Checking Connections 429External Call ControlUsers of ConneXtions-equipped NBX systems can place H.323 calls toother H.323 systems anywhere in the world without having to pay longdistance charges. Since there are no long distance charges for H.323calls, there is no need to restrict them for cost reasons.IP Type of Service andDifferentiatedServicesThe header of each IP packet contains an 8-bit Type of Service (TOS) fieldthat indicates the precedence (relative importance) of the packet. Routersthen examine the TOS field and give precedence to packets with a higherTOS setting.Although your telephone system supports prioritization using the TOSfield, this facility is not supported for H.323 calls. However, for H.323 callsover the WAN, routers can prioritize voice traffic using alternative means.For example, during installation, you can select a range of UDP or TCPport addresses to help with router setup.AlternateGatekeepersA zone can contain only one gatekeeper at a time, although multipledistinct devices can provide the gatekeeper function in a zone. Multipledevices that provide the RAS signaling function for the gatekeeper arecalled alternate gatekeepers. Each alternate gatekeeper appears to eachendpoint as a distinct Gatekeeper.To ensure system availability, redundancy, and scalability, the gatekeepercan provide RAS signaling function by using multiple physical or logicaldevices, referred to as alternate gatekeepers.CheckingConnectionsYou can use connection checks to pre-qualify an installation and to helplocalize connection problems. H.323 gateway installers can conductconnection checks for:■ Gateway Checks■ Network ChecksGateway Checks Gateway checks can verify that the NBX systems at each end of an H.323connection are working properly.Gateway Self-CheckA gateway self-check is simply an H.323 call that returns to the localIP address (loopback test).
