chapter two networking standards and the osi model

Chapter TwoChapter TwoNetworking StandardsNetworking Standards

and the OSI Modeland the OSI Model

ObjectivesObjectives

Identify organizations that set standards for Identify organizations that set standards for networkingnetworking

Explain the layers of OSI ModelExplain the layers of OSI Model

Describe specific networking services within Describe specific networking services within each layer of OSI Modeleach layer of OSI Model

ObjectivesObjectives

Explain how two systems communicate Explain how two systems communicate through OSI Modelthrough OSI Model

Discuss the structure and purpose of data Discuss the structure and purpose of data framesframes

Describe the two types of addressing Describe the two types of addressing contained in OSI Modelcontained in OSI Model

StandardsStandards

Documented agreements containing Documented agreements containing technical specifications or other precise technical specifications or other precise criteria that stipulate how a particular criteria that stipulate how a particular product or service should be designed or product or service should be designed or performedperformed

Many different industries use standards to Many different industries use standards to ensure that products, processes, and ensure that products, processes, and services suit their purposeservices suit their purpose

Networking Standards Networking Standards OrganizationsOrganizations

American National Standards Institute (ANSI)American National Standards Institute (ANSI) Comprised of industry and government Comprised of industry and government

representativesrepresentatives Determine standards for electronics industry in Determine standards for electronics industry in

addition to other fieldsaddition to other fields

Electronic Industries Alliance (EIA)Electronic Industries Alliance (EIA) Trade organization composed of representatives Trade organization composed of representatives

from electronics manufacturing firms across United from electronics manufacturing firms across United StatesStates

Sets standards for members, helps write ANSI Sets standards for members, helps write ANSI standards, and lobbies for legislation favorable to standards, and lobbies for legislation favorable to the industrythe industry


Institute of Electrical and Electronic Engineers Institute of Electrical and Electronic Engineers (IEEE)(IEEE) International society of engineering professionalsInternational society of engineering professionals Promotes development and education in electrical Promotes development and education in electrical

engineering and computer science fieldsengineering and computer science fields

International Organization for Standardization International Organization for Standardization (ISO)(ISO) Collection of standards organizationsCollection of standards organizations Goal is to establish international technological Goal is to establish international technological

standards to facilitate global exchange of standards to facilitate global exchange of information and barrier-free tradeinformation and barrier-free trade


International Telecommunication Union International Telecommunication Union (ITU)(ITU) Formerly called Consultative Committee on Formerly called Consultative Committee on

International Telegraph and Telephony International Telegraph and Telephony (CCITT)(CCITT)

United Nations agency that regulates United Nations agency that regulates international telecommunicationsinternational telecommunications

Assists developing countriesAssists developing countries

The OSI ModelThe OSI Model

Open Systems Interconnection (OSI) ModelOpen Systems Interconnection (OSI) Model Model for understanding and developing Model for understanding and developing

computer-to-computer communicationcomputer-to-computer communication Developed in the 1980s by ISODeveloped in the 1980s by ISO Divides network architecture into seven layersDivides network architecture into seven layers

Network architectNetwork architect Professional involved in network designProfessional involved in network design

The OSI ModelThe OSI Model

Figure 2-1: The OSI Model

Physical LayerPhysical LayerData Link LayerData Link Layer

Physical layerPhysical layer First layer of OSI ModelFirst layer of OSI Model Contains physical networking mediaContains physical networking media

Data Link layerData Link layer Second layer of OSI ModelSecond layer of OSI Model Primary function is to divide data it receives Primary function is to divide data it receives

from Network layer into distinct frames that from Network layer into distinct frames that can be transmitted by Physical layercan be transmitted by Physical layer

FramesFrames

Structured package for moving dataStructured package for moving dataIncludes raw data (or payload) along with sender’s and Includes raw data (or payload) along with sender’s and receiver’s:receiver’s:

Network addressesNetwork addresses Error-checking and control informationError-checking and control information

Figure 2-2: A simplified data frame

Network LayerNetwork Layer

Third layer of OSI ModelThird layer of OSI Model

Translates network addresses into their Translates network addresses into their physical counterpartsphysical counterparts

Decides how to route data from sender to Decides how to route data from sender to receiverreceiver

Network LayerNetwork Layer

Because Network layer handles routing, Because Network layer handles routing, routersrouters belong in Network layer belong in Network layer To To routeroute means to direct data based on means to direct data based on

addressing, usage patterns, and availabilityaddressing, usage patterns, and availability

Network layer protocols also accomplish:Network layer protocols also accomplish: SegmentationSegmentation ReassemblyReassembly

Transport LayerTransport Layer

Fourth layer of OSI ModelFourth layer of OSI Model

Ensures that data are transferred between Ensures that data are transferred between points reliably and without errorspoints reliably and without errors

Handles Handles flow controlflow control Method of gauging appropriate rate of data Method of gauging appropriate rate of data

transmissiontransmission

Transport LayerTransport Layer

SequencingSequencing Process of assigning a placeholder to each piece Process of assigning a placeholder to each piece

of a data block to allowing receiving node’s of a data block to allowing receiving node’s Transport layer to reassemble data in correct Transport layer to reassemble data in correct orderorder

Acknowledgement (ACK)Acknowledgement (ACK) Response generated in Transport layerResponse generated in Transport layer Confirms to sender that its frame was receivedConfirms to sender that its frame was received

Session LayerSession Layer

Fifth layer of OSI ModelFifth layer of OSI Model

Establishes and maintains communication Establishes and maintains communication between two nodes on the networkbetween two nodes on the network

SessionSession Refers to a connection for data exchange Refers to a connection for data exchange

between two partiesbetween two parties Term session is most often used in context of Term session is most often used in context of

terminalterminal and mainframe communications and mainframe communications

Presentation LayerPresentation Layer Application Layer Application Layer

Presentation layerPresentation layer Sixth layer of OSI ModelSixth layer of OSI Model Translates between application and networkTranslates between application and network

Application layerApplication layer Seventh, or top, layer of OSI ModelSeventh, or top, layer of OSI Model Provides interface to software enabling Provides interface to software enabling

programs to use network devicesprograms to use network devices

Application Program Interface (API)Application Program Interface (API)

Routine that allows a program to interact with Routine that allows a program to interact with the operating systemthe operating system

Belongs to Application layer of OSI ModelBelongs to Application layer of OSI Model

Microsoft Message Queueing (MSMQ)Microsoft Message Queueing (MSMQ) API used in network environmentAPI used in network environment Stores messages sent between nodes in queuesStores messages sent between nodes in queues Forwards these messages to their destinationForwards these messages to their destination

Applying the OSI ModelApplying the OSI Model

Table 2-1: Functions of the OSI layer

Communication Between Two Communication Between Two SystemsSystems

TokenToken Special control frame indicating to rest of Special control frame indicating to rest of

network that a particular node has right to network that a particular node has right to transmit datatransmit data

Frame Check Sequence (FCS)Frame Check Sequence (FCS) Field in a frame responsible for ensuring that Field in a frame responsible for ensuring that

data carried by frame arrives intactdata carried by frame arrives intact


Figure 2-3: Data transfer between two

systems


Figure 2-4: Data transformed through the OSI Model

Frame SpecificationsFrame Specifications

EthernetEthernet Networking technology originally developed in Networking technology originally developed in

1970s by Xerox1970s by Xerox Four types of Ethernet technology are used Four types of Ethernet technology are used

on LANs todayon LANs todayEach type is governed by a set of IEEE standardsEach type is governed by a set of IEEE standards

Frame SpecificationsFrame Specifications

Token RingToken Ring Networking technology developed by IBM in Networking technology developed by IBM in

the 1980sthe 1980s Relies upon direct links between nodes and a Relies upon direct links between nodes and a

ring topology, using tokens to allow nodes to ring topology, using tokens to allow nodes to transmit datatransmit data

A Typical Ethernet FrameA Typical Ethernet Frame

802.3 standard802.3 standard IEEE standard for Ethernet networking devices and IEEE standard for Ethernet networking devices and

data handlingdata handling

Figure 2-5: Ethernet frame as specified by the IEEE 802.3 standard

Components of the Ethernet Components of the Ethernet 802.3 Frame802.3 Frame

PreamblePreamble Marks beginning of entire frameMarks beginning of entire frame

Start of Frame Delimiter (SFD)Start of Frame Delimiter (SFD) Indicates beginning of addressing frameIndicates beginning of addressing frame

Destination AddressDestination Address Contains destination node addressContains destination node address


Source AddressSource Address Contains address of originating nodeContains address of originating node

Length (LEN)Length (LEN) Indicates length of packetIndicates length of packet

DataData Contains data, or segmented part of data, Contains data, or segmented part of data,

transmitted from originating nodetransmitted from originating node


PadPad Used to increase size of the frame to its Used to increase size of the frame to its

minimum size requirement of 46 bytesminimum size requirement of 46 bytes

Frame Check Sequence (FCS)Frame Check Sequence (FCS) Provides an algorithm to determine whether Provides an algorithm to determine whether

data were correctly receiveddata were correctly received

Most commonly used algorithm is Most commonly used algorithm is Cyclic Cyclic Redundancy Check (CRC)Redundancy Check (CRC)

Typical Token Ring FrameTypical Token Ring Frame

802.5 Standard802.5 Standard IEEE standard for Token Ring networking devices IEEE standard for Token Ring networking devices

and data handlingand data handling

Figure 2-6: Typical Token Ring frame

Components of Token Ring Components of Token Ring FrameFrame

Start Delimiter (SD)Start Delimiter (SD) Signifies beginning of packetSignifies beginning of packet

Access Control (AC)Access Control (AC) Contains information about priority of the Contains information about priority of the

frameframe

Frame Control (FC)Frame Control (FC) Defines type of frameDefines type of frame


Destination AddressDestination Address Contains destination node addressContains destination node address

Source AddressSource Address Contains address of originating nodeContains address of originating node

DataData Contains data transmitted from originating Contains data transmitted from originating

nodenode


Frame Check Sequence (FCS)Frame Check Sequence (FCS) Used to check integrity of the frameUsed to check integrity of the frame

End Delimiter (ED)End Delimiter (ED) Indicates end of the frameIndicates end of the frame

Frame Status (FS)Frame Status (FS) Indicates whether destination node Indicates whether destination node

recognized and correctly copied the framerecognized and correctly copied the frame

Addressing Through the LayersAddressing Through the Layers

Data Link layer addressData Link layer address Also called Also called MAC addressMAC address, after , after Media Media

Access Control (MAC) sublayerAccess Control (MAC) sublayer Number uniquely defining a network nodeNumber uniquely defining a network node Composed of Composed of Block IDBlock ID and and Device IDDevice ID Manufacturer-hard codes the address on the Manufacturer-hard codes the address on the

NICNIC

Addressing Through the LayersAddressing Through the Layers

Network layer addressNetwork layer address Resides at Network level of OSI ModelResides at Network level of OSI Model Follows hierarchical addressing schemeFollows hierarchical addressing scheme Can be assigned through operating system Can be assigned through operating system

softwaresoftware

IEEE Networking SpecificationsIEEE Networking Specifications

Table 2-2: IEEE 802 standards

IEEE Networking SpecificationsIEEE Networking Specifications

To accommodate shared access for To accommodate shared access for multiple network nodes, IEEE expanded multiple network nodes, IEEE expanded OSI Model by separating Data Link layer OSI Model by separating Data Link layer into two sublayers:into two sublayers: Logical Link Control (LLC) sublayerLogical Link Control (LLC) sublayer Media Access Control (MAC) sublayerMedia Access Control (MAC) sublayer

Data Link Layer SublayersData Link Layer Sublayers

LLC LLC Upper sublayerUpper sublayer Provides common interfaceProvides common interface Supplies reliability and flow control servicesSupplies reliability and flow control services

MACMAC Lower sublayerLower sublayer Appends physical address of destination Appends physical address of destination

computer onto the framecomputer onto the frame

Subdivided Data Link LayerSubdivided Data Link Layer

Figure 2-7: LLC and

MAC sublayers

Chapter SummaryChapter Summary

Standards are documented agreements containing Standards are documented agreements containing technical specifications or other precise criteria technical specifications or other precise criteria used as guidelines to ensure materials, products, used as guidelines to ensure materials, products, processes, and services suit their purposeprocesses, and services suit their purpose

Prominent standards organization include:Prominent standards organization include: ANSIANSI EIAEIA IEEEIEEE ISOISO ITUITU


OSI Model divides networking architecture OSI Model divides networking architecture into seven layers:into seven layers: Physical layerPhysical layer Data Link layerData Link layer Network layerNetwork layer Transport layerTransport layer Session layerSession layer Presentation layerPresentation layer Application layerApplication layer


A data request from a software program is received A data request from a software program is received by Application layer services and is transferred by Application layer services and is transferred down through layers of OSI Model until it reaches down through layers of OSI Model until it reaches the Physical layerthe Physical layer

Data frames are small blocks of data with control, Data frames are small blocks of data with control, addressing, and handling information attached to addressing, and handling information attached to themthem

Each node on a network can be identified by two Each node on a network can be identified by two types of addresses:types of addresses: Network layer addressNetwork layer address Data Link layer addressData Link layer address


In addition to frame types, IEEE networking In addition to frame types, IEEE networking specifications apply to connectivity, specifications apply to connectivity, networking media, error checking algorithms, networking media, error checking algorithms, encryption, emerging technologies, and moreencryption, emerging technologies, and more

ISO expanded OSI Model by separating the ISO expanded OSI Model by separating the Data Link layer into sublayers:Data Link layer into sublayers: LLC layerLLC layer MAC layerMAC layer

chapter two networking standards and the osi model

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