Introduction

Chinmay Raut
Assistant Professor
Universal College of Engineering
Data Communication
⚫ Before exchanging information, the creator and user of
the data should be agree how the information should be
presented?
⚫ An information that is presented in such a form is
called data.
⚫ Data communication can be defined as the exchange of
data between source and destination.
Characteristics of Data communication
⚫ Delivery
⚫ Accuracy
⚫ Timeliness
Components of Data communication
system
⚫ Message
⚫ Sender
⚫ Receiver
⚫ Protocol
⚫ Medium
Computer Network
⚫ A computer network is a set
of computers connected together for the purpose of
sharing resources.
⚫ The connection between computers can be done via
cabling, most commonly the Ethernet cable, or
wirelessly through radio waves.
⚫ Connected computers share recourses like access the
internet, printer, file server.
Goals of Computer Network
⚫ Sharing information
⚫ Increase the speed of communication
⚫ To reduce cost
⚫ To improve security
⚫ To provide access to remote location
⚫ To facilitate centralized management of recourses,
data, Software
Types of Networking Devices
⚫ Hub
⚫ Switch
⚫ Router
⚫ Repeater
⚫ Bridge
⚫ Gateway
Hub
⚫ Hub is a networking device which is used to connect
multiple network hosts.
⚫ A network hub is also used to do data transfer.
⚫ The data is transferred in terms of packets on a
computer network.
⚫ when a host sends a data packet to a network hub, the
hub copies the data packet to all of its ports connected
to.
Types of Hub
⚫ Active Hub
⚫ Passive Hub
Switch
⚫ Like a hub, a switch also works at the layer of LAN
(Local Area Network) but you can say that a switch is
more intelligent than a hub.
⚫ While hub just does the work of data forwarding, a
switch does 'filter and forwarding' which is a more
intelligent way of dealing with the data packets.
Router
⚫ A router is a device like a switch that routes data
packets based on their IP addresses.
⚫ Router is mainly a Network Layer device. Routers
normally connect LANs and WANs together and have
a dynamically updating routing table based on which
they make decisions on routing the data packets.
Repeater
⚫ Job of repeater 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.
⚫ An important point to be noted about repeaters is that
they do not amplify the signal.
Gateway
⚫ A gateway, as the name suggests, is a passage to
connect two networks together that may work upon
different networking models.
⚫ They basically work as the messenger agents that take
data from one system, interpret it, and transfer it to
another system.
⚫ Gateways are also called protocol converters and can
operate at any network layer. Gateways are generally
more complex than switch or router.
Bridge
⚫ A bridge operates at data link layer. A bridge is a
repeater, with add on the functionality of filtering
content by reading the MAC addresses of source and
destination.
⚫ It is also used for interconnecting two LANs working
on the same protocol.
Network classification by their
Geography
⚫ LAN (Local Area Network)
⚫ MAN(Metropolitan Area Network)
⚫ WAN(Wide Area Network)
Local Area Network
⚫ LAN is a group of computers connected to each other
in a small area such as building, offices.
⚫ LAN is used for connecting two or more personal
computers through a communication medium such as
cables.
⚫ It is less costly as it is built with inexpensive hardware
such as hub, cables.
⚫ The data rate is faster.
Metropolitan Area Network
⚫ A Metropolitan area network is a network that covers
larger geographic area by interconnecting different
LAN to from a larger network.
⚫ Government agencies use MAN to connect to the
citizens and private industries.
⚫ In MAN various LANs are connected to each other
through the telephone exchange line.
Wide Area Network
⚫ A Wide Area Network is a network that extends over a
large geographical area such as states or countries.
⚫ A WAN is quite bigger network than the LAN
network.
⚫ A WAN is not limited to single location, but it spans
over a large geographical area through telephone lines,
fibre optics cable or satellite links.
⚫ The internet is a biggest WAN in the world.
Topology
⚫ Network Topology is the schematic description of a
network arrangement, connecting various nodes(sender
and receiver) through lines of connection.
Types of topologies.
-Bus topology
-Star topology
-Ring topology
-Mesh topology
-Tree topology
Bus Topology
⚫ Bus topology is a network type in which every
computer and network device is connected to single
cable. When it has exactly two endpoints, then it is
called Linear Bus topology.
⚫ Features of Bus Topology
-It transmits data only in one direction.
-Every device is connected to a single cable
Bus 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
⚫ 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. Exactly two
neighbors for each device.
Ring Topology
⚫ Features of Ring Topology
-A number of repeaters are used for Ring topology with large
number of nodes, because if someone wants to send some
data to the last node in the ring topology with 100 nodes, then
the data will have to pass through 99 nodes to reach the 100th
node. Hence to prevent data loss repeaters are used in the
network.
-The transmission is unidirectional, but it can be made
bidirectional by having 2 connections between each Network
Node, it is called Dual Ring Topology.
-In Dual Ring Topology, two ring networks are formed, and
data flow is in opposite direction in them. Also, if one ring
fails, the second ring can act as a backup, to keep the network
up.
Ring Topology
⚫ 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.
-Cheap 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.
Star Topology
⚫ Features of Star Topology
-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.
-If the hub fails then the whole network is stopped because all the
nodes depend on the hub.
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.
Mesh Topology
⚫ Features of Mesh Topology
-Fully connected.
-Robust.
⚫ Advantages of Mesh Topology
-Each connection can carry its own data load.
-It is robust.
-Fault is diagnosed easily.
⚫ 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.
Tree Topology
⚫ Features of Tree Topology
-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.
⚫ Disadvantages of Tree Topology
-Heavily cabled.
-Costly.
-If more nodes are added maintenance is difficult.
-Central hub fails, network fails.
Design issues for layers
The following are the design issues for the layers:
⚫ Reliability: It is a design issue of making a network that
operates correctly even when it is made up of unreliable
components.
⚫ Addressing: There are multiple processes running on one
machine. Every layer needs a mechanism to identify senders and
receivers.
⚫ Error Control: It is an important issue because physical
communication circuits are not perfect. Many error detecting and
error correcting codes are available. Both sending and receiving
ends must agree to use any one code.
⚫ Flow Control: If there is a fast sender at one end sending data to
a slow receiver, then there must be flow control mechanism to
control the loss of data by slow receivers. There are several
mechanisms used for flow control such as increasing buffer size
at receivers, slow down the fast sender, and so on. Some process
will not be in position to accept arbitrarily long messages. This
property leads to mechanisms for disassembling, transmitting
Design issues for layers
⚫ Multiplexing and De-multiplexing: If the data has to be
transmitted on transmission media separately, it is inconvenient
or expensive to setup separate connection for each pair of
communicating processes. So, multiplexing is needed in the
physical layer at sender end and de-multiplexing is need at the
receiver end.
⚫ Scalability: When network gets large, new problem arises. Thus
scalability is important so that network can continue to work
well when it gets large.
⚫ Routing: When there are multiple paths between source and
destination, only one route must be chosen. This decision is
made on the basis of several routing algorithms, which chooses
optimized route to the destination.
⚫ Confidentiality and Integrity: Network security is the most
important factor. Mechanisms that provide confidentiality
defend against threats like eavesdropping. Mechanisms for
integrity prevent faulty changes to messages.
 Connectionless and Connection oriented
services
Sr. Connection oriented Connectionless
No.

In this communication service,

It is the communication service in which
packets are sent without creating
1 virtual connection is created before
any virtual connection over the
sending the packet over the internet.
internet.

It needs authentication of the It transfers the data message

2 destination node before transferring without authenticating
data. destination.

This connection does not ensure

3 This is a more reliable connection reliability on packet
transmission.
The handshaking is carried out to There is no handshaking
4 ensure both sender and receiver agree happens while sending a packet
with this connection. over the network.
Connectionless and Connection oriented
services
Sr. Connection oriented Connectionless
No.
5 It is faster than
It is slower than the connectionless
connection-oriented protocol
service.
service.
6 Sending packet in connection-oriented
It has less overhead and
service requires more parameters in
smaller packet header size.
the header.
7 Route is finalized and decided at the
time of handshaking before sending the The route is not finalized
actual packet.
8 Not necessary all the
packets transmitting
All the packets between sender and
between sender and
destination follows the same path.
receiver follows the same
path.
9 UDP is connectionless
TCP is connection-oriented protocol.
protocol.
 Layers of OSI Model
⚫ OSI stands for Open Systems Interconnection. It has
been developed by ISO – ‘International
Organization of Standardization‘, in the year 1984.
⚫ It is a 7 layer architecture with each layer having
specific functionality to perform.
⚫ All these 7 layers work collaboratively to transmit the
data from one person to another across the globe.
Layers of OSI Model
 Physical Layer
⚫ The lowest layer of the OSI reference model is the
physical layer. It is responsible for the actual physical
connection between the devices.
⚫ The physical layer contains information in the form
of bits. It is responsible for transmitting individual bits
from one node to the next.
⚫ When receiving data, this layer will get the signal
received and convert it into 0s and 1s and send them to
the Data Link layer, which will put the frame back
together.
 Physical Layer
The functions of the physical layer are :
⚫ Bit synchronization: The physical layer provides the
synchronization of the bits by providing a clock. This clock
controls both sender and receiver thus providing
synchronization at bit level.
⚫ Bit rate control: The Physical layer also defines the
transmission rate i.e. the number of bits sent per second.
⚫ Physical topologies: Physical layer specifies the way in
which the different, devices/nodes are arranged in a
network i.e. bus, star or mesh topology.
⚫ Transmission mode: Physical layer also defines the way
in which the data flows between the two connected devices.
The various transmission modes possible are: Simplex,
half-duplex and full-duplex.
 Data link Layer
⚫ The data link layer is responsible for the node to node
delivery of the message.
⚫ The main function of this layer is to make sure data
transfer is error-free from one node to another, over the
physical layer. When a packet arrives in a network, it
is the responsibility of DLL to transmit it to the Host
using its MAC address.
Data Link Layer is divided into two sub layers :
⚫ Logical Link Control (LLC)
⚫ Media Access Control (MAC)
 Data link Layer
The functions of the data Link layer are :
⚫ Framing: Framing is a function of the data link layer. It
provides a way for a sender to transmit a set of bits that are
meaningful to the receiver. This can be accomplished by
attaching special bit patterns to the beginning and end of the
frame.
⚫ Physical addressing: After creating frames, Data link layer adds
physical addresses (MAC address) of sender and/or receiver in
the header of each frame.
⚫ Error control: Data link layer provides the mechanism of error
control in which it detects and retransmits damaged or lost
frames.
⚫ Flow Control: The data rate must be constant on both sides else
the data may get corrupted thus , flow control coordinates that
amount of data that can be sent before receiving
acknowledgement.
⚫ Access control: When a single communication channel is shared
by multiple devices, MAC sub-layer of data link layer helps to
 Network Layer
⚫ Network layer works for the transmission of data from
one host to the other located in different networks.
⚫ It also takes care of packet routing i.e. selection of the
shortest path to transmit the packet, from the number
of routes available.
⚫ The sender & receiver’s IP address are placed in the
header by the network layer.
 Network Layer
The functions of the Network layer are :
⚫ Routing: The network layer protocols determine
which route is suitable from source to destination. This
function of network layer is known as routing.
⚫ Logical Addressing: In order to identify each device
on internetwork uniquely, network layer defines an
addressing scheme. The sender & receiver’s IP address
are placed in the header by network layer. Such an
address distinguishes each device uniquely and
universally.
 Transport Layer
⚫ Transport layer provides services to application layer
and takes services from network layer.
⚫ The data in the transport layer is referred to
as Segments.
⚫ It is responsible for the End to End Delivery of the
complete message.
⚫ The transport layer also provides the acknowledgement
of the successful data transmission and re-transmits the
data if an error is found.
 Transport Layer
The services provided by the transport layer :
⚫ Connection Oriented Service: It is a three-phase process
which include
– Connection Establishment
– Data Transfer
– Termination / disconnection
In this type of transmission, the receiving device sends an
acknowledgement, back to the source after a packet or
group of packet is received. This type of transmission is
reliable and secure.
⚫ Connection less service: It is a one-phase process and
includes Data Transfer. In this type of transmission, the
receiver does not acknowledge receipt of a packet. This
approach allows for much faster communication between
devices. Connection-oriented service is more reliable than
 Session Layer
⚫ This layer is responsible for establishment of connection,
maintenance of sessions, authentication and also ensures
security.
The functions of the session layer are :
⚫ Session establishment, maintenance and
termination: The layer allows the two processes to
establish, use and terminate a connection.
⚫ Synchronization : This layer allows a process to add
checkpoints which are considered as synchronization points
into the data. These synchronization point help to identify
the error so that the data is re-synchronized properly, and
ends of the messages are not cut prematurely and data loss
is avoided.
⚫ Dialog Controller : The session layer allows two systems
to start communication with each other in half-duplex or
 Presentation Layer
⚫ Presentation layer is also called the Translation layer. The
data from the application layer is extracted here and
manipulated as per the required format to transmit over the
network.
The functions of the presentation layer are :
⚫ Translation : For example, ASCII to EBCDIC.
⚫ Encryption/ Decryption : Data encryption translates the
data into another form or code. The encrypted data is
known as the cipher text and the decrypted data is known
as plain text. A key value is used for encrypting as well as
decrypting data.
⚫ Compression: Reduces the number of bits that need to be
transmitted on the network.
 Application Layer
⚫ At the very top of the OSI Reference Model stack of
layers, we find Application layer which is
implemented by the network applications.
⚫ These applications produce the data, which has to be
transferred over the network.
⚫ This layer also serves as a window for the application
services to access the network and for displaying the
received information to the user.
 TCP/IP Model
⚫ The OSI Model we just looked at is just a
reference/logical model. It was designed to describe
the functions of the communication system by dividing
the communication procedure into smaller and simpler
components.
⚫ But when we talk about the TCP/IP model, it was
designed and developed by Department of Defense
(DoD) in 1960s and is based on standard protocols.
⚫ It stands for Transmission Control Protocol/Internet
Protocol. The TCP/IP model is a concise version of
the OSI model. It contains four layers, unlike seven
layers in the OSI model.
TCP/IP Model
 Network Layer
⚫ This layer corresponds to the combination of Data
Link Layer and Physical Layer of the OSI model.
⚫ It looks out for hardware addressing and the protocols
present in this layer allows for the physical
transmission of data. We just talked about ARP being a
protocol of Internet layer, but there is a conflict about
declaring it as a protocol of Internet Layer or Network
access layer.
⚫ It is described as residing in layer 3, being
encapsulated by layer 2 protocols.
 Internet Layer
⚫ This layer parallels the functions of OSI’s Network layer. It
defines the protocols which are responsible for logical
transmission of data over the entire network.
The main protocols residing at this layer are :
⚫ IP – stands for Internet Protocol and it is responsible for
delivering packets from the source host to the destination
host by looking at the IP addresses in the packet headers.
⚫ ICMP – stands for Internet Control Message Protocol. It is
encapsulated within IP datagrams and is responsible for
providing hosts with information about network problems.
⚫ ARP – stands for Address Resolution Protocol. Its job is to
find the hardware address of a host from a known IP
address. ARP has several types: Reverse ARP, Proxy ARP,
Gratuitous ARP and Inverse ARP.
 Transport Layer
⚫ This layer is analogous to the transport layer of the OSI model. It
is responsible for end-to-end communication and error-free
delivery of data. It shields the upper-layer applications from the
complexities of data. The two main protocols present in this
layer are :
⚫ Transmission Control Protocol (TCP) – It is known to provide
reliable and error-free communication between end systems. It
performs sequencing and segmentation of data. It also has
acknowledgment feature and controls the flow of the data
through flow control mechanism. It is a very effective protocol
but has a lot of overhead due to such features. Increased
overhead leads to increased cost.
⚫ User Datagram Protocol (UDP) – On the other hand does not
provide any such features. It is the go-to protocol if your
application does not require reliable transport as it is very
cost-effective. Unlike TCP, which is connection-oriented
protocol, UDP is connectionless.
 Application Layer
⚫ This layer performs the functions of top three layers of the
OSI model: Application, Presentation and Session Layer. It
is responsible for node-to-node communication and
controls user-interface specifications. Protocols other than
those present in the linked article are :
⚫ HTTP and HTTPS – HTTP stands for Hypertext transfer
protocol. It is used by the World Wide Web to manage
communications between web browsers and servers. HTTPS
stands for HTTP-Secure. It is a combination of HTTP with
SSL(Secure Socket Layer). It is efficient in cases where the
browser need to fill out forms, sign in, authenticate and carry
out bank transactions.
⚫ SSH – SSH stands for Secure Shell. It is a terminal
emulations software similar to Telnet. The reason SSH is
more preferred is because of its ability to maintain the
encrypted connection. It sets up a secure session over a
TCP/IP connection.
Thank You