II Protocol Architecture OSI

8/2/2019 II Protocol Architecture OSI

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OSI

Open Systems Interconnection

developed by the International Organization

for Standardization (ISO)

has seven layers

is a theoretical system delivered too late!

TCP/IP is the de facto standard


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OSI Layers


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OSI v TCP/IP


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LAYER 1The PHYSICAL Layer

Converts bits into electronic signals for outgoing messages

Converts electronic signals into bits for incoming messages

This layer manages the interface between the the computer andthe network medium (coax, twisted pair, etc.)

This layer tells the driver software for the MAU (mediaattachment unit, ex. network interface cards (NICs, modems, etc.))what needs to be sent across the medium

The bottom layer of the OSI model

The physical layer is responsible for movements of

individual bits from one hop (node) to the next.


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Physical Layer


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LAYER 2The DATA LINK Layer

Handles special data frames (packets) between theNetwork layer and the Physical layer

At the receiving end, this layer packages raw data

from the physical layer into data frames for delivery to

the Network layer

At the sending end this layer handles conversion of

data into raw formats that can be handled by the PhysicalLayer

The data link layer is responsible for moving

frames from one hop (node) to the next.


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Data Link Layer


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Data Link Layer: Hop-to-hop delivery


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LAYER 3The NETWORK Layer

Handles addressing messages for delivery, as well as translatinglogical network addresses and names into their physical counterparts

Responsible for deciding how to route transmissions between

computers

This layer also handles the decisions needed to get data from one

point to the next point along a network path

This layer also handles packet switching and network congestion

control

The network layer is responsible for thedelivery of individual packets from

the source host to the destination host.


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Network Layer


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Network Layer : Source-to-destination delivery

LAYER 4 Th TRANSPORT


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LAYER 4

The TRANSPORT

Layer

Manages the transmission of data across a network

Manages the flow of data between parties by segmenting long

data streams into smaller data chunks (based on allowed packet

size for a given transmission medium)

Reassembles chunks into their original sequence at the

receiving end

Provides acknowledgements of successful transmissions and

requests resends for packets which arrive with errors

The transport layer is responsible for the delivery

of a message from one process to another


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Transport Layer


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Reliable process-to-process

delivery of a message


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LAYER 5The SESSION Layer

Enables two networked resources to hold ongoing communications(called a session) across a network

Applications on either end of the session are able to exchange data for

the duration of the session

This layer is:

Responsible for initiating, maintaining and terminating sessions

Responsible for security and access control to session information

(via session participant identification)

Responsible for synchronization services, and for checkpoint services

The session layer is responsible for

dialog

control and synchronization


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Session layer


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LAYER 6The PRESENTATION Layer

Manages data-format information for networkedcommunications (the networks translator)

For outgoing messages, it converts data into a generic formatfor network transmission; for incoming messages, it converts datafrom the generic network format to a format that the receiving

application can understand

This layer is also responsible for certain protocol conversions,data encryption/decryption, or data compression/decompression

A special software facility called a redirector operates at thislayer to determine if a request is network related on not andforward network-related requests to an appropriate networkresource

The presentation layer is responsible for

translation, compression, and encryption


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Presentation layer


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LAYER 7The APPLICATION Layer

The top layer of the OSI model

Provides a set of interfaces for sending and

receiving applications to gain access to anduse network services, such as: networked file

transfer, message handling and database query

processing

The application layer is responsible for

providing services to the user


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Application layer


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Standardized Protocol Architectures


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OSI Layers Devices Protocols

APPLICATION - layer 7 SNMP, SMTP, FTP, TELNET, HTTP, NCP,

SMB, AppleTalk

PRESENTATION layer 6 NCP, AFP, TDI

SESSION layer 5 NetBIOS

TRANSPORT layer 4 NetBEUI, TCP, SPX, NWlink

NETWORK layer 3 Routers, layer 3 (or IP) switches IP, IPX, NWlink, NetBEUI

DATA LINK

layer 2 Bridges and switches, Ethernet

incorporates both this layer and the

Physical layer

PHYSICAL layer 1 Hubs, repeaters, network adapters,

Parallel SCSI buses. Various physical-layer

Ethernet incorporates both this layer and

the data-link layer. Token ring, FDDI, and

IEEE 802.11


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Layer Specific Standards


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Service Primitives and Parameters

define services between

adjacent layers using:

primitives to specify

function performed

parameters to pass data

and control info


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Primitive Types

REQUEST A primitive issued by a service user to invoke someservice and to pass the parameters needed to specify

fully the requested service

INDICATION A primitive issued by a service provider either to:

indicate that a procedure has been invoked by the peer

service user on the connection and to provide theassociated parameters, or

notify the service user of a provider-initiated action

RESPONSE A primitive issued by a service user to acknowledge or

complete some procedure previously invoked by an

indication to that userCONFIRM A primitive issued by a service provider to acknowledge

or complete some procedure previously invoked by a

request by the service user

Documents

II Protocol Architecture OSI