Categories of Networks
Broadly speaking, there are two types of networks based on transmission technology
1. Broadcast networks
2. Point-to-point networks
Broadcast networks have a single communication channel that is shared by all the machines on the network. Short messages-called packets in certain contexts-sent 6 any machine are received by all the others. Upon receiving a packet intended for its a machine processes the packet. If the packet is intended for some other machine, i is just ignored.
Broadcast systems generally also allow the possibility of addressing a packet to all destinations by using a special code in the address field. When a packet with this code is transmitted, it is received and processed by every machine on the network. This mode of operation is called broadcasting.
Point-to-point networks consist of many connections between individual pairs o1 machines. To go from the source to the destination, a packet on this type of network may have to first visit one or more intermediate machines. Often, multiple routes of different lengths are possible, and, therefore, routing algorithms play an important role in point-to-point networks.
Today when we speak of networks, we are generally referring to the following categories: local area networks (LAN), metropolitan area networks (MAN), wide area networks (WAN) and multimedia networks. Network categories can be specified based on size, ownership, the distance it covers and its physical architecture.
1.Local Area Network (LAN)
Local area networks, which are normally referred to simply as LANs, are used to interconnect distributed communities of computer based data terminal equipment located within a single building or localized group of buildings. See Figures 1.9(a) and 1.9(b).
For example, we may use a LAN to interconnect workstations distributed around offices within a single building or group of buildings such as a university campus, to interconnect computer-based equipment distributed around a factory or hospital
(a) Single building LAN.
Figure (b) Multiple building LAN.us, as shown in Figure (a).
However, since all the equipment is located within angle establishment, LANs are normally installed and maintained by the organization. Hence they are also referred to as private data networks.
In addition to size, LANs are distinguished from other types of networks by their ,mission media and topology. In general, a given LAN will use only one type of submission medium. The most common LAN topologies are bus, ring and star. traditionally, LANs have data rates in the range 4 to 16 Mbps.
2 Metropolitan Area Network (MAN)
it is basically a bigger version of a LAN and normally uses similar technology. the is designed to extend over an entire city. It may be a single network such as a television network or it may be a means of connecting a number of LANs into a network so that resources may be shared LAN-to-LAN as well as device-to device The high speed links between LANs within a MAN are made possible by fibre connections.
3 Wide Area Network (WAN)
de area network is at the far end of the spectrum because it is for reaching system networks that form a complex whole. One WAN is composed of two or more LANs are connected across a distance of more than 30 miles. Large WANs may have y constituent LANs and MANs on different continents. The most well-known WAN e Internet, which consists of thousands of LANs and MANs throughout the world.
4 Multimedia Network
term "multimedia" is used to indicate that the information/data being transferred the network may be composed of one or more of the following media types:
• Text
• Images
• Audio
• Video
There are five basic types of communication network that are used to provide multimedia communication services:
1. Telephone networks 2. Data networks
3. Broadcast television networks
4. Integrated services digital networks 5. Broadband multiservice networks
As the names imply the first three network types were initially designed to provide just a single type of sevice; telephony, data communication, and broadcast television respectively. The last two network types, however, were designed from the outset to provide multiple services.
Public switched telephone networks have been in existence for many years and have undergone many changes during this time they were designed to provide a basic switched telephone service which, with the advent of the other network types, has become known as a plain old telephone service (OPTS). The term "switched" is used to indicate that a subscriber can make a call to any other telephone that is connected to the total network.
Data networks were designed to provide basic data communication services such such as electronic mail (e-mail) and general file fransfer. The user equipment connected to these networks, therefore, is a computer such as a PC, a workstation, or an e-mail/file server. The two most widely deployed networks of this type are the x.25 network and the Internet.
Broadcast television networks were designed to support the diffusion of analog television (and radio) programmes throughout wide geographical areas. In case of a large town or city, the broadcast medium is normally a cable distribution network which for a large area, a satellite network, or sometimes a terrestrial broadcast network is used.
Integrated services Digital Network (ISDN) has been promoted all over the world by the International Telecommunication Union (ITU), which is in progress since the 1980s in several counries. ISDN system has the capability of exchanging broadband information, i.e. voice, video, data all via the same network called ISDN.
Broadband multiservice networks were designed for use as public switched networks to support a wide range of multimedia communication applications. The term "broadband" was used to indicate that the circuits associated with a call could have bit rates in excess of the maximum bit rate of 2Mbps-30 x 64 kbps-provided by ISDN. As such, they were designed to be an enhanced ISDN and hence were called broadcast integrated services digital networks (B-ISDN).
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