The LAN (local) and WAN (world) Networks
A LAN (Local Area Network) is a system whereby individual PCs are connected together within a company or organization.
For instance if ten people are working together within an office it makes sense for them all to be connected. In this way, the office can have a single printer and all ten people can print to it. In a similar way, other devices such as modems or scanners can be shared. Even more useful is the ability to share information when connected to a network as described on the workgroup page. A local area network is really a large workgroup.
A WAN (Wide Area Network) as the name implies allows you to connect to other computers over a wider area (i.e. the whole world). This WAN connection can be shared to all the computers on the LAN.
The Telephone Network in Computing.PSDN ISDN leading through to ADSL
Internet Connections via Telephone Modems and ISDN preceded the High Speed Broadband Connections to the WAN
PSDN or Public Switched Data Network is simply the technical name for the telephone system in use today.
ISDN Stands for "Integrated Services Digital Network." ISDN dates back to 1984, and allowed faster transfer rates than when using PSDN modems. ISDN could transfer at 64K or 128K of data per second.
Satellite
Satellite communications makes it possible for you to make a telephone call or access the internet from almost anywhere on the planet.
Baud rate
The baud rate tells you how fast a modem can send/receive data. The old PSDN modems had a maximum baud rate of 56 Kilobits per second (Kb/sec).
Broadband connections
Broadband connections are the most common internet connections. Broadband can work over a phoneline connection (ADSL). Or over a cable connection (DSL). High speeds are now attained by both systems 10 to 20 mb's per second is now common in 2009 in the UK - some other counties have faster speeds. In the UK ADSL runs on the old BT copper phone cables, as a result a stable system was hard to achieve, the cable networks running on DSL were more reliable. Moves were underway to create High Speed wide area Wireless Broadband Networks.