H.323 is the protocol used for IP Telephony and Voice/Data/Video conferencing,etc. The feature set only means the current supported features under this protocol. H.323 is also usually responsible for call handling and call control of most IP switches for voice.
Couple of sites may expalin this much better:
has some tutorials on IP telephony
TDM is short for Time Division Multiplexing which is the switch matrix, blocking or non blocking, for most PBX and key systems.
All I meant was, before settling on multi-site sytems(5 sites) make sure the system has all the features your company requires for inter and intra office communications.
Traditional PBX and Key System manufacturers have more years R&D invested in their products for multi site, call center and centralized services than most IP only based systems.
If the NBX fits your current and future needs, it may be the system for you. My primary problem with the system is the cost of desktop instruments and the industry standards dictate what features are available.
Hope this helps. Good Luck. Jerry Pannell
techs@sclb.com