Wired Communication Media and Devices
Wired communication uses cables such as twisted pair, coaxial and fibre optic. Key devices: a modem (Modulation DEModulation) converts digital signals to analogue for transmission and back again at the other end; a multiplexer accepts many signals and transmits them on a single line, while a demultiplexer reverses the process.
Wireless Communication Media
- Infrared: very high frequencies close to visible light, used for close-range broadcast (e.g. remote controls, door systems); limited to short distances and blocked by opaque objects.
- Microwave: high frequencies for long or short distance communication, especially satellites; the emitter and receiver must be within line of sight.
- Radio waves: the old wireless technology used by FM and AM radio.
- Bluetooth: the most recent wireless technology, operating on a 2.4GHz band at about 1-2 Mbps, letting a device communicate continuously with several others.
Two major wireless hardware components: the Wireless Access Point (WAP/AP), which broadcasts radio waves within a range (hotspot) of 10m to 16km; and wireless adapters, similar to network interface cards. Benefits of wireless: cheaper, flexible, faster data, reduced installation/maintenance cost, accessible anywhere. Limitations: less secure, unreliable, more open to interference and jamming.
Types of Attacks on Networks
Four types are possible: freeloading (using the network/internet without permission), eavesdropping (picking up data including passwords), intrusion (tampering with the owner’s system), and jamming (deliberately transmitting interference to degrade or prevent network use).
Network Classification Based on Communication
- Private network: uses private IP address space to support a particular institution, e.g. a school or company.
- Public network: provides the public with voice, video and data communication for a fee, e.g. an ISP (Camtel, MTN, Orange, Nexttel, Ringo).
- International network: provides users from different continents with communication facilities using satellites.
Other network types: an intranet securely shares an organization’s information within that organization; an extranet extends part of a company’s intranet to outside users, usually via the internet; a VPN (virtual private network) is a private, secure connection established within a public network like the internet. A domain is a sub-network controlled by one central server, while a workgroup is a peer-to-peer collection of computers on a LAN sharing resources without central control.
Network/Communication Protocols
The Internet Protocol (IP) and Transmission Control Protocol (TCP) are the most important protocols, together called the TCP/IP suite. Commonly used protocols include:
- DHCP: automatically assigns IP addresses on a network.
- FTP: transfers files over a network.
- HTTP: transfers web pages over the internet.
- SMTP: transmits electronic mail.
- UDP: transfers packets of data called datagrams.
- VoIP: makes telephone calls over the internet.
Other protocols include IPX/SPX (Novell’s LAN protocol), ARP (converts logical to physical addresses), ICMP (manages internet errors), SCTP, and SNMP (remote administration).
