CUCME Conferencing

By Amy Ryan on August 25th, 2010

In CUCME 4.1 and later versions, it is possible to provide end users the flexibility of creating ad-hoc conferences involving more than 3 parties with each participant potentially using a low bit rate codec such as g729. As you might expect, IOS software is unable to provide this function natively without the aid of Digital Signal Processors (DSP’s) most likely hosted on the CUCME gateway.

The first step when configuring the DSP’s for conferencing is to enable DSPFarm services on the gateway. By default the DSP’s can only be utilized for voice termination.

BR1-RTR(config)#voice-card 0
BR1-RTR(config-voicecard)#dsp service dspfarm

The DSP resources can only be controlled by the Call Control Agent (UCME in this case) using Skinny (aka SCCP). Skinny needs to be enabled on the gateway and a Call Control Agent(s) defined. In the example below the gateway will source SCCP packets from the primary IP Address assigned to interface FastEthernet0/0.11. The CUCUM IP Address is then provided to the gateway- incidentally the default version of SCCP used is 4.x so it is important the version is specified especially when trying to register an IOS MTP device to UCM since this is an invalid media resource in SCCP version 4.x.

BR1-RTR(config)#sccp local FastEthernet0/0.11
BR1-RTR(config)#sccp ccm identifier 1 version 7.0

A UCM group containing a list of Call Control Agents needs to be specified to support redundancy. In a stand alone UCME environment only a single Call Control Agent might be provisioned but in a UCM environment the Subscriber UCM, Publisher UCM and backup SRST CME gateway are the priority 1, 2 and 3 Call Control Agents respectively.

BR1-RTR(config)#sccp ccm group 1
BR1-RTR(config-sccp-ccm)# associate ccm 1 priority 1

The profile defining the characteristics of the conference bridge will be the next bit of configuration required. The codecs are defined and the maximum sessions specified. The DSPFarm will also need to be associated to the SCCP protocol at this stage (no other options at the time of writing).

BR1-RTR(config)#dspfarm profile 1 conference
BR1-RTR(config-dspfarm-profile)# codec g711ulaw
BR1-RTR(config-dspfarm-profile)# codec g711alaw
BR1-RTR(config-dspfarm-profile)# codec g729ar8
BR1-RTR(config-dspfarm-profile)# codec g729abr8
BR1-RTR(config-dspfarm-profile)# codec g729r8
BR1-RTR(config-dspfarm-profile)# codec g729br8
BR1-RTR(config-dspfarm-profile)# maximum sessions 2
BR1-RTR(config-dspfarm-profile)# associate application SCCP
BR1-RTR(config-dspfarm-profile)# no shutdown

Each conference session supports up to 8 parties in the same conference call and consumes half a DSP (PVDM2-8). A single DSP (PVDM2-16) supporting conferencing cannot be used for any other media resource- therefore it makes sense to have an even number of conference sessions.

The DSPFarm profile will need to be associated with a SCCP Group- a unique name is given to the conference bridge and this name will serve as the SCCP unique identifier when registering to the UCME.

BR1-RTR(config)#sccp ccm group 1
BR1-RTR(config-sccp-ccm)# associate profile 1 register cvg-cfb

Within the telephony-service CLI the conference bridge needs to be added as a known media resource and the maximum number of DSP Units specified. The UCME will cease to use software conferencing as a result of specifying the “conference hardware” command.

BR1-RTR(config-telephony)# conference hardware
BR1-RTR(config-telephony)# sdspfarm units 1
BR1-RTR(config-telephony)# sdspfarm tag 1 br1cfb

Registration of the conference bridge to the UCME can be verified using the “show sdspfarm units” command.

Placeholder ephone-dn’s need to be added to support the number of active Ad-Hoc conference participants required. These DN’s do not need to be dialable numbers (unlike the case of Meet-me conferences). In this example 4 conference participants will be allowed due to there only being 4 available channels associated with ad-hoc conferencing. The ephone-dn’s are providing the lines to anchor the call whereas the DSP resource is used for the transcoding and audio mixing required for conferencing.  Conversely, if there were no restrictions placed on the number of available channels, an octo-line could be used to support 8 conference participants.

ephone-dn  5  dual-line
 number A1000
 conference ad-hoc
 preference 2
 no huntstop
ephone-dn  6  dual-line
 number A1000
 conference ad-hoc
 preference 1
 no huntstop

Tones can be provided to conference participants as and when a person joins or leaves a conference call. The frequency and cadence (including the tone-on and tone-off durations) are defined within the “voice class custom-cptone” CLI.

BR1-RTR(config)#voice class custom-cptone CONF-LEAVE
BR1-RTR(cfg-cptone)# dualtone conference
BR1-RTR(cfg-cp-dualtone)#  frequency 400 800
BR1-RTR(cfg-cp-dualtone)#  cadence 100 50 200 50 300 50 400 50
BR1-RTR(cfg-cp-dualtone)#voice class custom-cptone CONF-JOIN
BR1-RTR(cfg-cptone)# dualtone conference
BR1-RTR(cfg-cp-dualtone)#  frequency 1000 2000
BR1-RTR(cfg-cp-dualtone)#  cadence 100 50 200 50 300 50 400 50

The custom tones are then assigned to the DSPFarm profile.

BR1-RTR(config)#dspfarm profile 1 conference

Disabling profile will disconnect active CONFERENCING calls,
do you want to continue ? [yes/no] yes

BR1-RTR(config-dspfarm-profile)# conference-join custom-cptone CONF-JOIN
BR1-RTR(config-dspfarm-profile)# conference-leave custom-cptone CONF-LEAVE
BR1-RTR(config-dspfarm-profile)#no shut

To verify an active conference call is using DSP resources on a particular gateway use the “show sccp connections” command. To solve any unusual problems start of by bouncing the SCCP application from within the IOS (no sccp/sccp).

Amy Ryan – CCIE #24677 (Voice)
Technical Instructor – IPexpert, Inc.

CUCME Conferencing, 4.6 out of 5 based on 5 ratings
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    Tags: ccie voice cucme, cucme conferencing

    One Response to “CUCME Conferencing”

    1. Chevy Mannie says:

      Thanks for this Amy. I had several questions about this that you answered. When are you going to do something on CUCM services best practice?

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      Rating: 5.0/5 (1 vote cast)

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