Remote Gateway 911x Series Installation and Administration Guide 49June 2005 Planning for installationTranslation tables within NAT routers control the communication path from theprivate network to the public network. Most NAT devices contain timers thatmonitor the translation table entries. Each time the device uses a translation tableentry, the timer restarts. Individual table entries are deleted if thecommunications path is not used and the timer expires.It is possible, when using a Remote Gateway 911x series unit behind a NATdevice, that prolonged periods of silence cause the NAT translation table entriesto clear and drop the audio path. An example of this is a remote user listening toa conference call with the user’s digital telephone set on mute. After fiveminutes (the default NAT translation table timer on many NAT routers) therouter drops the voice path. The remote user is no longer able to hear theconference. To restore the NAT table entry and recover the audio path, theremote user can go off mute and speak into the digital telephone set.To prevent the NAT translation table from dropping the audio path: configure the translation tables on the NAT router with a large timer value(for example, two hours) configure a static translation table entry for UDP port 20480IP deploymentBefore deploying your Remote Gateway 911x series unit with IP capability,ensure that you engineer the IP network properly. You can configure apermanent (Model 1) or on-demand (Model 2) IP connection. The followingguidelines describe requirements, conditions, and characteristics of eachsupported IP deployment option:Model 1: IP permanentIf using DSL or a cable modem, configure an IP permanent connection. The Remote Gateway 911x series unit re-establishes its TCP/IP signalingsession to the RLC once per minute. The Remote Gateway 911x series unit supports both static IP and, throughDHCP, dynamic IP addressing Do not configure a remote IP address on the RLC. One virtual private network (VPN) supports multiple Remote Gateway911x series units.
