Iso Osi Reference Model Idatosi001

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1ISO-OSI Reference Model

ISO-OSI REFERENCE MODEL

MODULE ID: IDATOSI001

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OSI - Open System Interconnect

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1950s Computation - Batch Processing

?

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1960s - Host Computing

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1970s - Distributed Processing

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1980s

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Protocols Between Human beings

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Protocol in Telephone Communication

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Protocol in Data Communication

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ISO & CCITT (ITU-T)

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OSI

Purpose: To provide a common basis for the coordination of

standards development for: Systems interconnection, while allowing existing

standards to be placed into perspective within the overall reference model

Term OSI qualifies: Standards for exchange of info among systems that

are open to another by virtue of mutual use of applicable standards

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OSI

Reference model is primarily concerned with: Systems comprising of terminals, computers, and

associated devices and the means for transferring info between such systems

OSI does not intend: To be a basis for of implementation for systems

But provides: Conceptual and functional framework for definition of

services and protocols which fit within boundaries established by the model

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ISO & CCITT (ITU-T)

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The Wine Cup

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NETWORK ARCHITECTURE

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ISO Reference Model

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computers

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Physical Media - no Specs.

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Physical Layer

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DTE & DCE

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The Physical Layer

Responsibility: transmission of raw bits over a

communication channel. Issues:

mechanical and electrical interfaces time per bit distances

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DATA LINK LAYER

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The Data Link Layer-Data Link Control

Responsibility: provide an error-free communication link

Issues: framing (dividing data into chunks)

header & trailer bits addressing

10110110101 01100010011 10110000001

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Function of Data Link Layer

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Media Access Control - needed by multi-access networks.

MAC provides DLC with virtual wires on multi-access networks.

The Data Link Layer-Data Link Control

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Multi-access vs. Point-to-point

Point-to-point only 2 systems involved no doubt about where data came from !

Multi-access means shared medium. many end-systems share the same physical

communication resources (wire, frequency, ...) There must be some arbitration mechanism.

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Mechanism of Secure Data Transfer

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Frame Structure in HDLC

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Sequence of HDLCConnect Data Link

SABM: Set Asynchronous Balanced Mode

UA: Unnumbered Acknowledgement

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Sequence of HDLCData Transfer

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Sequence of HDLC

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Adjacent Layer Data Unit Mapping

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Layer Interaction

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Elements of Layer Operation

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Procedure of ISO Communication

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Relation Between 4 Primitives

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Network Layer

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Network

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Network

... communication system for connecting end-systems

End-systems a.k.a. hostsPCs, workstationsdedicated computersnetwork components

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The Network Layer

Responsibilities: path selection between end-systems (routing). subnet flow control. fragmentation & reassembly translation between different network types.

Issues: packet headers virtual circuits

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Relation Between Layers

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Connection Oriented and Connectionless

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Connection Type Network

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Connectionless Type Network

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X.25 Packet Switching Protocol

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X.25 Contd..

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Transport Layer

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The Transport Layer

Responsibilities: provides virtual end-to-end links between

peer processes. end-to-end flow control

Issues: headers error detection reliable communication

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Transport Layer in OSI Reference Model

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The Role of Transport Layer

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Data Transfer in Transport Layer

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Sequence of Class 0

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Session Layer

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The Session Layer

Responsibilities: establishes, manages, and terminates

sessions between applications. service location lookup

Many protocol suites do not include a session layer.

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Dialog Unit, Activity and Synchronization

Mj: Major SYNC point , Mn: Minor SYNC point

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The Role of Session Layer

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Session Connection Establishment Sequence

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Data Transfer SequenceDT: Data Transfer GT: Give Token

PT: Please Token

SSDU: Session Service Data Unit

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Data Transfer Sequence-Duplex(b) Duplex

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Session Connection Release Sequence

FN: Finish, DN: Disconnect

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Session Connection Release Sequence

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Presentation Layer

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The Presentation Layer

Responsibilities: data encryption data compression data conversion

Many protocol suites do not include a Presentation Layer.

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Semantics and SyntaxWorld of Semantics

World of Syntax

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The Role of Presentation

PresentationProtocol

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Abstract Sequence and Transfer Sequence

The Abstract syntax and Transfer syntax of ASN 1

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Application Layer

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The Application Layer

Responsibilities: anything not provided by any of the other

layers Issues:

application level protocols appropriate selection of type of service

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Message Handing System

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Mail and E-mail

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Concept of MHS

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MHS Functional Model

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Message Flow in MHS

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Structure of IP Message

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Repeater

ApplicationPresentation

SessionTransportNetwork

Data LinkPhysical

Source DestinationApplicationPresentation


Data LinkPhysical

Repeater

SignalAmplifier

Segment 1 Segment 2

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Copies bits from one network to another Does not look at any bits Allows the extension of a network beyond

physical length limitations

REPEATER

Repeater

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BridgeSource Destination



Data LinkPhysical



Data LinkPhysical

SignalAmplifier

andDL Header; EC

Examination

Segment 1 Segment 2

Bridge

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Copies frames from one network to another Can operate selectively - does not copy all

frames (must look at data-link headers). Extends the network beyond physical length

limitations.

BRIDGE

Bridge

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RouterSource Destination

Segment 1 Segment 2



Data LinkPhysical



Data LinkPhysical

End-to-End Communication

Repeater

Bridge

ROUTER

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Copies packets from one network to another. Makes decisions about what route a packet should take

(looks at network headers).

ROUTERROUTER

ROUTER

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Gateway

GatewaySource Destination

Segment 1 Segment 2



Data LinkPhysical



Data LinkPhysical

HL7-GW

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Internet Reference Model



Data LinkPhysical

ApplicationProcess

Host-to-HostInter-Network

NetworkAccess

OSI Model Internet Model

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Internet Protocols

NetworkAccess

Internet

Host-to-Host

Process/Application

Ethernet II, 802.x, FDDI, ATM,ISDN, X.25, Frame Relay

RoutingARP, RARP IP

TCP UDP

ICMP

FTP, Telnet, SMTP, NNTP,SNMP, DNS, POP3, SIP, ...

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Summary

Layer Characteristic(1)Physical Layer

Mechanical and Electrical means to Physical-connection for Bit Transfer

(2) Data Link LayerStructure of Bit Stream transmitted in Ph-Layer (Data Frame)

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(3) Network LayerRouting for T-LayerMultiplexing Network Connection to DL-connection

(4) Transport LayerTransparent data Transfer for Upper Layer

(5) Session LayerDialog Facility (Duplex, Half-duplex)

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(6) Presentation LayerSyntax Conversion

Abstract Syntax

Syntax Check

(7) Application LayerInterface with Application Process (User)

Transfer Syntax

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Iso Osi Reference Model Idatosi001