DSP Rule of thumb calculation for Voice Routers

[dan hale]

Hi All, I know Cisco has a DSP calculator however, there are some values that it asks that I'm unsure of when trying to use it.

Does anyone have a basic rule of thumb they use when deciding on how many DSP to add to a voice CME router?

I have a Cisco 2911 with 1 VIC2-4FXO , 1 VIC3-2FXS/DID port and currently I have a 1 PVDM3 DSP DIMM with 16 Channels. I would like to add one VIC2-2FXO card for additional analog lines. I've read that you at least need to have the same number or channels that you do FXS/FXO ports. If that's the case then I'm currently only using 6 of the 16 channels.

Below is the DSP group command:

DSP groups on slot 0:
dsp 1:
  State: UP, firmware: 32.1.2
  Max signal/voice channel: 16/16
  Max credits: 240, Voice credits: 240, Video credits: 0
  num_of_sig_chnls_allocated: 6
  Transcoding channels allocated: 1
  Group: FLEX_GROUP_VOICE, complexity: FLEX
    Shared credits: 100, reserved credits: 0
    Signaling channels allocated: 6
    Voice channels allocated: 0
    Credits used (rounded-up): 0
  Group: FLEX_GROUP_XCODE, complexity: MEDIUM
    Shared credits: 0, reserved credits: 20
    Transcoding channels allocated: 0
    Credits used (rounded-up): 0
  Group: FLEX_GROUP_CONF, complexity: CONFERENCE
    Shared credits: 0, reserved credits: 120
    Codec: CONF_G729, maximum participants: 8
    Sessions per dsp: 4
  Slot: 0
  Device idx: 0
  PVDM Slot: 0
  Dsp Type: SP2600

Thanks,

Dan

[Jaime Valencia · Accepted solution]

Yes, the most basic math is that you need, at least, the same number of channels on your DSP(s) as you would have TDM0 channels, this meaning you will only use G.711, as the number of channels, are in G.711. That just for TDM termination.

With what you have, if you chose to use G.729A/G.722, it would go down to 12 channels, with G.729/iLBC decreases to 10, and you only get 3 channels, if using ISAC.

[dan hale]

Thanks Jaime!