Networking Standards and the OSI Model

Networking Standards Organizations

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StandardDocumented agreement containing technical

specificationsStipulates design or performance of particular

product or serviceWhere would we be without standards?

Standards are essential in the networking worldWide variety of hardware and software

Ensures network design compatibility

Standards define minimum acceptable performance

Networking Standards Organizations (cont’d.)

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Many different organizations oversee computer industry standardsOrganizations may overlap responsibilities

Example: ANSI and IEEE set wireless standardsANSI -> kind of NICIEEE -> how communication gets there

ANSI

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ANSI (American National Standards Institute)1000+ representatives from industry and

governmentDetermines standards for electronics industry

and other fieldsRequests voluntarily compliance with

standardsObtaining ANSI approval requires rigorous

testingwww.ansi.org

IEEE

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IEEE (Institute of Electrical and Electronics Engineers)

Goal of IEEEPromote development and education in

electrical engineering and computer science fields

Maintains a standards board that establishes its own standards and works with ANSI

IEEE technical papers and standards are highly respected (www.ieee.org)

ISO

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ISO (International Organization for Standardization)Headquartered in Geneva, SwitzerlandCollection of standards organizations

Representing 57 countries

Goal of ISO Establish international technological standards

to facilitate global exchange of information and barrier free trade

Widespread authorityNot limited to just communications (ex.

banking)

EIA and TIA

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EIA (Electronic Industries Alliance)Trade organization

Representatives from United States electronics manufacturing firms

Lobbies for favorable computer and electronics industries legislation

TIA (Telecommunications Industry Association)Focus of TIA

Standards for information technology, wireless, satellite, fiber optics, and telephone equipment

TIA/EIA 568-B SeriesGuidelines for installing network cable in commercial

buildings

ITU

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ITU (International Telecommunication Union)Specialized United Nations agencyRegulates international telecommunications

Focus of ITUGlobal telecommunications issuesWorldwide Internet services implementation

ISOC

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ISOC (Internet Society)Founded in 1992Establishes technical Internet standards

ISOC oversees groups with specific missionsIETF (Internet Engineering Task Force)

Sets Internet system communication standardsParticularly protocol operation and interactionAnyone may submit standard proposalElaborate review, testing, and approval processes

IANA and ICANN

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IANA (Internet Assigned Numbers Authority) and ICANN (Internet Corporation for Assigned Names and Numbers)

IP (Internet Protocol) addressAddress identifying computers in TCP/IP

based (Internet) networksReliance on centralized management

authoritiesIP address management history

Initially: IANA (Internet Assigned Numbers Authority)

IANA and ICANN (cont’d.)

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IP address management history (cont’d.)Late 1990s: ICANN (Internet Corporation for

Assigned Names and Numbers) took overPrivate nonprofit corporationRemains responsible for IP addressing and domain

name managementIANA performs system administration

Users and business obtain IP addresses from ISP (Internet service provider) who get it from regional internet registries (RIR) who ultimately get it from ICANN

The OSI ModelWhat is the OSI Model?

The OSI Model

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Model for understanding and developing network computer-to-computer communications

Developed by ISO (1980s)OSI (Open Systems Interconnection Model)Divides network communications into

seven layersPhysical, Data Link, Network, Transport,

Session, Presentation, Application

The OSI Model (cont’d.)

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Protocol interactionProtocols interact with layer directly above

and belowApplication layer protocols (top)

Interact with software (ex. MS Word)Physical layer protocols (bottom)

Act on cables and connectors (UTP Cable)

The OSI Model (cont’d.)

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Theoretical representation describing network communication between two nodes

Hardware and software independentEvery network communication process is

representedPDUs (protocol data units)

Discrete amount of dataApplication layer functionFlow through layers 6, 5, 4, 3, 2, and 1

Generalized model Sometimes imperfect

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Figure 2.1 Flow of data through the OSI model

Application Layer

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Top (seventh) OSI model layerNo software applications hereProtocol functions

Facilitates communication between software applications and lower-layer network services

Network interprets application requestApplication interprets data sent from network

Software applications negotiate with application layer protocolsFormatting, procedural, security,

synchronization, and other requirements

Presentation Layer

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Protocol functionsAccept Application layer dataFormats data

Understandable to different applications and hosts

Servers as an interpreterEncoding – interpret coding

Presentation layer services manage data encryption and decryption (passwords)

Session Layer

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Protocol functionsCoordinate and maintain communications

between two nodesSession

Connection for ongoing data exchange between two partiesConnection between remote client and access

serverConnection between two devices

Session Layer (cont’d.)

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FunctionsEstablishing and keeping alive

communications linkKeeping communications secureSynchronizing dialogue between two nodesDetermining if communications ended

Determining where to restart transmissionTerminating communications

Transport Layer

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Protocol functionsAccept data from Session layerManage end-to-end data deliveryHandle flow control

Connection-oriented protocolsEstablish connection before transmitting data Handshake

Three steps ( SYN, SYN-ACK, ACK)Checksum

Unique character string allowing receiving node to determine if arriving data unit exactly matches data unit sent by source

Transport Layer (cont’d.)

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Connectionless protocolsDo not establish connection with another node

before transmitting dataMake no effort to ensure data is delivered free of

errorsMore efficient than connection-oriented protocolUseful when data must be transferred quickly

SegmentationBreaking large data units received from Session

layer into multiple smaller units called segmentsIncreases data transmission efficiency

Transport Layer (cont’d.)

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MTU (maximum transmission unit)Largest data unit network will carryEthernet default: 1500 bytesDiscovery routine used to determine MTU

ReassemblyProcess of reconstructing segmented data

unitsSequencing

Method of identifying segments belonging to the same group of subdivided data

Transport Layer (cont’d.)

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Figure 2-2 Segmentation and reassembly

Network Layer

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Protocols functionsTranslate network addresses into physical

counterpartsDecide how to route data from sender to

receiverAddressing

System for assigning unique identification numbers to network devices

Types of addresses for nodesNetwork addresses (0067973E97F3)Logical addresses (130.115.128.100)

Network Layer (cont’d.)

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Packet formation is hereTransport layer segment appended with logical

addressing informationRouting

Determine path from point A on one network to point B on another network

Routing considerationsDelivery priorities, network congestion, quality of

service, cost of alternative routesFragmentation

Network layer protocol (IP) subdivides Transport layer segments received into smaller packets

Data Link Layer

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Protocols functionsDivide data received into distinct frames for

transmission in Physical layerFrame

Structured package for moving dataIncludes raw data (payload), sender’s and receiver’s

network addresses, error checking and control information

Data Link Layer (cont’d.)

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Possible partial communication mistake Not all information received or correctly

Frames are not the sameCorrected by error checking

Possible glut of communication requestsData Link layer controls flow of information

Allows NIC to process data without error

Data Link Layer (cont’d.)

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Two Data Link layersSublayers

LLC (Logical Link Control) sublayerMAC (Media Access Control) sublayer

MAC address componentsBlock ID

Six-character sequence unique to each vendorDevice ID

Six-character number added at vendor’s factoryMAC addresses frequently depicted in

hexadecimal format (0067973E97F3)

Data Link Layer (cont’d.)

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Figure 2-5 The Data Link layer and its sublayers

Physical Layer

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Protocol functionsAccept frames from Data Link layerGenerates signals as changes in voltage at the

NICCopper transmission medium

Signals issued as voltage (electrical)Fiber-optic cable transmission medium

Signals issued as light pulses (light)Wireless transmission medium

Signals issued as electromagnetic waves

Physical Layer (cont’d.)

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Physical layer protocols responsibility when receiving dataDetect and accept signalsPass on to Data Link layerSet data transmission rateMonitor data error ratesNo error checking

Applying the OSI Model

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Table 2-1 Functions of the OSI layers

Communication Between Two Systems

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Data transformation (as seen through the 7 layers)Original software application data differs

from application layer - NIC dataHeader data added at each layer

PDUs (protocol data units)Generated in Application layer

SegmentsGenerated in Transport layerUnit of data resulting from subdividing larger

PDU

Communication Between Two Systems (cont’d.)

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PacketsGenerated in Network layerData with logical addressing information

added to segmentsFrames

Generated in Data Link layerComposed of several smaller components or

fields

Communication Between Two Systems (cont’d.)

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EncapsulationOccurs in Data Link layerProcess of wrapping one layer’s PDU with

protocol informationAllows interpretation by lower layer

Communication Between Two Systems (cont’d.)

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Figure 2-7 Data transformation through the OSI model

Frame Specifications

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FramesComposed of several smaller components or

fieldsFrame characteristic dependencies

Network type where frames runStandards frames must follow

EthernetFour different types of Ethernet framesMost popular: IEEE 802.3 standard

Frame Specifications (cont’d.)

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Token ringEthernet frames and token ring frames

differWill not interact with each otherDevices cannot support more than one frame

type per physical interface or NIC

IEEE Networking Specifications

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IEEE’s Project 802Effort to standardize physical and logical

network elements Frame types and addressingConnectivityNetworking mediaError-checking algorithmsEncryptionEmerging technologies

802.3: Ethernet802.11: Wireless

IEEE Networking Specifications (cont’d.)

41Table 2-2 IEEE 802 standards

Summary

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Standards and standard organizationsISO’s OSI (Open Systems Interconnection)

modelSeven layers

IEEE’s Project 802Significant IEEE 802 standards

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Thanks