Specifications

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local server’s Real Time Clock (RTC). Tardis includes a Network Time Protocol (NTP) timeserver that
periodically broadcasts time info over the LAN. A companion program, K9, runs on each client. It updates
the local RTC to match the time on the server. This insures all the computers on the LAN are slaved to the
local server and the local server in turn is synchronized to NIST.
NIST Network Time Service use multiple stratum-1 timeservers located in Boulder Colorado,
Gaithersburg, Maryland (Washington, D.C. area) and Redmond Washington. Tardis is configured for each
of the addresses. If a server is not accessible Tardis automatically gets time information from the next
server in the list.
The timeservers are extremely accurate, however accessing them via the Internet adds up to several
hundred milliseconds of round trip delay. This source of error is not a problem for our purpose.
Configuration Tip --Tardis 2000 defaults the NTP time broadcasts to all available interfaces. If
Tardis is run on a computer with direct access to the Internet the configuration should be changed
to limit broadcast to the LAN. IP broadcast is a reserved address x.x.x.255, so typical broadcast
address might be 192.168.2.255. If this is not done the time broadcast is sent out over all ports,
including the one connected to the Internet. This may prevent the dialup connection from timing
out and will likely annoy your ISP.
Configuration Tip -- Limit how often Tardis requests time from Internet Time servers. This
reduces unnecessary load on the public timeservers. We set Tardis to poll once every 12 hours. For
convenience the LAN broadcast occurs every 64 seconds so the client clock is updated as soon as
the machine boots.
Configuration Tip -- Tardis includes a provision to monitor for active dialup connection. This is
convenient if the PC running Tardis is directly attached to the Internet. In our case Tardis is behind
a router so it cannot determine if an Internet connection exists. On DSL this is of no import since
it is an always-on connection. However, in the event of fallback to dialup we do not want Tardis to
force dialup to be active for long periods. Tardis is set to access the NIST timeserver every 12
hours. So at most it will activate dialup twice a day. The router is set to timeout dialup after 30
minutes of idle, so Tardis will cause dialup to be active for an hour a day.
17.3 Private Web Server
The home page of IE on each PC points to the web server running on the local server. This allows relevant
information to be posted on the web server and shared with all systems on the LAN. The goal is to use the
server to distribute live information, weather data, security status, etcetera. Currently the server is limited to
static pages. Dynamic pages are another item on the to-do list. The server is freeware called Xitami from
iMatrix.
HTML pages can be created at a low level using a text editor or with software specifically designed for web
creation such as Microsoft FrontPage.
Security Note -- If the web server is running on a computer with direct access to the Internet
make sure the web server is only bound to the LAN interface. Otherwise anyone on the Internet
will be able to access your private web pages.
17.4 Local Weather Station
One of the reasons to run a local web server is to present live data. Davis Instruments has a line of personal
weather stations and software that can be use to post weather data to a web server. We configured the Davis
software to maintain history data and to create a GIF file of inside temp, outside temp, wind chill, and wind
speed every five minutes. These GIFs are displayed on the local web page.