VoIP DSP module

biggynet used Ask the Experts™
I am trying to get the right parts for my VoIP router. Basically, I am doing the dial-peer feature. I am planning to use the Cisco 1941. I need to get two voice cards (VWIC??) and I am not a voice guy, so I am not sure if I need a DSP module or not.
Watch Question

Do more with

Expert Office
EXPERT OFFICE® is a registered trademark of EXPERTS EXCHANGE®
Senior Systems Engineer
Yes you need a DSP, depending on how many calls, conferences and codec conversions you have going on depends on how many dsp's you need.
below is a link to the number of dsp's you can put in each router.
The 1941 can have a maximum of 0, this is not good!
Im not sure if you can buy a 1941 with dsp onboard so you might want to try a show inv.


To know how many dsp's you need got to this link
I dont have a login so i cant check its working.


I have 3 sites so that would be possible 2 voice calls. I checked the Cisco site and it said that the PVDM2 or 3 for the Cisco 2900 series supports all types of codec and the minimum is the PVDM2-8. I have  calls. So do I need the DSP card? Also, how do I know what type of codec I am using? I just plug my analog phone to the router and configure dial-peer pots and VoIP.
Top Expert 2007
Hey there,

you will need a different router, The 1900 series doesn't support voice cards or the right ios version to do what you are refering to.


Cisco does sell the 2901 in a voice bundle that will have a DSP module and the correct software then you would add the voice cards as needed.

Hope this helps
Bootstrap 4: Exploring New Features

Learn how to use and navigate the new features included in Bootstrap 4, the most popular HTML, CSS, and JavaScript framework for developing responsive, mobile-first websites.

greg wardSenior Systems Engineer
How many calls can it support


Also you need more pvdms if you want conferences.

If you want to do calls using a vic-fxs then you need pvdms in all routers.
Why not set up 7941's then you only need one voice router.
As above the 1941 does not look to be suitable.

Hi! This solution has been very useful for me today.
But I still have doubts. Hope you can help me.
My actual Carrier (who deliver us E1's with the CISCO router included) says it is possible to implement VoIP without using DSP's in the branch office router. The carrier solution designer says it is a way to do it with a bandwith cost not really defined.  
On the other hand, the engineer who is right now setting the Call Manager and checking routers capacity, says it's not possible to do it.
Who is right? Is there a way to implement VoIP without DSP's?
Thanks in advance.
greg wardSenior Systems Engineer

Yes it is possible.
Is it possible for you: i dont know your set up, so i can t answer.
what does a PVDM do http://www.cisco.com/en/US/prod/collateral/modules/ps3115/qa_c67_553073_ps10537_Products_Q_and_A_Item.html
Can it be software

The term media resources encompass a combination of cucm entities that perform functions like terminating media streams, mixing media streams, converting between compression types, amongst other things. They can be either software or hardware based and can be provided either by an IOS router or from the CUCM server.
Typical MR’s include:

Media Termination Points
Conference Bridges

hope that helps

Do more with

Expert Office
Submit tech questions to Ask the Experts™ at any time to receive solutions, advice, and new ideas from leading industry professionals.

Start 7-Day Free Trial