User's Manual

Nordic ID PL3000 user manual, v. 2.6, October 2006 71

LinkWatchdog works by periodically attempting to connect to one to ﬁ ve predeﬁ ned target machines. The

target machines are speciﬁ ed by entering their ip-address and port number separated by a semicolon. An

example of a valid target machine address is “194.168.100.1:8080”. No other address format is accepted.

You cannot use domain names because they usually resolve to more than one ip address. For this reason

there is a built in Domain Name Service lookup function. To use this, enter the target domain name in the

target machines ﬁ eld, and hit DNS lookup. Provided you have a working network connection you will be

presented with a list of ip addresses to which the domain resolves. You may then select which of these

addresses you want to use as target machines. When you approve your selection with OK, you will be

asked to enter the port number for each target machine. Please keep in mind that the port you enter must

be open and accessible to the PL3000. Firewalls and NAT devices between the PL3000 and your target

machine(s) may prevent you form connecting, if they are conﬁ gured to do so.

Once you have speciﬁ ed your target machines, you can set up the behaviour of the LWD service. It may

be best to try using the default settings before any other settings are tried. The interval value speciﬁ es

how often the LWD service should attempt to contact the target machine(s). Values shorter than half a

minute should be considered carefully. If you have a solution containing many units, you may cause a fair

amount of trafﬁ c over the network if this value is set too low. LinkWatchdog does not actually send any

data to the target machine, but it does attempt to open a link to the speciﬁ ed port. This requires a few

IP packets to accomplish. A too large interval value will lower the beneﬁ t of using LinkWatchdog as the

connection may be lost, and no corrective action will be taken for a long time. A suitable value needs to

be determined on a case by case basis.

The timeout value speciﬁ es how long the LWD service should wait for a reply from a target machine before

giving up and determining that the target machine does not respond. The retries value speciﬁ es how many

times the LWD service should attempt to contact a target machine before giving up and determining the

machine is not currently accessible. The LWD service contacts all target machines in the list concurrently,

and if any one of the connection(s) succeed the LWD service determines that the link is up. If all retry

attempts on all target machines fail, the LWD service will attempt to re-establish the connection. It does

this by disabling the connections that you have checked in the “Connections:” list and re-enabling them

again. For PC-Cards this means cutting the power from the card, and re-enabling it again. This causes the

card and driver to reload in a similar manner as if the device was reset. For RAS (GSM, GPRS and EDGE)

connections, this means hanging up and redialling the connection.

When closing the dialog box with OK, the conﬁ guration you have made is immediately applied. This

means that the LWD service is loaded and started or stopped and unloaded according to your settings

at this point. Keep this in mind when viewing the LWD service log on Page 4. If the service is not running,

you cannot read its log.