1. Real-world SIP Interoperability: Still an Elusive Quest
Archana Rao and Henning Schulzrinne
Department of Computer Science
Columbia University
December 3, 2007
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2. Systematic Study of Interoperability
A Framework for Identification and Analysis
Define a minimum set of call flows constituting basic interoperability
RFC 3665, RFC 3666, RFC 4317
Use a VoIP testbed to realize a variety of real-world SIP infrastructure setups
Columbia VoIP testbed
Study the behavior of SIP end-clients and servers in each of these scenarios
Interoperability matrices
Categorization of common issues 
Lack of clarity in the specification
Implementation of an older specification
Incomplete implementation of the specification
Incorrect implementation of the specification
Failure against robustness tests

3. your equipment here :-)
your equipment here :-)

4. Real-world SIP Interoperability
Summary
Tests indicate that basic-level interoperability is far from perfect
Instances of interoperability failures illustrated in our workshop paper
Achieving Interoperability shouldn’t be left to vendor
non-interoperability damages SIP brand, causes grief for third parties and harms customers
Going Ahead
Establish designated interop liaison for each vendor
calling customer support unlikely to be useful
Encourage vendors to publish interoperability reports
in standard format
Provide self-certification tests, supported by a remotely accessible test rig