SIP Firewall and NAT Traversal
TUTORIALS
What is NAT (Network Address Translation?) Why do we need ALG (Application Layer Gateway?)
964kb Zipped Powerpoint tutorial 
By SIPKnowledge 
A very well written and descriptive tutorial on NAT and the traversal problems for SIP Networks.
View the powerpoint tutorial here >>>
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WHITEPAPERS
(www.ingate.com) Solving the Firewall/NAT Traversal Issue of SIP: Who Should Control Your Security Infrastructure?
Best practices for SIP NAT traversal
Paradial Whitepaper - Connectivity Challenges for Real-time IP Communications - How NATs and firewall issues are solved efficiently and securely
Intertex AB The SIP Protocol and Firewall Traversal
Media Proxy - NAT traversal for geographically distributed Voice over IP networks
NAT Traversal in SIP
LINKS AND RESOURCES
IETF RFC 3489 - STUN - Simple Traversal of User Datagram Protocol (UDP) Through Network Address Translators (NATs)
iptel.org - Internet Drafts and RFCs: NAT-friendly
Using Asterisk as a SIP/IAX Gateway - The Asterisk open source telephony server can be used as a gateway in order to avoid SIP NAT Traversal.
SIPfoundry - The NAT & Firewall Traversal Problem
SIP Foundry - SIP NAT Traversal using the Astaro Security Linux Firewall
SIP Foundry - Introduction to STUN Servers
Sourceforge Project: STUN Client and Server library - This project implements a simple STUN (Simple Traversal of UDP through NATs) server and client on Windows, Linux, and Solaris.
PRODUCTS AND SERVICES
SIP Center products directory - Firewalls and Security
MediaProxy - distributed far-end NAT traversal
MediaProxy is a far-end NAT traversal solution for SIP Express Router.
MediaProxy employs a revolutionary concept that allows selection of the NAT traversal location by using DNS SRV records. Visit AG Projects' SIP Showcase >>>
SIPassure SIP Firewall
BorderWare’s SIPassure SIP Firewall is the industry’s first comprehensive SIP security device. It is a secure edge proxy that offers standard features such as NAT traversal, topology hiding, session management, and traditional firewall protection but also provides security to stop voice spam, phishing attacks, identity theft, session hijacking and redirection, registrar floods, denial of service, directory harvest attacks and more. SIPassure is also uniquely suited to help financial services organizations to comply with SEC, SOX and GLB regulations due to its built-in audit and reporting functionality. Further information >>>
SnowShore Media Firewall
The SnowShore Media Firewall is a high performance media processing platform that enables session-level security for internetworking across multiple carrier and/or enterprise IP networks. It performs critical real-time Network Address Translation (NAT) and dynamic firewalling functions and supports multiple signaling protocols and media transcoding functionality allowing secure traversal and interconnection of IP media streams across multiple network boundaries. Visit Cantata's SIP Showcase >>>
Session Border Controller (DC-SBC)
The experienced team at Data Connection has developed a fully portable Session Border Controller (DC-SBC) software solution designed specifically for system vendors. Data Connection’s extensive VoIP and IP routing heritage provides OEMs with a field-hardened SBC solution that is deployable immediately, delivering dramatic cost and time to market savings. Like all Data Connection products, DC-SBC is developed with the highest quality standards and is architected for unparalleled modularity, flexibility, scale, and reliability.
Further information >>>
Intertex Data AB SIP aware firewalls in the acclaimed Internet Gate series for home and office users. Built-in SIP server; FXS/FXO ports; WLAN; ADSL and can be upgraded with VPN termination and PBX functionality.
The Newport Networks 1460 carrier class session border controller is a key part of the infrastructure that Service Providers need in order to sell commercially viable, managed voice and multimedia services over IP to consumer and business customers, whilst also enabling IP peering to occur. It meets the need of Service Providers for carrier-class scalability, performance and resilience. It performs NAT and firewall traversal where required, provides network security, performs traffic management and, enables lawful intercept and emergency call handling in a real time VoIP and Multimedia environment.
The Newport Networks 1460 also allows physical separation of signalling and media providing ultimate deployment flexibility and scaling.
Visit Newport Networks SIP Showcase >>>