1. ACLI Configuration Guide
  2. SIP Signaling Services
  3. Early Media Support
  4. Early Media Support for Multiple Early Dialog Scenarios
  5. Many-to-Many Support within Early Dialog Support

Many-to-Many Support within Early Dialog Support

The ESBC provides early dialog support for many-to-many dialog scenarios, which are defined by working with multiple early dialogs established by and for both the callee and the caller. The ESBC establishes a one-to-one correspondence between to-tag identifiers for the dialogs it sends and receives. This support applies to both reliable and unreliable dialogs (with or without PRACK). It also provides this support for both transcoding and non-transcoding call flows.

While processing responses within different dialogs, the ESBC matches the dialogs of corresponding offers and answers and updates the flows to maintain SDP selection for the subsequent session. The ensuing behavior depends on whether the call is reliable, meaning it includes PRACKs, or unreliable:

  • If the flow is reliable, the ESBC does not restore the SDP for the final response in the same dialog, resulting in no SDP in the outgoing final response. If the final response, such as a 200 OK, arrives within a dialog that is different and doesn't include SDP, the ESBC participates in changing the dialog switching and a media update.
  • If the flow is unreliable and a final response arrives within the same dialog and without SDP, the ESBC restores the SDP from the matching dialog, updates the media flows and then sends the final response with SDP inserted.

The ESBC maintains the SDP version consistent across dialogs on both sides throughout the call.

Many-to-many cases require that you enable the merge-early-dialogs parameter. Also, the UAC must maintain same IP and port in the SDP c line across all dialogs.

The merge configuration either disables or supercedes the following features:

  • Offerless calls with add-sdp-invite
  • Preconditions interworking
  • PRACK IWF
  • multiple audio or video m-line
  • p-early-media-header with support option

The call flow below presents the ESBC supporting a Multiple Early dialog scenario, wherein both the called and calling plarforms are initiating dialogs using reliable exchanges.

This call flow depicts Multiple Early dialogs, using many to many operation mode in a Volte MRF audio-video scenario.