You are viewing an old version of this page. View the current version.

Compare with Current View Page History

« Previous Version 4 Current »

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

Implementing LMSD When SBC Cannot Play Tones

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

Unable to show "metadata-from": No such page "_space_variables"
 is not configured with tone profiles, the
Unable to show "metadata-from": No such page "_space_variables"
 relays the 180 ringing by storing the received SDP and forwards 180 ringing without SDP to ingress. Consider a scenario where the C-
Unable to show "metadata-from": No such page "_space_variables"
, 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

    Unable to show "metadata-from": No such page "_space_variables"
     cannot play the required LMSD specified tone or the tone and announcement profile is not configured on both legs of a call.

    Note

    In LMSD inter-working state, if the

    Unable to show "metadata-from": No such page "_space_variables"
    receives 18x ringing without SDP, it relays 180 without SDP and remains in the same state. The
    Unable to show "metadata-from": No such page "_space_variables"
    passes the Alert-Info transparently, regardless of the transparency setting of Alert-Info header.

The

Unable to show "metadata-from": No such page "_space_variables"
 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.

    Note

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

When SBC is Handling P-Com-DropEarlyMedia

The P-Com-DropEarlyMedia flag signals the C-

Unable to show "metadata-from": No such page "_space_variables"
 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 (
Unable to show "metadata-from": No such page "_space_variables"
) not to pass the normal ring back tone being played by the MSC. The 
Unable to show "metadata-from": No such page "_space_variables"
 processes this header and does not pass it to the egress call-leg.

The 

Unable to show "metadata-from": No such page "_space_variables"
 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 
Unable to show "metadata-from": No such page "_space_variables"
 blocks media streams, else the media streams are passed.

Note

If 180 ringing and 183 does not include SDP, it is passed normally.

When P-Com.DropEarlyMedia interworking is carried out in the 

Unable to show "metadata-from": No such page "_space_variables"
, 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 
Unable to show "metadata-from": No such page "_space_variables"
. The 
Unable to show "metadata-from": No such page "_space_variables"
 supports media cut-through only on receiving the final 200 OK response.

 

Calls Originating from MSC

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 

Unable to show "metadata-from": No such page "_space_variables"
 to send a 180 ringing with Alert-Info <http:/null> request to force the MSC to stop the ringback tone. To facilitate this, the 
Unable to show "metadata-from": No such page "_space_variables"
 uses a SIP trunk group flag, stopLmsdToneOnUpdate, to accomplish the following on the leg which received the update from the MSC:

  1. 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 
    Unable to show "metadata-from": No such page "_space_variables"
     has relayed the Alert-Info with the non-null URI.

  2. Send an update with the SDP offer.

Note

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

 

Ignoring ISUP MIME

The 

Unable to show "metadata-from": No such page "_space_variables"
 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 
Unable to show "metadata-from": No such page "_space_variables"
 adds the ISUP MIME to the outgoing messages.

Note

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

  • No labels