Capability Negotiation - Cisco BTS 10200 Softswitch User Manual

Cisco BTS 10200 Softswitch T.38 Fax Relay
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The CA-controlled mode for T.38 fax relay provided by this feature also imposes several restrictions:
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Capability Negotiation

For the CA-controlled media change, capabilities supported by the gateway are advertised in the SDP
exchange during connection establishment. This provides knowledge early and prevents unnecessary
messaging to switch to a media or voice format that is not supported by both gateways.
During the initial bearer path setup, the Cisco BTS 10200 Softswitch negotiates the T.38 Fax Relay
capabilities of both the originating and terminatinggateways (endpoints).
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Since the H.323 stack in the version 3.2 software does not support T.38 capability exchange during
Fast-start information exchanges, the Cisco BTS 10200 Softswitch initiates a Terminal Capability Set
(TCS) procedure to exchange T.38 Fax Relay capabilities along with DTMF capabilities.
MGCP Gateway Capabilities
The Cisco BTS 10200 Softswitch provides default provisioning parameters in the MGW-PROFILE table
for MGCP-controlled media gateways. The MGWs are also provisioned with static capabilities showing
the types of T.38 Fax Relay supported by the MGW.
connection parameters on the remote H.323 gateway after the logical channels are established. For
modifying the connection parameters, H3A implements a mechanism called "sending Empty
Capability Set (ECS)." In prior releases of the Cisco BTS 10200 Softswitch software, H3A
supported this capability only for IVR applications.
Any gateway that requires closure of both logical channels after sending ECS is not
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supported by the Cisco BTS 10200 Softswitch.
Clearing the call once the T.38 fax relay is completed—after the fax image transfer, the
connection remains established until one of the endpoints goes onhook, then the call is cleared.
Clearing the call if an H245 request mode rejection is received—if an H245 request mode
rejection is received from the remote media gateway, the call is cleared.
Seamless integration of various features—connection parameters on the remote H.323 gateway
can be modified after the connection is established by sending empty capability set (ECS).
Only partial support of MGCP fax package (fax start, fax stop, fax failure events only).
No voice fall back is supported—
when the fax call completes the call is cleared.
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if the T.38 fax invocation fails, the call is cleared.
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CA-controlled mode feature cannot function for H.323-to-H.323 calls transiting the CA.
If there are no common T.38 Fax Relay capabilities, the inband method is chosen.
If both sides have more than one capability in common, the common preferred T.38 mode is used.
If there is a common preferred mode, which is also present among the common capabilities, that
mode is chosen.
If no common preferred T.38 mode is available, then one of the common T.38 mode capabilities is
chosen.
Cisco BTS 10200 Softswitch T.38 Fax Relay Support
T.38 Benefits
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