Connection Considerations 417After an IP connection has been established, the ConneXtions softwarebegins a series of H.323 exchanges by using TCP packets on the IPconnection.These H.323 exchanges set up the call and negotiate the type of voicecompression that is used. They also cause the remote NBX (or PBX)system to begin setting up the remote end of the connection.ConnectionConsiderationsAs 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. TheNBX Business and Basic Telephones use their DSP to convert spokenwords into digital voice packets. The voice packets are transferred acrossthe Ethernet to the local H.323 gateway. The gateway strips off theEthernet frames, compresses the voice, and encapsulates it within UDPpackets which are delivered to the router, again via the Ethernet. The UDPpackets are placed on the WAN for IP delivery to a remote H.323gateway. The remote gateway undoes the process and sends thedecompressed voice to an extension.Connection considerations apply to two areas:■ Overall Connectivity■ Quality of ServiceOverall Connectivity An end-to-end NBX H.323 connection consists of a succession of PhysicalConnections and Logical Connections, both local and external.Physical ConnectionsAn NBX H.323 gateway has few physical connections. An installer canadd an H.323 gateway to an existing NBX system by creating one physicalconnection on the LAN that links a network interface card in an operatingsystem to a hub or to a switch. The same connection also gives the H.323gateway a direct connection to every other device on the near-end LAN.Those devices include any NBX Business or Basic Telephone, the CallProcessor, and the firewall or router.Alternatively, you can use a second NIC in the gateway system to providea separate connection between the H.323 gateway and the IP router.
