On the trunk side, the SIP interface conforms to RFC 3261, allowing support of video calls over the SIP trunk. But like other vendors, Cisco adds non-standard extensions to SIP to expand its functionality.
Cisco's SIP-implementation used to be called SKINNY but is now called "SIP with extensions," Thompson says.
"We will support both a SIP client as well as a SIP client with Cisco extensions, to add more functionality," Thompson says.
Kerravala says that even though SKINNY is proprietary, it represents the most "open" aspect of Cisco's unified communications implementation.
"Cisco's open when it comes to SKINNY," Kerravala says. "If you want to work in Cisco's ecosystem and you want to be able to tap into a lot of the advanced features, then you got to code to SKINNY. From a vendor perspective, their market share is big enough that it makes it worth it."
Among the major vendors Cisco has unified communications interoperability agreements with are IBM, Nokia and Microsoft. Analysts say Cisco, however, does not have the independent software vendors (ISV) development ecosystem that Microsoft has... or does it?
Thompson says Cisco is tapping its roster of channel, system integration and service provider partners to code to the Cisco unified communications blueprint.
"Most of our channel partners are actually ISVs in their own right," Thompson says.
The unified communications implementation decision, Herrell says, will ultimately lie with whomever in the enterprise is making the IT purchasing decisions - the desktops and server systems personnel, or the network engineers.
And Cisco says that's fine. "You can have OCS on your desktops," Thompson says, "but Cisco's going to make sure that all of the mobile clients participate."