Clear Channel Codec Support

Clear Channel Codec support adds to the IMG 2020 support for the Clear Channel Codec described as Clear Mode or Clear Channel Data in RFC 4040- RTP Payload Format for a 64 kbit/s Transparent Call. This Codec will be added to the list of Codecs supported and follow the same rules as the answer/offer model and Codec overlap currently supported. The second aspect to this feature is that the IMG 2020 will examine the Bearer Capabilities on an incoming TDM call. If the Bearer Capability value of the incoming call matches a certain set of requirements and the Clear Channel Override field in the SIP Profile object on the outgoing side is set to enable then the IMG 2020 will force the outgoing Codec to be clear channel. Below is information on forcing the outgoing Codec to Clear Channel.

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Example

Use the diagram above to follow the example call below.

• From the example diagram above, a call comes into the IMG 2020 using either SS7 or ISDN signaling. In order for this feature to function properly there must be certain values for the Bearer Capabilities. See tables below which explain what values need to be present. E1 and T1 will be looking for different values as shown below. These values are not configurable. They are hard coded to be used as triggers for a Codec Override in the outgoing SIP INVITE.

The IMG 2020 determines that one of the incoming values matches one of the values in the table. The IMG 2020 then looks at the value of the Clear Channel Override field in the SIP Profile object. If the field is set to Disable (Default) then normal Codec negotiation will take place. If the field is set to Enable the IMG 2020 will send an INVITE out the channel group configured and force the Codec to be Clear Channel. Any Codecs offered by the remote gateway will be overridden with the Clear Channel Codec.

Configuration

Create a Signaling Gateway Profile (SGP)

• Right click on the Profiles object and select New SIP Profile. The first SIP Profile created is a default SIP Profile and cannot be modified. Disregard this profile.

• Right click on the Profiles object and select New SIP Profile again. In the SIP Profile object either enter a name that identifies this profile in the Name field or accept the default entry. For more information refer to the SIP Profile - SGP topic.

• Right click on the SIP Profile just created and select New SIP Advanced Settings. Select Enabled from the Clear Channel Override field. Refer to the SIP Profile - SGP topic for more information on configuring the individual fields within this object.

Create SIP Channel Groups

• Right click on the Dialogic object and select New Routing Configuration. Refer to the IMG 1010 - Configuring Routing topic for more information.

• Right click on the Routing Configuration object and select New Channel Groups. The channel groups object is a container object and no configuration is needed. Refer to the Channel Groups topic for more information.

• Right click on Channel Groups object and select New Channel Group. Either enter a name that identifies this channel group or accept the default entry. Modify the Signaling Type field to SIP using the drop down menu. Refer to the Channel Group topic for more information on configuring the SIP channel group individual fields.

Create an External Network Element

The SIP Channel group needs to communicate with an external SIP entity. Create an external network element and then an external gateway that the SIP channel group will transmit messages to.

• Right click on the Dialogic object and select New External Network Elements. The External Network Elements object is a container object and no configuration is needed in this object. Refer to the External Network Elements for more information.

• Right click on External Network Elements object and select New External Gateways. The External Gateways object is also a container object. Under the External Gateways object, multiple individual gateways can be created. Refer to External Gateways topic for more information.

• Right Click on External Gateways object and select New External Gateway. Enter a name in the Name field to identify the gateway being created. Select SIP from drop down menu in the Gateway Signaling Type field and select the SIP Profile from SIP Profile field drop down menu. Refer to the External Gateway for more information.

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Insert SIP External Network Element into SIP Channel Group

• Right click on the SIP Channel group created and select New IP Network Element. Within the IP Network Element field, select from drop down menu, the gateway created. See screen capture below.

• Click on the Channel Groups object again. A yellow exclamation point will be displayed again. Click on the Download Resource Tables button to sent the updated configuration to the IMG 2020.

• The SIP Clear Channel Codec feature is now configured. Since the profile has the Clear Channel Override field set to Enabled, any calls routed out to the channel group created will use the Clear Channel Codec as long as the call coming into the IMG 2020 contains the correct information. 

Additional Information

• Clear Channel Codec negotiation follows RFC 4040 when Clear Channel Override field is set to Disable (Default).

• If the IMG 2020 forces the outgoing call to Clear Channel Codec and the remote endpoint does not support Clear Channel a 488 Nack will be sent back to the IMG 2020.

• The Default value for the Clear Channel Override field in the SIP Profile object is Disable.

• The Clear Channel Codec does not lower channel densities in any profile.

• Detection and Switching to Fax or Modem are not supported when utilizing the Clear Channel Codec.

• RTP Redundancy is supported when utilizing the Clear Channel Codec.

• The IP Profile settings for Silence Suppression, Echo Cancellation, DTMF transport, fax mode, bypass codec, and Media Inactivity detection are not supported when the Clear Channel Codec is used. These settings are ignored.