Transfer to original site consume DSP resource

Unanswered Question
Dec 22nd, 2008


- I have 2 ip phones in site 1 with CCM 6.0 and Voice GW and the same at site 2. Two sites connect over IP WAN and using g729 when call between site.

- The problem is when site 1 receive call from site 2, and then transfer back to ip phone in site 2, it consume additional DSP resource to transcode g711 to g729 and of course, more delay

- The same issue regardless of using Inter-Cluster Trunk or IP-to-IP GW.

How do I avoid using DSP resource in this case?

Thanks million!

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Overall Rating: 0 (0 ratings)
iptuser55 Mon, 12/22/2008 - 03:17

I did not think they would use DSP`s as the phones themselves can do the decoding?

huydien3384 Mon, 12/22/2008 - 17:39

Thank you, but...they did. The phones themselves cant do the transcoding, must use DSP.

Jaime Valencia Mon, 12/22/2008 - 19:53

if they're using DSPs there is no way to release them in the middle of the call, what phone models are u using???

most phones can support G711 and G729 natively



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huydien3384 Mon, 12/22/2008 - 21:21

this is the topology:


in LAN environment, I want to use G711, and call over IP WAN use G729. PVDM2 is installed on both GW1 and GW2 to provide transcoding resources.

I'm using IP Phone 7960 and 7940.

Java, what do you mean "support G729 natively"? I saw in datasheets it said it can support G729, but I think it is OK only if in all invironment we using G729, isnt it?


dezoconnor Tue, 12/23/2008 - 06:18

Huy, are your Regions configured correctly? As others have pointed out the phones can transcode so shouldn't be using any extra DSP's.

Site A (within this Site) G.711

Site B G.729

Jaime Valencia Tue, 12/23/2008 - 09:55

support G729 natively means exactly that, the phones understand the codec without need of external xcode.

to be sure configure a scenario on same cluster on which 2 phones talk g729 between them, give no access to xcoders and place a call



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huydien3384 Tue, 12/23/2008 - 18:00

Yeah, I tested with two region, one use G711 and one use G729. It works perfectly. But both phones use G729, not phone1 use G711 and phone2 use G729. The phones cant do the transcoding itself.

Thank you very much!

iptuser55 Wed, 12/24/2008 - 00:56

I`m not sure 79x0 phones can do the transcoding themselves hence may the need for external dsp - I would check with your cisco guys to confirm the transcoding is supported in these phones

Jaime Valencia Wed, 12/24/2008 - 10:56

of course they DO. xcoding is for Xcoders, phones as i've already mentioned twice support the codecs natively. no xcoders required.

i know for a fact they can connect (i gave training on CUCM along with traces and taught them how to identify codecs in traces) so, the question here is what have you done for this to happen because there is no need for a XCODER to be invoked unless misconfiguration

Other Cisco Unified IP Phone 7960G features include:

• G.711 and G.729a audio compression



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huydien3384 Wed, 12/24/2008 - 18:55

Java, Could you please give me an example (I mean a scenario) indicate that the phones themselves can do the transcoding?



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