Introduction Chapter 1

Introduction  A computer network is two or more computers connected together so they can communicate with one another.  Two computers are interconnected if they can exchange information among them.  These interconnected computers are called Computer networks  Today, single main frame computer is not serving all the computation needs, but a large number of interconnected computers will do.  Computers networks vary in their size, communication media and speed of data transmission.

Uses of Computer Networks Business Applications Home Applications Mobile Users Social Issues

Benefits and uses of computer networks (1/3)  Business applications : companies that have large number of computers can benefit from computer networks as follows: Hardware sharing: like printers, hard drives and scanners, Send files from one computer to another quite easily Connectivity and Communication: Networks connect computers and the users within a building or work group can be connected into local area networks (LANs); users in distant locations can be interconnected into larger wide area networks (WANs). Run programs that installed on central computers (servers) but are not installed on any other user's computer. Internal services E-commerce.

Business Applications of Networks A network with two clients and one server.

Business Applications of Networks (2) The client-server model involves requests and replies.

Benefits and uses of computer networks (contd. 2/3) Data Security and Management: computer networks allow the administrators to manage the company's critical data. Instead of having this data spread over a large number of small computers data can be centralized on shared servers. This makes it easy for everyone to find the data, backup data on regular basis, and allows for the implementation of security measures to control who can read or change critical information.

Home Network Applications Access to remote information Person-to-person communication Interactive entertainment Electronic commerce

Benefits and uses of computer networks (contd.3/3)  Home applications : Sharing resources like printers, scanners share a single Internet connection on all the home PCs. Interactive entertainment : e.g. Video on demand on the internet Peer to peer communication to share music Connecting home appliances together

Home Network Applications (2) In peer-to-peer system there are no fixed clients and servers.

Home Network Applications (3) Some forms of e-commerce.

Mobile users: The growth of notebook computers and PDAs enable people to stay connected to their offices or the Internet when they are away from their home even though there is no wire connection exists

Mobile Network Users Combinations of wireless networks and mobile computing.

Network Hardware Local Area Networks Metropolitan Area Networks Wide Area Networks Wireless Networks Home Networks Internetworks

Broadcast Networks Types of transmission technology Broadcast links Point-to-point links

Computer networks hardware Computer networks differ by their size and transmission technology. There are twp types of transmission technology: 1.Broadcast links 2.Point-to-point links. Broadcast links have a single transmission channel that is shared by all the computers on the network. If the destination of the sent messages is all the existing computers on the network this known as a broadcasting. If the destination of the sent messages is a specific computers this known as a multicasting. In Point-to-point networks messages are sent from one sending computer to one receiving computer.

Computer networks hardware Basically there are three sizes of computer networks:  Local area network (LAN): A local area network is a network that spans a small space (like a single building) and provides services to a small number of people. LAN may have different segments distributed across all building floors..  Metropolitan Area Network (MAN ): connects two or more LAN networks over a specific geographical area ( usually a city ).  Wide Area Network (WAN): A wide area network uses wide variety of resources are deployed across a large geographic and any available communication lines. The largest and best example of a WAN is the Internet, which is a network composed of many smaller networks. The Internet is considered the largest network in the world.  Wireless networks: In wireless network there are no wires between hosts and servers. The data is transferred over sets of radio transceivers. The most common wireless networks cover ranges from hundreds of meters to a few kilometers

LANs, MANs, & WANs One early solution was the creation of local-area network (LAN) standards which provided an open set of guidelines for creating network hardware and software, making equipment from different companies compatible. What was needed was a way for information to move efficiently and quickly, not only within a company, but also from one business to another. The solution was the creation of metropolitan-area networks (MANs) and wide-area networks (WANs).

Broadcast Networks (2) Classification of interconnected processors by scale.

Physical topology of computer networks: The physical topology of a network refers to the configuration of cables, computers, and other peripherals. The following slides discuss the physical topologies used in networks and other related topics. Linear Bus Star Ring Mesh Hybrid

Local Area Networks Two broadcast networks (a) Bus (b) Ring

Physical Topologies

Linear Bus topology : In linear bus computers are connected to a common line of information and this common line is called a bus, so it is called a bus topology. A linear bus topology consists of a main run of cable with a terminator at each end. All computers are connected to the linear cable. A bus topology uses a single backbone cable that is terminated at both ends. All the hosts connect directly to this backbone.

Fig.1 Linear bus topology Advantages of a Linear Bus Topology Easy to connect a computer or peripheral to a linear bus. Requires less cable length than a star topology. Disadvantages of a Linear Bus Topology Entire network shuts down if there is a break in the main cable. Terminators are required at both ends of the backbone cable. Difficult to identify the problem if the entire network shuts down. Not meant to be used as a stand-alone solution in a large building.

Star topology : A star topology is designed with each node (file server, workstations, and peripherals) connected directly to a central network hub Data on a star network passes through the hub before continuing to its destination. The hub or concentrator manages and controls all functions of the network.. This configuration is common with twisted pair cable; however, it can also be used with coaxial cable or fiber optic cable. Fig. 2. Star topology

Advantages of a Star Topology Easy to install and wire. No disruptions to the network then connecting or removing devices. Easy to detect faults and to remove parts. Disadvantages of a Star Topology Requires more cable length than a linear topology. If the hub or concentrator fails, nodes attached are disabled. More expensive than linear bus topologies because of the cost of the concentrators. A star topology connects all cables to a central point of concentration.

Ring Topology All computers in the network are connected in a closed loop. The ring topology is actually a logical ring, meaning that the data travels in circular fashion from one computer to another on the network. It is not a physical ring topology. The advantage of this topology is that every computer in the ring gets equal opportunity to send its data, and no computer can dominate the network. This also leads to the slow performance of the network, when more computers are added. In this topology, if one computer fails, the entire network goes down. Its troubleshooting is difficult, and addition or removal of any computer can disrupt the entire network. A ring topology connects one host to the next and the last host to the first. This creates a physical ring of cable.

Fig. 4 Ring topology Advantages of Ring topology Cable faults are easily located, making troubleshooting easier Ring networks are moderately easy to install. Disadvantages of Ring topology Expansion to the network can cause network disruption. A single break in the cable can disrupt the entire network

. Mesh topology : In a mesh topology, each computer on network has redundant data paths to other computers. The mesh topology provides fault tolerance- if a wire, hub, switch, or other component fails, data can travel along an alternate path.. A mesh topology is most often used in large backbone networks in which failure of a single switch or router can result in a large portion of the network going down A mesh topology is implemented to provide as much protection as possible from interruption of service. Each host has its own connections to all other hosts. Although the Internet has multiple paths to any one location, it does not adopt the full mesh topology.

Fig. 5 Mesh topology Advantages of Mesh topology Mesh networks are "self-healing" - if a node goes down the data takes another path. Relatively inexpensive to cover a large area. Disadvantages of Mesh topology Routing network traffic can be difficult because of all the different possible paths between nodes. No central infrastructure (the network relies on peer-to-peer connections ).

Hybrid topology Hybrid network is the combination of different topologies such as star, Ring, Mesh, Bus etc. All the networks of different types (can be connected together through a central hub (in the form of star network) as shown in the figure 6. Fig. 6 Hybrid topology