Supervision

This note descibes which provisions are taken by NetModule Routers to guarantee always-on and always-connected functionality.

The NetModule Routers are designed for high reliability and 24×7 operations. To guarantee best connection availability several levels and methods of supervision are used.

Depending on your hardware model, WAN links can be made up of either Wireless Wide Area Network (WWAN), Wireless LAN (WLAN), Ethernet or PPP over Ethernet (PPPoE) connections.

The highes level of monitoring is the Ping Supervision which is individually configurable for each active (up) link as well generic for any link based on the routing table. The user can define up to two host which are pinged every “ping interval” seconds. If there is no respones of at least one of the two hosts within “ping timeout” milliseconds a retry is done using the “retry interval” time up to “max. number of trial fails”. If still there is no answer the defined emergency action is executed. It's recommended to set “restart link services” on each link pinging the next hop e.g. the access point for a WiFi client link. Restarting the link service means, that it will be tried to re-establish the link e.g. redial on a modem connection. Emergency action “none” means that the link is defined as (inactive) down. If you are using a VPN you should also enable the dead pear detection or keep alive mechanisms. For the generic link “ANY” it's recommended to use the application host in your office. This ping will ensure that even interruptions in the back-bone can be detected and a full point-to-point connection is guaranteed.

The WWAN Manager who is responsible for the control of the mobile network modems checks every 15 seconds if the connection is still established. Different informations like configurable signal strenght, network registration status of service type are used to determine the status of the modem links.

The task of the Link Manager is to verify if a link is up or down and to select highest priority link as the so-called hotlink which holds the default route for outgoing packets. Every 5 seconds he checks for each active link if the following conditions are met: