Cisco T.38 Manuel d'utilisateur télécharger pdf (Page 10)

Cisco BTS 10200 Softswitch T.38 Fax Relay

External Interfaces

Cisco BTS 10200 Softswitch T.38 Fax Relay Support

The following steps describe in detail the T.38 Fax Relay functionality:

Step 1 The BCM checks the gateway profiles for their T.38 fax relay capabilites. It selects a common/preferred

capability supported by both the gateways.

Prior to establishing a connection, the BCM encodes the T.38 fax Local Connection Option (LCO) in the

SAI_CreateCxData_t . The t38fax LCO information is transmitted by the MGA in the CRCX.

Step 2 The BCM performs a check to ensure that the gateways are, in fact, MGA and H3A. The BCM initiates

an RQNT to the gateway by sending SAI_CCM_OOBINFO_REQ.

Based on these additional attributes in the RQNT, the MGA determines whether it can allow T.38 fax

calls. In order to detect whether T.38 fax calls are supported on the H3A, the BCM checks the trunk

group profile. In addition, the BCM checks the MGA static profile to ensure T.38fax is supported.

Step 3 The gateway detects fax transmission. It notifies the originating Signaling Adapter of the reception of

fax information. The Signaling Adapter in turn informs the BCM about the fax-start event in the

SAI_CCM_SVCFEATURE_IND primitive.

Step 4 The BCM upon reception of the SAI_CCM_SVCFEATURE_IND primitive looks for the

SAI_EI_FAX_START event. Then BCM checks to make sure that the passive_leg is in the

LEG_JOINED state; the remote BCSM state machine is in the active state. It then relays the T.38fax

information to the remote Signaling Adapter in the SAI_CCM_SVCFEATURE_REQ primitive. In the

case, where the passive_leg is not in the LEG_JOINED state, a FAX_FAILURE event is sent in the

SAI_CCM_SVCFEATURE_REQ towards the gateway.

Note Since T.38 fax is handled only in the ACTIVE state, the passive legs are in the LEG_JOINED

state and a valid bcsm_id exists for the remote end.

Step 5 The Signaling Adapter upon receipt of the T.38 fax_start information, invokes the CNM API

RemoteModifyCL_ex inorder to initiate a ModifyConnection request to the other Signaling Adapter

with the new SDP information. Two consecutive RemoteModifyCL_ex is sent to the peer Signaling

Adapter; one of them initiates the MDCX in the inactive mode while the other initiates an MDCX with

modified codec.

Step 6 The Signaling Adapter's CNM upon receipt of the RemoteModifyCL_ex from the remote CNM modifies

the SDP information. The codec information is also modified.The ACK/NACK that is received from the

originating gateway is then sent all the way back to the CNM of the terminating Signaling Adapter. This

is accomplished by retaining a copy of the remote Signaling Adapters identification.

Step 7 The gateway detects an end of fax and transmits it to the other Signaling Adapter. The Signaling Adapter

in turn transmits the fax stop information in the SAI_CCM_SVCFEATURE_IND primitive to the BCM.

Step 8 The BCM upon reception of the SAI_CCM_SVCFEATURE_IND primitive looks for the

SAI_EI_FAX_STOP event. It then relays the fax information to the other Signaling Adapter in the

SAI_CCM_SVCFEATURE_REQ. Following this, the call is cleared in a normal manner upon the receipt

of SAI_REL_IND from the H3A.

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Cisco T.38 Manuel d'utilisateur Page 10