OSI MODEL

&

TCP/IP MODEL AND PROTOCOLS

1
 The OSI (Open Systems Interconnection) Data Model
 ISO standard for computer networks design and functioning.
 OSI stands for Open System Interconnection 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 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.
 OSI consists of seven layers, and each layer performs a particular
network function when applications are communicating over the
net.
 Each layer is self-contained, so that task assigned to each layer
2
can be performed independently.
3
4
 …cont.
 The OSI model is divided into two layers: upper layers and lower layers.
 The upper layer of the OSI model mainly deals with the application related
issues, and they are implemented only in the software.
 The application layer is closest to the end user.
 Both the end user and the application layer interact with the software
applications. .
 The lower layer of the OSI model deals with the data transport issues.
 The data link layer and the physical layer are implemented in hardware and
software.
 The physical layer is the lowest layer of the OSI model and is closest to the
physical medium.
 The physical layer is mainly responsible for placing the information on the
physical medium.

 NB: layer 1-3 are in hardware, 4-5 in operating system 6 in library subroutines
and 7 in user program. 5
 Characteristics of the OSI Model
 Here are some important characteristics of the OSI model:
i. A layer should only be created where the definite levels of abstraction are
needed.
ii. The function of each layer should be selected as per the internationally
standardized protocols.
iii. The number of layers should be large so that separate functions should not
be put in the same layer. At the same time, it should be small enough so
that architecture doesn’t become very complicated.
iv. In the OSI model, each layer relies on the next lower layer to perform
primitive functions. Every level should able to provide services to the next
higher layer.
v. Changes made in one layer should not need changes in other lavers.

6
 Advantages of the OSI Model
 Here are the major benefits/pros of using the OSI model:
1. It helps you to standardize router, switch, motherboard, and other
hardware
2. Reduces complexity and standardizes interfaces
3. Facilitates modular engineering
4. Helps you to ensure interoperable technology
5. Helps you to accelerate the evolution
6. Protocols can be replaced by new protocols when technology changes.
7. Provide support for connection-oriented services as well as connectionless
service.
8. It is a standard model in computer networking.
9. Supports connectionless and connection-oriented services.
10. It offers flexibility to adapt to various types of protocols.
7
 Disadvantages of OSI Model
 Here are some cons/ drawbacks of using OSI Model:
1. Fitting of protocols is a tedious task.
2. You can only use it as a reference model.
3. It doesn’t define any specific protocol.
4. In the OSI network layer model, some services are duplicated in many
layers such as the transport and data link layers
5. Layers can’t work in parallel as each layer need to wait to obtain data
from the previous layer.

8
 Functions of the OSI Layers
 There are the seven OSI layers.
 Each layer has different functions.
 A list of seven layers is given below:
1. Physical Layer
2. Data-Link Layer
3. Network Layer
4. Transport Layer
5. Session Layer
6. Presentation Layer
7. Application Layer 9
10
 1. Physical layer
 The main functionality of the physical layer is to transmit
the individual bits from one node to another node.
 It provides a physical medium through which bits are
transmitted.
 It is the lowest layer of the OSI model.
 It establishes, maintains and deactivates the physical
connection.
 It specifies the mechanical, electrical and procedural
network interface specifications.
11
12
 Functions of a Physical layer:
1. Line Configuration: It defines the way how two or
more devices can be connected physically.
2. Data Transmission: It defines the transmission
mode whether it is simplex, half-duplex or full-duplex
mode between the two devices on the network.
3. Topology: It defines the way how network devices
are arranged.
4. Signals: It determines the type of the signal used for
transmitting the information.
13
 2. Data-Link Layer
 This layer is responsible for the error-free transfer of
data frames.
 Error detection, error correction, floe control and
reliable delivery is being done here.
 It defines the format of the data on the network.
 It provides a reliable and efficient communication
between two or more devices.
 It is mainly responsible for the unique identification of
each device that resides on a local network.
 It contains two sub-layers:
14
15
a. Logical Link Control Layer
•It is responsible for transferring the packets to
the Network layer of the receiver that is
receiving.
•It identifies the address of the network layer
protocol from the header.
•It also provides flow control.

16
b. Media Access Control Layer
•A Media access control layer is a link
between the Logical Link Control layer and
the network's physical layer.
•It is used for transferring the packets over the
network.

17
 Functions of the Data-link layer
 Framing: The data link layer translates the physical's raw bit stream
into packets known as Frames. The Data link layer adds the header
and trailer to the frame.
 The header which is added to the frame contains the hardware
destination and source address.
 Physical Addressing: The Data link layer adds a header to the
frame that contains a destination address. The frame is transmitted
to the destination address mentioned in the header.
 Flow Control: Flow control is the main functionality of the Data-link
layer.
 It is the technique through which the constant data rate is maintained
on both the sides so that no data get corrupted.
 It ensures that the transmitting station such as a server with higher processing
18
speed does not exceed the receiving station, with lower processing speed.
 …cont.
 Error Control: Error control is achieved by adding a
calculated value CRC (Cyclic Redundancy Check) that is
placed to the Data link layer's trailer which is added to the
message frame before it is sent to the physical layer.
 If any error seems to occur, then the receiver sends the
acknowledgment for the retransmission of the corrupted
frames.
 Access Control: When two or more devices are
connected to the same communication channel, then the
data link layer protocols are used to determine which
device has control over the link at a given time. 19
 3. Network Layer
 It is a layer 3 that manages device addressing, tracks the location
of devices on the network.
 It determines the best path to move data from source to the
destination based on the network conditions, the priority of
service, and other factors.
 The Data link layer is responsible for routing and forwarding the
packets.
 Routers are the layer 3 devices, they are specified in this layer
and used to provide the routing services within an internetwork.
 The protocols used to route the network traffic are known as
Network layer protocols.
 Examples of protocols are IPv4 and Ipv6. 20
 IPv4
 IPv4 is an IP version widely used to identify devices on a network
using an addressing system.
 It was the first version of IP deployed for production in the
ARPANET in 1983. It uses a 32-bit address scheme to store 2^32
addresses which is more than 4 billion addresses.
 It is considered the primary Internet Protocol and carries 94% of
Internet traffic.
 The address format of IPv4:

21
 IPv6
 IPv6 is the most recent version of the Internet Protocol.
 This new IP address version is being deployed to fulfill the need for
more Internet addresses.
 It was aimed to resolve issues that are associated with IPv4.
 With 128-bit address space, it allows 340 undecillion unique
address space.
 IPv6 is also called IPng (Internet Protocol next generation).
 Internet Engineer Taskforce initiated it in early 1994.
 The design and development of that suite are now called IPv6.
 The address format of IPv6:

22
 Ipv4 Ipv6

Address length IPv4 is a 32-bit address. IPv6 is a 128-bit address.

Fields IPv4 is a numeric address that consists of 4 fields which are separated IPv6 is an alphanumeric address that consists of 8 fields, which are
by dot (.). separated by colon.

Classes IPv4 has 5 different classes of IP address that includes Class A, Class IPv6 does not contain classes of IP addresses.
B, Class C, Class D, and Class E.

Number of IP address IPv4 has a limited number of IP addresses. IPv6 has a large number of IP addresses.

VLSM It supports VLSM (Virtual Length Subnet Mask). Here, VLSM means that It does not support VLSM.
Ipv4 converts IP addresses into a subnet of different sizes.

Address configuration It supports manual and DHCP configuration. It supports manual, DHCP, auto-configuration, and renumbering.

Address space It generates 4 billion unique addresses It generates 340 undecillion unique addresses.

End-to-end connection integrity In IPv4, end-to-end connection integrity is unachievable. In the case of IPv6, end-to-end connection integrity is achievable.

Security features In IPv4, security depends on the application. This IP address is not In IPv6, IPSEC is developed for security purposes.
developed in keeping the security feature in mind.

Address representation In IPv4, the IP address is represented in decimal. In IPv6, the representation of the IP address in hexadecimal.

Fragmentation Fragmentation is done by the senders and the forwarding routers. Fragmentation is done by the senders only.

Packet flow identification It does not provide any mechanism for packet flow identification. It uses flow label field in the header for the packet flow identification.

Checksum field The checksum field is available in IPv4. The checksum field is not available in IPv6.

Transmission scheme IPv4 is broadcasting. On the other hand, IPv6 is multicasting, which provides efficient network
operations.

Encryption and Authentication It does not provide encryption and authentication. It provides encryption and authentication.
23
Number of octets It consists of 4 octets. It consists of 8 fields, and each field contains 2 octets. Therefore, the total
number of octets in IPv6 is 16.
 IP addressing methods commonly used in networking
 There are mainly four types of IP addresses:
1. Public IP Addresses:
 A public IP address is an address where one primary address is associated
with your whole network.
 Each of the connected devices has the same IP address. Provided to your
router by your ISP.
2. Private IP Addresses:
 A private IP address is a unique IP number assigned to every device that
connects to your home internet network, which includes devices like
computers, tablets, smartphones, which is used in your household.
 It also likely includes all types of Bluetooth devices you use, like printers or
printers, smart devices like TV, etc.

24
 …cont.
3. Dynamic IP address:
 Dynamic IP addresses always keep changing.
 It is temporary and are allocated to a device every time it connects to the web.
Dynamic IPs can trace their origin to a collection of IP addresses that are
shared across many computers.
 Dynamic IP addresses are another important type of internet protocol
addresses. It is active for a specific amount of time; after that, it will expire.
4. Static IP Addresses:
 A static IP address is an IP address that cannot be changed. In contrast, a
dynamic IP address will be assigned by a Dynamic Host Configuration Protocol
(DHCP) server, which is subject to change.
 Static IP address never changes, but it can be altered as part of routine
network administration.
 Static IP addresses are consistent, which is assigned once, that stays the
same over the years.
25

 This type of IP also helps you procure a lot of information about a device.
 Functions of Network Layer:
 Internetworking: An internetworking is the main responsibility of
the network layer. It provides a logical connection between
different devices.
 Addressing: A Network layer adds the source and destination
address to the header of the frame. Addressing is used to identify
the device on the internet.
 Routing: Routing is the major component of the network layer,
and it determines the best optimal path out of the multiple paths
from source to the destination.
 Packetizing: A Network Layer receives the packets from the
upper layer and converts them into packets. This process is
known as Packetizing. It is achieved by internet protocol (IP).
26
 Transport Layer
 The Transport layer is a Layer 4 ensures that messages are
transmitted in the order in which they are sent and there is no
duplication of data.
 It provides reliable message delivery from process to process.
 The main responsibility of the transport layer is to transfer the
data completely.
 It receives the data from the upper layer and converts them into
smaller units known as segments.
 This layer can be termed as an end-to-end layer as it provides a
point-to-point connection between source and destination to
deliver the data reliably.

27
The two protocols used in this layer are:
 Transmission Control Protocol
–It is a standard protocol that allows the systems to
communicate over the internet.
–It establishes and maintains a connection between hosts.
–When data is sent over the TCP connection, then the TCP
protocol divides the data into smaller units known as
segments.
–Each segment travels over the internet using multiple routes,
and they arrive in different orders at the destination.
–The transmission control protocol reorders the packets in the
correct order at the receiving end.
28
 User Datagram Protocol
–User Datagram Protocol is a transport layer protocol.
–It is an unreliable transport protocol as in this case
receiver does not send any acknowledgment when
the packet is received, the sender does not wait for
any acknowledgment.
–Therefore, this makes a protocol unreliable.

29
 Functions of Transport Layer:
 Service-point addressing: Computers run several programs simultaneously
due to this reason, the transmission of data from source to the destination not
only from one computer to another computer but also from one process to
another process.
 The transport layer adds the header that contains the address known as a
service-point address or port address.
 The responsibility of the network layer is to transmit the data from one
computer to another computer and the responsibility of the transport layer is to
transmit the message to the correct process.
 Segmentation and reassembly: When the transport layer receives the
message from the upper layer, it divides the message into multiple segments,
and each segment is assigned with a sequence number that uniquely
identifies each segment.
 When the message has arrived at the destination, then the transport layer
reassembles the message based on their sequence numbers. 30
 …cont.
 Connection control: Transport layer provides two services Connection-
oriented service and connectionless service.
 A connectionless service treats each segment as an individual packet, and
they all travel in different routes to reach the destination.
 A connection-oriented service makes a connection with the transport layer at
the destination machine before delivering the packets.
 In connection-oriented service, all the packets travel in the single route.
 Flow control: The transport layer also responsible for flow control but it is
performed end-to-end rather than across a single link.
 Error control: The transport layer is also responsible for Error control.
 Error control is performed end-to-end rather than across the single link.
 The sender transport layer ensures that message reach at the destination
without any error.

31
5. Session Layer

 Itis a layer 5 in the OSI model.

 The Session layer is used to establish, manage,
maintain, terminate and synchronizes the
interaction between communicating devices.

32
 Functions of Session layer:
 Dialog control: Session layer acts as a dialog controller that creates a dialog
between two processes or we can say that it allows the communication
between two processes which can be either half-duplex or full-duplex.
 Synchronization: Session layer adds some checkpoints when transmitting the
data in a sequence.
 If some error occurs in the middle of the transmission of data, then the
transmission will take place again from the checkpoint.
 This process is known as Synchronization and recovery.

33
 6. Presentation Layer
 The Presentation layer is also known as the syntax
layer.
 It is mainly concerned with the syntax and semantics of
the information exchanged between the two systems.
 It is responsible for translation and compression of
encryption for a network.
 This layer is a part of the operating system that converts
the data from one presentation format to another
format.
34
 Functions of Presentation layer:
 Translation: The processes in two systems exchange the
information in the form of character strings, numbers and so on.
 Different computers use different encoding methods, the
presentation layer handles the interoperability between the different
encoding methods.
 It converts the data from sender-dependent format into a common
format and changes the common format into receiver-dependent
format at the receiving end.
 Encryption: Encryption is needed to maintain privacy. It is a process
of converting the sender-transmitted information into another form
and sends the resulting message over the network.
 Compression: Data compression is a process of compressing the
data, i.e., it reduces the number of bits to be transmitted, important in
35
multimedia such as text, audio, video.
 7. Application Layer
 An application layer serves as a window for users and
application processes to access network service.
 Therefore it provides services for the user.
 This layer allows the user to interact with the application.
 It is responsible for handling high-level protocols, handles
issues of representation such as network transparency,
resource allocation, etc.
 An application layer is not an application, but it performs
the application layer functions.

36
 Functions of Application layer:
 File transfer, access, and management (FTAM): An
application layer allows a user to access the files in a
remote computer, to retrieve the files from a computer
and to manage the files in a remote computer.
 Mail services: An application layer provides the facility
for email forwarding and storage.
 Directory services: An application provides the
distributed database sources and is used to provide that
global information about various objects.
37
 TCP/IP MODEL AND PROTOCOLS
 Introduction to Network Protocols
 A protocol is a set of rules that governing communication.
 It is also defines rules and conventions for communication
between network devices/ communicating parties.
 Protocols are sets of rules for message formats and
procedures that allow machines and application programs
to exchange information.
 These rules must be followed by each machine involved in
the communication in order for the receiving host to be
able to understand the message.
38
 Why do we needed this network protocol for:
1. Handling duplicate messages
2. Avoiding buffer overflows
3. Assuring proper message sequencing etc.

39
 Characteristics TCP/IP Model
 Here are the essential characteristics of the TCP/IP protocol:
i. Support for a flexible architecture
ii. Adding more systems to a network is easy.
iii. In TCP/IP, the network remains intact until the source and destination
machines were functioning properly.
iv. TCP is a connection-oriented protocol.
v. TCP offers reliability and ensures that data which arrives out of sequence
should put back into order.
vi. TCP allows you to implement flow control, so the sender never overpowers
a receiver with data.

40
 Advantages of TCP/IP
 Here, are pros/benefits of using the TCP/IP model:
1. It helps you to establish/set up a connection between different types of
computers.
2. It operates independently of the operating system.
3. It supports many routing-protocols.
4. It enables the internetworking between the organizations.
5. TCP/IP model has a highly scalable client-server architecture.
6. It can be operated independently.
7. Supports several routing protocols.
8. It can be used to establish a connection between two computers.

41
 Disadvantages of TCP/IP
 Here, are few drawbacks of using the TCP/IP model:
1. TCP/IP is a complicated model to set up and manage.
2. The shallow/overhead of TCP/IP is higher-than IPX
(Internetwork Packet Exchange).
3. In this, model the transport layer does not guarantee
delivery of packets.
4. Replacing protocol in TCP/IP is not easy.
5. It has no clear separation from its services, interfaces,
and protocols.
42
…cont.
 Computer networking is implemented using the concept of
“layered protocols” and the main reasons for layering include:
 Protocols are fairly complex thus layering makes implementation
more manageable
 Layering provides well defined interfaces between the layers so
that a change in one layer does not affect an adjacent layer
 Layering allows interaction between functionally pared layers in
different locations.
 Network systems communication protocols allow remote
computers to communicate with each other and allow users to
access remote resources, but those for distributed systems
enhance it by bringing in the concept of transparency.
43
TCP/IP MODEL
 The TCP/IP model was developed prior to the OSI model.
 The TCP/IP model is not exactly similar to the OSI model.
 The TCP/IP model consists of five layers:
1. Application layer,
2. Transport layer,
3. Network layer,
4. Data link layer
5. Physical layer.

44
Figure: TCP/IP Model Structure

45
 …cont.
 The first four layers provide physical standards, network
interface, internetworking, and transport functions that
correspond to the first four layers of the OSI model and
these four layers are represented in TCP/IP model by a
single layer called the application layer.
 TCP/IP is a hierarchical protocol made up of interactive
modules, and each of them provides specific functionality.
 Here, hierarchical means that each upper-layer protocol is
supported by two or more lower-level protocols.

46
 1. Network Access 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. 47
 2. 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 :
a) 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. IP has 2 versions:
IPv4 and IPv6. IPv4 is the one that most of the websites are using currently.
But IPv6 is growing as the number of IPv4 addresses are limited in number
when compared to the number of users.
b) ICMP – stands for Internet Control Message Protocol. It is encapsulated
within IP datagrams and is responsible for providing hosts with information
about network problems.
c) 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.
48
 3. Host-to-Host 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.
49
 4. 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.
 Some of the protocols present in this layer are: HTTP,
HTTPS, FTP, TFTP, Telnet, SSH, SMTP, SNMP, NTP,
DNS, DHCP, NFS, X Window, LPD. Have a look
at Protocols in Application Layer for some information about
these protocols.

50
 Other Protocols :
– 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.
– NTP – NTP stands for Network Time Protocol. It is used to synchronize the
clocks on our computer to one standard time source. It is very useful in
situations like bank transactions. Assume the following situation without the
presence of NTP. Suppose you carry out a transaction, where your
computer reads the time at 2:30 PM while the server records it at 2:28 PM.
The server can crash very badly if it’s out of sync. 51
 Functions of TCP/IP layers:
 We have two TCP/IP Layers:
1. Network Access Layer
2. Internet/Network Layer
 Network Access Layer
 A network layer is the lowest layer of the TCP/IP model.
 A network layer is the combination of the Physical layer and Data Link layer
defined in the OSI reference model.
 It defines how the data should be sent physically through the network.
 This layer is mainly responsible for the transmission of the data between two
devices on the same network.
 The functions carried out by this layer are encapsulating the IP datagram into
frames transmitted by the network and mapping of IP addresses into physical
addresses.
 The protocols used by this layer are Ethernet, token ring, FDDI, X.25, frame
relay. 52
 Internet Layer (Network layer)
 An internet layer is the second layer of the TCP/IP model.
 An internet layer is also known as the network layer.
 The main responsibility of the internet layer is to send the
packets from any network, and they arrive at the destination
irrespective of the route they take.

53
Other Protocols used in layers:
 IP Protocol:
 IP protocol is used in this layer, and it is the most significant part of the entire
TCP/IP suite.
 Following are the responsibilities of this protocol:
 IP Addressing: This protocol implements logical host addresses known as IP
addresses.
 The IP addresses are used by the internet and higher layers to identify the
device and to provide internetwork routing.
 Host-to-host communication: It determines the path through which the data
is to be transmitted.
 Data Encapsulation and Formatting: An IP protocol accepts the data from
the transport layer protocol.
 An IP protocol ensures that the data is sent and received securely, it
encapsulates the data into message known as IP datagram.
54
 …cont.
 Fragmentation and Reassembly: The limit imposed on the size of the
IP datagram by data link layer protocol is known as Maximum
Transmission unit (MTU).
 If the size of IP datagram is greater than the MTU unit, then the IP
protocol splits the datagram into smaller units so that they can travel over
the local network.
 Fragmentation can be done by the sender or intermediate router. At the
receiver side, all the fragments are reassembled to form an original
message.
 Routing: When IP datagram is sent over the same local network such as
LAN, MAN, WAN, it is known as direct delivery.
 When source and destination are on the distant network, then the IP
datagram is sent indirectly.
 This can be accomplished by routing the IP datagram through various
55
devices such as routers.
 Address Resolution Protocol (ARP)
 ARP is a network layer protocol which is used to find the physical address
from the IP address.
 The two terms are mainly associated with the ARP Protocol:
–ARP request: When a sender wants to know the physical
address of the device, it broadcasts the ARP request to the
network.
–ARP reply: Every device attached to the network will accept
the ARP request and process the request, but only recipient
recognize the IP address and sends back its physical address
in the form of ARP reply.
– The recipient adds the physical address both to its cache
memory and to the datagram header
56
Internet Control Message Protocol (ICMP)
 It is a mechanism used by the hosts or routers to send notifications regarding
datagram problems back to the sender.
 A datagram travels from router-to-router until it reaches its destination. If a
router is unable to route the data because of some unusual conditions such as
disabled links, a device is on fire or network congestion, then the ICMP
protocol is used to inform the sender that the datagram is undeliverable.
 An ICMP protocol mainly uses two terms:
– ICMP Test: ICMP Test is used to test whether the destination is reachable or not.
– ICMP Reply: ICMP Reply is used to check whether the destination device is
responding or not.
 The core responsibility of the ICMP protocol is to report the problems, not
correct them. The responsibility of the correction lies with the sender.
 ICMP can send the messages only to the source, but not to the intermediate
routers because the IP datagram carries the addresses of the source and
destination but not of the router that it is passed to.
57
User Datagram Protocol (UDP)
– It provides connectionless service and end-to-end delivery of transmission.
– It is an unreliable protocol as it discovers the errors but not specify the error.
– User Datagram Protocol discovers the error, and ICMP protocol reports the error to
the sender that user datagram has been damaged.
– UDP consists of the following fields:
 Source port address: The source port address is the address of the
application program that has created the message.
 Destination port address: The destination port address is the address of
the application program that receives the message.
 Total length: It defines the total number of bytes of the user datagram in
bytes.
 Checksum: The checksum is a 16-bit field used in error detection.
– UDP does not specify which packet is lost. UDP contains only checksum; it does not
contain any ID of a data segment.
58
 Transmission Control Protocol (TCP)
 It provides a full transport layer services to applications.
 It creates a virtual circuit between the sender and receiver, and it is active for
the duration of the transmission.
 TCP is a reliable protocol as it detects the error and retransmits the damaged
frames.
 Therefore, it ensures all the segments must be received and acknowledged
before the transmission is considered to be completed and a virtual circuit is
discarded.
 At the sending end, TCP divides the whole message into smaller units known
as segment, and each segment contains a sequence number which is
required for reordering the frames to form an original message.
 At the receiving end, TCP collects all the segments and reorders them based
on sequence numbers.

59
File Transfer Protocol (FTP).

–FTP is a standard internet protocol used for transmitting

the files from one computer to another computer.

60
 Hypertext Transfer Protocol (HTTP).
 This protocol allows us to access the data over the world wide
web.
 It transfers the data in the form of plain text, audio, video.
 It is known as a Hypertext transfer protocol as it has the
efficiency to use in a hypertext environment where there are
rapid jumps from one document to another.

61
 Simple Network Management Protocol (SNMP).

 Itis a framework used for managing the devices on the internet

by using the TCP/IP protocol suite.

62
Simple Mail Transfer Protocol (SMTP).
–The TCP/IP protocol that supports the e-mail is known as a
Simple mail transfer protocol.
–This protocol is used to send the data to another e-mail
address.

63
 Domain Name System (DNS).
 An IP address is used to identify the connection of a host to the
internet uniquely.
 But, people prefer to use the names instead of addresses.
 Therefore, the system that maps the name to the address is
known as Domain Name System.

64
 TELNET
 It is an abbreviation for Terminal Network.
 This is the internet standard protocols for remote login.
 It usually runs on top of TCP and IP.
 It establishes the connection between the local computer
and remote computer in such a way that the local terminal
appears to be a terminal at the remote system.

65
 Reverse Address Resolution Protocol (RARP)
 This
is a protocol a device uses when it does not know its own IP
address.

66
 ETHERNET
 Ethernet is a widely deployed LAN technology set of protocols which
serves the physical and data-link layers which utilizes a linear bus or star
topology.
 This technology was invented by Bob Metcalfe and D.R. Boggs in the
year 1970.
 It was standardized in IEEE 802.3 in 1980.
 Ethernet shares media.
 Network which uses shared media has high probability of data collision.
 Ethernet uses Carrier Sense Multi Access/Collision Detection (CSMA/CD)
technology to detect collisions.
 On the occurrence of collision in Ethernet, all its hosts roll back, wait for
some random amount of time, and then re-transmit the data.
 Ethernet connector is network interface card equipped with 48-bits MAC
address.
 This helps other Ethernet devices to identify and communicate with
remote devices in Ethernet. 67
 TOKEN RING
 This is a computer networking technology used to build Local
Area Networks (LAN).
 It uses a special three-byte frame called a token that travels
around a logical ring of workstations or servers.
 This token passing is a channel access method providing fair
access for all stations, and eliminating the collisions of
contention-based access methods.

68
 Token Passing Mechanism in Token Ring.
 A token-ring network is a local area network (LAN) topology that
sends data in one direction throughout a specified number of
locations by using a token.
 The token is the symbol of authority for control of the transmission
line.
 This token allows any sending station in the network (ring) to send
data when the token arrives at that location.
 Token Passing- access control method where all the stations are
logically connected to each other in the form of a ring.
 The access of stations to the transmission link is governed by a token.
 A station is allowed to transmit a data packet if and only if it possess
the token otherwise not.
 Each station passes the token to its neighboring station either
69

clockwise or anti-clockwise.
 Differences between the OSI and TCP/IP model:
OSI Model TCP/IP Model

It is developed by ARPANET (Advanced Research Project

It is developed by ISO (International Standard Organization)
Agency Network).

OSI model provides a clear distinction between interfaces, TCP/IP doesn’t have any clear distinguishing points between
services, and protocols. services, interfaces, and protocols.

OSI refers to Open Systems Interconnection. TCP refers to Transmission Control Protocol.

OSI uses the network layer to define routing standards and

TCP/IP uses only the Internet layer.
protocols.

OSI follows a vertical approach. TCP/IP follows a horizontal approach.

OSI layers have seven layers. TCP/IP has four layers.

In the OSI model, the transport layer is only connection- A layer of the TCP/IP model is both connection-oriented and
oriented. connectionless.

In the OSI model, the data link layer and physical are separate In TCP, physical and data link are both combined as a single
layers. host-to-network layer.

Session and presentation layers are a part of the OSI model. There is no session and presentation layer in the TCP model.

It is defined after the advent of the Internet. It is defined before the advent of the internet.
70
The minimum size of the OSI header is 5 bytes. The minimum header size is 20 bytes.