6 Replies Latest reply: May 10, 2010 7:43 AM by Anthony Holloway RSS

    DSP Question

    Abu Hadee

      Hi All,


      Hope everybody is doing fine. As a group leader of this group, I'm going to pose some question to start some discussion.


      Here is one for today.


      If I need 10 g729 call, 5 transcoding session along with 3 conference.


      How many DSP do I need?


      Thank you

      - abu

        • 1. Re: DSP Question
          Anthony Holloway

          I don't know the answer to this, I just wanted to say thank you for getting this going.  I have been monitoring this forum for quite some time now, and have found very little value in it thus far.


          I hope to see some good discussion around this question, and not just the correct answer.


          Thanks again for the push in the right direction, this community needed that.

          • 2. Re: DSP Question

            I agree with Anthony, this is a nice way to start participation and look forward to learning more.  Don't know the answer either but will do some research to gain a better understanding.

            • 3. Re: DSP Question

              The DSP calulator (on the cisco webpage) requires the router model and OS verision. Depending on what onboard DSP's the router has already, additional DSP's may not need to be added. If I choose : Cisco 3725 Router and Cisco IOS Release 12.4. the results are listed below. Link to the calculator is also listed.






              Onboard/NM SlotsG.711/ Fax passthrough/ Modem passthroughG.729a/ G.726/ Fax Relay/ T.37 FaxG.729b/ G.723.1/ G.728/ Modem Relay
              AIM Slot0
              WIC Slot 0VWIC2-1MFT-T1/E1(T1 voice)0100
              NM Slot 1NM-HDV2-1T1/E1One Onboard T10100
              VWIC2-1MFT-T1/E1(T1 voice)000


              Number of transcoding sessions
              G.711 a-law to/from u-lawG.711 to G.729aG.711 to G.729(b)
              NM Slot 1NM-HDV2-1T1/E1050
              Transcoding Type : CCM


              Number of conferences
              G.711 modeG.711 - G.729a/ G.729 mode
              NM Slot 1NM-HDV2-1T1/E103


              Analog reservation and Media Encryption
              Onboard/NM SlotsAnalog ReservationMedia Encryption




              DSP Calculator Result


              The AIM card(s) provide sufficient DSPs for the onboard Configuration.
              Minimum number of DSPs required to support the NM configuration is 4.


              DSP Requirements
              NM1CLI Information
              Optimized Result(Default)4 DSP(s).
              one PVDM2-48 + one PVDM2-8
              one PVDM2-16 + one PVDM2-32 + one PVDM2-8
              CLI Info
              Normal Result4 DSP(s).
              one PVDM2-48 + one PVDM2-8
              one PVDM2-16 + one PVDM2-32 + one PVDM2-8
              CLI Info
              Worst Case ResultN/AN/A
              • 4. Re: DSP Question

                Hi Abu

                Thanks for posing the question, I passed CCNA Voice this week so was keen to answer this, but looks like Cindy has done a fine job and answered this via the calculator. But I suppose this is not the full answer. I suppose it all depends on the model of Router in use. I understand that there are also two types of DSP C549 and C5510. I don't know the difference between these, I suppose this depends on router models too. Perhaps someone can advise?

                • 5. Re: DSP Question
                  Abu Hadee

                  Thank you all for participating in this question.


                  Yes, there are few requierement before some one can answer correctly. I posed this question because I had many TAC cases open on these kind of scenario.


                  If the conference is only for G711, it will take only 3 DSP.


                  One thing I must add here that DSP reserved for conference can not be shared even if there is resource left. Like if you only have on conference reservice, the whole DSP will be reserved for conference. So, some of the resource will be wasted.


                  If I have a PVDM2-8, and 1 conference session is configured, I wont be able to configure anything else. Like wise, if I have PVDM2-16, 1 conference session will take them all. Or, if I have 10 voice channel configured. Even though 6 dsp channel are left, but I can't configure any Conference sessoin, because no dedicated DSP is left


                  Voice call and Transcoder/MTP can share resource. That mean, they can be allocated on same DSP.


                  Hope this help.


                  Next Question coming shortly

                  - Abu

                  • 6. Re: DSP Question
                    Anthony Holloway

                    This is a disappointing end to what could have been a great discussion on DSP resources.


                    I was really looking forward to a discussion on DSP resources, to the core of why they even exist.  Not just a link to a calculator, and a dump of the output.


                    I'm not saying we need a discussion on micro controllers, and circuit boards, but let's at least be able to configure a solution if the web is down.  Are these calculators available in the CCIE voice lab?


                    An analogy:  I've seen many engineers use a subnet calculator, and have no idea how it arrived at a solution, to a problem they should really understand.


                    Let's get this discussion going again.  What does a DSP actually do?  It takes a digital voice stream as input, does something to it (what?), and output a copy of the original digital voice stream?  Is that right?  What are the operations it can perform on a voice stream?  Encode?  Decode?  Make me sound like T-Pain?