3Com NBX 100 Administrator's Manual - page 417
Connection Considerations
417
After an IP connection has been established, the ConneXtions software
begins a series of H.323 exchanges by using TCP packets on the IP
connection.
These H.323 exchanges set up the call and negotiate the type of voice
compression that is used. They also cause the remote NBX (or PBX)
system to begin setting up the remote end of the connection.
Connection
Considerations
As soon as an end-to-end connection has been set up, all three networks
(local LAN, WAN, and remote LAN) are ready to pass voice packets. The
NBX Business and Basic Telephones use their DSP to convert spoken
words into digital voice packets. The voice packets are transferred across
the Ethernet to the local H.323 gateway. The gateway strips off the
Ethernet frames, compresses the voice, and encapsulates it within UDP
packets which are delivered to the router, again via the Ethernet. The UDP
packets are placed on the WAN for IP delivery to a remote H.323
gateway. The remote gateway undoes the process and sends the
decompressed voice to an extension.
Connection considerations apply to two areas:
■
Overall Connectivity
■
Quality of Service
Overall Connectivity
An end-to-end NBX H.323 connection consists of a succession of Physical
Connections and Logical Connections, both local and external.
Physical Connections
An NBX H.323 gateway has few physical connections. An installer can
add an H.323 gateway to an existing NBX system by creating one physical
connection on the LAN that links a network interface card in an operating
system to a hub or to a switch. The same connection also gives the H.323
gateway a direct connection to every other device on the near-end LAN.
Those devices include any NBX Business or Basic Telephone, the Call
Processor, and the firewall or router.
Alternatively, you can use a second NIC in the gateway system to provide
a separate connection between the H.323 gateway and the IP router.