SIP Media-related Protocols
A SIP session makes use of a number of protocols. These are:
SDP Session Description Protocol (RFC 4566) is used for media session initialization.
RTP Real-time Transport Protocol (RFC 3550) is used as the underlying packet format for
delivering audio and video streaming via IP using the UDP protocol.
RTCP Real-time Control Protocol (RFC 3550) is used in conjunction with RTP to provide
out-of-band control flow management.
Either IP Rule or IP Policy Objects Can Be Used
When setting up SIP, either IP Rule or IP Policy objects can be used to control traffic flows.
When using an IP Rule object, a SIP ALG object must be used. When using an IP Policy object, a SIP
ALG object is not used. Instead, a VoIP Profile object is first created and the IP Policy object must
then refer to this.
In NetDefendOS version 11.03 and later, a predefined SIP ALG is not present in the default
configuration and therefore a new SIP ALG object must always be created when using an IP Rule
object with SIP. In older NetDefendOS versions that are upgraded to 11.03 or later, the
predefined SIP ALG object will be retained.
In addition, the predefined service object called sip-udp will have its Protocol property already
correctly set in the default configuration of NetDefendOS version 11.03 and later.
SIP Setup Using IP Rule Objects
When configuring NetDefendOS for SIP sessions with IP Rule objects, the following steps are
required:
• Define a SIP ALG object.
• Define a single Service object for SIP communication and associate it with the ALG.
• Define the appropriate IP Rule or IP Policy objects for SIP communications which uses the
defined Service object.
SIP Setup Using IP Policy Objects
When configuring using IP Policy the following steps are required:
• Define a single Service object for SIP communication. The Protocol property must be set to SIP
if the service is to be used with an IP Policy object.
• Define a VoIP Profile object. The settings that would have been input when using the SIP ALG
are input into this object.
• Define the appropriate IP Rule or IP Policy objects for SIP communications which use the
defined Service object.
• Associate the VoIP Profile object created previously with the IP Policy object.
Chapter 6: Security Mechanisms
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