Page 219 - Asterisk™: The Future of Telephony

considered a shortcoming in this protocol, and it causes no end of trouble to network
professionals needing to connect SIP endpoints using existing network infrastructure.

H.323
This International Telecommunication Union (ITU) protocol was originally designed
to provide an IP transport mechanism for video conferencing. It has become the stand-
ard 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 dep-
recated in favor of IAX and SIP. H.323 has not enjoyed much success among users and
enterprises, although it might still be the most widely used VoIP protocol among car-
riers.
The three versions of H.323 supported in Asterisk are handled by the modules
chan_h323.so (supplied with Asterisk), chan_oh323.so (available as a free add-on), and
chan_ooh323.so (supplied in asterisk-addons).

You have probably used H.323 without even knowing it—Microsoft’s
NetMeeting client is arguably the most widely deployed H.323 client.

History
H.323 was developed by the ITU in May of 1996 as a means to transmit voice, video,
data, and fax communications across an IP-based network while maintaining connec-
tivity with the PSTN. Since that time, H.323 has gone through several versions and
annexes (which add functionality to the protocol), allowing it to operate in pure VoIP
networks and more widely distributed networks.

Future
The future of H.323 is a subject of debate. If the media is any measure, it doesn’t look
good for H.323; it hardly ever gets mentioned (certainly not with the regularity of SIP).
H.323 is often regarded as technically superior to SIP, but, as with so many other tech-
nologies, that sort of thing is seldom the deciding factor in whether technology enjoys
success. One of the factors that makes H.323 unpopular is its complexity—although
many argue that the once-simple SIP is starting to suffer from the same problem.
H.323 still carries by far the majority of worldwide carrier VoIP traffic, but as people
become less and less dependent on traditional carriers for their telecom needs, the
future of H.323 becomes more difficult to predict with any certainty. While H.323 may
not be the protocol of choice for new implementations, we can certainly expect to have
to deal with H.323 interoperability issues for some time to come.

VoIP Protocols | 191