Networks, telecommunications Chapter 6 Networks, telecommunications and the Internet 1

Computer networks defined A computer network can be defined as: ‘a communications system that links two or more computers and peripheral devices and enables transfer of data between the components’. Telecommunications: The method by which data and information are transmitted between different locations. 2

Table 5.1 A summary of the key advantages and disadvantages of network technology 4

Types of Computer Networks : Network Communication Technology Types of Networks Types of Computer Networks : LAN MAN WAN Network Architecture Clint/Server Peer-to-Peer Network Topology Star Ring Bus Network Communication Technology Intranet Extranet internet

Types of Computer Networks Local-area network (LAN): A computer network that spans a limited geographic area, typically a single office or building. Wide-area networks (WANs) : Networks covering a large area which connect businesses in different parts of the same city, different parts of a country or different countries. Metropolitan-area networks (MANs): Network that spans a metropolitan area, usually a city and its major suburbs. Its geographic scope falls between a WAN and a LAN.

Types of Network Architecture Client/server: The client/server architecture consists of client computers such as PCs sharing resources such as a database stored on more powerful server computers. Server:is a computer that controls access to the hardware, software and other resources on the network and provides a centralized storage area for program Client: is a computer that request services from a server computer. 8

Client/server

Client/server Client/server benefits: Time lost by staff configuration Faster execution Distributed approach Customisation and flexibility. Client/server limitations: Time lost by staff configuration Instability caused by clashes with applications Maintenance Performance Cost – generally higher TCO.

Figure 5.2 Components of a client/server system 11

With peer-to-peer networks, there is no central server. Types of Network Architecture Peer-to-Peer : is a simple, inexpensive network that Peer-to-Peer typically connects fewer than 10 computers. All computers in the network have equal capabilities to use the resources (hardware, software, data and file) available on the network. With peer-to-peer networks, there is no central server.

Peer-to-peer

Types of Network Topology What is a Topology ? The physical topology of a network refers to the configuration of cables, computers and other peripherals. Bus: All computers and devices connected to central cable or bus. Ring: Cable forms closed ring or loop,with all computers and devices arranged along ring.Data travels from device to device around entire ring, in one direction Star: devices connect to a central device, called hub.All data transferred from one computer to another passes through hub.

NETWORK TOPOLOGIES

Telecommunications equipment Modem (modulator–demodulator): A modem is a communications device that allows users to ordinary telephone line. Analogue: Analogue data is continuous in that an infinite number of values between two given points can be represented. As an example, the hands of a clock are able to represent every single possible time of the day. Digital: Digital data can only represent a finite number of discrete values. For example, at the most basic level, a computer recognises only the values 0 (zero) and 1. Any values between 0 and 1, for example 0.15, cannot be represented. Hubs: Hubs are used to connect up to 20 PCs to a network in a convenient way. Bridges and routers: These are used to connect different LANs and transfer data packets from one network to the next. 16

Data transmission types Broadband: A relatively high-capacity, high-speed transmission medium such as cable. Can provide transfer rates of up to 24 Mbps. ADSL = Asynchronous digital subscriber line – upload and download speeds are different. ISDN (integrated services digital network): Data transfer rates of 64 kbps. An ISDN telephone line provides two separate ‘channels’ allowing simultaneous voice and data transmissions. 17

Types of Network Communication Technology Internet: A global network system made up of many smaller systems. Intranet :If information is limited to those inside an organization. Extranet : If access is extended to some others, but not everyone beyond the organization. Extranets can be accessed by authorized people outside the company such as collaborators, suppliers or major customers, but information is not available to everyone with an Internet connection – only those with password access. Note that the term ‘intranet’ is sometimes loosely used to refer to an extranet.

Figure 5.10 The relationship between intranets, extranets and the Internet 19

Wireless network standards Bluetooth (PAN) A wireless standard for transmission of data between devices over short ranges (normally less than 10 m). Wi-Fi (LAN) A high-speed wireless local-area network enabling wireless access to the Internet for mobile, office and home users. WiMax (MAN) A long distance transmission standard that allows an access range up to 30 miles at speeds up to 75 Mbps. 20

Wireless network standards Cellular systems Competing standards for cellular service CDMA: United States GSM: Rest of world, plus AT&T and T-Mobile Third-generation (3G) networks Suitable for broadband Internet access 144 Kbps – 2Mbps 4G networks Entirely packet-switched 100 Mbps – 1Gbps