuration, because I do not want to pass voice via the interfaces, but data. For connecting the two PBXes we normally would have to order a 64k leased line (64K =1 BRI channel in Germany). Because we already have the E1 connection between the locations. What I want to do is simulating a 64k leased line between the two BRI-interfaces and pass the traffic over the E1-interface

Thanks and best regards


Paolo Bevilacqua Thu, 06/14/2007 - 03:37

Hi Florian,

Actually, voip can also support data circuits using the "clear-channel" codec.

But, I'm sorry to tell you that to my knowledge, the cisco BRI interfaces that are configurable to be network-side, do not support leased-line.

Here is a link about TDM switching with ISDN BRI and PRI, but is all about dialed circuits, not leased lines:

if you can configure the PBX not to use leased lined, but dialed calls only, you can implement VoIP without problems.

Hope this helps, please rate it using the scrollbox below!


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