OSI and TCP/IP Layering Models

prunelimitNetworking and Communications

Oct 23, 2013 (3 years and 10 months ago)

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OSI and TCP/IP Layering Models

Presentation slides for the course


CSE 323


Computer Networks




by
Mohammad Mamun Elahi


Assistant Professor

Department of Computer Science and Engineering

United International University

mmelahi@uiu.ac.bd


The OSI Reference Model (contd.)

In the late 1970s, to promote the compatibility of network

designs, the
International Organization for Standardization

(ISO)

proposed an architecture model called the open

systems
interconnection references model (OSI model).

layer N


layer N
-
1

layer N


layer N
-
1

PDUs (protocol data unit)

actual data flow on the lowest level

services

2

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The OSI Reference Model (contd.)

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The OSI Reference Model (contd.)

application

application

presentation

session

transport

network

data link

physical

7

6

5

4

3

2

1

transmission of bits

transmission of packets on one given link

end
-
to
-
end transmission of packets

end
-
to
-
end delivery of messages

setup and management of end
-
to
-
end conversation

formatting, encryption, and compression

network services (email, file transfer)

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The OSI Reference Model (contd.)

application

application

presentation

session

transport

network

data link

physical

7

6

5

4

3

2

1

Encapsulation

data

data

AH

data

AH

PH

data

AH

PH

SH

data

AH

PH

SH

TH

data

AH

PH

SH

TH

NH

data

AH

PH

SH

TH

NH

bit streams

DT

H: header

T: trail

Each may be empty.

DH

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The TCP/IP Reference Model

(Transmission Control
Protocol/Internet Protocol)

The TCP/IP Reference Model

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The TCP/IP Reference Model (contd.)

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Application Layer

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Transport Layer


Five basic services



Segmenting upper
-
layer application data



Establishing end
-
to
-
end operations



Sending segments from one end host to another end host



Ensuring data reliability



Providing flow control

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Process A

Process B

Internet Layer


The purpose of the Internet layer is to select the best path through the
network for packets to travel.


IP performs the following operations:


Defines a packet and an addressing scheme


Transfers data between the Internet layer and network access layers


Routes packets to remote hosts

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Network Access


The
network access layer
is also called the
host
-
to
-
network

layer.


Concerned with all of the issues that an IP packet requires to actually
make a physical link to the network media.


Network access layer functions include
mapping IP addresses to physical
hardware addresses

and
encapsulation of IP packets into frames
.

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Comparison: OSI and TCP/IP Model


Similarities of the OSI and TCP/IP models:


Both have layers


Both have application layers, though they include different services


Both have comparable transport and network layers


Packet
-
switched, not circuit
-
switched, technology is assumed


Networking professionals need to know both models



Differences of the OSI and TCP/IP models:


TCP/IP combines the presentation and session layer into its
application layer


TCP/IP combines the OSI data link and physical layers into 1 layer


TCP/IP appears simpler because it has fewer layers


TCP/IP transport layer using UDP does not always guarantee
reliable delivery of packets as transport layer in the OSI model does

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Comparison: OSI and TCP/IP Model (contd.)

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Questions????

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