What is BGCF (Breakout Gateway Control Function)

The technical details of the Breakout Gateway Control Function (BGCF).

1. Definition and Purpose:
   • The BGCF is an essential component within the IP Multimedia Subsystem (IMS) architecture.
   • Its primary role is to determine the network where Public Switched Telephone Network (PSTN) breakout should occur for a given session.
   • When a user initiates a call or communication session that involves both IMS and PSTN, the BGCF plays a crucial part in routing the signaling appropriately.
2. Scenario and Decision-Making:
   • When a session requires PSTN breakout (e.g., calling a regular phone number), the BGCF comes into play.
   • The decision-making process involves choosing whether the breakout should happen within the same network as the BGCF or in another network.
   • Let’s explore the scenarios:
     • Intra-Network Breakout:
       • If the breakout is to occur within the same network as the BGCF, the BGCF selects a Media Gateway Control Function (MGCF) responsible for interworking with the PSTN.
       • The MGCF receives the Session Initiation Protocol (SIP) signaling from the BGCF and handles the necessary conversion between IMS and PSTN protocols.
     • Inter-Network Breakout:
       • If the breakout is destined for another network (e.g., a different operator’s network), the BGCF forwards the session signaling to either:
         • Another BGCF in the target network.
         • An MGCF in the target network (if the BGCF-to-BGCF route is not available).
3. Functions Performed by BGCF:
   • Let’s break down the specific functions carried out by the BGCF:
     • Request Reception:
       • The Serving-Call Session Control Function (S-CSCF) sends a request to the BGCF, asking for the appropriate PSTN breakout point for the session.
     • Network Selection:
       • The BGCF selects the network where interworking with the PSTN will occur.
       • If the interworking is within another network, the BGCF forwards the SIP signaling to the BGCF of that network.
     • MGCF Selection:
       • If the interworking involves the same network, the BGCF identifies the MGCF responsible for PSTN interworking.
       • It then forwards the SIP signaling to the chosen MGCF.
4. Summary:
   • In a nutshell, the BGCF acts as a traffic director, ensuring that IMS sessions seamlessly connect with the PSTN when needed.
   • Its decisions impact call quality, routing efficiency, and overall service reliability.