Zyxel ZyWALL USG 20 [94/185] Voip in nat scenario

ZyWALL USG Support Notes

3.2. VoIP in NAT Scenario

SIP VoIP in nature is an NAT unfriendly application, since it uses a different port for

the RTP traffic (voice stream) other than the session initiation port which is by default

uses UDP 5060.

There‟re currently the following solutions to solve the SIP and NAT incompatibility

issue.

 SIP ALG on the NAT gateway

 STUN

 Outbound Proxy

 Solutions in SIP client devices (such as Use NAT in ZyXEL VoIP clients)

USG ZyWALL supports SIP ALG. Network administrator just needs to enable SIP

ALG on the ZyWALL. Then he can deploy VoIP solutions in various NAT scenarios,

no matter the SIP server is in the internet, or in the local network.

3.2.1. SIP Server on the Internet

3.2.1.1. Application Scenario

In the scenario below, the SIP server is on the Internet. There‟re SIP clients both in the

USG local network, and on the internet side. All the clients are registered to the SIP

server. We want all the clients can call each other:

The local clients can call out to the clients on the Internet.

The Internet clients can call in the local clients.

The local clients also can call each other.