I recently participated in a SIP interoperability panel at Interop in NYC. My four Cs of SIP compliance: complementary, carrier, co-integration and competitive.
> Complementary connecting third party clients and gateways to comm servers. Allen Sulkin, a VoIP analyst, observes that many customers are taking their Cisco SIP phones and re-using them on other vendor's comm servers, thus preserving their investment.
> Carrier meaning enterprise-carrier SIP trunking. SIP trunking is supported by carriers worldwide and is important for managed service plays. We are also heavily engaged in carrier IMS deployments within the cloud, these based on multivendor SIP interoperability. In this case, the carrier technology groups invest heavily in making SIP happen.
> Co-integration, for example leveraging SIP in our integration with Microsoft OCS. We (Nortel with Microsoft) are leading the industry in testing implementations of SIP RFC 3261and TR87 (CTI over SIP) to integrate our respective products.
> Competitive SIP trunking between multivendor PBX networks. Don't expect a lot of cooperation- e.g. I don't expect to see another PBX vendor join Nortel's developer partner program, or vice versa! That said we have Avaya and Cisco call servers in our labs to test basic interoperability. Historically, leveraging each vendor's interoperability with carriers has enabled PBX-PBX interoperability.
SIP is critically important to the industry, but SIP compliance is a many sided coin. Do my four C's help?