Interoperability is something I deal with every single day of my working life. Just today I spent a significant amount of time researching which session border controllers successfully interoperate with which call recorders. While it might seem like a fairly straightforward task, this level of detail is rarely found in marketing brochures or product bulletins. You have to make phone calls, send emails, and call in favors to get the straight scoop. Even then, one man’s definition of “interoperate” isn’t necessarily mine.
In my latest article for No Jitter, I introduce you to an important topic I will be speaking about at this year’s Enterprise Connect.
Tao, Zen, and Tomorrow 
Dear Sir,. i need complete document on SIP Protocol, kindly share me, i very thanks for to you.
Read this and you will be a SIP expert. https://www.ietf.org/rfc/rfc3261.txt