Management Information Systems

Lection 04Networks

CLARK UNIVERSITY

College of Professional and Continuing Education (COPACE)

Plan

• Basic terms• Classification of networks• Topology of networks• Model OSI• Types of environmental data

Basic terms

Computer network is a collection of computers and other hardware interconnected by communication channels that allow sharing of resources and information.

Basic terms

• Server• Client• Client-server

Computer entirely dedicated to servicing the requests of other computers, plays the role of a dedicated

server

Basic terms

Basic terms

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The computer that combines the functions of a client and a server, is a peer node.

Basic terms

Classification of networks

Environment datatransmission

Territorial prevalence

Organization of interaction of

computers

Speed of data transfer

Speed of data transfer:Speed of data transfer:

High speed (more then 100

Мbit/sec)Middle speed(less then 100

Мbit/sec)

Low speed

(less then 10 Мbit/sec)

Classification of networks

Territorial prevalence Territorial prevalence

Urban network(MAN)Speed:

dozens Mbit/sec

Global networks(WAN)Speed:

dozens Kbit/sec – dozens Mbit/sec

Local networks

(LAN)Speed:

10 Мbit/sec - 10 Gbit/sec

Classification of networks

Environment data transmission:Environment data transmission:

Wireless network

Wires network

Classification of networks

Organization of interaction of computers:Organization of interaction of computers:

Hybrid networkNetwork with

dedicated server

Peer-to-peer network

Classification of networks

Peer-to-peer network

Peer-to-peer network

Peer-to-peer operating systems include server and client components of network services.

Examples: LANtastic Windows for Workgroups Windows NT Workstation Windows 95/98

Advantages:1. Low price2. Simplicity of installation and operation

Peer-to-peer network

Disadvantages:1. Complexity of the information protection2. Efficiency depends on the number of

computers

1. Number of computers in the network 10-202. Security problems are not critical3. You don’t wait significant expansions of your

company

When do we use peer-to-peer networks?

Network with a dedicated server

Network with a dedicated server

Advantages:• Division of resources• Protection• Data backup• Big number of users

Disadvantages: Necessity of additional OS

for the server High complexity of

installation and modernization of the network

Necessity of a separate PC as a server

Hybrid network

Network topology

Network topology describes the physical location of the computers, cables and other network components

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Network topologies

Fully connected topology

Fully connected topology

It is the topology of a network in which each workstation is connected to all the others.

The physical fully connected topology is generally too costly and complex for practical networks, although the topology is used when there are only a small number of nodes to be interconnected

• Topology "bus" is a topology with a common cable (called the bus), which is connected to all workstations.

• At the ends of the cable there are terminators to prevent signal reflection.

Bus topology

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When building large networks there is a problem if a limited length of cables between nodes, in this case, the network is divided into segments. Segments are connected by various devices - repeaters, concentrators or hubs. For example, the technology allows the use of Ethernet cable up to 185 meters.

Bus topology

Advantages:• a little time of

setting up a network

• the cheapness (requires less cable and network devices)

• easy set-up• the failure of some

workstation does not affect the work of the whole network

Bus topology

Disadvantages:• any failures in the

network, as the cable break, leads to the failure of the whole network

• complex localization of faults

• The network performance falls with the addition of new workstations

"Star“ is the basic topology of a network in which all computers are connected to the central node (usually a switch or a hub), forming a physical network segment.

This segment can function both individually and like a part of a complex topology as “tree”.

Star topology

24-port switch

• Better performance• Isolation of devices• We can increase the size of the network very

easily. • Easy to detect faults and to remove parts.

Advantages of star networks

Disadvantages of star networks

failure of the central switch will result to an inability of the network (or network segment)

it often requires more cable than for most other topologies

number of workstations in the network (or network segment) is limited by the number of ports in the central switch

Ring is the basic topology of a network in which workstations are connected sequentially to each other, forming a closed network.

Ring topology

• ease of installation• practically complete absence of the

additional equipment• the possibility of stable work without a

significant drop in speed of data transmission with heavy network traffic

Advantages of ring topology

Disadvantages of ring topology

the failure of a single workstation, and other problems (the cable break) leads to the failure of the whole network

the complexity of the configuration and customization

the complexity of troubleshooting

Star-bus (hybrid) topology

Tree topology

OSI model

• In 1984 the number of international standardization organizations (ISO, ITU-T and others) developed the Open System Interconnection model (OSI).

• The OSI model defines the different levels of interoperability, gives them the standard names and indicates which functions levels must perform.

OSI levels

Physical layer

It means the transferring of bits by physical channels, such as a coaxial cable, “twisted pair”, optic cable, wireless networks.

Data link level

• This level is a very powerful and complete set of functions for sending messages between network nodes.

• It gives us the opportunity of detection and correction of errors.

• Bits are grouped into sets called frames

Network layer

• Agreement of different technologiessimplification of addressing in large networks.

• Creation of reliable and flexible barriers on the way of unwanted traffic between networks.

• Messages on this level are called packages

Transport layer

• guaranteed delivery of data (it gives an acknowledgement of reception of packages)

• detection of errors at the level of the sender and recipient (it allows the host system to detect bad packages)

Session layer

It manages the dialogue, i.e. it fixes which side is currently active and provides the synchronization

Presentation layer

• It works only with the form of data, without changing the its content.

• The information is always clear to the application layer of another system.

• Can overcome the syntactic differences in the data models, or differences in the codes of characters, such as ASCII codes

• Encrypt data

Application layer

It gives a set of protocols which allow users an access to shared resources, such as files, printers or web-pages, and organizes their work together

Types of networks:• Wires networks• Wireless networks

Coaxial cable

Coaxial cable

Twisted pair

Optic fiber cable

Wireless networks

• The difficulty of cable laying• Mobility• Remoteness• Urgency

Bluetooth

• Bluetooth is designed for the construction of personal wireless networks (Wireless Personal Area Network, WPAN). The coverage is up to 100 m

• Line of sight is not required• Bluetooth works on the none-licensed in the

whole world frequency of 2.45 GHz, which allows free usage of the bluetooth device.

• The speed of 721 Kbps and the transfer of 3 voice channels

Wi-Fi

The most widespread technology of the organization of wireless networks is WI-FI.

Speed of data transmission depends on the distance between the points, and on other factors, for example, on the level of interference.

At a speed of 54 Mbit/s, which is the limit for WI-FI, the range is 30 to 50 m.

The distance increases up to several hundreds of meters at a speed of 1 Mbit/sec.

IR-port

• IrDA (Infra red Data Association) allows you to connect to peripherals without cables using infrared waves.

• IrDA port operates at data rates 2400-115200 bit/sec.

• The main disadvantage is the need for direct line of sight between the transmitter and receiver.