the iso - osi model
TRANSCRIPT
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Established in 1947, the International StandardsEstablished in 1947, the International Standards
Organization (Organization (ISOISO) is a multinational body) is a multinational body
dedicated to worldwide agreement on internationaldedicated to worldwide agreement on international
standards. An ISO standard that covers all aspectsstandards. An ISO standard that covers all aspects
of network communications is the Open Systemsof network communications is the Open Systems
Interconnection (Interconnection (OSIOSI) model. It was first introduced) model. It was first introducedin the late 1970s.in the late 1970s.
THE ISO - OSI MODELTHE ISO - OSI MODEL
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Layered Architecture
Networks are organized aslayersor levels.
Reduces design complexity. Each network architecture has
different:- number of layers- names of layers- functions of each layer
Between adjacent layers there
is an interface. Reference models exist to
architect a network.
OSI Protocols
Physical
Data
Network
Transport
SessionPresentation
Application
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Protocols
Rules and conventions used by two communicatingentities are collectively known as protocol.
Each layer of network architecture has its ownprotocol.
Two communicating entities at the same layer arecalled peers.
A list of protocols used by a system is calledprotocol stack.
A set of layers and protocols is referred to asnetwork architecture.
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THE THEORETICAL NETWORK - OSI MODEL
Peer communication between two computers
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OSI Model OverviewOSI Model Overview
Data FlowLayers
Transport Layer
Data Link
Network Layer
Physical
Application(Upper)Layers
Session
Presentation
Application
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Keeping differentapplicationsdata separate
User Interface
How data is presentedSpecial processingsuch as encryption
TelnetHTTP
ASCIIEBCDICJPEG
Operating System/Application Access
SchedulingTransport Layer
Data Link
Network Layer
Physical
EXAMPLES
Session
Presentation
Application
Role of Application LayersRole of Application Layers
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TCPUDPSPX
802.3 / 802.2HDLC
EIA/TIA-232
V.35
IPIPX
Presentation
Application
SessionEXAMPLES
Role of Data Flow LayersRole of Data Flow Layers
Reliable or unreliable delivery Error correction before retransmit
Combines bits into bytes and
bytes into frames Access to media using MAC address Error detection not correction
Move bits between devices Specifies voltage, wire speed and
pin-out cables
Transport
Data Link
Physical
NetworkProvide logical addressing whichrouters use for path determination
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Encapsulating DataEncapsulating Data
Transport
Data Link
Physical
Network
Upper Layer Data
Upper Layer DataTCP Header
DataIP Header
DataLLC Header
0101110101001000010
DataMAC Header
Presentation
Application
Session
Segment
Packet
Bits
Frame
PDU
FCS
FCS
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Upper Layer Data
De-encapsulating DataDe-encapsulating Data
LLC Hdr + IP + TCP + Upper Layer Data
MACH
eader
IP + TCP + Upper Layer Data
LLCHe
ader
TCP+ Upper Layer Data
IPHead
er
Upper Layer Data
TCPH
eader
0101110101001000010
Transport
Data Link
Physical
Network
Presentation
Application
Session
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An exchange using the OSI model
Osi.swf
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The interaction between layers in the OSI model
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The physical layer is responsible for movements of
individual bits from one hop (node) to the next.
Note
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Physical layer
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The data link layer is responsible for movingframes from one hop (node) to the next.
Note
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Data link layer
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The network layer is responsible for thedelivery of individual packets from
the source host to the destination host.
Note
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Hop-to-hop delivery
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Network layer
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Source-to-destination delivery
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The transport layer is responsible for the deliveryof a message from one process to another.
Note
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Transport layer
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Reliable process-to-process delivery of a message
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The session layer is responsible for dialogcontrol and synchronization.
Note
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Session layer
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The presentation layer is responsible for translation,compression, and encryption.
Note
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Presentation layer
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The application layer is responsible forproviding services to the user.
Note
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Application layer
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Summary of layers
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The layers in theThe layers in the TCP/IP protocol suiteTCP/IP protocol suite do not exactlydo not exactly
match those in the OSI model. The original TCP/IPmatch those in the OSI model. The original TCP/IP
protocol suite was defined as having four layers:protocol suite was defined as having four layers: host-host-to-network, internet, transport,to-network, internet, transport, andand application.application.
However, when TCP/IP is compared to OSI, we can sayHowever, when TCP/IP is compared to OSI, we can say
that the TCP/IP protocol suite is made of five layers:that the TCP/IP protocol suite is made of five layers:
physical, data link, network, transportphysical, data link, network, transport, and, andapplication.application.
TCP/IP PROTOCOL SUITETCP/IP PROTOCOL SUITE
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TCP/IP Reference Model
PRESENTATION
SESSION
TRANSPORT
NETWORK
DATA LINK
PHYSICAL
APPLICATION APPLICATION
TRANSPORT
INTERNET
HOST-TO-NETWORK
(Data Link/
Physical)
OSI
Notpresent
In themodel
TCP/IP
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TCP/IP and OSI model
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Physical LayerPhysical Layer
MAC LayerMAC Layer
LLC LayerLLC Layer
Network LayerNetwork Layer
Transport LayerTransport Layer
AddressingAddressing
SchemesSchemes
Network AddressingNetwork Addressing
Addressingis used to
ensure that messagesbetween any two of themachines are notreceived by other users.
Addressing schemesexist at multiple layersof the OSI Model. Atypical TCP/IP packetwill contain addressesthat are designed to beused at the MAC Layer,the Network Layer and
the Transport Layer.
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MAC Layer Addresses
Network Layer Addresses
Transport Layer Addresses
The addresses are stored in specifically definedparts of the IP packet and the LAN frame.
The consistent position of addresses is a keyfactor that allows software to interpret addressinginformation correctly. In other words, if we putaddresses in the wrong format, or in the wrong
place, our communication software will not workcorrectly.
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Addresses in TCP/IP
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Relationship of layers and addresses in TCP/IP
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A node with physical address 10 sends a frame to a node
with physical address 87. The two nodes are connectedby a link (bus topology LAN). As the figure shows, the
computer with physical address 10 is the sender, and the
computer with physical address 87is the receiver.
Example
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Most local-area networks use a 48-bit (6-byte) physicaladdress written as 12 hexadecimal digits; every byte (2
hexadecimal digits) is separated by a colon, as shown
below:
07:01:02:01:2C:4B
A 6-byte (12 hexadecimal digits) physical address.
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Figure next shows a part of an internet with two routers
connecting three LANs. Each device (computer or
router) has a pair of addresses (logical and physical) for
each connection. In this case, each computer is
connected to only one link and therefore has only one
pair of addresses. Each router, however, is connected to
three networks (only two are shown in the figure). So
each router has three pairs of addresses, one for eachconnection.
Example
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IP addresses
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Port addresses
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The physical addresses will change from hop to hop,but the logical addresses usually remain the same.
Note
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A port address is a 16-bit address represented by onedecimal number as shown.
753
A 16-bit port address represented
as one single number.
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The physical addresses change from hop to hop,but the logical and port addresses usually remain the same.
Note
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