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Questions regarding PVDM/DSP calculations

I have questions regarding DSP requirements. The link I am using as a refernce:

http://www.cisco.com/en/US/products/hw/routers/ps221/products_tech_note09186a00800c3399.shtml

1. PVDM-256k-4 supports 4 analog calls (medium complexity), or 6 digital T1/E1 calls. Why can it support more digital calls than analog? So a PVDM-256K-16 can support all channels on a VWIC-1MFT-T1? (contrary to the believe that PVDM-256k-24 is required). Do these same rules govern regular PVDM on a NM-HDV, meaning that two PVDM-12s can support all channels on a VWIC-1MFT-T1 with DSP resources left over?

2. When a PVDM says it can support x channel, then are we to assume the x channel means the number of analog calls at medium complexity?

3. How do people typically calcuate DSP requirements for digital T1/E1s? Memorize that chart?

4. When connected to PSTN, I don't believe the CO uses G.7xx, so what you are really converting is from G.7xx to either PCM for digital, or analog, is that correct?

5. When you use DSPs to transocode, one DSP on a PVDM-12 can support 4 transcoding sessions. Why are the number of transcoding sessions different compared to the same DSP used for voice termination? (converting from G7xx to digital/analog) Isn't that consider transcoding anway? Or, is the resources needed to convert from G7xx to analog/digital greater (or less) than converting from a G7xx to a different G7xx codec?

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Community Member

Re: Questions regarding PVDM/DSP calculations

For the 1700 platforms, please use the DSP calculator at http://www.cisco.com/cgi-bin/Support/DSP/cisco_prodsel.pl to determine DSP provisioning.

1. No, the same rules do not govern the NM-HDV as for the 1700 DSP modules.

3. With the calculator above. On ehte NM-HDV, the process is more manual.

4. Correct. The G.xxx codecs apply only on the VoIP side. The TDM conenction is always PCM.

5. For the NM-HDV (PVDM-12) the number of xcoding sessions per DSP is 4, and the number of voice terminations in medium complexity per DSP is also 4. You only need xcoding when a VoIP call needs to be xlated from say G.729 to G.711 at some point in the network. Xcoding does not apply to TDM - VoIP connections, the conversion from digital/analog to VoIP codec is implicitly done in the DSP as part of voice termination.

CH

Community Member

Re: Questions regarding PVDM/DSP calculations

Thanks for the answer, especially question 5. After doing more research, I realized that the DSP usage on the 1700s is a bit different compared to the NM-HDV. Since both the PVDM and PVDM-256K use the same kind of DSP (TI 549), the only reason I can come up with regarding why the PVDM-256k-x can support more digital T1/E1 voice calls than a comparable PVDM-x is the way DSP resources are tapped. Or maybe hardware/software issue.

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