SBC Back-to-Back User Agent Call Transfer Topology
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current Session Border Controllers (SBCs) face challenges in enabling seamless call transfers across network boundaries, particularly when transferring between private and public networks, as they fail to accurately convey the new call topology to transferee endpoints, leading to issues in conference calls and assuming routability of public addresses from private networks.
Innovation Solution
An enhanced SBC operates as a Back-to-Back User Agent (B2BUA), processing transfer events through a two-step process: replacing Refer-To addresses with appropriate network interface addresses and generating mapping keys to facilitate call transfers between endpoints across network borders, while also managing memory to prevent leaks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the SBC acts on the REFER message itself and replaces addresses, then simple transfers can work, but the new topology of the call is not made apparent to the transferee or transfer target endpoints
Solution Approach 1:
The SBC acts as an intermediary B2BUA that terminates the REFER message from the transferor and generates a new INVITE message to the transferee. This intermediary role allows the SBC to maintain the original Refer-To address information while establishing the correct routing path, thus preserving topology information while enabling transfers to work across network boundaries.
2Device complexity
If the SBC passes the REFER with its addresses through without processing, then public addresses are assumed routable, but this assumption is often inaccurate
Solution Approach 1:
The SBC performs preliminary address validation and replacement before the REFER message reaches the transferee. By checking whether the Refer-To address matches its network interfaces and pre-replacing addresses with appropriate routing information, the SBC ensures that the transferee receives a REFER message with routable addresses, eliminating the need for the transferee to assume public address routability.
3Adaptability or versatility
If the SBC replaces Refer-To addresses with its network interface addresses, then call transfers can work across network boundaries, but the SBC must generate and manage mapping keys
Solution Approach 1:
The SBC generates a mapping key that associates its public network interface address with the original Refer-To address. This mapping key acts as an intermediary reference that allows the SBC to translate between public and private addresses without requiring complex routing tables or databases, simplifying the address management while enabling cross-network transfers.
4Reliability
If the SBC is positioned between transferee and transferor to process REFER requests, then call transfers can be enabled, but the SBC must check and replace addresses in the REFER request
Solution Approach 1:
The SBC performs localized address replacement only in the Refer-To field of the REFER message, checking whether it matches its network interfaces and replacing only when necessary. This localized processing approach enables reliable call transfers while minimizing the complexity of REFER message processing by focusing only on the critical address field rather than processing the entire message structure.
Data Source
Figure 1
Figure 2
Figure 3A
AI summary
A communication system, method, and components are described. Specifically, a communication system having the ability to facilitate call transfer across a Session Border Controller (SBC) is provided. The transfer is facilitated by an intelligent mapping process performed at the SBC on one or more messages transmitted during a call transfer.