SIP Protocol

SIP usually uses ports 5060 TCP or UDP for unencrypted signaling or 5061 for encrypted transportation using TLS.

SIP is an ASCII based protocol which has some similar elements like in the HTTP protocol by using a request/response model. Much like an HTTP request from a browser a SIP client request is made using a SIP URI a user agent and a method/request. SIP uses e-mail like addresses format:

SIP Requests/Methods

Example SIP INVITE Request

INVITE sip:201@ SIP/2.0
Via: SIP/2.0/UDP;rport;branch=z9hG4bKvbxaoqar
Max-Forwards: 70 

From: "NightRanger" ;tag=eihgg
Call-ID: hfxsabthoymshub@backtrack
CSeq: 649 INVITE
Content-Type: application/sdp 

Supported: replaces,norefersub,100rel
User-Agent: Twinkle/1.2 

Content-Length: 310

SIP Responses

Example SIP Call