Networks in brief

In brief

- A network is two or more computers linked together with cables, microwave links or wireless radio connections.

- Network topology describes its logical wiring shape: bus, ring, star, tree, mesh

- A network message is called a packet, frame or datagram, and contains (at least) a source network address, a destination network address and data.

 - A network's architecture or technology (e.g. Ethernet, Token Ring or ATM) describes how packets are handled and transported.

- A protocol is an agreed set of rules that describe how communications should occur (e.g. TCP/IP, HTTP, FTP, POP)

- Network sizes are local (LAN), metropolitan (MAN) and wide (WAN).  The Internet is an interconnection of WANs.  Peer-to-peer networks are simple, trusting networks with no server.

- File servers run the Network Operating System and control the network's services.  Powerful application servers run applications, such as word processors, for users. 

- In Client-Server networking, one program requests another program to provide a service or data.

- Networks can save money by sharing expensive devices between users.  They allow quick and easy communication, collaboration and information exchange.

- IP (Internet Protocol) addresses give each Internet user a unique address.  DHCP is a service that allocates IP addresses to network users.

- Telnet lets users log on to and control a remote computer

- Virtual Private Networks (VPN) give private network channels across the Internet.

- Remote control software lets technicians and help desk operators view and control remote computers as if they were sitting at the keyboard.

- Videoconferencing over networks saves organisations travel time and expense

- An intranet is a local version of the Internet which not available beyond the LAN or WAN.

- Networks can centralise file storage, backups, virus scanning, CD-ROM distribution, Internet caching, software distribution etc.

- Servers are powerful, expandable and robust computers at the heart of a network.  Specialist servers (e.g. print servers, web servers, login servers) help ease the workload of a single server.

- The Network Operating System is the software that controls network operations and services.  Workstations need client software to interact with the NOS.

- The NIC (Network Interface Card) connects a workstation to the network.

- A router is a security device between a network and the outside world.

- A hub lets one network cable be divided amongst many workstations.  A switch is a hub that intelligently filters out irrelevant network traffic.

- Every device that needs to communicate with other devices needs a network address, and is called a node.

- Bandwidth is a measure of data-carrying capacity in bits per second.

- The most common network cable is Category 5 (CAT5), a form of UTP (Unshielded Twisted Pair).  Coaxial cable is often used as network backbone cables.  Fibre Optic Cable has very high speed, very high bandwidth capacities.

- A backbone is a high-speed, high capacity data channel, usually connecting different network segments.

- Network security requires user authentication using individual user logins with passwords or biometric identification.

- Servers must be physically protected against damage and unauthorised access.  They must be backed up regularly to protect against data loss, and organisations should have a data disaster recovery plan.

- Encryption of data prevents anyone being able to use it, even if they can get access to it.

- Firewalls protect computers against hacking attacks by blocking unauthorised incoming or outgoing Internet traffic.  Virus scanners protect against viruses.

- In a bus topology, a single cable has nodes branching from it.

- In a ring topology each node has a neighbour before and after it, and packets travel around the ring to each node.

- In a star topology all nodes are connected directly to a central device such as a server and a switch.

- A tree topology is made up of a bus connected to a star.

- In a mesh topology nodes have multiple connections to other nodes to provide multiple redundancy in case any connection fails.

- Modems convert digital computer data to analogue (sound) and transmit it over telephone systems.  At the other end, another modem converts analogue back to digital data.

- ADSL also uses telephone lines, but operates digitally at high speed.

- Microwave connections are high-bandwidth line-of-sight data channels, most frequently used within cities.

- Satellite connections offer high speed downloads, but need a normal modem connection to upload data.

- ISDN are high-speed digital landlines, often leased as private channels between LANs.

- Cable Internet provides a high-speed data channel to an Internet Service Provider (ISP).

- Wireless networking uses radio transmissions to connect a node to the network.

- NICs have a unique network address built into them to identify a node to the network.

- Dynamic IP addresses only last the duration of an Internet connection.  Static IP addresses are more or less permanently assigned to a node on the Internet.

- A URL (Uniform Resource Locator) is a human-friendly word-based version of a numeric IP address (e.g. www.microsoft.com).

- A DNS (Domain Name Server) looks up URLs in a distributed database and converts them into IP addresses that are actually used to route Internet traffic

- An email address is made up of a username, "@" and a domain name, e.g. fred@somewhere.com

- MAC (Media Access Control) addresses commonly identify nodes in a wireless network.

- Ethernet is the most widely used LAN technology, and uses Carrier Sense Multiple Access with Collision Detection (CSMA/CD) to manage network traffic flow.- Token Ring technology uses a special Token frame that circulates around the network.  A node must hold the Token to transmit across the network.

- ATM (Asynchronous Transfer Mode) combines packet switching and circuit switching protocols to get fast and reliable transmissions of video and audio in real-time.

- TCP/IP, Ethernet and Token Ring all use packet switching to send network messages.  Files and network messages are broken up into packets before being sent.

 - TCP/IP is a pair of protocols universally used for Internet communications.  TCP breaks files into packets before they are sent and reassembles incoming packets into files.  IP manages the packets' journey to their destination.

- The Internet is an interconnection of WANs, is based on TCP/IP communications, and forms a mesh topology.  It includes the World Wide Web, Usenet (newsgroups), FTP, ICQ chat, email and more.