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  VoIP Protocols The mechanism for carrying a VoIP connection generally involves a series of signaling transactions between the endpoints (and gateways in between), culminating in two persistent media streams (one for each direction) that carry the actual conversation. There are several protocols in existence to handle this. In this section, we will discuss some of those that are important to VoIP in general and to Asterisk specifically. 8.2.1. IAX (The "Inter-Asterisk eXchange" Protocol) The test of your Asterisk-ness comes when you have to pronounce the name of this protocol. Newbies say "eye-ay-ex"; those in the know say "eeks." IAX [*] is an open protocol, meaning that anyone can download and develop for it, but it is not yet a standard of any kind. [*] Officially, the current version is IAX2, but all support for IAX1 has been dropped, so whether you say "IAX" or "IAX2," it is expected that you are talking about the V...

 About VoIP Pre-Paid Phone Cards VoIP has become an important technology for phone services to travelers, migrant workers and ex-pats, who either, due to not having a fixed or mobile phone or high overseas roaming charges, choose instead to use placa VoIP services to make their phone calls. Pre-paid phone cards can be used either from a normal phone or from Internet cafes that have phone services. Developing countries and areas with high tourist or immigrant communities generally have a higher uptake. VoIM Voice over Instant Messenger, like popular Skype, Voice over MSN, Yahoo, QQ in China and Google Talk. VoIM is one kind of general VoIP that was based on an IM. VoIP , specifically, usually is referred as traditional SIP or H.323 IP phone, as opposed to VoIM as newly emerged Skype-like services/phones.

    FXO and FXS are the ports used by analog phone lines and analog phones and faxes. These two interfaces are always paired (FXO is always connected to FXS and vice versa). In telecommunications, FXS and FXO are used to indicate whether VoIP equipment is designed to support analog phones (stations, FXS) and analog lines (office, FXO). FXS is the port used by analog lines, example: telephone jack on the wall / FXS ports of an analog telephone exchange used to connect analog devices. To connect analog devices to VoIP PBX, use FXS media gateway (media gateway with FXS port). FXO is the port used by analog devices, example: FXO port of an analog phone, modem, fax (these devices are often called FXO devices ), FXO port of an analog telephone exchange used to connect lines.