DSP question

ciscoforum · ‎08-12-2007

If a cisco voice router has two PRI and one connects to PSTN, the other one connects to PBX, do we need DSP, why? I think DSP is only required when from IP to PRI or voice versa? Thanks

paolo bevilacqua · ‎08-12-2007

You need DSP anyway.

IOS does does not even let you configure the pri-group in lack of DSP resources, as it doesn't know what are you intentions. Beside, DSPs are not used only for VoIP, but also for tone detection and generation, TCL/IVR applications, etc.

If for some reason you want to place a router in between anyway, configure two tdm-groups and connect them with connect command. That does not require DSP resources, on the other hand doesn't do anything else than using two interfaces.

user-cisco · ‎08-12-2007

?

Majdi Harb · ‎08-12-2007

in fact the two cases u mentioned are the same, in first case u configure PRI to connect to PSTN, what u do actually is that u connect to a PBX (Telco PBX) , and in the second case u aslo configure ur PRI and connect to a PBX, so keep in mind that u basically need DSP hardware resourses for voice termination in addition to other features if u want to appl any..

in addition to what paulo mentioned in his nice post, that if u want to config ur pri without enough dsp's, it won't be configured and will display an error message that u do not have enough dsp resourses to add timeslots.

hth

/majdi

ciscoforum · ‎08-13-2007

Thanks guys.

Actually I know that we are not able to enter the command if there no enough DSP resource. I experienced this many years ago. But really my question is why it is required.

One exception is "local-bypass", not sure you guys know it? The explanation is :Using this command enables intra-network-module hairpinning (no DSPs).

Though it is restricted in one module, but at least it means it's possible that calls from pri to pri do not need DSP.

The customer is trying to save some money on DSP in the particular case I described since calls are from PRI to pRI and I want to give

them a good reason why dsp is required other than the command error. They only need voice between these two pris. No other special things required