NETWORKING
The object of this unit is to give students the basic understanding of networks: topologies,
cables and communications devices (network adapter cards, modems, hubs, repeater, bridges,
routers, gateway), Client -Server environment. Teaching this unit will take no more than three
days. A QUIZ will follow. This unit will be taught at the same time the students have just
begun to work on their Independent study about computer careers. The resources for this unit
include:
1.
2.
3.
4.
Handouts(3)
Power Point Presentations (3)
Networking Demos (3) with fill in forms
Glossary of Terms
Unit Schedule:
Day 1: Network Topologies
Day 2: Network Adapters and Cabling
Day 3: Internetworking and Network Types
The objectives of the unit are stated as follows:
1. Students will be able to state the differences and similarities between a star, a ring and a
linear bus network
2. Students should be able to describe various network media used in data communications
3. Students should know which type of medium is being used in their classroom
4. Students will be able to outline the advantages of computer networking
5. Students should understand the differences between a WAN and a LAN, and between a
client-server network and a peer-to-peer network
7. Students will know the difference between an internal and an external modem
8. Students will be able to outline the important features of a modem.
In the early days of PCs, the "sneaker net" was used to transfer files from one computer to the
other via floppy disk. Then direct cable and peer-to-peer networks began to evolve. Next Client /
Server networks evolved where large centrally located servers managed the network and people
worked at workstations or client machines.
In the Information Age that we are presently in, corporations cannot function without the speedy
flow of information. Imagine that if banks and stock markets did not use networked computers
how long every thing would take to do. The computer network has become an integral part of
our lives and in this concept you will look at the basics of the hardware and topologies that
allow computers to be networked.
What is a Network?
Networking is a productive way of utilizing a group of computers. If all of machines in an office,
for example, are linked together though a network, you can share an expensive printer, pass files
from one PC to another and send messages to other users. Computer networks include all the
hardware and software required to connect computers and other devices to a channel so that they
can communicate with each other.
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Components of a Network
The major hardware components are:
• Cables
• Adapter Cards
• Servers
• Workstations
Other components include:
• Printers
• Modems
In a PC-based network, computers act in the functional roles of servers and client workstations.
The servers make their attached disk drives, modems and printers available to the client
workstations.
Network Topologies
A network topology is a description of the possible physical connections within a network. The
topology is the configuration of the hardware and shows which pairs of nodes can communicate.
A network's topology describes the physical layout of the network medium and attached devices.
Theoretically, there are several ways of physically running the cables connecting a group of
computers. These are as follows:
• Mesh
• Bus
• Star
• Ring
Mesh Topology
A pure mesh network has point-to-point links (a direct connection between two
devices) between every node in the network. This type of network is rarely used.
ADVANTAGES
Provides multiple paths to a destination
DISADVANTAGES
Requires an interface for every node on the network
Network bandwidth may be wasted
A large network requires a huge amount of
Bus Topology
A bus topology is a linear transmission medium terminated at both ends. All nodes attach directly
to this medium via relatively short links. Ethernet acts as a bus topology. In a bus topology the
signal is broadcast to all nodes, but only the destination node responds to the signal. Bus
topologies are most appropriate when the linked devices are physically close to one another.
ADVANTAGES
Uses a minimal amount of cable
DISADVANTAGES
No central distribution point (hub)
Difficult to troubleshoot
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Star Topology
In a star network, each device connects to a central point called a hub or concentrator.
Information sent from a device always goes to the hub first and is then routed as appropriate.
10BaseT, which is described later, is an example of star topology. The star topology involves a
centralized host computer connected to several other computer systems that are usually smaller
than the host. The smaller computer systems communicate with one another through the host and
usually share the host computer's database. The host could be anything from a PC to a supercomputer. Any computer can communicate with any other computer in the network. The banks often
have a large home-office computer system with a star network of smaller main frame systems in
the branch banks.
ADVANTAGES
Easy to troubleshoot
Provides a central point for performing
network maintenance and testing
Easy to add devices
DISADVANTAGES
May use more cabling than other topologies
depending on the location of the hub
Hub failure can disable large sectors of the
network
Ring Topology
The ring topology consists of a closed loop of-directly linked devices between repeaters. The
ring
topology involves computer systems approximately the same size, with no one computer system
as
the local point of the network. When one system routes a message to another system, it is passed
around the ring until it reaches its destination address.
ADVANTAGES
Stability
DISADVANTAGES
Malfunction of an adapter card can bring
down a whole network
Hybrid Topologies
Hybrids use multiple topologies. For example, Wide Area Networks often use direct links to
connect remote rings or stars. Hybrid topology is very common now that internetworking is
becoming increasingly popular. Internetworking is the joining together of two or more networks
to form a larger network. The Internet is a good example of intemetworking. Internetworking
will be discussed in detail later.
The OSI Reference Model
A subcommittee that was set up in 1977 by the International Organization for Standardization
(ISO) created the Open Systems Interconnection (OSI) Reference Model. The ISO is used to
develop communication standards to promote multi-vendor interoperability and universal
accessibility.
Many functions must be performed to accomplish the task of data communication. There is a
protocol for each of these functions, making it necessary to have several protocols to complete a
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job. The model shows each protocol as a layer that performs certain functions for the protocol or
layer above it. The OSI Model does not specify the details of each protocol; it specifies the
layers that should be present and what function each layer should perform. Many protocols
written for use on LANs follow the ISO Model very loosely.
The OSI Model consists of seven layers:
LAYER
Application
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FUNCTION
Applications move files, emulate terminals
and generate other traffic
RESPONSABILITY
Presentation
6
Programs format data and convert
characters
Data formats, data format
translation, data compression
and data encryption
Session
5
Programs negotiate and establish
connections between nodes
Session management, session
Error control, dialog control
and remote procedure calls
(RPC)
Transport
4
Programs ensure end-to-end delivery
Reliable end-to-end
communication, flow control,
error control and message
multiplexing
Network
3
Data Link
2
Programs route packages across multiple
inter LAN links
Firmware transfers packets or frames
Physical
1
Firmware sequences packets or frames for
transmission
Routing, message
fragmentation and re-assembly
Sending to and receiving bits
from the Physical layer, data
framing, error control, flow
control and physical addressing
Physical media connection
specifications, data
transmission and reception to
and from media
User interface and user