The Sip Alg - D-Link NetDefendOS User Manual

PPTP ALG Settings
The following settings are available for the PPTP ALG:
Name
Echo timeout
Idle timeout
In most cases only the name needs to be defined and the other settings can be left at their
defaults.

6.2.9. The SIP ALG

Overview
Session Initiation Protocol (SIP) is an ASCII (UTF-8) text based signaling protocol used to establish
sessions between clients in an IP network. It is a request-response protocol that resembles HTTP
and SMTP. The session which SIP sets up might consist of a Voice-Over-IP (VoIP) telephone call or
it could be a collaborative multi-media conference. Using SIP with VoIP means that telephony
can become another IP application which can integrate into other services.
SIP Sets Up Sessions
SIP does not know about the details of a session's content and is only responsible for initiating,
terminating and modifying sessions. Sessions set up by SIP are typically used for the streaming of
audio and video over the Internet using the RTP/RTCP protocol (which is based on UDP) but they
might also involve traffic based on the TCP protocol. An RTP/RTCP based session might also
involve TCP or TLS based traffic in the same session.
The SIP RFC
SIP is defined by IETF RFC 3261 and this is considered an important general standard for VoIP
communication. It is comparable to H.323, however, a design goal with SIP was to make SIP more
scalable than H.323. (For VoIP, see also Section 6.2.10, "The H.323 ALG".)
A descriptive name for the ALG.
Idle timeout for Echo messages in the PPTP tunnel.
Idle timeout for user traffic messages in the PPTP tunnel.
Important: Third Party Equipment Compliance
NetDefendOS is based on the SIP implementation described in RFC 3261. However,
correct SIP message processing and media establishment cannot be guaranteed unless
local and remote clients as well as proxies are configured to follow RFC 3261.
Unfortunately, some third party SIP equipment may use techniques that lie outside RFC
3261 and it may not be possible to configure the equipment to disable these. For this
reason, such equipment may not be able to operate successfully with the NetDefendOS
SIP ALG.
For example, analog to digital converters that do not work with the SIP ALG may come
preconfigured by service providers with restricted configuration possibilities.
NAT traversal techniques like STUN also lie outside of RFC 3261 and need to be disabled.
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Chapter 6: Security Mechanisms