Use the Early Media window to configure parameters related to early media processing for a specified SIP trunk group.

To View and Edit Early Media Parameters

On the SBC main screen, go to Configuration > System Provisioning > Category: Trunk Provisioning > Trunk Group > SIP Trunk Group > SIP Trunk Advanced > SIP Trunk - Media - Advanced > Early Media or
All > Address Context > Zone > SIP Trunk Group > Media > Early Media

The Early Media window is displayed.

Use the drop-down boxes to select an Address Context, Zone and SIP Trunk Group.

Early Media Window

The following fields are displayed:

Early Media Parameters

Parameter

Description

Method

 Method used to provide early media. Additional options appear based on your choice for Method.

  • P Early Media – P-Early-Media header value is used for selection the RTP streams. For information on Delayed Local Ring Back Tone (DLRBT) and P-Early-Media, see here.
    • Default Gating Method – Select an option to specify the cut-through method if the P- Early-Media header is not received from the peer.
      • Inactive
      • None
      • Recvonly
      • Sendonly
      • Sendrecv (default)
    • Egress Support - Use this flag to include a PEM=supported message in the egress INVITE.
      • Disabled - Egress INVITE does not include PEM=supported message regardless of the presence/absence of PEM in the ingress INVITE.
      • Enabled (default) – Egress INVITE includes PEM=supported message regardless of the presence/absence of the PEM in the ingress INVITE.
    • Monitor Rtp - Use this flag to monitor RTP for early media authorization when the flag Default Gating Method is set to None.
      • Disabled (default)
      • Enabled
  • Rtp Server Table – Enter an RTP Server Table name to specify the RTP server profile. This option uses RTP Server Profile to determine whether early media is enabled. If the c-line of the session description matches an   entry in the RTP profile, early media is allowed. RTP Server Profiles are configured per Address Context. One RTP Server Profile is tied to a single Early Media Profile if this option is selected.
  • Session Answer (default) – Use this option for media cut-through on receipt of session answer.

Forking Behaviour

 Use this parameter to identify the method to provide early dialog media selection.
  • First Prov Response – First Reliable Provisional response. Cut through for first provisional response and suppress the rest until final response is received.
  • First Rtp – When this option is selected, the SBC's selection of provisional response for cut-through is determined by the arrival of media packets corresponding to that provisional response. Select this option and set Dynamic LRBT flag to 'enabled' when forking is enabled. With First Rtp enabled, forking behavior is the last provisional response until 180 is received. If First Rtp is enabled, but the Dynamic LRBT flag is disabled, forking behavior defaults to the last provisional response
  • Last Received SDP (default) – Cut through is based on the latest SDP received.
  • Pem Priority – PEM (P-Early-Media) based. Cut through occurs based on the value of the PEM header (default value is sendrecv if not configured).

Make the required changes and click Save.

 

P-Early-Media and DLRBT

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.

    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).

    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.

Note

If the egress call leg responds with P-Early-Media header in its 18x response, the SBC transparently relays it to the ingress call leg.