Module 1 Introduction to Computer Networks.pptx

Definition:
Computer Network is a series of points, or nodes, interconnected by
communication paths for the purpose of transmitting, receiving and
exchanging data, voice and video traffic.
• Nodes/Endpoints can include servers, personal computers, phones
and many types of network devices.
• Network devices including switches and routers use a variety
of protocols and algorithms to exchange information and to
transport data to its intended endpoint.

▪ Every endpoint (sometimes called a host) in a network has a unique
identifier, often an IP address or a Media Access Control address
▪ Networks may also be divided into subnetworks, also called subnets.
▪ Types of networks
• Networks may also be categorized by the scope of their domains.
• Storage area networks interconnect storage devices and resources.
• Size/ Geographical area
• Local area networks interconnect endpoints in a single domain.
• Wide area networks interconnect multiple LANs, Metropolitan
area networks interconnect computer resources in a geographic
area.

LAN
•Privately owned
•Connect hosts in single
office, building or campus
•Connects host
WAN
•Wider geographical span – town, state country
•Connects switches, routers
•Types: Point to Point WAN and switched WAN
MAN
•long-distance communication systems.

How are nodes connected?
• Point to Point WAN
• Switched WAN

• An internetwork is a collection of individual networks connected by
networking devices and that function as a single large network.
• Networks may use a mix of wired (optical fiber, coaxial cable or
copper wires)and wireless technologies (broadcast radio, cellular
radio, microwave and satellite).
• Internet is a switched network

Need for Computer Networks
• File Sharing
• Resource Sharing
• Data Protection and Redundancy
• Distributed Computing
• Ease of Administration
• Internal Communications

Circuit switching
⮚Dedicated physical path
established between source and
destination in 3 phases
i) Connection Establishment.
ii) Data Transfer.
iii) Connection Released.
⮚In circuit switching, each data
unit know the entire path address
which is provided by the source,
through the switch
⮚In Circuit switching, data is
processed at source system only
Packet switching
⮚In Packet switching directly data
transfer takes place, in available
path. No Dedicated physical path
⮚In Packet switching, each data
unit just know the final destination
address intermediate path is
decided by the routers
⮚In Packet switching, data is
processed at all intermediate node
including source system.
Switching

Circuit switching
⮚Delay between data units in
circuit switching is uniform.
⮚Resource reservation is the
feature of circuit switching
because path is fixed for data
transmission.
⮚Circuit switching is more
reliable.
⮚Wastage of resources are more
in Circuit Switching
Packet switching
⮚Delay between data units in
packet switching is not uniform.
⮚There is no resource reservation
because bandwidth is shared
among users.
⮚Packet switching is less
reliable.In Packet switching, data is
processed at all intermediate node
including source system.
⮚Less wastage of resources as
compared to Circuit Switching.

Network Criteria
▪ Performance
• rate of transferring error free data.
• measured by the Response Time.
• Factors that affect Response Time are:
– Number of Users: More users on a network - slower the
network will run
– Transmission Speed: speed that data will be transmitted
measured in bits per second (bps)
– Media Type: Type of physical connection used to connect nodes
together
– Hardware Type: Slow computers such as XT or fast such as
Pentiums
– Software Program: How well is the network operating system
(NOS) written

Other metric used to measure performance
•Bandwidth : number of bits per second that a channel, a link, or even
a network can transmit.
•Throughput : throughput is a measure of how fast we can actually
send data through a network
•Latency: how long it takes for an entire message to completely arrive
at the destination from the time the first bit is sent out from the source.
Latency =propagation time +transmission time +queuing time +
processing delay
•Jitter: problem if different packets of data encounter different delays
and the application using the data at the receiver site is time

▪ Consistency
• predictability of response time and accuracy of data
▪ Reliability
• measure of how often a network is useable.
• MTBF (Mean Time Between Failures) is a measure of the
average time a component is expected to operate between
failures.
• A network failure can be: hardware, data carrying medium and
Network Operating System.
▪ Recovery
• Network's ability to return to a prescribed level of operation after
a network failure.
• is based on having Back-up Files.

▪ Security
– protection of Hardware, Software and Data from unauthorized
access.
– Restricted physical access to computers, password protection,
limiting user privileges and data encryption are common security
methods.
– Anti-Virus monitoring programs to defend against computer
viruses are a security measure

Physical Structures
▪ Here we’ll discuss the physical connections for Networks.
▪ Two possible connection types :
▪ Point-to-point or Multipoint
Point-to-point connections
• provides a dedicated link or between two devices.
• The entire capacity of the link is reserved for transmission between
those two devices. (actual length of wire or cable to connect )
Multipoint connections
• more than two devices are sharing a link
• The entire capacity of the link is either shared spatially or temporally.

Network Topology – the way a network is laid out physically
▪Types
BUS Topology
•only one computer can send data on the bus at any one time.
•Every device is connected to a single cable
Network Topology

Advantages of Bus Topology
•It is cost effective.
•Cable required is least compared to other network topology.
•Used in small networks.
•It is easy to understand.
•Easy to expand joining two cables together.
Disadvantages of Bus Topology
•Cables fails then whole network fails.
•If network traffic is heavy or nodes are more the performance of the
network decreases.
•Cable has a limited length.
•It is slower than the ring topology.

RING Topology
•It is called ring topology because it forms a ring as each computer is
connected to another computer, with the last one connected to the first.
•A number of repeaters are used
•The transmission is unidirectional /bidirectional (Dual Ring)

Advantages of Ring Topology
•Transmitting network is not affected by high traffic or by adding
more nodes, as only the nodes having tokens can transmit data.
•Cost effective to install and expand
Disadvantages of Ring Topology
•Troubleshooting is difficult in ring topology.
•Adding or deleting the computers disturbs the network activity.
•Failure of one computer disturbs the whole network.

STAR Topology
•In this type of topology all the
computers are connected to a
single hub through a cable. This
hub is the central node and all
others nodes are connected to the
central node.
•Every node has its own dedicated
connection to the hub.
•Hub acts as a repeater for data
flow.
•Can be used with twisted pair,
Optical Fibre or coaxial cable.

Advantages of Star Topology
•Fast performance with few nodes and low network traffic.
•Hub can be upgraded easily.
•Easy to troubleshoot.
•Easy to setup and modify.
•Only that node is affected which has failed, rest of the nodes can work
smoothly.
Disadvantages of Star Topology
•Cost of installation is high. ( cable and extra device)
•If the hub fails then the whole network is stopped because all the
nodes depend on the hub.
•Performance is based on the hub that is it depends on its capacity

MESH Topology
•It is a point-to-point
connection to other nodes or
devices.
•All the network nodes are
connected to each other.
•Mesh has n(n-1)/2 physical
channels to link n devices.
There are two techniques to
transmit data over the Mesh
topology, they are :
1.Routing
2.Flooding

Routing
•In routing, the nodes have a routing logic as per the network
requirements - shortest distance, information about the broken links
Flooding
•In flooding, the same data is transmitted to all the network nodes,
•The network is robust, and the its very unlikely to lose the data. But it
leads to unwanted load over the network.
Types of Mesh Topology
•Partial Mesh Topology : In this topology some of the systems are
connected in the same fashion as mesh topology but some devices are
only connected to two or three devices.
•Full Mesh Topology : Each and every nodes or devices are
connected to each other.

Advantages of Mesh Topology
•Each connection can carry its own data load.
•It is robust.
•Fault is diagnosed easily.
•Provides security and privacy.
Disadvantages of Mesh Topology
•Installation and configuration is difficult.
•Cabling cost is more.
•Bulk wiring is required.

TREE Topology
•It has a root node and all
other nodes are
connected to it forming a
hierarchy.
•It is also called
hierarchical topology.
• It should at least have
three levels to the
hierarchy
•Ideal if workstations are
located in groups.
•Used in Wide Area
Network.

Advantages of Tree Topology
•Extension of bus and star topologies.
•Expansion of nodes is possible and easy.
•Easily managed and maintained.
•Error detection is easily done.
Disadvantages of Tree Topology
•Heavily cabled.
•Costly.
•If more nodes are added maintenance is difficult.
•Central hub fails, network fails.

HYBRID Topology
•It is two different types of topologies which is a mixture of two or more
topologies.
•It is a combination of two or topologies
•Inherits the advantages and disadvantages of the topologies included

Advantages of Hybrid Topology
•Reliable as Error detecting and troubleshooting is easy.
•Effective.
•Scalable as size can be increased easily.
•Flexible.
Disadvantages of Hybrid Topology
•Complex in design.
•Costly.

OSI Reference Model
• OSI stands for Open Systems Interconnection model
(OSI model)
• developed by ISO – ‘International Organization of
Standardization‘, in 1974
• It is a 7 layer architecture with each layer having specific
functionality to perform
• conceptual framework that describes functions of the
networking or telecommunication system independently
from the underlying technology infrastructure.
•

Why layering?
Dealing with complex systems:
❑ explicit structure allows identification, relationship of
complex system’s pieces
❑ modularization eases maintenance, updating of
system
�change of implementation of layer’s service
transparent to rest of system
■ e.g. change in gate procedure doesn’t affect
rest of system
❑ was originally developed to facilitate interoperability
between vendors and to define clear standards for
network communication.

• OSI is not a physical model; rather it is a set of
guidelines that application developer can use to create
application that run on network.
• It provides framework for creating and implementing
networking standards, devices, internetworking scheme.
• O.S.I Has 7 Layer, divided into 2 groups.
– The Layer 4-3-2-1 layer defines how data is
transmitted end-to-end.
– The Layer 7-6-5 defines how the application within
one station will communicate with each other.
Responsible for application communication between
hosts.

• Layers are as under:
– A layer should be created where a different level of
abstraction is needed.
– Each layer should perform a well defined function.
– The function of each layer should be chosen with an
eye towards defining internationally standardized
protocols.
– The layer boundaries should be chosen to minimize
the information flow across the interfaces.
– The number of layers should be large enough that
distinct functions need not be thrown together in the
same layer out of necessity.

• protocol data unit (PDU) is a single unit of information transmitted among
peer entities of a computer network.

Module 1 Introduction to Computer Networks.pptx

Application Layer:
• This layer provides the operational system with direct
access to the network services and is responsible to
generate Data ( user info/ system commands)
• It also provides an interface so that Application (Web
Browser) that are running on the local machine can
access the network services. So It enables user or
software to access the network.
• It provides user interfaces and support for services such
as electronic mail, remote file access and transfer,
shared database management, and other types of
distributed information services.

Presentation Layer:
• This layer is concern with the syntax and semantics of
the information exchanged between 2 systems.
• The presentation layer is concerned with translating,
interpreting, and converting the data from various
formats.
• Data is compressed for transmission and uncompressed
on receipt in this layer.
• Encryption techniques are also implemented at the
presentation layer.
• Function: Present Data, Handles Processing Such as
Encryption, Compression and Translation Services

• Translation: Information should be changed to bit
streams before being transmitted. Because different
computers us e different encoding system, the
presentation layer is responsible for interoperability
between these different encoding methods.
• Encryption: To carry sensitive information, a system
must be able to assure privacy. Transformation is carried
out at this layer.
• Compression: Data compression reduces the number of
bits to be transmitted. It is highly required when
transmitting data of text, audio and video.

Session Layer:
• The session layer is responsible for establishing,
managing, and terminating a connection called
session.
• A session is an exchange of messages between
computers.
• Logon, name recognition and security functions occur
while establishing a session.
– Managing the session involves synchronization of
user tasks and messages.
– Synchronization involves the use of checkpoints in
the data stream. In the event of a failure, only the
data from the last checkpoint has to be resent.

• Function: Keeps different application data separate,
Dialog control, Synchronization
– Dialog control: The session layer allows two systems
to enter into a dialog. It allows the communication
between two processes to take place either in half-
duplex or full duplex.
– Synchronization: This layer allows a process to add
checkpoints into a stream of data.

Transport Layer:
• The transport layer is responsible for the control of
flow and ensuring that messages are delivered error
free source -to-destination (end-to-end).
• On the originating side, messages are packaged for
efficient transmission and assigned a tracking number.
• On the receiving side, the packets are reassembled,
checked for errors, and acknowledged.
• The transport layer performs error handling by ensuring
that all data is received in the proper sequence without
errors. If there are errors the data is retransmitted.

• This layer ensures that the whole message arrives
intact and in order, overseeing both error control and
flow control at the source-to-destination level.
• For security purpose, this layer may create a connection
between the two end ports, a logical path between
source and destination.
• Function: End-to-End Connection, Perform error
correction before retransmit
– Service -point addressing: Computer runs several
programs at the same time. So this layer is
responsible for delivering data to specific process
(port) of computer.

– It contains service-point address (port address) and
therefore, network layer gets each packet to the
correct computer on correct network.
– Segmentation and Reassembly: A message is
divided into transmittable segments, each
segment containing sequence number, which
enables layer to reassembling the message correctly
upon arriving at the destination and can identify
those packets which are lost during the
transmission.

– Connection control: The transport layer can be
either connection or connection oriented.
• A connection-less transport layer treats each
segment as an independent packet and delivers
it to the transport layer at the destination
machine.
• Whereas connection oriented transport layer
makes a connection with the transport layer at
the destination machine first before delivering the
packet.

– Error control: This layer is more concern with end -
to-end control rather than single link control of data
link layer. The receiving transport layer makes sure
that the entire message arrives without error.
Error correction is usually achieved through
retransmission.

Network Layer:
• The network layer is primarily concerned with
addressing and routing.
• Logical addresses or IP addresses are translated into
physical addresses or machine addresses for
transmission at the network layer.
– On the receiving side, the translation process is
reversed.
– The network layer also determines the route from
the source to the destination computer to deliver
packets.

• Routes are determined based on packet addresses
and network conditions. Traffic control measures are
also implemented at the network layer.
– If 2 systems are connected in the same network,
there is no need for the network layer.
• Function: Routing, Provides Logical addressing
which router used for path determination
– Logical Addressing: The physical addressing
implemented by the data link layer handles the

– addressing problem locally. If packet passes the
network boundary, it needs another addressing
system to help distinguish the source and
destination system.
– Routing: When independent networks or links are
connected together to create internetwork, the
connecting device (router or gateway) route the
packets to their final destination. This is one more
mechanism provided by this layer.

Data Link Layer:
• The data link layer defines how the signal will be
placed.
• In this layer, the data frames are broken down into
individual bits that can be translated into electronic
signals and sent over network. On the receiving end the
bits are reassembled into frames for processing by
upper levels.
• If an acknowledgement is expected and not received,
the frame will be resent.
• Error and corrupt data detection and correction is also
performed at the data link layer

● The data link layer transforms the physical layer, a raw
transmission facility, to a reliable link and is responsible
for node-to-node delivery.
● Function: Framing, Combine Packets into Bytes
And bytes into Frame
– Framing: the data link layer divides the stream of
bits received from the network layer into
manageable data units called frames.
– Physical Addressing: If frames are to be
distributed to different systems on the network, the
data link layer adds a header to the frame to define
the physical address of the sender and receiver of

– Flow control: If the rate at which the data are
absorbed by the receiver is less than the rate
produced in the sender, the data link layer imposes
the flow control mechanism to prevent overwhelming
the receiver.
– Error control: The data link layer adds reliability to
the physical layer by adding mechanisms to detect
and retransmit damaged or lost frames. It uses the
mechanism to prevent duplication of frames. Error
control is normally achieved through a trailer added
to the end of the frame.

– Access control: When two or more devices are
connected to the same link, data link layer protocols
are necessary to determine which device has control
over the link at any given time.

Physical Layer:
● The physical layer of the OSI model establishes the
physical characteristics of the network such as the
type of cable, connectors, and the length of the
cable.
● This layer also defines the electrical characteristics of
the signals used to transmit the data.
● The physical layer transmits the binary data (bits) as
electrical or optical signals depending on medium.

● This layer is concern with the following:
– Physical characteristics of interface and
medium: This layer defines the characteristics of
the interface between the devices and the
transmission medium.
– Representation of bits: Data of this layer consists
of a stream of bits without any interpretation. They
must be encoded into signals (electronics or optical),
which is defined by the physical medium.
– Data rates: The number of bits sent each second, is
also defined b the physical layer.

– Line configuration: They physical layer is
concerned with the connection of device to the
medium. It can be Point-to-Point or Multipoint
Configuration.
– Transmission Mode: The physical layer also
defined the direction of transmission between two
devices (Simplex, Half-Duplex or Full-Duplex).

Summary of OSI
Physical Layer: To transmit bits over a medium.
Data Link Layer: To organize bits into frames; to provide
node-to-node delivery.
Network Layer: To move packets from source to
destination.
Transport Layer: To provide reliable end-to-end message
delivery and error recovery.
Session Layer: To establish, manage and terminate
sessions.
Presentation Layer: To translate, encrypt, and compress
data.
Application Layer: To generate data and allow access to

Protocols, Functions of OSI Model

Comparison between OSI Reference Model and
TCP/IP Reference Model
• TCP refers to Transmission Control Protocol.
OSI refers to Open Systems Interconnection.

Similarities between OSI Reference and TCP/IP
Reference Model
•Both are layered architecture.
•Layers provide similar functionalities.
•Both are protocol stack.
•Both are reference models

Comparison of OSI Reference Model and
TCP/IP Reference Model
❑ OSI has seven layers
❑ OSI emphasis on providing a
reliable data transfer service,
Each layer of the OSI model
detects and handles errors, all
data transmitted includes
checksums.
❑ Is a general model. The OSI
model was devised before the
protocols were invented. It can
be made to work in diverse he.
terogeneous networks.
❑ TCP/IP has four layers
❑ TCP/IP treats reliability as an end
to end Problem. The transport
layer handles all error detection
and recovery, it was checksums,
acknowledgments, and timeouts
to control transmissions and
provides end-to-end verification.
❑ Cannot be used in other
applications

Comparison of OSI Reference Model and
TCP/IP Reference Model (contd)
❑ OSI model supports both
connectionless and connection
oriented communication in the
network layer, but only connection
transport layer, where it counts.
❑ OSI makes the distinction between
services, interfaces, and protocol.
❑ The OSI model supports both
connectionless and connection-
network layer, but only connection-
transport layer.
❑ The TCP/IP model has only one
mode in the network layer
(connectionless) but supports both
modes in the transport layer, giving
the user choice.
❑ TCP/IP does not originally clearly
distinguish between services,
interface, and protocol.
❑ TCP/IP model was just a
description of the existing
protocols. The model and the
protocol fit perfectly.

Network devices
Repeater
• A repeater operates at the physical layer.
• Its job is to regenerate the signal over the same network before the
signal becomes too weak or corrupted so as to extend the length to
which the signal can be transmitted over the same network.
• It regenerate it to the original strength.
• It is a 2 port device.

Hub
• multiport repeater.
• A hub connects multiple wires like in star topology which connects
different stations.
• Does not find out best path for data packets which leads to
inefficiencies and wastage.

Bridge
• A bridge operates at data link layer.
• A bridge is a repeater, with add on functionality of filtering content
by reading the MAC addresses of source and destination.
• used for interconnecting two LANs working on the same protocol.
• It has a single input and single output port, it is a 2 port device.

Switch
• A switch is a multi port bridge with a buffer and a design that can
boost its efficiency(large number of ports imply less traffic) and
performance.
• Switch is data link layer device.
• Switch can perform error checking before forwarding data, that
makes it very efficient as it does not forward packets that have
errors and forward good packets selectively to correct port only.

Routers
• Switchs the routes data packets based on their IP addresses.
• Is a Network Layer device.
• connect LANs and WANs together
• dynamically updating routing table based on which they make
decisions on routing the data packets.
• Router divide broadcast domains of hosts connected through it

Gateway
• connects two networks together that may work upon different
networking models.
• They basically works as the messenger agents that take data from
one system, interpret it, and transfer it to another system.
• Operates at network layer.
• are generally more complex than switch or router.

Module 1 Introduction to Computer Networks.pptx

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Module 1 Introduction to Computer Networks.pptx