DSP for (IP_to_TDM) necessary ???

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May 8th, 2008
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Hello all,

after reading alot of docs about DSP and transcoding and MTP, im confused. lets talk about most real scenario. i have 2 call manager 7835 and media service activated. i have also 2 2821 router with E1 Card each. users around 600 cisco ip phones and 120 3rd party sip phones. do we need DSP resources to call over ISDN.?? we are signle site no transcoding or .. h323 endpoint. does the Cisco 2821 embeded built with one DSP ??? i mean no need to buy another PVDM? i know 2821 can have up 2 3PVDM.

and incase i want to configure a transcoder and enhaced conferencing on the router , will enable SCCP , but also i want to use it AS MGCP gateway with E1 connected to PSTN? so can both SCCP and MGCP be active at the same time? SCCP for enhaced conf and transcoding and MGCP to control ISDN and FXO?

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paolo bevilacqua Thu, 05/08/2008 - 05:55
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Hi, one DSP channels is taken for each call over ISDN.

And yes you can have mgcp/dsp services running concurrently.

Do show diag to know which DSP resources you have in the routers.

Hope this helps, please rate post if it does!

t-alkhalidi Thu, 05/08/2008 - 09:22
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ok can i run both SCCP and MGCP on the same router. SCCP for transcode and conf and MGCP for media gateway control? well i have 2 PVDM2_64 and 2 PVDM2_32. ok as u said for each i need what excatly? configure the DSP as xcode or as MTP or as what? i have around 600 ip phones mix sccp and sip. your advice and if u can provide me with sample configuration

paolo bevilacqua Thu, 05/08/2008 - 09:25
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Yes, you can do that.

You should refer to the CCM documentation for configuring transcoding, it should cover the GW configuration as well.

t-alkhalidi Thu, 05/08/2008 - 09:29
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ok this channel which is taken for each isdn call , whats considered? as MTP or transcoding or what excatly? so at least i will program the DSPM for

Jaime Valencia Sat, 05/10/2008 - 11:29
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go thru this for a better understanding,

High-Density Packet Voice Digital Signal Processor Module for Cisco IP Com Sol


also the IOS enhanced conferencing guide contains a lot of explanation of the usage and capabilities.

As Paolo mentioned the calculation is not as simple as asking how and what, you need to know the HW, where the cards are located, where the DSPs are, how many interfaces will be working, which codecs they will handle, etc



if this helps, please rate


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