SIP Signalling Transport Protocol Switching for Call Continuity

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Solution Overview

Problem

Current SIP signalling protocols face challenges in maintaining communication when a server fails, as TCP ensures message transmission but not resilience, while UDP allows signalling continuity but lacks guaranteed delivery, particularly for clients behind NAT devices.

Innovation Solution

Switching from TCP to UDP mid-call by specifying UDP as the transport protocol in response messages, using headers like 'Contact' and 'Via' in SIP messages to open a UDP pinhole and enable two-way communication, allowing continued signalling even if the TCP connection fails.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If TCP is used for SIP call setup, then message transmission is guaranteed, but call continuity fails when server becomes unavailable

Engineering Contradiction:

Improvemessage transmission guaranteeVSAvoidcall continuity after server failure

Core Design Contradiction:

ReliabilityVSAdaptability or versatility

Solution Approach 1:

The system dynamically switches transport protocols from TCP during call setup to UDP during call execution. The SIP server sends a transport protocol indication in the SIP response message (e.g., 200 OK) telling the client to use UDP for subsequent in-call signalling, enabling adaptability while maintaining initial reliability.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The transport protocol parameter changes from TCP to UDP mid-call. The server indicates this parameter change through SIP message headers (Contact, Via, or Transport header), allowing the system to transition from connection-oriented to connectionless operation for improved resilience.

Inventive Principle:

Principle #35Parameter changes

2Adaptability or versatility

If UDP is used for SIP signalling, then signalling continuity is maintained after server failure, but message transmission is not guaranteed

Engineering Contradiction:

Improvesignalling continuity after failureVSAvoidmessage transmission guarantee

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The system uses UDP dynamically during the call execution phase rather than from the beginning. This allows the benefits of UDP (resilience to server failure) to be realized while maintaining TCP for the critical call setup phase where reliable delivery is essential.

Inventive Principle:

Principle #15Dynamics

3Reliability

If TCP connection is used behind NAT, then secure authentication is achieved, but switching to UDP requires opening NAT pinhole first

Engineering Contradiction:

Improveauthentication securityVSAvoidNAT pinhole management

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The client opens a UDP pinhole through NAT in advance by sending a UDP message (such as an OPTIONS request or early SIP message) before the server needs to send UDP signalling. This preliminary action eliminates the complexity of waiting for communication re-establishment after server failure.

Inventive Principle:

Principle #10Preliminary action

Data Source

PatentUS10116708B2SIP signalling

Publication Date: 2018.10.30 MICROSOFT TECHNOLOGY LICENSING LLC

AI summary

The present invention relates to signalling between entities in a SIP protocol communication in which the transport protocol can be changed during the call to provide improved call reliability.