ZyXEL Communications 100 Series, 200 Series ALG, 18.1 ALG Overview, 18.1.1 What You Can Do in the ALG Screen

Application Layer Gateway (ALG) allows the following applications to operate properly through the ZyWALL’s NAT.

•FTP - File Transfer Protocol (FTP) is an Internet file transfer service.

•SIP - Session Initiation Protocol (SIP) is an application-layer protocol that can be used to create voice and multimedia sessions over Internet.

•H.323 - This is a teleconferencing protocol suite that provides audio, data and video conferencing.

The following example shows SIP signaling (1) and audio (2) sessions between SIP clients A and B and the SIP server.

Figure 232 SIP ALG Example

The ZyWALL only needs to use the ALG feature for traffic that goes through the ZyWALL’s NAT.

Use the ALG screen (Section 18.2 on page 328) to set up SIP, H.323, and FTP ALG settings.

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