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  H.323 https://www.chinaroby.com/ This International Telecommunication Union (ITU) protocol was originally designed to provide an IP transport mechanism for video-conferencing. It has become the standard in IP-based video-conferencing equipment, and it briefly enjoyed fame as a VoIP protocol as well. While there is much heated debate over whether SIP or H.323 (or IAX) will dominate the VoIP protocol world, in Asterisk, H.323 has largely been deprecated in favour of IAX and SIP. H.323 has not enjoyed much success among users and enterprises, although it is still the most widely used VoIP protocol among carriers. The two versions of H.323 supported in Asterisk are handled by the modules chan_h323.so (supplied with Asterisk) and chan_oh323.so (available as a free add-on). You have probably used H.323 without even knowing itMicrosoft's NetMeeting client is arguably the most widely deployed H.323 client. 8.2.3.1. History H.323 was developed by the ITU i...

  SIP The Session Initiation Protocol ( SIP ) has taken the world of VoIP by storm. Originally considered little more than an interesting idea, SIP now seems poised to dethrone the mighty H.323 as the VoIP protocol of choicecertainly at the endpoints of the network. The premise of SIP is that each end of a connection is a peer, and the protocol negotiates capabilities between them. What makes SIP compelling is that it is a relatively simple protocol, with a syntax similar to that of other familiar protocols such as HTTP and SMTP. SIP is supported in Asterisk with the chan_sip.so module. 8.2.2.1. History SIP was originally submitted to the Internet Engineering Task Force (IETF) in February of 1996 as "draft-ietf-mmusic-sip-00." The initial draft looked nothing like the SIP we know today and contained only a single request type: a call setup request. In March of 1999, after 11 revisions, SIP RFC 2543 was born. At first, SIP was all but ignored, as H.323 was consider...

  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...