Cisco IPT and G.711 a-law

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Jul 20th, 2003
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When installing a Cisco IP Telephony solution in Europe for example, how the u-law and a-law handled ? Do CM, IP phones, Unity, IPCC Express and others can all run a-law ? Or everything works u-law inside and the PSTN gateway will do the u-law-to-a-law conversion ? What are the options ?



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dugrant Sun, 07/20/2003 - 09:09
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Yes, they all handle both ulaw and alaw.

peter_tsonis Sun, 07/20/2003 - 16:33
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Now where do I go to configure an all a-law environment ?


Alejandro Cadar... Mon, 07/21/2003 - 23:30
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As far as I know,Unity, CCM and IP phones only use G.711ulaw, never G.711alaw, you configure alaw in your pstn trunks in the gateways and inside always ulaw is used. Is the gateway who makes some sort of transcoding between alaw and ulaw.


peter_tsonis Tue, 07/22/2003 - 04:07
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The tests that I've done show that the IP phones do support alaw also. Setting alaw from the gateway to CM, will make any calls coming from the gateway to be alaw inside CIPT. You can see this on the IP phone when hitting the "I" button.

Now, as far as I undertstand this right now is "it doesn't matter". CIPT devices support both standards so you can set your gateway to be ulaw inside (IP network) and alaw on the PSTN side. Then everything inside will be ulaw. On the other hand, you can let the gateway transport alaw inside (no conversion) and all CIPT devices will ajust to it on the fly.

However, I would like somebody tell me if I'm right or not, as I've never set a full system with this type of setup and I don't know if they are some gotcha in each option.



slauwers Mon, 07/28/2003 - 02:59
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Hi Peter,

You are correct. It is possible to create an all alaw environment. You can select the default encoding in the service parameters.


Steven Lauwers

VOIP Consultant


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