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P-Early-Media and Delayed RBT

To use the Force Local Ring Back Tone (FLRBT) feature, set the PSX flag DelayedRBTWithToneContinuation to enabled. The flag is available under the entity Tone Generation Criteria > Delayed RBT in the PSX.

• To create a Tone Generation Criteria entity with the flag DelayedRBTWithToneContinuation:
  create Tone_Generation_Criteria_Data Tone_Generation_Criteria_Id <string> Sequence_Number <int> [Response_Code <short>] [Attributes <int>] [Ingress_Tg <string>]
  
  
• To update a Tone Generation Criteria entity with the flag DelayedRBTWithToneContinuation:
  update Tone_Generation_Criteria_Data Tone_Generation_Criteria_Id <string> Sequence_Number <int> [Response_Code <short>] [Attributes <int>] [Ingress_Tg <string>]
  
  
• To delete a Tone Generation Criteria entity with the flag DelayedRBTWithToneContinuation:
  delete Tone_Generation_Criteria_Data Tone_Generation_Criteria_Id <string> Sequence_Number <int>
  
  

For more information on the flag DelayedRBTWithToneContinuation, refer to the PSX document Tone Generation Criteria Screen.

When a caller sends a SIP INVITE to the SBC (irrespective of the presence of "P-Early-Media: supported" header in the Session Description Protocol (SDP) of the INVITE), the SBC adds P-Early-Media header in its 18x (180 or 183) response towards ingress call leg only if:

• The SBC monitors and detects early media from the egress call leg.

  Info
  title Note
  The SBC has an "observation" window for monitoring the stream of RTP packets. It also has a "silence" window before it restarts monitoring, to reject RTP packets from a previous announcement.

  
  

• The SBC plays a Ring Back Tone (RBT).

  Info
  title Note
  The SBC plays LRBT only if it does not receive any early media from the egress call leg at the end of a monitoring cycle. If the SBC starts playing LRBT, it continues to play even if it detects RTP in the subsequent monitoring cycles, or exchanges a new set of SDP answers with the egress call leg. When the SBC receives an UPDATE from the egress call leg, and the caller (ingress call leg) does not support UPDATE, the SBC continues to feed tone in the same codec. When the ingress call leg supports UPDATE, the SBC feeds tone in a modified codec after a successful offer-answer negotiation.