Chapter 4: Computer Networks

Department of Computer ScienceFoundation Year ProgramUmm Alqura University, Makkah

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Chapter 4 Computer Networks

Local Area Network (LAN):• Definition• LAN Topologies

Bus or Linear Network Ring Network Star Network

Wide Area Network (WAN):• Definition

Network

• A computer network is a collection of computers and devices connected by communications channels that facilitate communication and sharing of resources among users.

• They may be classified according to a wide variety of characteristics.

Local Area Network (LAN)

• It is a combination of programs and equipment that connect a number of personal computers.

• It serves a local area.

• Supplies networking capability to a group of computers in close proximity to each other such as in an office building, a school or a home.

Local Area Network (LAN)

• Feasible for the owning organization to install high quality, high-speed communication links interconnecting nodes.

• Typical data transmission speeds are one to 100 megabits per second.

• Useful for sharing resources like files, printers, games or other applications.

• A LAN, in turn, often connects to other LANs and to the Internet or other WAN.

• Specialized operating system software may be used to configure a local area network.

Examples: industrial plants, office buildings, college or university campuses or similar locations.

Local Area Network (LAN)

Ethernet LAN

• The smallest home LAN can have precisely two computers; a large LAN can accommodate many thousands of computers.

• Many LANs are divided into logical groups called subnets.

• It sets up the predictable and inevitable conflict between PCs, office automation equipment and the larger midrange and mainframe computers.

Local Area Network (LAN)

LAN TOPOLOGIES

• Selecting the topology of the LAN is to interconnect PCs, minicomputers, or both.

• This choice dictates the cable, cabling methodology and the networking software that can operate on the LAN.

• The three basic topologies are the ring, the star and the bus or tree.

LAN TOPOLOGIES

Linear Bus Topology

• Consists of a main run of cable with a terminator at each end.

• All nodes (file server, workstations, and peripherals) are connected to the linear cable.

Linear Bus Topology II

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.

Ring Topology

Ring Topology, all the nodes are connected to each other in such a way that they make a closed loop.

Advantages of a Ring Topology

• This type of network is very organized

• It has better performance than Bus topology.

• Each computer has equal access to resources.

Disadvantages of a Ring Topology

• If a computer in the network goes down, the entire

network gets affected.

• The network is dependent on the wire, which connects

different components.

Ring Topology II

Star Topology

• Designed with each node (file server, workstations, and peripherals) connected directly to a central network hub, switch, or concentrator.

• Data on a star network passes through the hub, switch, or concentrator before continuing to its destination.

The hub, switch, or concentrator manages and controls all functions of the network.

• It also acts as a repeater for the data flow.

• Common with twisted pair cable.

• Can also be used with coaxial cable or fiber optic cable.

Star Topology II

Star Topology III

Advantages of a Star Topology

• Easy to install and wire.

• No disruptions to the network when 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, switch, or concentrator fails, nodes attached are disabled.

• More expensive than linear bus topologies because of the cost of the hubs, etc.

Tree or Expanded Star

• It combines characteristics of linear bus and star topologies.

• It consists of groups of star-configured workstations connected to a linear bus backbone cable.

• They allow for the expansion of an existing network.

• They enable schools to configure a network to meet their needs.

Tree or Expanded Star II

Tree or Expanded Star III

Advantages of a Tree Topology

• Point-to-point wiring for individual segments.

• Supported by several hardware and software venders.

Disadvantages of a Tree Topology

• Overall length of each segment is limited by the type of cabling used.

• If the backbone line breaks, the entire segment goes down.

Star and ring network topologies are sometimes combined into one network to provide a higher degree of fault tolerance. Because a star network is susceptible to a failure in the hub and a ring network is sensitive to a break in the ring, combining both forms offer an alternate route in case one topology fails.

Wide Area Network (WAN)

• It is a collection of LANs.

• It spans a large geographic area, such as a state, a province or a country.

• WANs often connect multiple smaller networks, such as local area networks (LANs) or metro area networks (MANs).

• Many WANs are corporate or research networks that utilize leased lines.

• Wide Area Network (WAN) is a computer network that covers a broad area (i.e. any network, whose communications links cross metropolitan, regional, or national boundaries).

Wide Area Network (WAN)