Thanks everyone for the amazing response on the blog ! In the last post, we discussed SIP SYSTEM ARCHITECTURE. Now, I hope you know “ understanding SIP” means not just knowing about Protocol. Every component mentioned in the architecture plays a vital role of its own. I have already reveal the secret of each component what it does. Now, in this post and further, we will be dealing each component a bit deeper. So, today's component is Proxy Server. RFC 3261 says: SIP proxies are elements that route SIP requests to user agent servers and SIP responses to user agent clients. A request may traverse several proxies on its way to a UAS. Each will make routing decisions, modifying the request before forwarding it to the next element. Responses will route through the same set of proxies traversed by the request in the reverse order. Why do we need it? The actual question should be why do we need a proxy server if two UAs able to communicate each ...