OSI and TCP/IP Models

Computer Network

Welcome to Unify Study

• I am Priyanka Chatterjee.

• UGC NET Qualified with 99.46 Percentile. (Dec 2019)

• 5 years Industry Experience.

• MCA (2008 – 2011 )

• BSc. Honors in Computer Science (2004 - 2007)

• From last 15 years I am learning Computer Science in a Practical Way.

• Less is More……………….

Previous Years Analysis of Networking

Previous Year Total No of

Questions

Topics

Dec 2019 9 Classful Addressing -1 Q

Numerical (Throughput) – 1 Q

Data Encryption Standard(DES) -1 Q

Fiber Optic Cable – 1 Q

Full Form (ICANN) – 1 Q

Network Security – 1 Q

Numerical (Router) 1 Q

Concept of Different layers of OSI Model – 1Q

Cryptography – 1Q

Previous Year Total No of

Questions

Topics

June 2019 10 TCP/IP Layer Concept – 1Q

Numerical(Fully Connected Topology) – 1Q

Concept of Different layers of OSI Model – 1Q

Classful Addressing -1 Q

IP fishing, Spoofing, Sniffing Concept – 1Q

RSA Algorithm – 1Q

Sub netting – 1Q

Concept of ICMP,DNS,ARP,RARP- 1 Q

Loopback address and Classful addressing – 1Q

Numerical (Propagation delay) – 1Q

Dec 2018 8 Sub netting – 1Q

Different types of Secret Key Algorithm – 1 Q

Concept of TCP, UDP – 1Q

Sequence of different stages of transmitting packet – 1Q

ISO Layers Concept – 1Q

Ethernet address Concept – 1Q

Cryptography – 1 Q

Classful Addressing -1 Q

What is the OSI model?

The Open Systems Interconnection (OSI) model is a conceptual model created by

the International Organization for Standardization which enables diverse

communication systems to communicate using standard protocols. In plain

English, the OSI provides a standard for different computer systems to be able to

communicate with each other.

The OSI model can be seen as a universal language for computer networking. It’s

based on the concept of splitting up a communication system into seven abstract

layers, each one stacked upon the last.

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.

An illustration of hops in a network. The hop count between the computers in this case is 2.

a hop occurs when a packet is passed from one network segment to the next. Data packets pass

through routers as they travel between source and destination. The hop count refers to the number of intermediate devices through which data must pass between source and destination.

Important Terminology

Hop to Hop(Node to Node): Use MAC address, Data link layer deals with this.

Host to Host :Use IP address, Network layer deals with this, One host to another

host.

End to End: Use IP + Port No, Transport layer deals with this,

Specific Application of a host to that Application of another host.

MAC address A media access control address is a unique identifier assigned to a network

interface controller for use as a network address in communications within a network segment.

Application layer

The Application Layer is the seventh layer in OSI network model. Real traffic data will be often

generated from the Application Layer. It is responsible for providing networking service to the user,

and also known as desktop layer. Port Number used to Identification of service . Port are entry and

exit point of layer.

The functions of the Application layer are :

Network Virtual Terminal

FTAM-File transfer access and management

Mail Services

Directory Services

Presentation layer

Presentation layer is used to convert the data into standard format and transfer the

data in the format that will be accept by application layer.

Example : ASCII, EDCDIC, JPEG, MPEG, BMP, MIDI etc.

It performs these task also such as

Encoding – Decoding

Encryption – Decryption

Compression – Decompression

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.

Compression : It compress the data which need to transmitted over the network

Session layer

Session layer is responsible for establishing and maintaining the session for

communication. It terminate the session after communication.

Session ID work at session layer

Example :

RPC : Remote Procedure Call

SQL : Structured Query Language

NFS : Network File System

Transport layer

Transport layer actual transmission of the data is done here it is also known as the layer of end-to-

end delivery of the data.

It is also called as the Heart of OSI model. The data in this layer is in segment format.

Data in the Transport Layer is called as Segments.

Transport layer is operated by the Operating System. It is a part of the OS .

Segmentation : The process of dividing the data into smaller part is called segmentation. Every small

part are unit known as one segment.

Transport layer perform the following task as well

Identification service.

Multiplexing and Demultiplexing

Segmentation of data.

Sequencing and Reassembling.

Error correction.

Flow Control => means control the bandwidth and speed of transmission.

Network layer

Network layer is responsible for providing best part for data to reach next

destination. Logical address work on this layer.

Its is essential for providing source to destination delivery of packet.

It is divided into two part

1) Routed protocol : IP, Ipx and Appletalk

2) Routing protocol : RIP,IGRP, EIGRP,OSPF

The functions of the Network layer are :

1.Routing: Its determine the best route form source to destination. This function of

network layer is known as routing.

1.Logical Addressing: It is unique address given to internetwork device for

identification. The sender & receiver’s IP address are placed in the header by

network layer.

Data link layer

Data link layer is used to handle the data transfer between network layer and

physical layer. The data in this layer is in form of frame.

Data Link Layer is divided into two sub layers :

i) Logical Link Control (LLC)

ii) Media Access Control (MAC)

i) Logical Link Control (LLC)

Error detection and flow control

Talks about WAN Protocls

E.g. PPP , Frame Relay.

ii) Media Access Control (MAC)

Talks about physical address and it have 12 digit Hexadecimal number .

Also responsible for error detection

Primary responsibility of MAC Data Encapsulation and Media Access Control

Data Encapsulation includes frame Assembly.

The functions of the data Link layer are :

Framing : Framing is a function of the data link layer.

Physical addressing : It adds physical addresses (MAC address) of sender and/or

receiver in the header of each frame.

Error control : It control the error by re transmitting damage or lost frame when

detects.

Flow Control : It control the flow that is the amount of data to be sent.

Physical layer :

Physical layer is used to establish and terminate physical connection to a

communication medium. It also define the electrical, mechanical specification likes

cable connection and signalling option of medium and also responsible for procedure

check.

Data in this layer is in the form of electrical pules if it is coaxial cable and twisted

pair cable, and if the cable is fibre optic the data will be in the form of light

Devices : Hub, Repeater, Cable modem etc.

The functions of the physical layer are :

Bit synchronization

Bit rate control

Physical Topologies

Transmission mode

TCP/IP Model

The TCP/IP model is a short version of the OSI reference model.

Following are the different layer of TCP/IP1.Process/Application Layer

2.Host-to-Host/Transport Layer

3.Internet Layer

4.Network Access/Link Layer

Advantage of TCP/IP modeloperated independently.

It is scalable.

It supports a number of routing protocols.

Disadvantage of TCP/IP modelIn this, the transport layer does not guarantee delivery of packets.

The model cannot be used in any other application.

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. The layers are:

1.Process/Application Layer

2.Host-to-Host/Transport Layer

3.Internet Layer

4.Network Access/Link Layer

Network Devices

(Hub, Repeater, Bridge, Switch, Router, Gateways)

1. 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 (Attenuation) 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. When the signal becomes weak, they copy the

signal bit by bit and regenerate it at the original strength. It is a 2 port device.

2. Hub – A hub is basically a multiport repeater. A hub connects multiple wires coming from different

branches, for example, the connector in star topology which connects different stations. Hubs cannot

filter data, so data packets are sent to all connected devices. In other words, collision domain of all

hosts connected through Hub remains one. Also, they do not have intelligence to find out best path for data packets which leads to inefficiencies and wastage.

Types of Hub

•Active Hub:- These are the hubs which have their own power supply and can clean, boost and relay

the signal along with the network. It serves both as a repeater as well as wiring centre. These are

used to extend the maximum distance between nodes.

•Passive Hub :- These are the hubs which collect wiring from nodes and power supply from active

hub. These hubs relay signals onto the network without cleaning and boosting them and can’t be used

to extend the distance between nodes.

3. 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. It has a single input and single output port,

thus making it a 2 port device.

Types of Bridges

•Transparent Bridges:- These are the bridge in which the stations are completely unaware of the

bridge’s existence i.e. whether or not a bridge is added or deleted from the network, reconfiguration of

the stations is unnecessary. These bridges make use of two processes i.e. bridge forwarding and bridge

learning.

•Source Routing Bridges:- In these bridges, routing operation is performed by source station and the

frame specifies which route to follow. The hot can discover frame by sending a special frame called

discovery frame, which spreads through the entire network using all possible paths to destination.

4. Switch – A switch is a multiport bridge with a buffer and a design that can boost its efficiency(a large

number of ports imply less traffic) and performance. A switch is a data link layer device. The 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. In other words, switch divides collision domain of hosts, but broadcast domain remains same.

5. Routers – 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. Router divide broadcast domains of hosts connected through it.

6. 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.

NTA NET Dec 2019

NTA NET Dec 2019

NTA NET June 2019

NTA NET June 2019

NTA NET June 2019

NTA NET June 2019

1. Which of the following devices takes data sent from one network

device and forwards it to the destination node based on MAC address

?

(1)Hub (2) Modem (3) Switch (4) Gateway(nov 2017/p2)

1. Which of the following devices takes data sent from one network

device and forwards it to the destination node based on MAC address

?

(1)Hub (2) Modem (3) Switch (4) Gateway(nov 2017/p2)

4. Which of the following layer of OSI Reference model is also called

end-to-end layer ?

(1)Network layer (2) Datalink layer

(3) Session layer (4) Transport layer(nov 2017/p2)

4. Which of the following layer of OSI Reference model is also called

end-to-end layer ?

(1)Network layer (2) Datalink layer

(3) Session layer (4) Transport layer(nov 2017/p2)

9. Match the following :

List – I List - II

(a) Data link layer (i) Encryption

(b) Network layer (ii) Connection control

(c) Transport layer (iii) Routing

(d) Presentation layer (iv) Framing

Code :

(a) (b) (c) (d)

(1) (iv) (iii) (i) (ii)

(2) (iii) (iv) (ii) (i)

(3) (iv) (ii) (iii) (i)

(4) (iv) (iii) (ii) (i)

(nov 2017/p2)