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--- VOIP (SIP) Cheatsheet


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: user/phone@domain/ip A typical SIP URI looks like:

sip:205@192.168.1.100, sip:username@pbx.com , sip:205@192.168.1.100:5060


[+] SIP Requests / Methods

Request		Description
INVITE		Used to invite and account to participate in a call session.
ACK			Acknowledge an INVITE request.
CANCEL		Cancel a pending request.
REGISTER	Register user with a SIP server.
OPTIONS		Lists information about the capabilities of a caller.
BYE			Terminates a session between two users in a call.
REFER		Indicates that the recipient(identified by the Request URI) should contact a third party using the contact information provided in the request.
SUBSCRIBE	The SUBSCRIBE method is used to request current state and state updates from a remote node.
NOTIFY		The NOTIFY method is used to notify a SIP node that an event which has been requested by an earlier SUBSCRIBE method has occurred.


[+] An Example SIP “INVITE” Request:

INVITE sip:201@192.168.1.104 SIP/2.0
Via: SIP/2.0/UDP 192.168.1.102;rport;branch=z9hG4bKvbxaoqar
Max-Forwards: 70