There's not just the story about the protocol, but how SIP is capable of changing the world of communications.
PBX vendors have always worked hard to keep the phones tightly coupled to the system. They say it's necessary for feature transparency, but also has the benefit to vendors of tightly coupling the sale of phones to the sale of systems. This runs counter to the architectural shift written elsewhere in this blog that the design of enterprise telephony is shifting to a 'horizontal' view. This horizontification of telephony means that the end points should be interoperable, that the end points should leverage applications and network services from lower layers in the architecture.
So, Nortel's MCS-5100 is flawed since it assures SIP interoperability only through their API. Cisco's CallManager is flawed since they claim proper quality of service ONLY with a Cisco network. [Yuck!]
3. SIP is a standard.
Despite being a standard, SIP implementations do vary. Some vendors such as Avaya, Cisco and Nortel offer SIP interoperability as an Applications Programming Interface (API) so that their world of proprietary signaling between endpoints and the call controller can be controlled. This approach has the vendor advantage of maintaining account and feature control. Some vendors and Cisco, in particular, charge extra for SIP support, enabling only the most rudimentary features in the SIP mode, compared to the Cisco Skinny Call Control Protocol, their proprietary implementation.
Alone among the leading IP PBX vendors, 3Com has implemented a different approach. Strictly using SIP between endpoints such as IP phones, video cameras, call controllers and gateways to the public telephone network enable an inexpensive, robust and vendor-neutral environment capable of rapidly delivering a portfolio of advanced applications for presence, conferencing, contact center, messaging and mobility services.
Furthermore, 3Com promotes the Voice Solutions Provider Program as an initiative to promote the benefits of SIP-based interoperability. 3Com is a founding member of the SIP Forum. The website at http://www.3com.com/voip/interoperability.html lists over 30 vendors, service providers and solutions that are proven to interoperate with 3Com IP Telephony modules.
I was speaking at a conference recently and an audience member asked for the vendors would promote their interoperability. I grabbed the mic and told them we do, and read out the URL.
