T1 Codec

[MrNitch]

Our T1 provider is asking that we make sure we are using the G711 codec. I see where I can set IP Call Configurations with the phone system but that seems only on the internal network. Is there a spot to make sure we are using G711 compression going out of the system to the PSTN?


Thank you
Kenny

[Sorry left PBX info out]
HX5000 box running CP version 5.1

[Tech Electronics]

Mr. Nitch,

G.711 A-Law or Mu-Law are voice codecs not T-1 codecs. Normally the only setup we worry about is the Switch Type, Framing, and Line Code when setting up a T-1 along with what type of channels we have to support on them. First of all do you even have a T1/E1 card installed in the system in order to take a T-1?

My guess is that you are getting SIP Trunking not a T-1 and if that is the case then you are most likely looking in the wrong place to set that up.
 
Your best bet is to get your vendor out there to work with the carrier so you don't have the headache of trying to figure things out for yourself and ordering features that the system may not be able to support.

Thanks,

TE

[DND ON]

Ditto. SIP trunking is not for the faint of heart.

[MrNitch]

It is not SIP, we are getting a PRI hand off over AT&T's BVOIP network. We do have a T1/PRI card, and I have all the switch type and pick order setup properly. We are going from 15 concurrent calls to 23 and I have prepped the system for that as well but they came back and said if we are doing 23 channels then we will need to make sure to only use G711.

Thank you
Kenny

[dwayneg]

G711 is probably what they will use on their side of the network.  At your site they will install equipment to convert VOIP to T1/PRI.  And there's nowhere on the T1 side to set G711 at all, each channel is a straight digital 64k.

[DND ON]

Curious about the decision to use PRI integration. AT&T BVOIP works just fine with the 5000 in its native SIP configuration.

Conversion to PRI adds the cost of a T1/PRI card, which is also a potential point of failure. As SIP trunks, additional channels are just a license upgrade.

[johnp]

I think you will find that most North American T1 carriers utilize mu law companding. The nature of T1 being 8 bit sampled at 8KHZ gives the 64K rate which is what G.711 is based on.

As the traditional telephone network is bandwidth limited, somewhere between 300-3600 Hz(alway a debate), according to the Nyquist theorem for accuracy you must sample at twice the highest frequency, hence 8KHZ. Kind if why CD recordings are in the 44KHZ range, 22,000 being the highest audible frequency for the human ear.

Bell labs spend a lot of research to determine that most speech can be carriered in what would be considered the power band for verbal comprehension, and designed their equipment for that transmission.

[MrNitch]

Cool guys thank you for the info. Sorry about confusing subject title, I have poor technical vocabulary.

Thank you
Kenny