osi and tcp reference models rd-csy10171. to understand basic definitions protocol application ...
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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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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 events.
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mailserver
useragent
useragent
useragent
mailserver
useragent
useragent
mailserver
useragent
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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
mailserver
useragent
useragent
useragent
mailserver
useragentuser
agent
mailserver
useragent
SMTP
SMTP
SMTP
POP3,IMAPSMTP
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RD-CSY1017
Network Applications are Programs that run on different end systems and communicate over a network.
application
transport
networkdata link
physical
application
transport
networkdata link
physical
application
transport
networkdata link
physical
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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. 2004 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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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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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
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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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RD-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
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RD-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?
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Phrase to remember 7 layers is:All People Seem To Need Data Processing 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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Physical Layer◦ Media◦ Topology◦ Making Cables
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