Networks

Networks

A network is a collection of computers and devices connected together via communication devices and transmission media.

LAN

A local area network (LAN) is a network that connects computers and devices in a limited geographical area such as a home, school computer laboratory, office building or closely positioned group of buildings.

Advantages

Advantages• Speed

Sharing within networks is very rapid and can save time.• Cost

Site-licensed (shared) versions are available at considerable savings. Programs stored on a network’s server allow for easy upgrading.

• SecuritySensitive files and programs on a network are easily password-protected.

• Peripheral equipment sharingResources such as printers, modems can be shared.

• Electronic mail• Centralised software management

Greatly reduces the need to spend time and energy installing updates and tracking files on independent computers throughout the building.

• Workgroup computingWorkgroup software allows many users to work on a document or project concurrently

Disadvantages of networking

Disadvantages of networking• The cabling, network cards, file servers, etc that are

required to set up a network are expensive.• If a server fails the entire network may stop operating.• Viruses can spread from one computer to another over a

network.• Decisions on resource planning tend to become centralised.• Networks that have grown with little thought or appropriate

planning can be inefficient in the long term.• As traffic increases on a network, performance declines

unless it is properly designed.

Network Architectures

Client/Server

Client/ServerOn a client/server network, one or more computers act as a server, and the other computers on the network request services from the server. The other computers and mobile devices on the network are referred to as clients.

Peer-to-Peer

Peer-to-Peer

Peer-to peer network is a simple inexpensive network that typically connects fewer than 10 computers. Each computer called a peer, has equal responsibilities and capabilities, sharing hardware (such as a printer), data etc.

Network Topologies

A network topology refers to the layout of the computers and devices in a communications network. Three commonly used network topologies are bus, ring and star. Networks usually use combinations of bus and star topologies.

Bus Network

Bus NetworkA bus network consists of a single central cable, to which all computers and other devices (nodes) connect. The bus is the physical cable that connects the computers and other devices. It transmits data, instructions, and information in both directions. When a sending device transmits data, the address of the receiving device is included with the transmission so the data is routed to the appropriate receiving device.

Bus Network

Bus networks are popular on LANs because they are inexpensive and easy to install. Computers and other devices can be attached and detached at any point on the bus without disturbing the rest of the network. The main disadvantage is the limit in size of the bus.

Star Network

Star Network

On a star network, all of the computers and devices (nodes) on the network connect to a central device, thus forming a star. Two types of device that provide a common central connection point on the network are a hub and a switch.

Star Network

• Star networks are fairly easy to install and maintain. Nodes can be added and removed from the network no disruption to the network.

Star Network

If one node fails, only that node is affected. If the hub/switch fails the entire network is inoperable. Most star networks consist of multiple switches though and in that case only the part of the network connected to that switch will fail

Network Communication Standards

A network standard defines guidelines that specify the way computers access a network, the types of medium used, the speeds used and the type/s of physical cable and/or wireless technology used. A standard that outlines how two network devices communicate is called a protocol.

Ethernet

Ethernet

• Ethernet is the most popular network standard for LANs because it is relatively inexpensive and easy to install and maintain.

• Ethernet is based on the bus topology, but Ethernet networks can wired in a star pattern.

Ethernet 802.3• The Ethernet (IEEE 802.3) standard for Local Area Networks (LANs). The

802.3 standard (also called Twisted Pair Ethernet) uses a twisted-pair cable for distances up to 100m.

• 10Base-T - operates at 10 Mbps - uses a twisted-pair cable with maximum lengths of 100 meters.

• 100Base-T – operates at 100 Mbps – often referred to as fast internet – can use – two or four paris of twisted wires or fibre optic cables.

• 1000Base-T – operates 1Gb/s – CAT-5 cabling• 10GbE – operates 10Gb/s – copper (CAT6a or better) or fibre cabling

WiFi

WiFiA wireless network uses radio waves, just like cell phones, televisions and radios do. In fact, communication across a wireless network is a lot like two-way radio communication. Here's what happens:1. A computer's wireless adapter translates data into a radio signal and

transmits it using an antenna.2. A wireless router receives the signal and decodes it. The router

sends the information to the Internet using a physical, wired Ethernet connection.

802.11• IEEE 802.11 is a set of standards for implementing wireless local area

network (WLAN) computer.

Building a Wireless Network

1. A port to connect to your cable or DSL modem

2. A router3. An Ethernet hub4. A firewall 5. A wireless access point

Bluetooth

Bluetooth

Bluetooth takes small-area networking to the next level by removing the need for user intervention and keeping transmission power extremely low to save battery power.

The big draws of Bluetooth are that it is wireless, inexpensive and automatic.

Wireless Security

WiFi Protected Access (WPA) is now part of the 802.11i wireless network security protocol. It uses encryption and involves signing on with a password. Most public hotspots are either open or use WPA or 128-bit WEP technology (Wired Equivalency Privacy – an older form of security)

Wireless Application Protocol

• Wireless Application Protocol (WAP) is a technical standard for accessing information over a mobile (phone) wireless network. A WAP browser is a web browser for mobile devices such as mobile phones that uses the protocol.

TCP/IP

TCP/IPTransmission Control Protocol/Internet Protocol, TCP/IP is a network standard, that defines how data is routed from one end of a network to the other end, ensuring the data arrives correctly. It describes rules for;

• dividing data into small pieces, called packets • providing addresses for each packet, • checking for and detection of errors,• sequencing packets and,• regulating the flow of messages along the network

TCP/IP has been adopted as a network standard for Internet communications.

Short for HyperText Transfer Protocol, HTTP is the underlying protocol used by the World Wide Web. HTTP defines how messages are formatted and transmitted, and what actions Web servers and browsers should take in response to various commands.

HTTPS is a communications protocol for secure communication over a computer network, with especially wide deployment on the Internet.

Historically, HTTPS connections were primarily used for payment transactions on the World Wide Web, e-mail and for sensitive transactions in corporate information systems. In the late 2000s and early 2010s, HTTPS began to see widespread use for protecting page authenticity on all types of websites, securing accounts and keeping user communications, identity and web browsing private.

Routers, Packets, Switches, Hubs, and Firewalls

RoutersWhen you send e-mail to a friend on the other side of the country, how does the message know to end up on your friend's computer, rather than on one of the millions of other computers in the world? Much of the work to get a message from one computer to another is done by routers, because they're the crucial devices that let messages flow between networks, rather than within networks.

Packets

Internet data, whether in the form of a Web page, a downloaded file or an e-mail message, travels over a system known as a packet-switching network. In this system, the data in a message or file is broken up into packets about 1,500 bytes long. Each of these packets includes information on the sender's address, the receiver's address, the packet’s place in the entire message, and how the receiving computer can be sure that the packet arrived intact.

NIC

• Network Interface Card (NIC), an expansion board you insert into a computer so the computer can be connected to a network.

• These days this functionality is already built into the motherboard and so a NIC is not needed.

Modem

• Short for MOdulator-DEModulator. A modem is a device or program that enables a computer to connect to the internet or simply transmit data over, for example, telephone or cable lines. Ye olden modems converted from analogue to digital and back again but modern modems do not need to do this anymore.

Switch• Switches allow different nodes (a

network connection point, typically a computer) of a network to communicate directly with one another in a smooth and efficient manner.

• Essentially, a LAN switch creates a series of instant networks that contain only the two devices communicating with each other at that particular moment.

Firewall

• A firewall is simply a program or hardware device that filters the information coming through the Internet connection into your private network or computer system.

More Hardware Stuff

• DSL Modem• Hotspt (Wifi)• Network Interface Card• Ethernet Cabling• Fibre Optic Cable