Early Media Connection Proxy for SIP PSTN Interworking
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Solution Overview
Problem
SIP networks face challenges in providing early media due to the requirement of a 2xx response from a user agent server before media can be exchanged, and existing SIP entities may not support early media extensions, leading to failures when calls cross the PSTN boundary where the PSTN gateway does not support SIP early media extensions.
Innovation Solution
Implementing an early media connection proxy system that determines the need for early media connections and proxying based on call setup signaling messages, using a service creation interaction manager to establish early media connections by signaling on behalf of a network entity, even when SIP entities do not support early media extensions, through a service mediation function that intercepts SIP INVITE messages and processes provisional responses to facilitate early media handling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If SIP networks require a 2xx response before media exchange, then call signaling control is maintained, but early media exchange before called party answers becomes impossible
Solution Approach 1:
The patent introduces a back-to-back user agent (B2BUA) as an intermediary entity that sits between the user agent client and user agent server. The B2BUA independently manages two separate SIP dialogs: one with the UAC and another with the UAS. This intermediary structure allows the B2BUA to send early media indicators and establish media paths before the UAS sends a 2xx response, thereby enabling early media exchange while maintaining proper signaling control through the intermediary's coordinated management of both dialogs.
2Adaptability or versatility
If PSTN gateway does not support SIP early media extensions, then legacy PSTN compatibility is maintained, but early media connections fail when calls cross the PSTN boundary
Solution Approach 1:
The B2BUA acts as a mediator between SIP networks and legacy PSTN gateways. It translates and adapts signaling between the two systems, converting SIP early media indicators into appropriate forms that can be processed even when the PSTN gateway lacks native SIP early media extension support. The B2BUA manages the media path establishment independently, allowing early media to flow through the SIP side while maintaining compatibility with the legacy PSTN gateway on the other side.
Solution Approach 2:
The patent modifies SIP signaling parameters and message flows to enable early media functionality. The B2BUA sends early media indicators in provisional responses (such as 183 Session in Progress) that carry SDP information, allowing media parameters to be negotiated and established before the final 2xx response. This parameter modification approach enables early media exchange without requiring changes to the legacy PSTN gateway's core functionality.
3Adaptability or versatility
If early media connection is established before called party answers, then early media exchange is enabled, but media connection timing conflicts with traditional call establishment procedures
Solution Approach 1:
The patent segments the traditional monolithic call establishment procedure into distinct phases managed by the B2BUA. It separates the early media dialog establishment from the final call connection, allowing the B2BUA to first set up a provisional dialog for early media exchange, then later complete the full media connection when the called party answers. This segmentation allows early media to flow through a dedicated provisional path without disrupting the overall call establishment stability.
Solution Approach 2:
The B2BUA performs preliminary actions by establishing the early media dialog and sending SDP offers/answers before the called party answers. It proactively sets up the media path parameters, codec negotiations, and network routing in advance, so that when the called party does answer, the media connection can be quickly activated without re-negotiation. This preliminary action maintains stability by preparing all necessary parameters beforehand.
Data Source
AI summary
Methods, systems, and computer readable media for early media connection proxying are disclosed. According to one method, a call setup signaling message is received for establishing a call between a calling entity and a called entity. Based on at least one parameter in the call setup signaling message, it is determined whether an early media connection is required for the call. It is also determined whether early media connection proxying is required for the call. In response to determining that an early media connection and early media connection proxying are required for the call, signaling is performed on behalf of a network entity to establish an early media connection for the call.