Bearer Capability on SCCP-controlled FXS

Answered Question
Jul 16th, 2009

We have 4 VG 224s connected to a CCM-Cluster running 6.1.3.3190. PSTN-Connection is made via E1-PRI as H323 GW. The FXS-ports on the VG224 are controlled by SCCP.

If a device on a FXS is calling out the PSTN-GW, the bearer capability in the ISDN-SETUP-message is Speech. Is it possible to change this to 3100 kHZ like it is possible under H323-controlled FXS-Ports?

I have tried

voice-port 2/0

cptone DE

timeouts initial 60

timeouts interdigit 60

timeouts ringing infinity

bearer-cap 3100Hz

but this has obviously no effect on SCCP-controlled ports.

I have this problem too.
0 votes
Correct Answer by pcameron about 7 years 4 months ago

Unfortunately you can't change the bearer cap of the FXS port under SCCP or MGCP control. The bearercap is only actively used when a call is sent to an ISDN interface, so this interface has the appropriate config commands.

As you have mentioned, for H323 you can use voice port bearer-capability' command or the D channel 'isdn outgoing-voice info-transfer-capability 3.1kHz-audio' command.

For MGCP ISDN, you can add the string "BC=3.1khz" in the gateway port description field to overwrite the default speech behavior.

With both these fixes the bearercap is overwritten for all calls out the particular interface.

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Correct Answer
pcameron Thu, 07/16/2009 - 05:14

Unfortunately you can't change the bearer cap of the FXS port under SCCP or MGCP control. The bearercap is only actively used when a call is sent to an ISDN interface, so this interface has the appropriate config commands.

As you have mentioned, for H323 you can use voice port bearer-capability' command or the D channel 'isdn outgoing-voice info-transfer-capability 3.1kHz-audio' command.

For MGCP ISDN, you can add the string "BC=3.1khz" in the gateway port description field to overwrite the default speech behavior.

With both these fixes the bearercap is overwritten for all calls out the particular interface.

philippgrafl Thu, 07/16/2009 - 05:23

These two options are not applicable in my environment, because i need this capability setting only for a few FXS-ports, but for all other calls i need speech.

So i think i have to convert those few ports to h323. :-(

Sounds like a feature request...

pcameron Thu, 07/16/2009 - 05:44

Contact your local Cisco account manager and get them to open a PERS (Product Enhancement Request)and state the Business Impact of why this feature is needed.

When the account mangers wave a fist full of dollars/schillings/euros/ at the Cisco Business Unit, they sit up and listen :-)

Paolo Bevilacqua Thu, 07/16/2009 - 10:24

Thing is even if the AM listens, the BU responds they have other priorities, so let's set the right expectation: ever very reasonable feature request typically takes multiple years to complete.

Yorick Petey Wed, 11/09/2011 - 08:14

Hello,

I have the same problem. I already used the BC=3.1kHz parameter for MGCP PRI in the past to dedicate a line to be used by analog equipments only and let the other telco lines to use Speech bearer capability.

But today, I don't have the possibility to dedicate a line for analog equipments because there are too much sites and I need to deal with high availability aspects, and duplicating all physical lines just for some devices is not an option, it's too much expensive.

All the gateways are MGCP controlled (~10 VGW, ~8VG224, ~12 PRI, 8 BRI...) and I cannot change to H323 globally just because of this 3.1kHz problem, there are too much dependancies.

I know that the VG224, MGCP or SCCP controlled, cannot specify, call-based, a special bearer capability to use with the end ISDN lines. Is it something possible when the VG224 is controlled by H323? Or this setting can only be applied on the ISDN interface side?

What I understand is that there is still no possibility within Cisco VoIP solution to set a FXS port to use 3.1kHz BC instead of the default Speech one, and without globally set this parameter on an ISDN line, impacting all other calls. This is something possible for decades in the legacy PBXs... What a pity.

Also, is there a problem to set the 3.1kHz BC for all lines, all calls, that is to say disabling Speech everywhere? I never heard a difference in voice quality between both bearer caps... Any bad experience?

Thank you for your feedback.

Yorick Petey

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