Allworx 24X Bedienungsanleitung PDF herunterladen (Seite 16)

VoIP White Paper

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Revised: February 8, 2007

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SIP/SDP sessions going back and forth, the audio data coming from the remote is simply blocked as illegal

data, even if it did manage to route from end-to-end.

Since both NAT/Firewall and VoIP services are desirable, what do we do about SIP and NAT? There are

several pieces required to get this to work correctly. The key element is a special device called an Application

Level Gateway (ALG). This is traditionally a separate type of special NAT firewall that is SIP-aware. It is

specially configured to monitor the context of everything going back and forth between end-points – altering

SIP/SDP/RTP packets and opening/closing holes through the firewall to allow the audio to negotiate and flow

correctly.

Alternatively, you can use Allworx as your VoIP gateway with Allworx phones. They work together to solve all

these problems for you automatically – even when using third-party firewalls. The details of this are explored in

the next section.

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Allworx 24X Bedienungsanleitung Seite 16