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.
For many years the whole network shared a single dial up modem connection to the Internet. While this provided enough speed for a dozen or so simultaneous IRC connections, it was severely lacking when more than one person tried to surf to different web sites.
In recent years we have been fortunate enough to have had access to a wireless Internet connection through Unwired.com.au. Where the dialup modem was lucky to give us 50 kilobits per second, the wireless connection gives us a minimum of 512 kilobits per second. While not breathtaking by newer broadband speeds, it is still a substantial step up from the dialup modem.
The higher 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.
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 or IRC.
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 types of network traffic to pass. All other traffic, including virus, email, attacks, etc, is ignored.
In our case the firewall computer also provides some additional services.
One service provided by the firewall is a 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 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.
A generic proxy service, called SOCKS, is used to relay the traffic for IRC clients. This ensures that the relatively insecure PCs do not have direct access to untrusted servers on the Internet.
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.
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 proivides 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.
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, for example, can be set up. The client PC 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 PC.