The document discusses reference models and the OSI reference model. It provides background on the need for a reference model to standardize network communication and promote interoperability between different network implementations. It then describes the key aspects of the OSI reference model, which divides communication problems into seven layers - physical, data link, network, transport, session, presentation and application layer. The OSI model was created in 1984 and became an international standard to ensure greater network compatibility.

1. REFERENCE
MODELS

2. • Over the past couple of decades many of the networks
that were built used different hardware and software
implementations, as a result they were incompatible and it
became difficult for networks using different specifications
to communicate with each other.
• To address the problem of networks being incompatible
and unable to communicate with each other, the
International Organisation for Standardisation (ISO)
researched various network schemes.
• The ISO recognised there was a need to create a
NETWORK MODEL that would help vendors create
interoperable network implementations.

3. • A reference model is a conceptual layout that
describes how communication between devices
should occur. A reference model has many
advantages such as it defines standards for
building network components thereby permitting
multiple-vendor development and also defines
which functions should be performed at each
layer of the model thereby promoting the
standardization of network.

4. • In 1984 in order to aid network interconnection without
necessarily requiring complete redesign, the Open Systems
Interconnection (OSI) reference model was approved as an
international standard for communications architecture.
• The Open Systems Interconnection (OSI) reference model is a
descriptive network scheme. It ensures greater compatibility
and interoperability between various types of network
technologies.
• The OSI model describes how information or data makes its
way from application programmes (such as spreadsheets)
through a network medium (such as wire) to another
application programme located on another network.
• The OSI reference model divides the problem of moving
information between computers over a network medium into
SEVEN smaller and more manageable problems.

5. In 1983, Day and Zimmerman laid down certain principles that were
applied to arrive at the seven layers can be briefly summarized as
follows:
 A layer should be created where a different abstraction is needed.
 Each layer should perform a well-defined function.
 The function of each layer should be chosen with an eye toward
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 and
small enough that the architecture does not become unwieldy

8. 8

9. Layer 5
Layer 6
Layer 7 Application
Presentation
Session
Application
DATA
DATA
Format
When to start
Signaling
9
Mukesh Chinta, Asst Prof, CSE

10. Transport
Network
Data Link
Physical
Layer 1
Layer 2
Layer 3
Layer 4 Reliability
0101
0101
Data transmission
at the node interval
Routing
Physical connection

11. 11
Provides physical interface for transmission of
information.
Defines rules by which bits are passed from one
system to another on a physical communication
medium.
Covers all - mechanical, electrical, functional and
procedural - aspects for physical communication.
Such characteristics as voltage levels, timing of
voltage changes, physical data rates, maximum
transmission distances, physical connectors, and
other similar attributes are defined by physical layer
specifications.

12. The physical layer is responsible for movements of
individual bits from one hop (node) to the next.
12

13. Data link layer attempts to provide reliable
communication over the physical layer interface.
Breaks the outgoing data into frames and reassemble
the received frames.
Create and detect frame boundaries.
Handle errors by implementing an acknowledgement
and retransmission scheme.
Implement flow control.
Supports point-to-point as well as broadcast
communication.
A special sublayer Medium access control sublayer
deals with the problem of access control of shared
channel.
13

14. The data link layer is responsible for moving
frames from one hop (node) to the next.
14

15. 15

16. 16
Implements routing of frames (packets) through the
network.
Defines the most optimum path the packet should take
from the source to the destination
Defines logical addressing so that any endpoint can be
identified.
Handles congestion and Quality of service issues in the
network.
Facilitates interconnection between heterogeneous
networks (Internetworking).
The network layer also defines how to fragment a
packet into smaller packets to accommodate different
media.
In broadcast networks, the network layer is
thin(nonexistent)

17. The network layer is responsible for the
delivery of individual packets from
the source host to the destination host.

19. 19
Purpose of this layer is to provide a reliable
mechanism for the exchange of data between two
processes in different computers.
Accepts data from above, split into smaller units in
needed
Ensures that the data units are delivered error free.
Ensures that data units are delivered in sequence.
Ensures that there is no loss or duplication of data
units.
Provides connectionless or connection oriented
service.
Provides for the connection management.
Multiplex multiple connection over a single channel.

20. The transport layer is responsible for the delivery
of a message from one process to another.

22. 22
Session layer provides mechanism for controlling the dialogue
between the two end systems. It defines how to start, control
and end conversations (called sessions) between applications.
This layer requests for a logical connection to be established
on an end-user’s request. Responsible for maintenance and
termination of sessions.
Token Management: Prevents two parties from attempting the
same critical operation simulatenously.
This layer provides services like dialogue discipline which can
be full duplex or half duplex: dialog control
Session layer can also provide check-pointing mechanism
such that if a failure of some sort occurs between checkpoints,
all data can be retransmitted from the last checkpoint:
Synchronization.

23. The session layer is responsible for dialog
control and synchronization.

24. 24
Presentation layer defines the format in which the data is to be
exchanged between the two communicating entities. It deals
with syntax and semantics of the information transmitted.
Also handles data compression and data encryption
(cryptography).
Responsible for protocol conversion, character conversions,
data encryption / decryption, expanding graphics commands
and data compression

25. • Used for applications specially written to run over the network
• Allows access to network services that support applications
• Directly represents the services that directly support user
applications (e.g., file transfer and email)
• What the user sees or does
• Contains a variety of protocols that are commonly needed by
users
25

26. The application layer is responsible for
providing services to the user.

27. End
System
Intermediate
Systems

29. 29

30. 30

31. 31

32. 32

33. Meet the Protocol Family in
the Internet
DNS
IP QoS
Winsock SMTP
NTCIP POP3
SLIP
tester
developer
administrator
OSPF
BGP
RTP
WWW

34.  TCP/IP originated out of the investigative research into networking
protocols that the US Department of Defense (DoD) initiated in 1969.
In 1968, the DoD Advanced Research Projects Agency (ARPA) began
researching the network technology that is called packet switching.
 The network that was initially constructed as a result of this research
to provide a communication that could function in wartime., then
called ARPANET, gradually became known as the Internet. The TCP/IP
protocols played an important role in the development of the
Internet. In the early 1980s, the TCP/IP protocols were developed. In
1983, they became standard protocols for ARPANET.
 Because of the history of the TCP/IP protocol suite, it's often referred
to as the DoD protocol suite or the Internet protocol suite 34

35. 35
The Internet Protocol Suite (commonly known
as TCP/IP) is the set of communications
protocols used for the Internet and other similar
networks.
It is named from two of the most important protocols
in it:
the Transmission Control Protocol (TCP)
The Internet Protocol (IP), which were the first two
networking protocols defined in this standard.

36. 36

37. TCP/IP Network
Architecture
Application Layer
Transport Layer
Network Layer
Link Layer
operating-system/computer-architecture independent
LAN/MAN/WAN applicable
physical-medium independent
host host
network network
media media
process process
client-server model

38. TCP/IP Protocol Suite
Ethernet
ARP RARP
IPv4 IPv6
TCP UDP
ICMP
Telnet
FTP
ping SNMP TFTP
Serial line
PPP
SMTP POP3
21 23 110
25 69
161
port
number
IP
address

39. TCPIP Protocol Suite
39

40.  The internet layer is the linchpin that holds the whole architecture
together. Its job is to permit hosts to inject packets into any network
and have them travel independently to the destination (potentially on
a different network).
 Internet Protocol (IP) is the most important protocol in this layer. It
is a connectionless protocol and does not provide reliability, flow
control, or error recovery. IP provides a routing function that
attempts to deliver transmitted messages to their destination.
 A message unit in an IP network is called an IP datagram. This is
the basic unit of information transmitted across TCP/IP networks.
 Other internetwork-layer protocols are ICMP {Internet Control
Message Protocol}, IGMP {Internet Group Management Protocol},
ARP {Address Resolution Protocol}, and RARP {Reverse ARP}.
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41.  Transport layer (host-to-host) is designed to allow peer entities on the
source and destination hosts to carry on a conversation, just as in the OSI
transport layer. Two end-to-end transport protocols namely TCP
{Transmission Control Protocol} and UDP {User Datagram Protocol}
have been defined.
 TCP is a reliable connection-oriented protocol that permits a byte stream
originating on one machine to be transported without error on any
machine in the internet. It divides the incoming byte stream into discrete
message and passes each one onto the internet layer. It reassembles
these messages at the receiver. It also handles flow control.
 UDP is an unreliable, connectionless protocol for applications that do not
want TCP's sequencing or flow control and wish to provide their own. It is
also widely used for one-shot, client-server-type request-reply queries
and applications in which prompt delivery is more important than
accurate delivery, such as transmitting speech or video.
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42. 42
 The network interface layer, also called the link layer or the
data-link layer, is the interface to the actual network hardware. This
interface may or may not provide reliable delivery, and may be
packet or stream oriented. In fact, TCP/IP does not specify any
protocol here, but can use almost any network interface available,
which illustrates the flexibility of the IP layer.
 Examples are IEEE 802.2, X.25, ATM, FDDI, and even SNA.
 It varies from implementation to implementation with vendors
supplying their own version

43. • The Application layer is equivalent to the combined OSI session,
presentation and Application Layers.
• All the functions handled by these 3 layers in the OSI model are handled by
the Application layer in TCP/IP model.
• It provides a way for applications to have access to networked services.
• The Application Layer has the responsibility for authentication, data
compression, and end-user services such as terminal emulation, file transfer,
e-mail, web browsing/serving, and other network control and management
services. An application header and following data are packaged as a
message
• Application layer is present on the top of the Transport layer. It includes all
the higher-level protocols which are virtual terminal (TELNET), file
transfer (FTP), electronic mail (SMTP) & HTTP (Hyper Text Transfer
Protocol) 43

44. • IMAP4 - Internet Mail Access Protocol version 4 lets clients access an IMAP4 mail
server to download their e-mail to a local computer program. It works using TCP as
its transport protocol.
• FTP - File Transfer Protocol uses TCP as transport and allows the transfer of files
between two computer systems with login required by the requester.
• Telnet – Sometimes incorrectly called Terminal Emulation across a network, it is
used to remotely open a session on another computer acting as a server. It relies on
TCP for transport.
• SMTP - Simple Mail Transfer Protocol is a TCP-transported application layer
protocol used to send electronic mail.
• HTTP - Hypertext Transfer Protocol uses the TCP transport protocol to carry web
browsing requests to a web server, and web pages from web servers to web
browsers.
• POP3 - Post Office Protocol version 3 uses TCP as a way to offer clients access to a
POP3 mail server to transfer their e-mail to a local program on their computer.
• BGP4 - Border Gateway Protocol version 4 is a routing protocol most often used
between organizations. Two routers using BGP will establish a TCP connection to
send each other their BGP routing tables. In that exchange is information about
reachable networks including the full path to all BGP-known networks. 44

45. • DNS3 - Domain Names System provides the ability to refer to IP devices
using names instead of numerical IP addresses. It lets Domain Name Servers
resolve these names to their corresponding IP addresses.
• DHCP - Dynamic Host Configuration Protocol uses UDP as its transport
protocol to dynamically and automatically assign IP addresses and other
networking configuration information to computers starting up on a given
network.
• TFTP - Trivial File Transfer Protocol is a UDP-transported protocol that
allows file transfer between two computers with no login or user required for
its limited use.
• SNMP - Simple Network Management Protocol is used to manage all types of
network elements based on various data sent and received using UDP as its
transport protocol.
• RIP2 - Routing Information Protocol is an internal routing protocol used to
dynamically update router tables on internal organization networks. It uses
UDP as its transport protocol.
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46. • ARP - Address Resolution Protocol supports the packaging of IP data into
Ethernet frames. It finds the local Ethernet (MAC) address that matches a
specific local IP address.
• ICMP4 - Internet Control Message Protocol provides diagnostics and logical
error reporting to help manage the sending of data between computers. Its
best-known function is ping.
• IGMP - Internet Group Management Protocol supports multicasting by
letting multicast routers track group memberships on each of its connected
networks.
• IPsec - Internet Protocol Security is an end-to-end security scheme for
securing Internet Protocol (IP) communications by authenticating and
encrypting each IP packet of a communication session.
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47. • IP4 - Internet Protocol provides connectionless communication support
for all protocols’ data, except ARP, by packaging that data into an IP
datagram.
• OSPF - Open Shortest Path First is an internal routing protocol for use
inside an organization. It checks the function of its link to each of its
neighbor OSPF routers. Then, it sends the acquired routing information to
those neighbor routers.
• EIGRP - Enhanced Interior Gateway Routing Protocol is a local routing
protocol that is proprietary to Cisco. It is an advanced distance-vector
routing protocol that shares internal organizational routing information
found in three tables.
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48. • The application layer in TCP/IP handles the responsibilities of multiple
layers in the OSI model.
• The OSI model numbers and names its layers, whereas the TCP/IP stack
only names the layers.
• Unlike the transport layer in OSI, TCP/IP only guarantees reliable delivery
of packets when TCP is the chosen protocol.
• OSI has much more complexity in its 7 layers than TCP/IP has in its 4
layers.
• In TCP/IP, protocols are deliberately designed to have more layer
flexibility than the strict layers of the OSI model.
• TCP/IP functions are implemented, then standardized. OSI is standardized
in concept only, though some functions work.
• OSI has more limited Network Management and Network Security.
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