Multitech RF500S Instrukcja Użytkownika Pobierz pdf (Strona 39)

maintain a number of public timeservers. Tardis uses this information to set the 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 computers are slaved to the local server and the local server in turn is

synchronized to NIST time.

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 the server via the Internet adds up to several

hundred milliseconds of round trip delay. That is not a problem for our purposes.

Configuration Tip --Tardis 2000 defaults to time broadcasts on all available interfaces. If Tardis

is run on a computer with direct access to the Internet the configuration should be changed to limit

broadcasts to the LAN. IP broadcast is a reserved address x.x.x.255, so typical broadcast address

may be 192.168.0.255. If this is not done the 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

probably 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 minute so the client clock is updated as soon as the

machine boots.

16.3 Private Web Server

The home page of 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, and 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 server is only bound to the LAN interface. Otherwise anyone on the Internet will be

able to access your private web pages.

16.4 Local Weather Station

Once of the reasons to run a local web server was 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. The weather

station is installed but the web software is still a work in progress.

17 So Many Computers So Little Space – KVM to the Rescue

Replacing the laptop server with a desktop PC required another set of

user I/O devices. We did not want to use a second set of devices. The

solution is to use a KVM (keyboard, video, mouse) switch. KVM’s have

been used in server farms for years to allow single point of control for

multiple servers. We purchased a 4 port Belkin Omni View SE KVM.

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Multitech RF500S Instrukcja Użytkownika Strona 39