ZyXEL Communications ZyWALL USG 300 User Manual page 440

Chapter 21 ALG
connections to the second (passive) interface when the active interface's
connection goes down. When the active interface's connection fails, the client
needs to re-initialize the connection through the second interface (that was set to
passive) in order to have the connection go through the second interface. VoIP
clients usually re-register automatically at set intervals or the users can manually
force them to re-register.
FTP
File Transfer Protocol (FTP) is an Internet file transfer service that operates on the
Internet and over TCP/IP networks. A system running the FTP server accepts
commands from a system running an FTP client. The service allows users to send
commands to the server for uploading and downloading files.
H.323
H.323 is a standard teleconferencing protocol suite that provides audio, data and
video conferencing. It allows for real-time point-to-point and multipoint
communication between client computers over a packet-based network that does
not provide a guaranteed quality of service. NetMeeting uses H.323.
SIP
The Session Initiation Protocol (SIP) is an application-layer control (signaling)
protocol that handles the setting up, altering and tearing down of voice and
multimedia sessions over the Internet. SIP is used in VoIP (Voice over IP), the
sending of voice signals over the Internet Protocol.
SIP signaling is separate from the media for which it handles sessions. The media
that is exchanged during the session can use a different path from that of the
signaling. SIP handles telephone calls and can interface with traditional circuit-
switched telephone networks.
RTP
When you make a VoIP call using H.323 or SIP, the RTP (Real time Transport
Protocol) is used to handle voice data transfer. See RFC 1889 for details on RTP.
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ZyWALL USG 300 User's Guide