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The following sections describe the LMSD inter-working without tones:

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Implementing LMSD When SBC Cannot Play Tones

When 180 ringing with SDP and valid Alert-Info header is received, but the

Spacevars
0 product

 is not configured with tone profiles, the

Spacevars
0 product

 relays the 180 ringing by storing the received SDP and forwards 180 ringing without SDP to ingress. Consider a scenario where the C-

Spacevars
0 product

, which is not configured with tone profile, receives Alert-Info header in the 180 ringing. It performs inter-working only when the following conditions are met:

• Accept Alert-Info is enabled on the leg which receives 180 ringing.
• 180 ringing is received with SDP answer.
• Alert-Info is received in LMSD format <http:/LMSD/tone?sig-id=x>, where x = (rt).

• Sends 180 ringing with Alert-Info header and without SDP when the

  Spacevars
  0 product

   cannot play the required LMSD specified tone or the tone and announcement profile is not configured on both legs of a call.

  Info
  title Note
  In LMSD inter-working state, if the Spacevars 0 product receives 18x ringing without SDP, it relays 180 without SDP and remains in the same state. The Spacevars 0 product passes the Alert-Info transparently, regardless of the transparency setting of Alert-Info header.

The

Spacevars
0 product

 aborts a transaction by sending appropriate error response code to the IMS network and CANCEL to the other leg (MSC) when following conditions are met:

• Egress leg IPSP flag Accept Alert-Info is enabled.

• Initial INVITE received with SDP.

• 180 ringing is received from the MSC with SDP.

• Alert-Info received in LMSD format <http:/LMSD/tone?sig-id=x>, where x = ct or bt.

  Info
  title Note
  If the tone is not in ct, bt or rt format, SMM is used to convert that string to rt.

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When SBC is Handling P-Com-DropEarlyMedia

Multiexcerpt
MultiExcerptName P-Com-DropEarlyMedia
The P-Com-DropEarlyMedia flag signals the C- Spacevars 0 product  to cut-through or not cut-through the early media (before receiving an answer), if a SDP response is received from a CDMA network. This header added by the IMS network indicates media anchoring element ( Spacevars 0 product ) not to pass the normal ring back tone being played by the MSC. The  Spacevars 0 product  processes this header and does not pass it to the egress call-leg. The  Spacevars 0 product  accepts the P-Com.DropEarlyMedia header in the initial INVITE in the format  ̶  P-Com.DropEarlyMedia:Value, where Value is set to true or false. If the value is set to True, the  Spacevars 0 product  blocks media streams, else the media streams are passed. Info title Note If 180 ringing and 183 does not include SDP, it is passed normally. When P-Com.DropEarlyMedia interworking is carried out in the  Spacevars 0 product , it will continue to drop media packets till the final answer is received. Any intermediate UPDATE messages altering SDP is handled normally but the media is not cut-through at the  Spacevars 0 product . The  Spacevars 0 product  supports media cut-through only on receiving the final 200 OK response.

 

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Calls Originating from MSC

Multiexcerpt
MultiExcerptName Stop LMSD Tones on Update
For calls originating from the MSC server, a 180 ringing with SDP response triggers a flag in the MSC to play a ringback tone. This causes the need for the  Spacevars 0 product  to send a 180 ringing with Alert-Info <http:/null> request to force the MSC to stop the ringback tone. To facilitate this, the  Spacevars 0 product  uses a SIP trunk group flag, stopLmsdToneOnUpdate, to accomplish the following on the leg which received the update from the MSC: Send a 180 ringing without SDP with Alert-Info <http:/null> to stop the LMSD tone. NOTE: The 180 ringing is sent only if the  Spacevars 0 product  has relayed the Alert-Info with the non-null URI. Send an update with the SDP offer.

Info
title Note
This flag is disabled by default. Refer to SIP Trunk Group TG - Signaling - Stop LMSD Tone On Update - CLI for configuration details.

 

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Ignoring ISUP MIME

Multiexcerpt
MultiExcerptName Drop Isup Mime Body
The  Spacevars 0 product  uses the trunk group flag, dropIsupMimeBody, to drop the ISUP MIME body received in SIP-I messages and then treat the call as a normal SIP call. If SIP-I is configured for incoming messages, the  Spacevars 0 product  adds the ISUP MIME to the outgoing messages.

Info
title Note
This flag is disabled by default. Refer to SIP Trunk Group TG - Signaling - Drop ISUP Mime Body - CLI for configuration details.

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