CHAPTER 4

Computer Networks

Chapter 4• 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.

4.1 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.

4.1 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.

4.1 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.

4.1 Local Area Network (LAN)

4.1.1 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.

4.1.1 LAN TOPOLOGIES

4.1.2 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.

4.1.2 Linear Bus TopologyA- 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.

B- 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.

4.1.3 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.

4.1.3 Star Topology

4.1.3 Star Topologya- 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.

b-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.

4.1.4 Tree or Expanded StarIt 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.

4.1.4 Tree or Expanded Star

a- Advantages of a Tree Topology • Point-to-point wiring for individual segments. • Supported by several hardware and software venders. b-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.

4.2 Wide Area Network (WAN)

4.2 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).