Hardware Conferencing with PVDM Module on 2801 Call Manager Express

A PVDM (Packet Voice DSP Module) is a router hardware module that looks like a computer memory chip and is used to provide Digital Signal Processing voice services to routers working as voice gateways or as Call Manager Express devices. The high-density PVDM2 module enables Integrated services routers (such as 2800, 3800 models) to provide high-density voice services such as transcoding, hardware conferencing and voice encoding in IP communications solutions.

The following configuration example is about a cisco 2801 router working as Call Manager Express version 4.1 with both local IP phones and IP Phones located in remote branches over IPSEC VPN. The remote phones work with G729 codec and the local phones use normal G711 voice encoding. The requirement is to enable hardware ad-hoc conferencing between remote G729 and local G711 phones.

Here is the configuration snapshot (only commands related to hardware conferencing are shown):

voice-card 0
dsp services dspfarm
!
voice class custom-cptone leavetone
dualtone conference
frequency 400 800
cadence 400 50 200 50 200 50
!
voice class custom-cptone jointone
dualtone conference
frequency 600 900
cadence 300 150 300 100 300 50
!
interface FastEthernet0/0
ip address 192.168.10.1 255.255.255.0

sccp local FastEthernet0/0
sccp ccm 192.168.10.1 identifier 100 priority 1 version 4.1
sccp
!
sccp ccm group 2
bind interface FastEthernet0/0
associate ccm 100 priority 1
associate profile 2 register DSPprofile2
keepalive retries 5
!
dspfarm profile 2 conference
! Configure codecs allowed to participate in conference
codec g711ulaw
codec g711alaw
codec g729ar8
codec g729abr8
codec g729r8
codec g729br8
maximum sessions 2
conference-join custom-cptone jointone
conference-leave custom-cptone leavetone
associate application SCCP

telephony-service
sdspfarm units 2
sdspfarm tag 2 DSPprofile2
conference hardware
max-ephones 24
max-dn 48
ip source-address 192.168.10.1 port 2000 strict-match
max-conferences 4 gain -6

!
ephone-dn  43  dual-line
number A000
description Ad-Hoc Conference
conference ad-hoc
no huntstop
!
!
ephone-dn  44  dual-line
number A000
description Ad-Hoc Conference
conference ad-hoc
preference 1
no huntstop
!
!
ephone-dn  45  dual-line
number A000
description Ad-Hoc Conference
conference ad-hoc
preference 2
!
!
ephone-dn  46  dual-line
number A000
description Ad-Hoc Conference
conference ad-hoc
preference 3

Notice on the configuration above that we have to create some dummy phone directory numbers (ephone-dn 43 to 46) to facilitate the ad-hoc conference operation. An Ad-hoc conference is an unscheduled conference. It occurs when a third party is added into any conversation by the participants. The ad-hoc initiators can add/delete/drop participants to/from the conference.

CME hardware conferencing supports a maximum of 8 participants in an ad-hoc conference.
Each DSP can support a maximum of 64 G.711 participants only (single-mode), this translates to:

  • 8 conferences of 8 participants each.

Each DSP can support a maximum of 16 G.711/G.729A/G.729 participants (mixed-mode), so this translates to:

  • 2 conferences of 8 participants each.

Verify DSP registration

If your DSPfarm is not registered to CME, you will not be able to use the DSP resources to initiate a conference call. To check if the dspfarm is registered, perform the following command – “show dspfarm all

Example: Registered – good example

Router#show dspfarm all

<output omitted>

Profile Operation State : ACTIVE

Application : SCCP Status : ASSOCIATED

<output omitted>

Example: Unregistered – bad example

<output omitted>

Profile Operation State : ACTIVE IN PROGRESS

Application : SCCP Status : ASSOCIATION IN PROGRESS

<output omitted>

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