Solved

Configuring G.711 A-law in cisco callmanager 5

Posted on 2007-11-22
3
1,965 Views
Last Modified: 2013-12-27
We are using Cisco callmanager 5 in the UK with an MGCP gateway connecting to the PSTN via an E1 PRI.

The problem is, whenever we make a call and check the codec being used, it says it is using G711u i.e. U-Law. As far as I understand it, the PSTN in the UK uses A-law. How can we configure callmanager to use A-law between the gateway and the IP Phones? As it stands it works, it just bugs me why we have to use u-law.
0
Comment
Question by:cstosgale
  • 2
3 Comments
 
LVL 22

Expert Comment

by:Reid Palmeira
ID: 20353794
If you have an MGCP gateway, then you're PSTN termination should be coming there. beyond that point (on your LAN) the codec that you use for VoIP is pretty much up to you, doesn't matter much at all since it's only VoIP from the MGCP gateway to the endpoint. As long as the phones and CM setup both support it.
0
 
LVL 10

Author Comment

by:cstosgale
ID: 20354105
Good point, so why is Europe so keen on using A-law as opposed to U-law? Is this because the encoding used in E1 ISDN is closer to G.711 A-law than to U-Law?

And why is there no way of choosing which variant you want to use in callmanager? I'm guessing your codec choice in callmanager will affect what codec is used between the endpoints as it is an mgcp gateway.
0
 
LVL 22

Accepted Solution

by:
Reid Palmeira earned 500 total points
ID: 20354853
the codec negotiation is part of the session setup so you can look at the SDP packets and see exactly how the CM and the MGCP gateway are negoitating but my guess is that in the list of supported codecs that both devices supports g.711u is earlier than g.711a so it just negotiates to that codec. So when they're comparing lists the two sides just pick u-law first.

as for why the difference, there's a decent wikipedia entry http://en.wikipedia.org/wiki/G.711 and it's not so much the E1/T1 differences, just a different algorithm. I've seen a-law in Japan as well which seems to contradict what wikipedia says.

You should be able to set that list of supported codecs in CM but I'm not sure about the MGCP gateway, depends on make/model.
0

Featured Post

Better Security Awareness With Threat Intelligence

See how one of the leading financial services organizations uses Recorded Future as part of a holistic threat intelligence program to promote security awareness and proactively and efficiently identify threats.

Join & Write a Comment

How To Create Custom / Distinctive Ring Tones on Polycom Phones Purpose and Overview When creating a custom ring tone, you have simple aspirations: to make your phone cooler than everyone else's. Perhaps you need a louder ringer. Perhaps you w…
As companies replace their old PBX phone systems with Unified IP Communications, many are finding out that legacy applications such as fax do not work well with VoIP. Fortunately, Cloud Faxing provides a cost-effective alternative that works over an…
When you create an app prototype with Adobe XD, you can insert system screens -- sharing or Control Center, for example -- with just a few clicks. This video shows you how. You can take the full course on Experts Exchange at http://bit.ly/XDcourse.
You have products, that come in variants and want to set different prices for them? Watch this micro tutorial that describes how to configure prices for Magento super attributes. Assigning simple products to configurable: We assigned simple products…

744 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question

Need Help in Real-Time?

Connect with top rated Experts

12 Experts available now in Live!

Get 1:1 Help Now