Transcript 1_hProtocolsOSI

HIGHER COMPUTER NETWORKING
Lesson 1 – Protocols and OSI
What is a network protocol
Description of the OSI model
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HIGHER COMPUTER NETWORKING
Introduction
Protocols
Are sets of rules that govern how two devices communicate and
exchange data when connected over a network. Examples are
TCP/IP, HTTP, FTP, SMTP etc.
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HIGHER COMPUTER NETWORKING
The Open Systems Connection (OSI) model
The OSI is a theoretical model that standardises network
architecture and protocols within a seven layer hierarchy.
Layer 7
Application
Layer 6
Presentation
Layer 5
Session
Layer 4
Transport
Layer 3
Network
Layer 2
Data Link (MAC)
Layer 1
Physical
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“Application
layers”
“Transport
layers”
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HIGHER COMPUTER NETWORKING
The Open Systems Connection (OSI) model
7 Application layer
• Top level layer where users actually interact with applications
that create the data that will be sent over the network.
e.g. when using a web browser the browser requests a web
page from a server
• Examples of application-layer programs include web browsers,
ftp programs, telnet, email, and so forth.
• The user interacts with these directly.
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HIGHER COMPUTER NETWORKING
The Open Systems Connection (OSI) model
6 Presentation layer
• This layer is concerned with the actual format that the data is
presented in.
• It is home to a number of data presentation standards
including JPG, GIF, and MPEG.
• This layer is also usually responsible for data encryption and
compression.
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HIGHER COMPUTER NETWORKING
The Open Systems Connection (OSI) model
5 Session layer
• The responsibility of this layer is to create, manage, and
terminate communication sessions between systems.
• Think of the session layer as a coordinator of communication
between systems
• A variety of protocols exist at the session layer, including
Remote Procedure Calls (RPCs), the Network File System
(NFS), SQL, and the AppleTalk Zone Information Protocol (ZIP).
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HIGHER COMPUTER NETWORKING
The Open Systems Connection (OSI) model
4 Transport layer
Its responsibilities include :
• segmenting data that comes from the upper layers
• establishing a connection between end-to-end systems that
defines the parameters of the connection
• and ensuring that data actually gets to its destination in the
correct order and error free
• Examples of protocols found at this layer include TCP and UDP.
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HIGHER COMPUTER NETWORKING
The Open Systems Connection (OSI) model
3 Network layer
• This layer is responsible for two main functions – network
addressing and routing.
• It identifies systems uniquely on an internetwork, and also
handles how to get from one part of the network to another.
• Most of the network configuration takes place, since protocols
such as IP, IPX, and equipment such as routers work here
• Its concerned with ‘where am I going (the address), and how
do I get there (the routing).
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HIGHER COMPUTER NETWORKING
The Open Systems Connection (OSI) model
2 Data Link (MAC) layer
• is concerned with how upper level data is formatted for
transmission over a given network technology.
• For example, if your network is running Ethernet, this layer will
format data packets accordingly, and follow the rules of
Ethernet transmission on the network.
• Examples of Data Link protocols include Ethernet, Token Ring
and FDDI
• At this layer, systems are generally identified by what is
referred to as their hardware or MAC address.
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HIGHER COMPUTER NETWORKING
The Open Systems Connection (OSI) model
1 Physical layer
• it defines the actual media and characteristics used to send the
1’s and 0’s over the network.
• This includes the actual wiring itself, the connectors used,
voltage levels, maximum media distances and so forth.
• For example, a packet might start on twisted-pair wiring, move
onto a wireless network, and then ultimately end up on fibre –
each of which using different media and methods during the
transfer process. In this case, copper wiring, then air, and then
fibre optic cable.
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HIGHER COMPUTER NETWORKING
The Open Systems Connection (OSI) model
So, in summary…
Type of communications
Layer 7
Application
Layer 6
Presentation
Layer 5
Session
Starts, stops session
Layer 4
Transport
Ensures delivery of
entire file or message
Layer 3
Network
Layer 2
Data Link (MAC)
Transmits packets via
MAC address
Layer 1
Physical
Electrical signals and
cabling
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e.g. email, ftp
Encryption, data
conversion
Routes data over LANs
or WANs via IP address
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