Cisco Support Community
Showing results for 
Search instead for 
Did you mean: 
Community Member

DSPs (PVDMs) vs. Memory

      I work on a large voip conversion project and a lot of terms get mixed up (DSPs vs Memory) and people get confused.  I was wondering if there was a good way to explain what the difference is between DSPs and Memory on a router connected to the PSTN which terminate PRIs.  The routers also have a Conference Profile built, and are the SRST routers.

I have a couple of questions.  We had a 3945e router, and it was maxed out with PVDMs on all the slots (NM-HDV modules).  We were having dropped calls during peak hours after we converted the site to Cisco VoIP.  Now the router was configured to use each slot as a dspfarm

voice-card 0

dsp services dspfarm

voice-card 1

dsp services dspfarm

voice-card 2

dsp services dspfarm

voice-card 3

dsp services dspfarm

Then the only dspfarm profile that was built was:

dspfarm profile 10 conference

codec g711ulaw

codec g711alaw

codec g729ar8

codec g729abr8

codec g729r8

codec g729br8

max sessions 20

associate application SCCP

The SRST was built like this below.  When SRST is active, is it using DSPs or memory when all the phones register?


max-conferences 8 gain -6

transfer-system full-consult

limit-dn 7962 1

timeouts interdigit 5

ip source-address port 2000

ip qos dscp af31 signal

max-ephones 1500

system message primary SRST-Limited Functionality

transfer-pattern .......

voicemail 18553186245

no huntstop

translation-profile incoming intrasite


multicast moh port 16384 route

When calls dropped they removed the "dsp services dspfarm" from voice-card 1, voice-card 2, and voice-card 3, while also making some other adjustments and rebooting the router.

We also we getting errors when we tried to add dial-peers because the memory was full. 

My question is, would the dropped calls be more of a result from all the voice-cards being configured as dspfarms, or the lack of physical memory?  Can you use the DSPs on the voice-cards for other reasons besides local conferencing and transcoding when configured that way?  Meaning, does the router reserve them only for conferencing and transcoding or can they be used to bring up a new 4 port PRI module that is inserted, things like that?

And if any could explain the main differences between DSPs and physicl memory in regards to the perfomance of Voice Routers (routers that termiante PSTN circuits).

Thank you.


DSPs (PVDMs) vs. Memory

Have you checked out

Goes over the PVDM3 modules which you should be using in the ISR G2 Router.

Unless your using PVDM2 with the adapter.

Can you do a show inventory?

DSPs (PVDMs) vs. Memory

CreatePlease to create content