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Computer Network for JOTI

The computers are connected together using a network. A firewall protects us from the unwanted elements of the Internet, while allowing access to the Scoutlink Chat servers and websites.

Internet Connection

The Internet connection is through a 3G wireless dongle, which gives speeds around 5-6Mb/s.

This speed makes all sorts of uses possible. One we have trialled is the use of Echolink. Echolink uses the Internet to carry Voice over IP to connect radios that are far away from each other.

Other possible uses would be a web-cam, allowing others to see us via a web site.

Network Diagram

Local Network

In a LAN the computers are wired to a central switch. The connection uses an 8 wire cable, known as UTP. Inside the cable are four pairs of wires. Each pair of wires is twisted together to minimise interference.

The switch takes care of amplifying and relaying the electrical signal to the other computers.

Higher layers in the protocol handle arranging the electrical signals into packets. Then the network layer adds IP addresses.

After that is the transport protocol, typically TCP or UDP.

Sitting on top of that is the application layer with things such as HTTP, FTP, SMTP, IRC, NTP, or DHCP.

As the laptops have Wi-Fi a wireless network might be used. However, that many wireless clients require special wireless base stations. Most home wireless base stations can typically only cope with 5-10 clients.

Firewall

A firewall is used to protect us from the nasty elements of the Internet. A firewall is a computer or router that can be configured to allow only certain classes of network traffic to pass. All other traffic, including virus, email, attacks, etc, is blocked.

In this network the firewall computer also provides some additional services.

Web Proxy

A Web Proxy server accepts requests to download web pages from the Internet. If the source, destination, request type and content pass the rules, then the page is downloaded to your browser. In addition, a copy of the page is saved, and if someone else requests the same page or image then it can be delivered from the local cache, rather than downloading it again. This speeds up the loading of web pages, and also minimises the use of Internet traffic.

Chat Proxy

The Web proxy also relays the traffic for IRC clients. This ensures that the laptops do not have direct access to untrusted servers on the Internet.

Web Server

A Web server provides access to local web pages, such as the one you are reading now. The local site, or Intranet, contains information about the JOTA camp, photos, rules, the weekend program, and general information about JOTA, JOTI, Scouts and Guides.

During the weekend we have guest photographers capturing the weekend's events. These photos are made available on the local web server.

Other handy tools are the Morse Code and Phonetic Alphabet translators. Type in a message and get it instantly converted to morse code or phonetic alphabet.

DNS

The Domain Name System (DNS) is the glue that holds the whole Internet together. Computers use an IP address to talk to each other, but these are hard for people to remember, so we need a way to be able to use names. DNS provides a way to map names to IP addresses across the whole Internet.

We run a name service for our LAN, and also forwards any other requests out to the Internet to resolve them. For example when you type in www.scouts.com.au, DNS translates that into an IP address for the computer to use.

NTP

The Network Time Protocol allows the clock to be synchronised very accurately, typically to around 1 millisecond. The server's clock it synchronised to very accurate clocks on the Internet. So when you need to know the time, the little clock in the corner of the screen is exactly the right time.

DHCP

The Dynamic Host Configuration Protocol (DHCP) is used to provide configuration information to computers. Things such as IP address, subnet mask, default router, domain name servers, can be set on the server and sent to the client computer when it starts up. The client computer is set to get an address automatically, but it is the DHCP server that does all the work. This also allows changes to be made centrally, rather than having to visit each computer.