Asterisk is an open source pbx and telephony toolkit.

this channel driver (chan_h323) provides support for the h.323 protocol for asterisk. this is an implementation originally contributed by nufone and nowdays maintained and distributed by digium, inc. hence, it is considered the official h.323 chanel driver.

there is another h.323 channel implementations for asterisk: chan_ooh323, distributed by debian as asterisk-ooh323c.

for more information about the asterisk pbx, have a look at the asterisk package.