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6 Further System Fundamentals (HL)

6.4 Further Network Fundamentals

6.4.1 Network Characteristics

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Server - client

•Network server: with a network OS, serves out files (e.g. shared databases), controls security and permissions, and access to (through firewall) the web proxy server.

•Client : a normal workstation with application software.

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Peer-to-peer

•Two or more computers connect without one having more authority.

•Such networks can be faster, but are less secure.

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Local vs. wide

•Local area network (LAN): within one building or site (e.g. a school), connection requires a network interface card (NIC).

•Wide area network (WAN): involves many LANs, connection to a WAN requires a modem for digital/analogue conversion of the signal on a telephone line.

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ISPs

•Internet service providers offer servers for their clients and connection to the internet

•Also email, web hosting, etc. services.

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Transmission speed•Measured in bits per second (bps).

•Typical dial-up bandwidth was 56kbps.

•Broadband is achieved using different channels over the same line (allowing up to 10Mbps).

•Serial transmission is faster over long distances, parallel over shorter.

•Ethernet (a common network protocol) can transmit up to 100Mbps.

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Transmission speed

•Simplex: data transmission is only possible in one direction e.g. a radio broadcast.

•Half-duplex: in both directions, but not at the same time e.g. a walkie-talkie.

•Full-duplex: two-way all the time e.g. telephone or IRC.

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Transmission media

•A telephone wire is a pair of copper wires (slow, poor quality and liable to interference).

•Coaxial cable (TV aerial cable) is thicker, some shielding , cheap.

•UTP: standard network cable, cheap (also called CAT5 or ethernet cable).

•Wi-Fi : convenient for mobile devices, avoids cables.

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Transmission media

•Optic fibre: fast but expensive, uses light, no metal so no interference.

•Microwave: for long distances, expensive and needs line-of-sight connection.

•Satellite: very expensive, available anywhere so useful for remote locations.

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Network devices

•Hub: a simple junction box.

•Switch: like a hub, but it filters the data according to what it’s connected to.

•Gateway: allows connections between LANs.

•Router: actually directs data traffic across a network, therefore allow the internet to function.

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ISDN and ASDL

•ISDN is still used in business, requires a special modem and line, and can transmit voice, data and video.

•ADSL uses a normal telephone line, but splits the voice and data into channels, also with a greater download than upload capacity (asynchronous).

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Public vs. private

•Most internet connections are over public telephone networks.

•Private telephone lines are possible for very secure needs or heavily-used networks.