The OSI reference Model. - WordPress.com

mustardpruneNetworking and Communications

Oct 23, 2013 (3 years and 9 months ago)

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Reference Model

1

Layered network


Why network are layered ?!


-
Easy to change

-
Easy to troubleshoot

-
Give general idea of each layer


2



OSI

Reference Model



Reference Model


3

TCP/IP

OSI


History :

-
Developed By ISO (international standard
organization)

-
OSI shortened from ( open system Inter
connection)

-
OSI has 7 layers and there were principle to arrive
to these seven layers

1)
-

layers should be created where different
abstraction is needed.

2) Each layer should perform specific function.

4

OSI (cont)


3) The function of each layer should defined
looking to protocol.

4) Minimize information flow

5) Not too small not too large

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Figure 1
-
20:

The OSI reference Model.

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Physical layer


Where the actual connection happens

7

Data link layer



Transform row data into data frames and send
it to receiver and the receiver will send
acknowledgment frame .


Flow control .

8

Network Layer



Routing packets from source to destination


Control congestion.


Solve problems of addressing.

9

Transport Laye
r


Accept data from above split it up into smaller
units pass these to network layer and ensure
all these pieces arrives correctly to other end.


Error free point
-
to
-
point connection


End


to


end layer

10

Session layer


Start or establish the connection between
users of different machines ,


and it offers:

1
-
dialog control.

2
-
token management.

3
-
syncronization.

11

Presentation layer


Concerned with data presentation.

12

The application layer



Contains protocol needed by users :


HTTP _ SMTP _ FTP

13

TCP/IP

History:

ARPANET “research network sponsored by
D.O.D to connect universities and
governments institution using leased
telephone line .

What led's to producing TCP/IP ?

14

TCP/IP has 4 Layers

Figure 1
-
21:

The TCP/IP reference Model.

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1) Internet layer


-
Deliver packet to desired destination.

-
Defining official packet format and
protocol called (IP)“internet protocol”.


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2)Transport Layer

Main job to allow peer entities in source and
destination to carry on conversation.

has two protocols:

1) TCP _ transmission control protocol.

-
Reliable connection oriented protocol

-
Flow control

2)UDP _ User Datagram Protocol

-

Unreliable connection protocol.

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The application layer



Contains protocol needed by users :


HTTP _ SMTP _ FTP

18

Host_To_Network



Main job to connect host to network.


Rarely discussed on TCP/IP papers.


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Comparison Between OSI and TCP/IP


Similarities

-

both based on concept of stack of
independent protocols.

-

layers in both models have the same
function.

20

Comparison Between OSI and TCP/IP


Differences

1)there are Three concepts that are centralized

to OSI Model:

1
-

services

2
-

interfaces

3
-

protocols

2)number of layers.

3)Connectionless and connection oriented

21

Critique of OSI Model and protocols


1.Bad timing .

2.Bad technology.

3.Bad implementation.

4.Bad politics.

22

Figure 1
-
23: The apocalypse of the two elephants

Bad Timing


23

Critique of TCP/IP reference model



First:
does not distinguish between
services interface and protocol.


Second:

it is not all general.


Third:
host to network layer .


Fourth:

physical and data link layer .


Last:

many other protocol were ad hoc.


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