Border Gateway Function Confusion

BGFs have me confused.

I am doing some research on SBC's in IMS for and came across the Core Border Gateway Function (C-BGF). We did not identify this element in the book or poster and now it seems to be referenced fairly frequently.

After my colleagues (Gordon Beith and Darius Minai-Azary) and I did some research we have yet to find a consistent definition of the C-BGF's various interfaces. In some references the C-BGF appears to be the same as the A-BGF. In others the C-BGF talks to the A-BGF.

Some of access-network to core call flows I found include:

• A-BGF->P-CSCF
• C-BGF->P-CSCF
• A-BGF->RACF->P-CSCF
• C-BGF->SPDF->P-CSCF
• A-BGF->C-BGF->P-CSCF
• PDN/WAG->C-BGF->P-CSCF

In the book and poster we showed the A-BGF talking to both the PDF and P-CSCF. It was assumed the PDF was part of a larger RACS and therefore we did not show a RACF.

The MSF R3 architecture defines 7 different Session Border Gateway variants:

• SBG - Session Border Gateway (combined S-SBG and D-SBG)
• D-SBG - Data Path Session Border Gateway
• D-SBG-NC - Data Path Session Border Gateway, Network Core (i.e., facing a peer network)
• D-SBG-NE - Data Path Session Border Gateway, Network Edge (i.e., customer-facing)
• S-SBG - Signaling Path Session Border Gateway
• S-SBG-NC - Signaling Path Session Border Gateway, Network Core (i.e., facing a peer
• network)
• S-SBG-NE - Signaling Path Session Border Gateway, Network Edge (i.e., customer-facing)

2 Border Gateway Functions:

• C-BGF - Core Border Gateway Function
• I-BGF - Interconnection Border Gateway Function

A several policy and resource control functions:

• PDF - Policy Decision Function
• SPDF - Service Policy Decision Function
• BM - Bandwidth Manager

I was considering building a big table to map and compare the various architectural differences, but I am not sure if it is worth it at this stage given most BGF vendors could probably fit their products to any of the architectures if needed. Most IMS implementations include a single SBC. A few include a distributed SBC, but nothing as distributed as what is called out in the specs. So I guess I will go on being confused by all this until I find a good unifying reference or make one myself.

Comments

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