Still celebrating National IT Professionals Day with 3 months of free Premium Membership. Use Code ITDAY17

x
?
Solved

Configuring G.711 A-law in cisco callmanager 5

Posted on 2007-11-22
3
Medium Priority
?
2,033 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
[X]
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
  • 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 2000 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

Free Tool: SSL Checker

Scans your site and returns information about your SSL implementation and certificate. Helpful for debugging and validating your SSL configuration.

One of a set of tools we are providing to everyone as a way of saying thank you for being a part of the community.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Ever wanted to query Cisco Call Manager CDR records from MS SQL Server? Here's how! CUCM can be configured to upload a CDR file to a given FTP server every minute. This article will show you how to set this up, schedule the import of this data an…
Although VoiceOver IP has been around for a while, internet connections have only recently become fast enough to provide good call quality. Now, VoIP has become a real option for businesses looking at ways to improve their business model. In this ar…
Have you created a query with information for a calendar? ... and then, abra-cadabra, the calendar is done?! I am going to show you how to make that happen. Visualize your data!  ... really see it To use the code to create a calendar from a q…
In this video, Percona Solution Engineer Dimitri Vanoverbeke discusses why you want to use at least three nodes in a database cluster. To discuss how Percona Consulting can help with your design and architecture needs for your database and infras…

705 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