4.1 Public Network Features
4.1.1 SIP (Session Initiation Protocol) Trunk
Description
Through a V-SIPGW card, the PBX can connect to an Internet telephony service provided by an ITSP (Internet
Telephony Service Provider).
An ITSP provides its telephony service partly through the conventional telephone network (e.g., ISDN and
Mobile), which is fee-based. An ISP (Internet Service Provider), which can also act as a SIP provider, does
not provide the telephone connection itself. However, providing its users with Internet access, an ISP provides
voice communication on the Internet for free. In this way, with VoIP technology based on the SIP protocol, the
cost of voice communication can be much cheaper than conventional telephone networks.
Conditions
• A subscription with an ISP is required for an Internet connection.
• A subscription with an ITSP is required for a telephone connection. The ISP and ITSP may be part of the
same company.
320 Feature Guide
4.1.1 SIP (Session Initiation Protocol) Trunk
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