E1 and pbx

Unanswered Question
Mar 9th, 2008

Dear all

I have three locations connected via E1 trunk.each location also connected to pbx via E1 trunk again.

The CO told me that its E1 line is unprotocol.

I want to integrate voice ( pbx call ) and data for each location (devide E1 timeslots into voice and data)

any hint? idea? or configuration example


I have this problem too.
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Paolo Bevilacqua Sun, 03/09/2008 - 07:20


Telco probably meant unframed E1.

I do not to suggest you do static TDM dividing timeslots, because this cause bandwidth waste You siimply trunk the PBX together with VoIP and thse will work nicely. Use ISR routers and VWIC or VWIC2 cards for that.

Hope this helps, please rate post if it does!

emadehsan Sun, 03/09/2008 - 11:17


thank you for your post

do you have any sample configuration?

Joseph W. Doherty Sun, 03/09/2008 - 13:44

Two additional points, that might be worth noting.

When you share digital voice with data on the same link, QoS often should be configured to insure the digital voice obtains the level of performance it requires.

Depending on the voice codec, it could use more bandwidth then your existing analog voice signal. (I.e. an E1 might not be able to carry as many voice calls.) I recall Cisco recommends not using more than a third of the path's bandwidth for voice. (This I believe so QoS will have the sufficient bandwidth to guarantee the necessary performance.)

emadehsan Mon, 03/10/2008 - 00:42

thank you for your follow up

but in your example the link between two routers is ethernet , but in my case its E1

royalblues Mon, 03/10/2008 - 03:05

The only thing to note when the media is Ethernet is the overhead..

A g729 call on a traditional serial link would take about 24 kbps whereas the same call on Ethernet would take 32kbps. This might need to be looked upon when sizing the bandwidth


Joseph W. Doherty Mon, 03/10/2008 - 04:40

"but in your example the link between two routers is ethernet , but in my case its E1 "

Although Narayan mentions Ethernet, there's the additional overhead of IP and the overhead of L2 encapsulation (e.g. HDLC), also on your E1. Narayan also mentions using a compressed codec, but an uncompressed codec like the g711 starts at 64 K before adding L2/L3 encapsulation.


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