Comparison between OSI and TCp.for students in Information Technology ppt

Good Notes on Comparison between OSI and TCP for students in Information Technology

1. Comparison and Comparison and
Contrast between the Contrast between the
OSI and TCP/IP ModelOSI and TCP/IP Model

2. IntroductionIntroduction

This presentation would discuss some This presentation would discuss some
comparison and contrast between the 2 comparison and contrast between the 2
main reference models which uses the main reference models which uses the
concept of protocol layering.concept of protocol layering.

Open System Interconnection Model (OSI)Open System Interconnection Model (OSI)

Transport Control Protocol /Internet Transport Control Protocol /Internet
Protocol (TCP/IP)Protocol (TCP/IP)

3. IntroductionIntroduction

The topics that we will be discussing The topics that we will be discussing
would be based on the diagram would be based on the diagram
below.below.
 
OSI TCP
/ IP
Application
(Layer7)
Application
Presentation
(Layer6)
Session
(Layer 5)
Transport
(Layer 4)
Transport
Network
(Layer 3)
Internet
Data
Link (Layer 2)
Subnet
Physical
(Layer 1)

4. OutlineOutline

Compare the protocol layers that Compare the protocol layers that
correspond to each other. correspond to each other.

General ComparisonGeneral Comparison

Focus of Reliability ControlFocus of Reliability Control

Roles of Host systemRoles of Host system

De-jure vs. De-factoDe-jure vs. De-facto

5. The Upper LayersThe Upper Layers
OSI TCP
/ IP
Application
(Layer7)
Application
Presentation
(Layer6)
Session
(Layer 5)
 

SessionSession

PresentationPresentation

ApplicationApplication

6. The Session LayerThe Session Layer
The Session layer The Session layer permits two parties permits two parties
to hold ongoing communications to hold ongoing communications
called a session across a networkcalled a session across a network..

Not found in TCP/IP modelNot found in TCP/IP model

In TCP/IP,its In TCP/IP,its characteristicscharacteristics are are
provided by the TCP protocol. provided by the TCP protocol.
(Transport Layer)(Transport Layer)

7. The Presentation LayerThe Presentation Layer
The Presentation Layer handles data The Presentation Layer handles data
format information for networked format information for networked
communications. This is done by communications. This is done by
converting data into a generic format that converting data into a generic format that
could be understood by both sides.could be understood by both sides.
Not found in TCP/IP modelNot found in TCP/IP model
In TCP/IP, this function is provided by the In TCP/IP, this function is provided by the
Application Layer. Application Layer.
e.g. e.g. External Data Representation Standard (XDR)External Data Representation Standard (XDR)
Multipurpose Internet Mail ExtensionsMultipurpose Internet Mail Extensions (MIME) (MIME)

8. The Application LayerThe Application Layer
The Application Layer is the top layer of the reference The Application Layer is the top layer of the reference
model. It provides a set of interfaces for applications to model. It provides a set of interfaces for applications to
obtain access to networked services as well as access to the obtain access to networked services as well as access to the
kinds of network services that support applications directly.kinds of network services that support applications directly.
OSIOSI- FTAM,VT,MHS,DS,CMIP- FTAM,VT,MHS,DS,CMIP
TCP/IPTCP/IP - FTP,SMTP,TELNET,DNS,SNMP- FTP,SMTP,TELNET,DNS,SNMP
Although the notion of an application process is common to Although the notion of an application process is common to
both, their approaches to constructing application entities is both, their approaches to constructing application entities is
different.different.

9. Approaches use in constructing Approaches use in constructing
application entitiesapplication entities

The diagram below provides an overall view on The diagram below provides an overall view on
the methods use by both the the methods use by both the OSI and and TCP/IP
model.model.

10. ISO ApproachISO Approach

Sometime called Sometime called Horizontal Approach
OSI asserts that distributed applications operate OSI asserts that distributed applications operate
over a strict hierarchy of layers and are over a strict hierarchy of layers and are
constructed from a common tool kit of constructed from a common tool kit of
standardized application service elements.standardized application service elements.
In OSI, each distributed application service In OSI, each distributed application service
selects functions from a large common “toolbox” selects functions from a large common “toolbox”
of application service element (ASEs) and of application service element (ASEs) and
complements these with application service complements these with application service
elements that perform functions specific to given elements that perform functions specific to given
end-user service .end-user service .

11. TCP/IP ApproachTCP/IP Approach
Sometime called Sometime called Vertical Approach

In TCP/IP, each application entity is composed In TCP/IP, each application entity is composed
of whatever set of function it needs beyond of whatever set of function it needs beyond
end to end transport to support a distributed end to end transport to support a distributed
communications service.communications service.

Most of these application processes builds on Most of these application processes builds on
what it needs and assumes only that an what it needs and assumes only that an
underlying transport mechanism (datagram underlying transport mechanism (datagram
or connection) will be provided. or connection) will be provided.

12. Transport LayerTransport Layer

The functionality of the transport The functionality of the transport
layer is to provide “transparent layer is to provide “transparent
transfer of data from a source end transfer of data from a source end
open system to a destination end open system to a destination end
open system” (ISO / IEC 7498: 1984).open system” (ISO / IEC 7498: 1984).
OSI TCP
/ IP
Transport
(Layer 4)
Transport
(TCP/UDP)

13. Transport LayerTransport Layer

Transport is responsible for creating Transport is responsible for creating
and maintaining the basic end-to-end and maintaining the basic end-to-end
connection between communicating connection between communicating
open systems, ensuring that the bits open systems, ensuring that the bits
delivered to the receiver are the same delivered to the receiver are the same
as the bits transmitted by the sender; as the bits transmitted by the sender;
in the same order and without in the same order and without
modification, loss or duplicationmodification, loss or duplication

14. OSI Transport LayerOSI Transport Layer

It takes the information to be sent and It takes the information to be sent and
breaks it into individual packets that are breaks it into individual packets that are
sent and reassembled into a complete sent and reassembled into a complete
message by the Transport Layer at the message by the Transport Layer at the
receiving nodereceiving node

Also provide a signaling service for the Also provide a signaling service for the
remote node so that the sending node is remote node so that the sending node is
notified when its data is received notified when its data is received
successfully by the receiving nodesuccessfully by the receiving node

15. OSI Transport LayerOSI Transport Layer

Transport Layer protocols include the Transport Layer protocols include the
capability to acknowledge the receipt capability to acknowledge the receipt
of a packet; if no acknowledgement is of a packet; if no acknowledgement is
received, the Transport Layer received, the Transport Layer
protocol can retransmit the packet or protocol can retransmit the packet or
time-out the connection and signal time-out the connection and signal
an erroran error

16. OSI Transport LayerOSI Transport Layer

Transport protocols can also mark packets Transport protocols can also mark packets
with sequencing information so that the with sequencing information so that the
destination system can properly order the destination system can properly order the
packets if they’re received out-of-sequence packets if they’re received out-of-sequence

In addition, Transport protocols provide In addition, Transport protocols provide
facilities for insuring the integrity of facilities for insuring the integrity of
packets and requesting retransmission packets and requesting retransmission
should the packet become garbled when should the packet become garbled when
routed.routed.

17. OSI Transport LayerOSI Transport Layer

Transport protocols provide the Transport protocols provide the
capability for multiple application capability for multiple application
processes to access the network by processes to access the network by
using individual local addresses to using individual local addresses to
determine the destination process for determine the destination process for
each data streameach data stream

18. TCP/IP Transport LayerTCP/IP Transport Layer

Defines two standard transport Defines two standard transport
protocols: TCP and UDPprotocols: TCP and UDP
TCP implements a reliable data-TCP implements a reliable data-
stream protocolstream protocol

connection orientedconnection oriented
UDP implements an unreliable data-UDP implements an unreliable data-
stream stream

connectionlessconnectionless

19. TCP/IP Transport LayerTCP/IP Transport Layer

TCP provides reliable data transmissionTCP provides reliable data transmission

UDP is useful in many applicationsUDP is useful in many applications

eg. Where data needs to be broadcasted or eg. Where data needs to be broadcasted or
multicastedmulticasted

Primary difference is that UDP does not Primary difference is that UDP does not
necessarily provide reliable data necessarily provide reliable data
transmissiontransmission

20. TCP/IP Transport LayerTCP/IP Transport Layer

Many programs will use a separate TCP Many programs will use a separate TCP
connection as well as a UDP connectionconnection as well as a UDP connection

21. TCP/IP Transport LayerTCP/IP Transport Layer

TCP is responsible for data recoveryTCP is responsible for data recovery

by providing a sequence number with by providing a sequence number with
each packet that it sendseach packet that it sends

TCP requires ACK (ackowledgement) TCP requires ACK (ackowledgement)
to ensure correct data is receivedto ensure correct data is received

Packet can be retransmitted if error Packet can be retransmitted if error
detecteddetected

22. TCP/IP Transport LayerTCP/IP Transport Layer

Use of ACKUse of ACK

23. TCP/IP Transport LayerTCP/IP Transport Layer

Flow control with Flow control with WindowWindow

via specifying an acceptable range of via specifying an acceptable range of
sequence numbers sequence numbers

24. TCP/IP Transport LayerTCP/IP Transport Layer

TCP and UDP introduce the concept TCP and UDP introduce the concept
of of portsports

Common ports and the services that Common ports and the services that
run on them: run on them:

FTP FTP 21 and 20 21 and 20

telnet telnet 23 23

SMTP SMTP 25 25

http http 80 80

POP3 POP3 110 110

25. TCP/IP Transport LayerTCP/IP Transport Layer

By specifying ports and including port By specifying ports and including port
numbers with TCP/UDP data, numbers with TCP/UDP data, multiplexingmultiplexing
is achievedis achieved

Multiplexing allows multiple network Multiplexing allows multiple network
connections to take place simultaneouslyconnections to take place simultaneously

The port numbers, along with the source The port numbers, along with the source
and destination addresses for the data, and destination addresses for the data,
determine a determine a socketsocket

26. Comparing Transport for both Comparing Transport for both
ModelsModels
The features of UDP and TCP defined at The features of UDP and TCP defined at
TCP/IP Transport Layer correspond to many TCP/IP Transport Layer correspond to many
of the requirements of the OSI Transport of the requirements of the OSI Transport
Layer. There is a bit of bleed over for Layer. There is a bit of bleed over for
requirements in the session layer of OSI requirements in the session layer of OSI
since sequence numbers, and port values since sequence numbers, and port values
can help to allow the Operating System to can help to allow the Operating System to
keep track of sessions, but most of the TCP keep track of sessions, but most of the TCP
and UDP functions and specifications map to and UDP functions and specifications map to
the OSI Transport Layer.the OSI Transport Layer.

27. Comparing Transport for both Comparing Transport for both
ModelsModels
The TCP/IP and OSI architecture models both The TCP/IP and OSI architecture models both
employ all connection and connectionless employ all connection and connectionless
models at transport layer. However, the models at transport layer. However, the
internet architecture refers to the two models internet architecture refers to the two models
in TCP/IP as simply “connections” and in TCP/IP as simply “connections” and
datagrams. But the OSI reference model, with datagrams. But the OSI reference model, with
its penchant for “precise” terminology, uses its penchant for “precise” terminology, uses
the terms connection-mode and connection-the terms connection-mode and connection-
oriented for the connection model and the oriented for the connection model and the
term connectionless-mode for the term connectionless-mode for the
connectionless model.connectionless model.

28. Network vs. InternetNetwork vs. Internet

Like all the other OSI Layers, the network Like all the other OSI Layers, the network
layer provides both connectionless and layer provides both connectionless and
connection-oriented services. As for the connection-oriented services. As for the
TCP/IP architecture, the internet layer is TCP/IP architecture, the internet layer is
exclusively connectionless.exclusively connectionless.
OSI TCP
/ IP
Network
(Layer 3)
Internet

29. Network vs. InternetNetwork vs. Internet

X.25 Packet Level Protocol – OSI’s X.25 Packet Level Protocol – OSI’s
Connection-oriented Network ProtocolConnection-oriented Network Protocol
The CCITT standard for X.25 defines the DTE/DCE The CCITT standard for X.25 defines the DTE/DCE
interface standard to provide access to a packet-interface standard to provide access to a packet-
switched network. It is the network level interface, switched network. It is the network level interface,
which specifies a virtual circuit (VC) service. A which specifies a virtual circuit (VC) service. A
source host must establish a connection (a VC) source host must establish a connection (a VC)
with the destination host before data transfer can with the destination host before data transfer can
take place. The network attempts to deliver take place. The network attempts to deliver
packets flowing over a VC in sequence.packets flowing over a VC in sequence.

30. Network vs. InternetNetwork vs. Internet
Connectionless Network ServiceConnectionless Network Service

Both OSI and TCP/IP support a connectionless Both OSI and TCP/IP support a connectionless
network service: OSI as an alternative to network network service: OSI as an alternative to network
connections and TCP/IP as the only way in use.connections and TCP/IP as the only way in use.
Internetworking ProtocolsInternetworking Protocols

OSI’s CLNP (ISO/IEC 8473: 1993) is functionally OSI’s CLNP (ISO/IEC 8473: 1993) is functionally
identical to the Internet’s IP (RPC 791). Both CLNP identical to the Internet’s IP (RPC 791). Both CLNP
and IP are best-effort-delivery network protocols. and IP are best-effort-delivery network protocols.
Bit niggling aside, they are virtually identical. The Bit niggling aside, they are virtually identical. The
major difference between the two is that CLNP major difference between the two is that CLNP
accommodates variable-length addresses, whereas accommodates variable-length addresses, whereas
IP supports fixed, 32-bit address. IP supports fixed, 32-bit address.

31. Network vs. InternetNetwork vs. Internet
Internet
(IP) Addresses
Internet
(IP) Addresses

The lnternet network address is more The lnternet network address is more
commonly called the “IP address.” It consists of commonly called the “IP address.” It consists of
32 bits, some of which are allocated to a high-32 bits, some of which are allocated to a high-
order network-numberorder network-number part and the remainder part and the remainder
of which are allocated to a low-order host-of which are allocated to a low-order host-
numbernumber part. The distribution of bits - how part. The distribution of bits - how
many form the network number, and how many form the network number, and how
many are therefore left for the host number - many are therefore left for the host number -
can be done in one of three different ways, can be done in one of three different ways,
giving three different giving three different classes classes of IP address of IP address

32. Network vs. InternetNetwork vs. Internet
OSI
Network Layer Addressing
OSI
Network Layer Addressing

ISO/IEC and CCITT jointly administer the global ISO/IEC and CCITT jointly administer the global
network addressing domain. The initial network addressing domain. The initial
hierarchical decomposition of the NSAP address is hierarchical decomposition of the NSAP address is
defined by (ISO/IEC 8348). The standard specifies defined by (ISO/IEC 8348). The standard specifies
the syntax and the allowable values for the high-the syntax and the allowable values for the high-
order part of the address - the Initial Domain Part order part of the address - the Initial Domain Part
(IDP), which consists of the Authority and Format (IDP), which consists of the Authority and Format
Identifier (AFI) and the Initial Domain Identifier Identifier (AFI) and the Initial Domain Identifier
(IDI) - but specifically eschews constraints on or (IDI) - but specifically eschews constraints on or
recommendations concerning the syntax or recommendations concerning the syntax or
semantics of the domain specific part (DSP).semantics of the domain specific part (DSP).

33. Network vs. InternetNetwork vs. Internet
OSI Routing ArchitectureOSI Routing Architecture

End systems (ESs) and intermediate systems End systems (ESs) and intermediate systems
(ISs) use routing protocols to distribute (ISs) use routing protocols to distribute
(“advertise”) some or all of the information (“advertise”) some or all of the information
stored in their locally maintained routing stored in their locally maintained routing
information base. ESs and ISs send and receive information base. ESs and ISs send and receive
these routing updates and use the information these routing updates and use the information
that they contain (and information that may be that they contain (and information that may be
available from the local environment, such as available from the local environment, such as
information entered manually by an operator) information entered manually by an operator)
to modify their routing information base. to modify their routing information base.

34. Network vs. InternetNetwork vs. Internet
TCP/IP Routing ArchitectureTCP/IP Routing Architecture

The TCP/IP routing architecture looks very much like The TCP/IP routing architecture looks very much like
the OSI routing architecture. Hosts use a discovery the OSI routing architecture. Hosts use a discovery
protocol to obtain the identification of gateways and protocol to obtain the identification of gateways and
other hosts attached to the same network other hosts attached to the same network
(subnetwork). Gateways within autonomous (subnetwork). Gateways within autonomous
systems (routing domains) operate an interior systems (routing domains) operate an interior
gateway protocol (intradomain IS-IS routing gateway protocol (intradomain IS-IS routing
protocol), and between autonomous systems, they protocol), and between autonomous systems, they
operate exterior or border gateway protocols operate exterior or border gateway protocols
(interdomain routing protocols). The details are (interdomain routing protocols). The details are
different but the principles are the same.different but the principles are the same.

35. Data link / Physical vs. Data link / Physical vs.
SubnetSubnet

Data link layerData link layer
The function of the Data Link Layer is “provides for the control of the
physical layer, and detects and possibly corrects errors which may
occur” (IOS/IEC 7498:1984). In another words, the Data Link Layer
transforms a stream of raw bits (0s and 1s) from the physical into a data
frame and provides an error-free transfer from one node to another,
allowing the layers above it to assume virtually error-free transmission
OSI TCP
/ IP
Data
Link (Layer 2)
Subnet
Physical
(Layer 1)
 

36. Data link / Physical vs. Data link / Physical vs.
SubnetSubnet

Physical layerPhysical layer
The function of the Physical Layer is to provide
“mechanical, electrical, functional, and procedural
means to activate a physical connection for bit
transmission” (ISO/IEC 7498:1984). Basically, this
means that the typical role of the physical layer is to
transform bits in a computer system into
electromagnetic (or equivalent) signals for a particular
transmission medium (wire, fiber, ether, etc.)

37. Data link / Physical vs. Data link / Physical vs.
Subnet Subnet

Comparing to TCP/IP Comparing to TCP/IP
These 2 layers of the OSI correspond directly to the subnet layer
of the TCP/IP model.
Majority of the time, the lower layers below the Interface or
Network layer of the TCP/IP model are seldom or rarely
discussed. The TCP/IP model does nothing but to high light the
fact the host has to connect to the network using some protocol so
it can send IP packets over it. Because the protocol used is not
defines, it will vary from host to host and network to network

38. Data link / Physical vs. Data link / Physical vs.
SubnetSubnet

Comparing to TCP/IPComparing to TCP/IP
After much deliberation by organizations, it was
decided that the Network Interface Layer in the TCP/IP
model corresponds to a combination of the OSI Data
Link Layer and network specific functions of the OSI
network layer (eg IEEE 203.3).
Since these two layers deal with functions that are so
inherently specific to each individual networking
technology, the layering principle of grouping them
together related functions is largely irrelevant.

39. General ComparisonGeneral Comparison

Focus of Reliability ControlFocus of Reliability Control

Roles of Host SystemRoles of Host System

De-jure vs. De-factoDe-jure vs. De-facto

40. Focus of Reliability ControlFocus of Reliability Control
Implementation of the OSI model places emphasis on Implementation of the OSI model places emphasis on
providing a reliable data transfer service, while the TCP/IP providing a reliable data transfer service, while the TCP/IP
model treats reliability as an end-to-end problem.model treats reliability as an end-to-end problem.

Each layer of the OSI model detects and handles errors, all Each layer of the OSI model detects and handles errors, all
data transmitted includes checksums. The transport layer data transmitted includes checksums. The transport layer
of the OSI model checks source-to-destination reliability.of the OSI model checks source-to-destination reliability.

In the TCP/IP model, reliability control is concentrated at In the TCP/IP model, reliability control is concentrated at
the transport layer. The transport layer handles all error the transport layer. The transport layer handles all error
detection and recovery. The TCP/IP transport layer uses detection and recovery. The TCP/IP transport layer uses
checksums, acknowledgments, and timeouts to control checksums, acknowledgments, and timeouts to control
transmissions and provides end-to-end verificationtransmissions and provides end-to-end verification..

41. Roles of Host SystemRoles of Host System
Hosts on OSI implementations do not Hosts on OSI implementations do not
handle network operations (simple handle network operations (simple
terminal), but TCP/IP hosts participate terminal), but TCP/IP hosts participate
in most network protocols. TCP/IP hosts in most network protocols. TCP/IP hosts
carry out such functions as end-to-end carry out such functions as end-to-end
verification, routing, and network verification, routing, and network
control. The TCP/IP internet can be control. The TCP/IP internet can be
viewed as a data stream delivery viewed as a data stream delivery
system involving intelligent hosts. system involving intelligent hosts.

42. De-jure vs. De-facto (OSI)De-jure vs. De-facto (OSI)
OSIOSI

Standard legislated by official recognized body. (ISO)Standard legislated by official recognized body. (ISO)

The OSI reference model was devised The OSI reference model was devised before before the protocols were the protocols were
invented. This ordering means that the model was not biased invented. This ordering means that the model was not biased
toward one particular set of protocols, which made it quite toward one particular set of protocols, which made it quite
general. The down side of this ordering is that the designers general. The down side of this ordering is that the designers
did not have much experience with the subject and did not did not have much experience with the subject and did not
have a good idea of which functionality to put in which layer.have a good idea of which functionality to put in which layer.

Being general,the protocols in the OSI model are better hidden Being general,the protocols in the OSI model are better hidden
than in the TCP/IP model and can be replaced relatively easily than in the TCP/IP model and can be replaced relatively easily
as the technology changes.as the technology changes.

Not so widespread as compared with TCP/IP. (complex , costly)Not so widespread as compared with TCP/IP. (complex , costly)

More commonly used as teaching aids.More commonly used as teaching aids.

43. De-jure vs. De-facto (TCP/IP)De-jure vs. De-facto (TCP/IP)

TCP/IPTCP/IP

Standards adopted due to widespread use. (Internet)Standards adopted due to widespread use. (Internet)

The protocols came first, and the model was really just a The protocols came first, and the model was really just a
description of the existing protocols. There was no problem description of the existing protocols. There was no problem
with the protocols fitting the model, but it is hardly possible to with the protocols fitting the model, but it is hardly possible to
be use to describe other modelsbe use to describe other models..

““Get the job done" orientation. Get the job done" orientation.
Over the years it has handled most challenges by growing to Over the years it has handled most challenges by growing to
meet the needs.meet the needs.

More popular standard for internetworking for several reasons :More popular standard for internetworking for several reasons :

relatively simple and robust compared to alternatives such as OSIrelatively simple and robust compared to alternatives such as OSI

available on virtually every hardware and operating system platform (often available on virtually every hardware and operating system platform (often
free)free)

the protocol suite on which the Internet depends. the protocol suite on which the Internet depends.

44. The EndThe End

Project team membersProject team members

ANDREW TAN TENG HONG ANDREW TAN TENG HONG

MAH CHEE MENGMAH CHEE MENG

CHEE YEW WAICHEE YEW WAI

TAN YOKE CHUANTAN YOKE CHUAN

CHEONG KIM MINGCHEONG KIM MING