1-Lect_1.pptxLecture 5 array in PHP.pptx

Computer Networks
Lecture 1
Introduction to
Network

Lecture Outlines
1
 Data communication
Components of a data
communication system
Data flow
Topologies of networks
Categories of networks

Data Communication
 The term telecommunication means communication at a
distance.
 Data communications are the exchange of data between two
devices via some form of transmission medium such as a wire
cable, or microwave.
 A data communications system must transmit data to the
correct destination in an accurate and timely manner
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Components of Data Communications
 The five components that make up a data communications
system are the message, sender, receiver, medium, and
protocol.
 Text, numbers, images, audio, and video are different forms of
information.
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Elements of Data Communication
1. Sender:
The computer or device that is used for sending data is called
sender, source or transmitter. In modern digital communication
system, the source is usually a computer.
2. Medium:
The means through which data is sent from one location to
another is called transmission medium. If the receiver and
transmitter are within a building, a wire connects them. If they are
located at different locations, they may be connected by telephone
lines, fiber optics or microwaves.

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3. Receiver:
The device or computer that receives the data is called receiver.
The receiver can be a computer, printer or a fax machine.
4. Protocols:
There are rules under which data transmission takes place
between sender and receiver. The data communication s/w are
used to transfer data from one computer to another. The s/w
follows same communication protocols can communicate and
exchange data.

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 Delivery.
The system must deliver data to the correct destination. Data must
be received by the intended device or user and only by that device
or user.
 Accuracy.
The system must deliver the data accurately. Data that have been
altered in transmission and left uncorrected are unusable.

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 Timeliness.
The system must deliver data in a specific time. Data delivered late
are useless.
 In the case of video and audio, timely delivery means delivering
data as they are produced, in the same order that they are
produced, and without significant delay. This kind of delivery is
called real-time transmission.

Data Flow
 Data flow between two devices can occur in one of three
ways:
 simplex,
 half-duplex,
 full-duplex.
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1. Simplex:
 Data is transmitted in only one direction. A terminal can only
send data and cannot receive it.
 Simplex mode is usually used for a remote device that is meant
only to receive data. It is not possible to confirm successful
transmission of data in simplex mode.
 e.g. Speaker, radio and television broadcasting are examples of
simplex transmission, on which the signal is send from the
transmission to your TV antenna. There is no return signal.
Data Flow

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2. Half duplex:
 In half duplex mode, data can be transmitted in both directions
but only in one direction at a time.
 During any transmission, one is the transmitter and the other is
receiver.
 So each time for sending or receiving data, direction of data
communication is reversed, this slow down data transmission
rate.
Data Flow

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3. Full duplex.
 In full mode, data can be transmitted in both directions
simultaneously (at the same time).
 It is a faster mode for transmitting data because no time wastes
in switching directions.
Data Flow

Networks
 A network is a set of devices (referred to nodes) connected by
communication links.
 A node can be a computer, printer, or any other device capable
of sending and/or receiving data generated by other nodes on
the network.
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Connection Types
 point-to-point connection,
 Only two devices are connected by a link.
 Point-to-point networks contains exactly two hosts
(computer or switches or routers or servers) connected back
to back using a single piece of cable.
 The receiving end of one host is connected to sending to the
other end and vice-versa.
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Connection Types
 Multi-Point connection,
 Three or more devices share a link.
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Categories of topology
 Topology is the physical or logical arrangement of a network.
 Devices may be arranged in a mesh, star, bus, or ring
topology.
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A fully Connected - Mesh Topology
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 A host is connected to one, two or more than two hosts.
 This topology may have hosts having point-to-point connection
to every other hosts or may also have hosts which are having
point to point connection to few hosts only.

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 Advantages
 Each node has the possibility to transmit data from one node
to many other nodes at the same time.
 The failure of a single node does not cause the entire network
to fail as there are alternate paths for data transmission.
 It can handle heavy traffic.
 Point-to-point contact between every pair of nodes, makes it
easy to identify faults
Advantages and Disadvantages of Mesh Network

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 Disadvantages
 Every network node is connected to every other node of the
network. This leads to redundancy of many network
connections.
 A lot of cabling is required. Thus, the costs incurred in setup
and maintenance are high.
 The complexity, the administration of a mesh network is
difficult.
Advantages and Disadvantages of Mesh Network

A star Topology
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 All hosts in star topology are connected to a central device,
known as Hub device, using a point-to-point connection.
 Hosts and Hubs use point to point connection.

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 Advantages
 Due to its centralization, the topology offers simplicity of
operation and it is easy to detect faults in the network devices.
 It achieves isolation of each device in the network.
 Adding or removing network nodes is easy, and can be done
without affecting the entire network.
 As the analysis of traffic is easy, the security risk can be
discovered.
 Data packets do not have to pass through many nodes.
Advantages and Disadvantages of Star Network

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 Disadvantages
 Network operation depends on the functioning of the central hub.
Hence, central hub failure leads to failure of the entire network.
 Also, the number of nodes that can be added, depends on the
capacity of the central hub.
 The setup cost is quite high.
Advantages and Disadvantages of Star Network

A bus Topology
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 In contrast to point-to-point, in bus topology all device share
single communication line or cable.
 All devices are connected to this shared line.
 Bus topology may have problem while more than one hosts
sending data at the same time.

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Advantages and Disadvantages of Bus Network
 Advantages
 It is easy to set up, handle, and implement.
 It is best-suited for small networks.
 It costs very less.

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 Disadvantages
 The cable length is limited. This limits the number of network
nodes that can be connected.
 It works well only for a limited number of nodes. When the
number of devices connected to the bus increases, the
efficiency decreases.
 It is heavily dependent on the central bus. A fault in the bus
leads to network failure.
 It is not easy to isolate faults in the network nodes.
 Each device on the network "see" all the data being
transmitted, thus posing a security risk.

A ring Topology
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 Each host machine connects to exactly two other machines,
creating a circular network structure.
 When one host tries to communicate or send message to a host
which is not adjacent to it, the data travels through all
intermediate hosts.

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 Advantages
 The data being transmitted between two nodes passes
through all the intermediate nodes.
 The traffic is uni-directional and the data transmission is high-
speed.
 In comparison to a bus, a ring is better at handling load.
 The adding or removing of network nodes is easy, as the
process requires changing only two connections.
 The configuration makes it easy to identify faults in network
nodes.
 Each node has the opportunity to transmit data.
 It is less costly than a star topology.
Advantages and Disadvantages of Ring Network

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 Disadvantages
 The failure of a single node in the network can cause the entire
network to fail.
 Data sent from one node to another has to pass through all the
intermediate nodes. This makes the transmission slower in
comparison to that in a star topology. The transmission speed
drops with an increase in the number of nodes.
 There is heavy dependency on the wire connecting the
network nodes in the ring.
Advantages and Disadvantages of Ring Network

Categories of networks
 A network can be categorized as :
 A local area network (LAN),
 A metropolitan-area network (MAN),
 A wide area network (WAN).
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LAN
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 A LAN is a data communication system within a building,
plant, or campus, or between nearby buildings.
 Covers distance up to 100-1000meters.

WANs: A switched WAN and a point-to-
point WAN
 A WAN is a data communication system spanning states, countries, or the
whole world.
 Covers distance up to 1000 kilo-meters and also goes up to 100km.
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MAN
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 A MAN is a data communication system covering an area the size of a town or
city.
 MAN occupies coverage in between LANs and WANs. MAN has distance coverage
and data rate higher than LAN, but less than WAN.
 A typical example of MAN is Local Cable TV system.

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