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Community Member

DSP Math

Hi Community,

I need some help with this DSP Math.

A central gateway (2851) will have a E1 link connected to PSTN  and will receive 30 call simultaneously on this link. Also this gw will receive 86 g729a calls from another gateways. All calls will be redirected to an IVR system using g711 codec and SIP. How many DSPs will be needed?

Thank you all.

Paulo Roque

12 REPLIES
Cisco Employee

Re: DSP Math

There's already a tool for that:

DSP Calculator

http://www.cisco.com/cgi-bin/Support/DSP/dsp-calc.pl

HTH

java

if this helps, please rate

www.cisco.com/go/pdihelpdesk

HTH

java

if this helps, please rate

www.cisco.com/go/pdi
Community Member

Re: DSP Math

Thank you javalenc.

It helped. But I have one more question.

The DSP Calculator considers only incoming calls, right? So I need if I have, let´s say, 10 G729a incoming calls and all calls transcoded to G.711 calls to another device. How many DSPs should I consider.

Paulo Roque

Community Member

Re: DSP Math

Hi Paulo,

I find the problem is always with the understanding of how Many DSP will be required.

Start with:

- how many Handsets (Local and Remote)

- How many ISDN channels ie: 3, 10 or 30 on each Site

- do a "sho inv" - send it to me

- Upgrade to the Latest T Traing SP Service IOS

+ always include Transcoding (the more the better) and Conferancing (one session is enough for small offices) resouce

Your Call Manager System will always need Hardware Transcoding resource even it there are no more MTP resource your UCM system will use a Transcoding as a substitute.

If additianal UC Applications is used like UCCX and G729, having Hardware transcoding is a must (local to each Site).

Let me know if you need more help?

Kind Regards,

Nico

Community Member

Re: DSP Math

Hi nwkotze.

I attached the topology. We are in the design phase yet. I need to find out how many DSPs is needed on R1 and R2. I am not sure if I can solve this problem using the DSP Calculator tool, because all incoming call will be redirected (transcoded) to the IVR and, I guess, DSP Calculator does not include the transcoding in its calculation. There will not be any handset neither Call Manager only gateway functions.

Paulo

IVR.jpg

Community Member

Re: DSP Math

Hi nwkotze.

I attached the topology. We are in the design phase yet. I need to find out how many DSPs is needed on R1 and R2. I am not sure if I can solve this problem using the DSP Calculator tool, because all incoming call will be redirected (transcoded) to the IVR and, I guess, DSP Calculator does not include the transcoding in its calculation. There will not be any handset neither Call Manager only gateway functions.

Paulo

IVR.jpg

Community Member

Re: DSP Math

Hi nwkotze.

I attached the topology. We are in the design phase yet. I need to find out how many DSPs is needed on R1 and R2. I am not sure if I can solve this problem using the DSP Calculator tool, because all incoming call will be redirected (transcoded) to the IVR and, I guess, DSP Calculator does not include the transcoding in its calculation. There will not be any handset neither Call Manager only gateway functions.

Paulo

IVR.jpg

Community Member

Re: DSP Math

Hi nwkotze.

I attached the topology. We are in the design phase yet. I need to find out how many DSPs is needed on R1 and R2. I am not sure if I can solve this problem using the DSP Calculator tool, because all incoming call will be redirected (transcoded) to the IVR and, I guess, DSP Calculator does not include the transcoding in its calculation. There will not be any handset neither Call Manager only gateway functions.

Paulo

IVR.jpg

Community Member

Re: DSP Math

Hi nwkotze.

I attached the topology. We are in the design phase yet. I need to find out how many DSPs is needed on R1 and R2. I am not sure if I can solve this problem using the DSP Calculator tool, because all incoming call will be redirected (transcoded) to the IVR and, I guess, DSP Calculator does not include the transcoding in its calculation. There will not be any handset neither Call Manager only gateway functions.

Paulo

Community Member

Re: DSP Math

Hi Paulo,

I do understand... but you need to tell me:

- how many Channels will be active on the ISDN interface?

- based on ISDN 30 with 30 Chnnels:

If you are going to do G729 on all calls, it will be best to install a single PVDN2-64, as the router only has two PVDM Slots, this will allow for future upgrades. You might get away with one PVDM2-48 at minimum. The big thing is that you will need Hardware Transcoding Resource (config on the router) for your ACD this is why its best to go for the PVDM2-64.

If the customer want to save money go for a single PVDM2-48. Not my recomendation!!!!!

The problem is that the it is cheeper to buy a Voice Bundle, but most come with a single PVDN2-32, that will not be enough for what you trying to do here. Beleve me it will save you allot of problems in the furure...

If this helped please rate.

Let me know if you need more information?

Kind Regards,

Nico

Community Member

Re: DSP Math

Hi Nico. Thank you.

Just one more question.

If I receive a call on one remote router R1 on a E1 connection to PSTN (G.711, I suppose) and this call is redirected via WAN using g729a to another site, do I need transcoding in R1 for this call?

Paulo

Community Member

Re: DSP Math

Hi Paulo, let me try and break it down...

1st you need to understand the Codecs: - refer to cisco docs for finer detail, here is how i understand it:

G711ulaw - This is a low overhead Codec with very good Voice Quality but Big Data Packets (80kbps+L2 Transport)
G722 - This is the new Cisco G711 replacement - it use less CPU and require less bandwidth (more efficient) 40kbps
G729 - This is your high overhead (CPU intensive) Codes that use compression 8knps+L2

In a VoIP environment, Only DSP's (Digital Signal Processors) can process Voice, so for each session you will need DSP resource (Processors)

G722, G711 - Use less than G729 (for ISDN 30 you can get away with PVDM2-32)
G729 - Use more CPU resource than G722 and G711 (with ISDN 30 you will need a PVDM2-48 or better PVDM2-64)

The Endpoints (Phones or Routers) can choose or select the Codec  (only be concerned with: g722"newg711replacement", g711ulaw"old best quality, g729r8Wan)

Transcoding do not come in when a call is set up, the endpoints negotiate the codec and as each Endpoint has its DSP's (Phones included) the will setup the call with what ever Codec is configured for them to use.

Transcoding come into a Voice Stream when the "Call" use one Codec "g711" and need to change to "G729". This will happen in your UCCX ICD Port, when the Agent Call need to be transcoded to "G729". Supplementary Services (Call Park, Hold, Transfer), also use Transcoding.

Conferencing will also eat up your Router DSPs (recommended config)

Hope This help, if so please Rate.

Kind Regards,
Nico

Cisco Employee

Re: DSP Math

Refer to this tables, they're the same used by the DSP calculator but you need to do the math manually

Table 5     DSP Theoretical Session Capacities

http://www.cisco.com/en/US/docs/ios/voice/cminterop/configuration/guide/vc_enh_confr_vgr_ps6441_TSD_Products_Configuration_Guide_Chapter.html#wp1068869

HTH

java

If this helps, please rate

www.cisco.com/go/pdihelpdesk

HTH

java

if this helps, please rate

www.cisco.com/go/pdi
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