OSI and TCP Reference Models

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23 Οκτ 2013 (πριν από 3 χρόνια και 9 μήνες)

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OSI and TCP Reference Models

RD
-
CSY1017

1


To understand


Basic definitions



Protocol



Application


Understand communication process using
Reference models


OSI Reference Model



TCP/IP
-

Internet Model


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CSY1017

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A
network protocol

defines the



format
and the
order

of messages


exchanged between two or more
communicating entities, as well as the



actions

taken on the transmission
and/or receipt of a message or other
event
s
.

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CSY1017

3

mail

server

user

agent

user

agent

user

agent

mail

server

user

agent

user

agent

mail

server

user

agent

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CSY1017

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Messages
format

and
order


From a client to a mail server


HELO


MAIL FROM: <address>


RCPT TO: <address>


DATA

<This is the text end with a
line with a single .>


QUIT


From a mail server to a client


status code


1xx
-

Informative message


2xx
-

Command ok


3xx
-

Command ok so far, send the rest of
it.


4xx
-

Command was correct, but couldn't
be performed for some reason.


5xx
-

Command unimplemented, or
incorrect, or a serious program error
occurred.


content

user mailbox

outgoing

message queue

mail

server

user

agent

user

agent

user

agent

mail

server

user

agent

user

agent

mail

server

user

agent

SMTP

SMTP

SMTP

POP3,

IMAP

SMTP

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-
CSY1017

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RD
-
CSY1017


Network Applications
are
Programs

that

run on different end
systems and
communicate over
a network.


applicati
on

transpor
t

network

data link

physical

applicati
on

transpor
t

network

data link

physical

applicati
on

transpor
t

network

data link

physical

7

Number of Hosts on the
Internet:

Aug. 1981
213

Oct. 1984

1,024

Dec. 1987 28,174

Oct. 1990 313,000

Jul. 1993 1,776,000

Jul. 1996 19,540,000

Jul.

1999


56
,
218
,000

Jul. 200
4

285,139,
000

Jul. 2005 353,284,
000

Jul. 2007 489,774,000

Jul. 2008 570,937,000

Jan. 2009 625,226,000

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CSY1017

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All standards of the Internet are published as
RFC (Request for Comments)


e.g., the SMTP protocol is specified in RFC821




A typical (but not the only) way of standardization:



Internet draft



RFC



proposed standard



draft standard (requires 2 working implementations)



Internet standard (declared by Internet Architecture Board)

We reject: kings, presidents, and voting. We believe in: rough
consensus and running code.




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CSY1017

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CSY1017



Why need standards?


The use of standards in protocols ensures that
products from different manufacturers can work
together


Do you know of name of a standards body for :


food industry


FSA


Computer Science and Engineering



IEEE


And many others


10


The problem of moving information
between computers over a network
medium is divided into smaller and
more manageable problems


This separation into smaller more
manageable functions is known as
layering.


Two Reference Models:



OSI
-
7 Layer Model


TCP/IP Model



Also known as the Internet model



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CSY1017

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CSY1017

여보세요


She is
saying
hello

Ambassador
in Korea

Translator

Secretary

The Korean
ambassador said
“Hello”

Bonjour!

Ambassador
in France

Translator

Secretary

12

RD
-
CSY1017


A
standard

reference

model
called
OSI (Open Systems
Interconnect )
is now considered
the primary Architectural model
for inter
-
computer
communications


The OSI model divides the
networking process into

seven

layers.


Each layer in the model has a
unique function in the
communication process and
communicates with the layer
directly above and below it.


OSI Model

Application


Presentation

Session

Transport


Network


Data Link

Physical

13

RD
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CSY1017



Information passed from
source to destination has to
pass through each layer on
each side.



Which layer does the user
interact with:



Application or Physical ?


Which layers are connected
by a cable?







14



Phrase to remember 7 layers is:

A
ll
P
eople
S
eem
T
o
N
eed
D
ata
P
rocessing



What is a protocol?



Examples of some network applications?



Need for standardisation?



Example of a standard?


How many layers in OSI model?

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CSY1017

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Physical Layer



Media



Topology



Making Cables


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CSY1017

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