COMPUTER NETWORK

UNIT 1
NETWORK SOFTWARE
• Protocol Hierarchies
• To reduce their design complexity, most networks are organized as a
stack of layers or levels, each one built upon the one below it.
• protocol is an agreement between the communicating parties on
how communication is to proceed.
• Data are directly transferred from layer n on one machine to layer n
on another machine. Instead, each layer passes data and control
information to the layer immediately below it, until the lowest layer
is reached
• layer 1 is the physical medium through which actual communication
occurs.
• virtual communication is shown by dotted lines and physical
communication by solid lines.
• A list of the protocols used by a certain system, one protocol per
layer, is called a protocol stack
Design Issues For The Layers
• Reliability is the design issue of making a network that operates
correctly even though it is made up of a collection of components
that are themselves unreliable.
• One mechanism for finding errors in received information uses codes
for error detection.
• Another reliability issue is finding a working path through a network.
• A second design issue concerns the evolution of the network.
• There are many computers on the network, every layer needs a
mechanismfor identifying the senders and receivers that are involved
in a particular message.This mechanism is called addressing or
naming, in the low and high layers,respectively.
• Third design issue is resource allocation. Networks provide a service
to hosts from their underlying resources, such as the capacity of
transmission lines.
Connection Oriented Connectionless
Service Primitives
OSI Reference Model
• OSI stands for Open System Interconnection.
• It is a reference model that describes how information from a
software application in one computer moves through a physical
medium to the software application in another computer.
• OSI consists of seven layers, and each layer performs a particular
network function.
• OSI model was developed by the International Organization for
Standardization (ISO) in 1984, and it is now considered as an
architectural model for the inter- computer communications.
• The Physical Layer
• The physical layer is concerned with transmitting raw bits over a
communication channel. The design issues have to do with making
sure that when one side sends a 1 bit it is received by the other side
as a 1 bit, not as a 0 bit.
• The Data Link Layer:The main task of the data link layer is to
transform a raw transmission facility nto a line that appears free of
undetected transmission errors.
• The sender break up the input data into data frames (typically a few
hundred or a few thousand bytes) and transmit the frames
sequentially
• The network layer controls the operation of the subnet. A key design
issue is determining how packets are routed from source to
destination.
• The basic function of the transport layer is to accept data from above
it, split it up into smaller units if need be, pass these to the network
layer, and ensure that the pieces all arrive correctly at the other end.
• Session layer allows users on different machines to establish sessions
between them. Sessions offer various services, including dialog
control (keeping track of whose turn it is to transmit), token
management (preventing two parties from attempting the same
critical operation simultaneously),
• The presentation layer manages these abstract data structures and
allows higher-level data structures (e.g., banking records) to be
defined and exchanged.
• The Application Layer
• The application layer contains a variety of protocols that are
commonly needed by users. One widely used application protocol is
HTTP (HyperText Transfer Protocol).
TCP/IP Protocol
Transmission Media (Physical Layer)
• Transmission media is a communication channel that carries the
information from the sender to the receiver. Data is transmitted
through the electromagnetic signals.
• Transmission media is of two types are wired media and wireless
media. In wired media, medium characteristics are more important
whereas, in wireless media, signal characteristics are more
important.
• Different transmission media have different properties such as
bandwidth, delay, cost and ease of installation and maintenance.
• The transmission media is available in the lowest layer of the OSI
reference model, i.e., Physical layer.
Guided Media
• It is defined as the physical medium through which the signals are
transmitted. It is also known as Bounded media.
• Twisted Pair
• Twisted pair is a physical media made up of a pair of cables twisted
with each other. A twisted pair cable is cheap as compared to other
transmission media.
An unshielded twisted pair is widely used in telecommunication.
• Category 1: Category 1 is used for telephone lines that have
low-speed data.
• Category 2: It can support upto 4Mbps.
• Category 3: It can support upto 16Mbps.
• Category 4: It can support upto 20Mbps. Therefore, it can be
used for long-distance communication.
• Category 5: It can support upto 200Mbps.
• Limit is 1000 meter
• Installation is easy
• A shielded twisted pair is a cable that contains the mesh surrounding
the wire that allows the higher transmission rate.
• The cost of the shielded twisted pair cable is not very high and not
very low.
• An installation of STP is easy.
• It has higher capacity as compared to unshielded twisted pair cable.
• It is shielded that provides the higher data transmission rate
Coaxial cable
• Coaxial cable is very commonly used transmission media, for
example, TV wire is usually a coaxial cable.
• The name of the cable is coaxial as it contains two conductors parallel
to each other.
• The inner conductor of the coaxial cable is made up of copper, and
the outer conductor is made up of copper mesh. The middle core is
made up of non-conductive cover that separates the inner conductor
from the outer conductor.
1.Baseband transmission: It is defined as the process of
transmitting a single signal at high speed.
2.Broadband transmission: It is defined as the process of
transmitting multiple signals simultaneously.
• Fibre optic cable is a cable that uses electrical signals for
communication.
• Fibre optic is a cable that holds the optical fibres coated in plastic
that are used to send the data by pulses of light.
• The plastic coating protects the optical fibres from heat, cold,
electromagnetic interference from other types of wiring.
• Fibre optics provide faster data transmission than copper wires.
Fiber Optics
• Core: The optical fibre consists of a narrow strand of glass or plastic
known as a core. A core is a light transmission area of the fibre. The
more the area of the core, the more light will be transmitted into the
fibre.
• Cladding: The concentric layer of glass is known as cladding. The main
functionality of the cladding is to provide the lower refractive index
at the core interface as to cause the reflection within the core so that
the light waves are transmitted through the fibre.
• Jacket: The protective coating consisting of plastic is known as a
jacket. The main purpose of a jacket is to preserve the fibre strength,
absorb shock and extra fibre protection.
Unguided Transmission Media
• An unguided transmission transmits the electromagnetic waves
without using any physical medium. Therefore it is also known
as wireless transmission.
• In unguided media, air is the media through which the
electromagnetic energy can flow easily.
Radio Waves
• Radio waves are the electromagnetic waves that are transmitted in all
the directions of free space.
• Radio waves are omnidirectional, i.e., the signals are propagated in
all the directions.
• The range in frequencies of radio waves is from 3Khz to 1 khz.
• The Omnidirectional characteristics make them useful for
multicasting, the sending and receiving antenna are not aligned, i.e.,
the wave sent by the sending antenna can be received by any
receiving antenna.
• An example of the radio wave is FM radio, television, cordless phones
are examples of a radio wave.
• Radio waves propogate in the sky mode,can travel long distance.
• Radio waves with low and medium frequency can penetrate on walls.
Microwaves
• Terrestrial Microwave transmission is a technology that transmits
the focused beam of a radio signal from one ground-based
microwave transmission antenna to another.
• Microwaves are the electromagnetic waves having the frequency in
the range from 1GHz to 1000 GHz.
• Microwaves are unidirectional as the sending and receiving antenna
is to be aligned, i.e., the waves sent by the sending antenna are
narrowly focussed.
• It works on the line of sight transmission, i.e., signal transmit in
straight line free of material obstacles.
• EX.Dish Antenna
Microwave Application
Satellite Microwave Transmission
• A satellite is a physical object that revolves around the earth at a
known height.
• Satellite communication is more reliable nowadays as it offers more
flexibility than cable and fibre optic systems.
• We can communicate with any point on the globe by using satellite
communication.
• An infrared transmission is a wireless technology used for
communication over short ranges.
• The frequency of the infrared in the range from 300 GHz to 400 THz.
• It is used for short-range communication such as data transfer
between two cell phones, TV remote operation, data transfer
between a computer and cell phone resides in the same closed area.
•