OSI 7-Layer Reference Model

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

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Computer Crime

Multiple Scene Crimes

Networking Basics

Protocol Stack


Rather than have one network function
do everything necessary to move data,
several protocols operate on the data.
Each fulfills a necessary function.


Since these protocols operate in a
specific order, they are called the
protocol stack.


One comparable protocol can be
substituted for another in the stack.


Networking Basics

Encapsulating Protocols


An encapsulating protocol receives
data from another source and
performs its required duties without
modifying the data; rather, it wraps it in
new commands and sends it down the
stack.


The content of the data is completely
irrelevant to the operation of lower
protocols.


Networking Basics

Analogy


Data Content is like
a letter.


It is intended to
transported and
needs protection
and instructions for
proper delivery.

Networking Basics

Analogy


That data can be
sealed into an
envelope
(encapsulated).


The contents of the
letter are irrelevant
to postage and
addressing.

Networking Basics

Encapsulating Protocols


Further encapsulation is also
possible. The entire message can
be encapsulated by the next
protocol. It doesn’t distinguish
between the original content of
the added instructions from the
last protocol.


OSI 7
-
Layer Reference Model

Open Systems Interconnection

(ISO 35.100)


The International Organization for
Standardization created a model for
network interactions.


It divides network functions into seven
autonomous “layers.”


Function within each layer is
independent, but they work together to
provide network interconnection.

OSI 7
-
Layer Reference Model

OSI, ISO, or IOS?



Because "International Organization
for Standardization" would have
different abbreviations in different
languages:


"IOS" in English


"OIN" in French for
Organisation
internationale de normalisation
).

ISO is Correct


I
t was decided at the outset to use a
word derived from the Greek isos,
meaning "equal".


Therefore, whatever the country,
whatever the language, the short form
of the organization's name is always
ISO.

OSI 7
-
Layer Reference Model

Application

Protocols used by applications to
exchange data

HTTP

SMTP

Presentation

Standardizes data formats to allow
exchange, encryption, and
compression

ASCII

JPEG

Session

Creates and manages communication
sessions between computers

RPC

NetBIOS

Transport

Communication between processes or
programs

TCP

UDP

Network

Delivers information between network
segments

IP

IPX

Data Link

Delivers information within a network
segment

Ethernet

PPP

Physical

Wiring, cabling, and other media that
transmit voltage, light pulses, or radio

Copper

Radio

Fiber

OSI 7
-
Layer Reference Model

OSI 7
-
Layer Reference Model

7

Application Layer


This layer manages communication
between network applications. It is
not the application itself; rather, it is
the protocol used by the application.


For example, a Web browser is a
network application that uses
Hypertext Transfer Protocol
(HTTP)

a layer 7 protocol.

Layer

OSI 7
-
Layer Reference Model

Presentation Layer


This layer organizes data into
standard patterns for decoding.
Thus, the presentation layer is
concerned with the content of the
data exchanged.


The presentation layer can also
compress and/or encrypt the content
of the transmission.

Layer

6

OSI 7
-
Layer Reference Model

Session Layer


Sessions allow a network to
differentiate between the type of data
flow being served. Large
-
volume
data transmissions can be broken
-
up
with synchronization points to allow
interrupted transmissions to be
resumed.


*Other functions of the session layer are no longer used regularly.

Layer

5

OSI 7
-
Layer Reference Model

Transport Layer


This layer allows multiple processes
to communicate across the network.
Processes are assigned “Ports;”
communication directed to that
process specifies a port number.


The transport layer specifies a
reliable (constant
--
TCP) or unreliable
(as needed
--
UDP) connection.

Layer

4

OSI 7
-
Layer Reference Model

Network Layer


This layer is charged with identifying
each host on the network and
determining the appropriate routing
for packets.


The network layer does not
distinguish between reliable and
unreliable service. All packets are
addressed ‘datagrams.’


Layer

3

OSI 7
-
Layer Reference Model

Data Link Layer


This layer operates within a network
segment. Data grouping are called
frames. They move depending on the
specific protocol.


Data link protocols operate on one
physical carrier segment unless a
bridge is used.

Layer

2

OSI 7
-
Layer Reference Model

Physical Layer


The physical layer provides the basic
capability of connection. Physical
layers simple transmit light, radio, or
electromagnetic impulse without
logical controls.

Layer

1