Hardware DSP allocation

Unanswered Question
Oct 20th, 2008

We have 3 locations:


- Call Mgr 4.2(3)

- Unity Connection 1.2(1)

- VGW, Cisco 2821 w/ PVDM2-64 (4 DSPs)

- Approx 60 phones, 7911's & 7960's


- Call Mgr 4.1(3)

- Unity 4.0

- VGW, Cisco 2821 w/ PVDM2-48 (3 DSPs)

- Approx 60 phones, 7911's & 7960's


- CME 3.4(0)

- Unity Express 2.1

- VGW, Cisco 2851 w/ PVDM2-48 (3 DSPs) & NM-CUE

- Approx 30 phones, 7911 - 7960

We want to enable WAN calling between the locations; G.711 on the LAN, G.729 between locations. Will eventually deploy some Video via VT Advantage SW.

I'll definitely need HW Conf Bridge resources. I was going to configure all DSP resources for HW CB, should I consider carving out DSPs for HW MTP/Transcoding resources as well?

Note, the DSPs have never been configured at any of the locations.


I have this problem too.
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Tommer Catlin Mon, 10/20/2008 - 13:01

Well, you have to break down how many sessions you want, etc. The DSP calc should help you. Im not sure how many PRIs you have, or FXO, etc you have the router, but in put your specs into the calc and see what you get.


Here is a note:

Note: On the 5510 DSPs (NM-HD-xx, NM-HDV2 and onboard on 28xx/38xx) voice and transcoding can share, and conference requires a dedicated DSP.

The NM-HD-xx has limited number of DSPs. The voice termination and transcoding can share the DSPs, but the conferencing requires a dedicated DSP.

The 5510 DSPs (NM-HD-xx, NM-HDV2 and onboard on 28xx/38xx) and 549 DSPs (NM-HDV-FARM and NM-HDV-xT1/E1-xx cards) cannot be configured for transcoding and conferencing at the same time.

* - Transcoding to GSM codecs (GSM-FR and GSM-EFR) is not supported on the 549 DSP.

CSCO10203269 Tue, 10/21/2008 - 05:40

Unfortunately, the existing PVDM's is what I have to work with. The equipment was spec'd by 3rd party integrators that are no longer in the picture.

Let me rephrase the question...

Is there a function(s) the "software" based (Publisher/Subscriber defined) MTP/Xcoder resources won't be able to support requiring "hardware" MTPs/Xcoder be defined?

Take for instance conference calling. Our software defined Conf Bridges will not join G729 & G711 calls; get fastbusy. To provide those capabilities, I had to define HW Conf Bridges.

Are there other functions -- functionality the phones or software resources won't be able to support -- I haven't thought of that would require "hardware" MTP/Xcode resource?

If I don't need "hardware" MTP/Xcode resources then I'd prefer to allocate all the DSPs for conferencing.


Tommer Catlin Tue, 10/21/2008 - 07:13

Hopefully I can word this correctly, Transcoding is confusing.... not one of my favorite things.. but here it goes.

Cisco Phones phones for example can transcode calls between each other without hardware transcoding. Not until you call across to another entity that cannot handle both g.729 and g.711 would a hardware transcoder be required.

So basically if you were in Site A with an IP phone, and want to use Site B's PSTN, you would need to have a Transcoder to change from g711 to g729 and back g711 out the pstn. (hopefully I got this right, correct me if Im wrong someone)

That would be (1) session of transcoding.

PVDM2-64 supports up to 128 max sessions of Transcoding.

So in your resource list you can have the following:

xcode_routerB (on the router register xcode_routerB to CUCM)

CFB_routerB (on the router register CFB_routerB)

You will need to define the sessions for each. example:

sccp ccm group 1

associate ccm 2 priority 2

associate ccm 1 priority 1

associate profile 2 register CFB_routerB

associate profile 1 register xcode_routerB


dspfarm profile 1 transcode

codec g711ulaw

codec g711alaw

codec g729ar8

codec g729abr8

codec gsmfr

maximum sessions 8

associate application SCCP

dspfarm profile 2 conference

codec g711ulaw

codec g711alaw

codec g729ar8

codec g729abr8

codec g729r8

codec g729br8

maximum sessions 2

associate application SCCP

Create the correct MRG and Lists and you should be set to go.

When a person creates a conference call, they will use the hardware resource on the router itself (which you specified in the MRG/List). They will also have access to the transcoding sessions if needed so their local hardware is transcoding.

Im still getting the coffee rolling through me here, if Im mistaken somewhere, please correct!


CSCO10203269 Tue, 10/21/2008 - 07:38


Your explanation cleared it up, thanks! Our site to site calling will be plain vanilla (IP-phone to IP-phone, IP-phone to Unity which supports both codecs) so for now I'll only configure HW conf bridges. Thanks again for your help.


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