ZyXEL UAG715 User Guide - Page 209
ALG Overview
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CHAPTER 18 ALG 18.1 ALG Overview Application Layer Gateway (ALG) allows the following applications to operate properly through the UAG's NAT. • SIP - Session Initiation Protocol (SIP) - An application-layer protocol that can be used to create voice and multimedia sessions over Internet. • H.323 - A teleconferencing protocol suite that provides audio, data and video conferencing. • FTP - File Transfer Protocol - an Internet file transfer service. The following example shows SIP signaling (1) and audio (2) sessions between SIP clients A and B and the SIP server. Figure 133 SIP ALG Example The ALG feature is only needed for traffic that goes through the UAG's NAT. 18.1.1 What You Can Do in this Chapter Use the ALG screen (Section 18.2 on page 212) to set up SIP, H.323, and FTP ALG settings. 18.1.2 What You Need to Know Application Layer Gateway (ALG), NAT and Firewall The UAG can function as an Application Layer Gateway (ALG) to allow certain NAT un-friendly applications (such as SIP) to operate properly through the UAG's NAT and firewall. The UAG dynamically creates an implicit NAT session and firewall session for the application's traffic from the WAN to the LAN. The ALG on the UAG supports all of the UAG's NAT mapping types. UAG715 User's Guide 209
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