Sip Alg Overview - Juniper NETWORK AND SECURITY MANAGER 2010.4 - CONFIGURING SCREENOS DEVICES GUIDE REV 01 Manual

Related
Documentation

SIP ALG Overview

Copyright © 2010, Juniper Networks, Inc.
Select Pass unidentified Skinny message in Route mode check box.
9.
Select Pass unidentified Skinny message in NAT mode check box.
10.
NOTE: When you select the "pass unidentified message" option in either
Route or NAT mode, the message that had an error in decoding (because
of unidentified message ID or parameter) is forwarded as-is without any
processing.
Click OK to apply your settings.
11.
SCCP Support in ScreenOS Devices Overview on page 279
SIP ALG Overview on page 281
ALG Overview on page 286
SDP Session Description Overview on page 288
Session Initiation Protocol (SIP) is an Internet Engineering Task Force (IETF) standard
protocol for initiating, modifying, and terminating multimedia sessions over the Internet.
Such sessions might include conferencing, telephony, or multimedia, with features such
as instant messaging and application-level mobility in network environments.
Juniper Networks security devices support SIP as a service and can screen SIP traffic,
allowing and denying it based on a policy that you configure. SIP is a predefined service
in ScreenOS and uses port 5060 as the destination port.
SIP's primary function is to distribute session-description information and, during the
session, to negotiate and modify the parameters of the session. SIP is also used to
terminate a multimedia session.
Session-description information is included in INVITE and ACK messages and indicates
the multimedia type of the session, for example, voice or video. Although SIP can use
different description protocols to describe the session, the Juniper Networks SIP ALG
supports only Session Description Protocol (SDP).
SDP provides information that a system can use to join a multimedia session. SDP might
include information such as IP addresses, port numbers, times, and dates. Note that the
IP address and port number in the SDP header (the "c=" and "m=" fields, respectively)
are the address and port where the client wants to receive the media streams and not
the IP address and port number from which the SIP request originates (although they
can be the same). See "SDP Session Description Overview" on page 288 for more
information.
SIP messages consist of requests from a client to a server and responses to the requests
from a server to a client with the purpose of establishing a session (or a call). A User
Chapter 9: Voice Over Internet Protocol
281