Patent ID: 8719926

Claim:
A method comprising: receiving a session initiation protocol (SIP) request message; determining whether a dialog exists corresponding to the request message; determining whether the dialog is in a first phase of the dialog or a second phase of the dialog when the dialog exists corresponding to the request message; querying a table indicating valid types of requests for the first phase of the dialog, when determined that the dialog is in the first phase, to determine whether the received request message is one of the valid types of requests for the first phase or querying a table indicating valid types of requests for the second phase of the dialog, when determined that the dialog is in the second phase, to determine whether the received request message is one of the valid types of requests for the second phase; and rejecting the received request message when determined that the request message is not one of the valid types of requests for the first phase when determined that the dialog is in the first phase, or not one of the valid types of requests for the second phase when determined that the dialog is in the second phase.