open systems interconnection model (osi).pdf

7/27/2019 Open Systems Interconnection model (OSI).pdf

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Physical layer

In the seven-layerOSI modelofcomputer networking,the physical layeror layer 1is the first

(lowest) layer.[1]The implementation of this layer is often termed PHY.

The physical layer consists of the basicnetworking hardwaretransmission technologies of

anetwork.[2]It is a fundamental layer underlying the logical data structures of the higher level

functions in a network. Due to the plethora of available hardware technologies with widely

varying characteristics, this is perhaps the most complex layer in the OSI architecture.

The physical layer defines the means of transmitting raw bits rather than logicaldata

packetsover a physicallinkconnectingnetwork nodes.Thebit streammay be grouped into

code words or symbols and converted to a physicalsignalthat is transmitted over ahardwaretransmission medium.The physical layer provides an electrical, mechanical, and

procedural interface to the transmission medium. The shapes and properties of theelectrical

connectors,the frequenciesto broadcast on, themodulationscheme to use and similar low-

level parameters, are specified here.

Within the semantics of the OSI network architecture, the physical layer translates logical

communications requests from thedata link layerinto hardware-specific operations to effect

transmission or reception of electronic signals.

Contents

[hide]

1 Physical signaling sublayer

2 List of services

3 List of protocols

4 Hardware equipment (network node) examples

5 Relation to TCP/IP model

6 See also

7 References

8 External links

Physical signaling sublayer

In alocal area network(LAN) or ametropolitan area network(MAN) usingopen systems

interconnection(OSI) architecture, thephysical signaling sublayeris the portion of the physical

layer that:[3][4]

interfaces with thedata link layer'smedia access control(MAC) sublayer,

performscharacterencoding,transmission,reception and decoding and,

performsgalvanic isolation.

List of services
http://en.wikipedia.org/wiki/OSI_modelhttp://en.wikipedia.org/wiki/OSI_modelhttp://en.wikipedia.org/wiki/OSI_modelhttp://en.wikipedia.org/wiki/Computer_networkhttp://en.wikipedia.org/wiki/Computer_networkhttp://en.wikipedia.org/wiki/Computer_networkhttp://en.wikipedia.org/wiki/Physical_layer#cite_note-Data_and_Computer_Network_Communications-1http://en.wikipedia.org/wiki/Physical_layer#cite_note-Data_and_Computer_Network_Communications-1http://en.wikipedia.org/wiki/Physical_layer#cite_note-Data_and_Computer_Network_Communications-1http://en.wikipedia.org/wiki/Networking_hardwarehttp://en.wikipedia.org/wiki/Networking_hardwarehttp://en.wikipedia.org/wiki/Networking_hardwarehttp://en.wikipedia.org/wiki/Computer_networkhttp://en.wikipedia.org/wiki/Computer_networkhttp://en.wikipedia.org/wiki/Physical_layer#cite_note-Fundamentals_of_Sensor_Network_Programming-2http://en.wikipedia.org/wiki/Physical_layer#cite_note-Fundamentals_of_Sensor_Network_Programming-2http://en.wikipedia.org/wiki/Physical_layer#cite_note-Fundamentals_of_Sensor_Network_Programming-2http://en.wikipedia.org/wiki/Network_packethttp://en.wikipedia.org/wiki/Network_packethttp://en.wikipedia.org/wiki/Network_packethttp://en.wikipedia.org/wiki/Network_packethttp://en.wikipedia.org/wiki/Data_linkhttp://en.wikipedia.org/wiki/Data_linkhttp://en.wikipedia.org/wiki/Data_linkhttp://en.wikipedia.org/wiki/Network_nodehttp://en.wikipedia.org/wiki/Network_nodehttp://en.wikipedia.org/wiki/Network_nodehttp://en.wikipedia.org/wiki/Bit_streamhttp://en.wikipedia.org/wiki/Bit_streamhttp://en.wikipedia.org/wiki/Bit_streamhttp://en.wikipedia.org/wiki/Signal_(electronics)http://en.wikipedia.org/wiki/Signal_(electronics)http://en.wikipedia.org/wiki/Signal_(electronics)http://en.wikipedia.org/wiki/Transmission_mediumhttp://en.wikipedia.org/wiki/Transmission_mediumhttp://en.wikipedia.org/wiki/Transmission_mediumhttp://en.wikipedia.org/wiki/Electrical_connectorhttp://en.wikipedia.org/wiki/Electrical_connectorhttp://en.wikipedia.org/wiki/Electrical_connectorhttp://en.wikipedia.org/wiki/Frequencyhttp://en.wikipedia.org/wiki/Frequencyhttp://en.wikipedia.org/wiki/Modulationhttp://en.wikipedia.org/wiki/Modulationhttp://en.wikipedia.org/wiki/Modulationhttp://en.wikipedia.org/wiki/Data_link_layerhttp://en.wikipedia.org/wiki/Data_link_layerhttp://en.wikipedia.org/wiki/Data_link_layerhttp://en.wikipedia.org/wiki/Physical_layerhttp://en.wikipedia.org/wiki/Physical_layerhttp://en.wikipedia.org/wiki/Physical_layerhttp://en.wikipedia.org/wiki/Physical_layer#Physical_signaling_sublayerhttp://en.wikipedia.org/wiki/Physical_layer#Physical_signaling_sublayerhttp://en.wikipedia.org/wiki/Physical_layer#List_of_serviceshttp://en.wikipedia.org/wiki/Physical_layer#List_of_serviceshttp://en.wikipedia.org/wiki/Physical_layer#List_of_protocolshttp://en.wikipedia.org/wiki/Physical_layer#List_of_protocolshttp://en.wikipedia.org/wiki/Physical_layer#Hardware_equipment_.28network_node.29_exampleshttp://en.wikipedia.org/wiki/Physical_layer#Hardware_equipment_.28network_node.29_exampleshttp://en.wikipedia.org/wiki/Physical_layer#Relation_to_TCP.2FIP_modelhttp://en.wikipedia.org/wiki/Physical_layer#Relation_to_TCP.2FIP_modelhttp://en.wikipedia.org/wiki/Physical_layer#See_alsohttp://en.wikipedia.org/wiki/Physical_layer#See_alsohttp://en.wikipedia.org/wiki/Physical_layer#Referenceshttp://en.wikipedia.org/wiki/Physical_layer#Referenceshttp://en.wikipedia.org/wiki/Physical_layer#External_linkshttp://en.wikipedia.org/wiki/Physical_layer#External_linkshttp://en.wikipedia.org/wiki/Local_area_networkhttp://en.wikipedia.org/wiki/Local_area_networkhttp://en.wikipedia.org/wiki/Local_area_networkhttp://en.wikipedia.org/wiki/Metropolitan_area_networkhttp://en.wikipedia.org/wiki/Metropolitan_area_networkhttp://en.wikipedia.org/wiki/Metropolitan_area_networkhttp://en.wikipedia.org/wiki/Open_systems_interconnectionhttp://en.wikipedia.org/wiki/Open_systems_interconnectionhttp://en.wikipedia.org/wiki/Open_systems_interconnectionhttp://en.wikipedia.org/wiki/Open_systems_interconnectionhttp://en.wikipedia.org/wiki/Physical_layer#cite_note-FS1037C-3http://en.wikipedia.org/wiki/Physical_layer#cite_note-FS1037C-3http://en.wikipedia.org/wiki/Physical_layer#cite_note-FS1037C-3http://en.wikipedia.org/wiki/Data_link_layerhttp://en.wikipedia.org/wiki/Data_link_layerhttp://en.wikipedia.org/wiki/Data_link_layerhttp://en.wikipedia.org/wiki/Media_access_controlhttp://en.wikipedia.org/wiki/Media_access_controlhttp://en.wikipedia.org/wiki/Media_access_controlhttp://en.wikipedia.org/wiki/Character_(computing)http://en.wikipedia.org/wiki/Character_(computing)http://en.wikipedia.org/wiki/Character_(computing)http://en.wikipedia.org/wiki/Transmission_(telecommunications)http://en.wikipedia.org/wiki/Transmission_(telecommunications)http://en.wikipedia.org/wiki/Transmission_(telecommunications)http://en.wikipedia.org/wiki/Galvanic_isolationhttp://en.wikipedia.org/wiki/Galvanic_isolationhttp://en.wikipedia.org/wiki/Galvanic_isolationhttp://en.wikipedia.org/wiki/Galvanic_isolationhttp://en.wikipedia.org/wiki/Transmission_(telecommunications)http://en.wikipedia.org/wiki/Character_(computing)http://en.wikipedia.org/wiki/Media_access_controlhttp://en.wikipedia.org/wiki/Data_link_layerhttp://en.wikipedia.org/wiki/Physical_layer#cite_note-FS1037C-3http://en.wikipedia.org/wiki/Physical_layer#cite_note-FS1037C-3http://en.wikipedia.org/wiki/Open_systems_interconnectionhttp://en.wikipedia.org/wiki/Open_systems_interconnectionhttp://en.wikipedia.org/wiki/Metropolitan_area_networkhttp://en.wikipedia.org/wiki/Local_area_networkhttp://en.wikipedia.org/wiki/Physical_layer#External_linkshttp://en.wikipedia.org/wiki/Physical_layer#Referenceshttp://en.wikipedia.org/wiki/Physical_layer#See_alsohttp://en.wikipedia.org/wiki/Physical_layer#Relation_to_TCP.2FIP_modelhttp://en.wikipedia.org/wiki/Physical_layer#Hardware_equipment_.28network_node.29_exampleshttp://en.wikipedia.org/wiki/Physical_layer#List_of_protocolshttp://en.wikipedia.org/wiki/Physical_layer#List_of_serviceshttp://en.wikipedia.org/wiki/Physical_layer#Physical_signaling_sublayerhttp://en.wikipedia.org/wiki/Physical_layerhttp://en.wikipedia.org/wiki/Data_link_layerhttp://en.wikipedia.org/wiki/Modulationhttp://en.wikipedia.org/wiki/Frequencyhttp://en.wikipedia.org/wiki/Electrical_connectorhttp://en.wikipedia.org/wiki/Electrical_connectorhttp://en.wikipedia.org/wiki/Transmission_mediumhttp://en.wikipedia.org/wiki/Signal_(electronics)http://en.wikipedia.org/wiki/Bit_streamhttp://en.wikipedia.org/wiki/Network_nodehttp://en.wikipedia.org/wiki/Data_linkhttp://en.wikipedia.org/wiki/Network_packethttp://en.wikipedia.org/wiki/Network_packethttp://en.wikipedia.org/wiki/Physical_layer#cite_note-Fundamentals_of_Sensor_Network_Programming-2http://en.wikipedia.org/wiki/Computer_networkhttp://en.wikipedia.org/wiki/Networking_hardwarehttp://en.wikipedia.org/wiki/Physical_layer#cite_note-Data_and_Computer_Network_Communications-1http://en.wikipedia.org/wiki/Computer_networkhttp://en.wikipedia.org/wiki/OSI_model


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The major functions and services performed by the physical layer are:

Bit-by-bit orsymbol-by-symboldelivery

Providing a standardized interface to physicaltransmission media,including

Mechanical specification ofelectrical connectorsandcables,for example maximumcable length

Electrical specification oftransmission linesignal levelandimpedance Radio interface, includingelectromagnetic spectrumfrequency allocationand

specification ofsignal strength,analogbandwidth,etc.

Specifications forIRoveroptical fiberor a wireless IR communication link

Modulation

Line coding

Bit synchronizationin synchronousserial communication

Start-stop signallingandflow controlinasynchronous serial communication

Circuit switching

Multiplexing

Establishment and termination ofcircuit switchedconnections

Carrier senseandcollision detectionutilized by some level 2multiple access protocols

Equalizationfiltering,training sequences,pulse shapingand othersignal processingof

physical signals

Forward error correction[5]for example bitwise convolutional coding

Bit-interleavingand otherchannel coding

The physical layer is also concerned with

Bit rate

Point-to-point,multipoint orpoint-to-multipointline configuration

Physicalnetwork topology,for examplebus,ring,meshorstar network Serialorparallelcommunication

Simplex,half duplexorfull duplextransmission mode

Autonegotiation

List of protocol

Telephone networkmodems-V.92

IRDAphysical layer

USBphysical layer

EIARS-232,EIA-422,EIA-423,RS-449,RS-485 Ethernet physical layerIncluding10BASE-T,10BASE2,10BASE5,100BASE-

TX,100BASE-FX,100BASE-T,1000BASE-T,1000BASE-SXand other varieties

Varieties of 802.11Wi-Fiphysical layers

DSL

ISDN

T1 and otherT-carrierlinks, and E1 and otherE-carrierlinks

SONET/SDH

Optical Transport Network(OTN)

GSMUm air interfacephysical layer

Bluetoothphysical layer ITURecommendations: seeITU-T

IEEE 1394 interface
http://en.wikipedia.org/wiki/Symbol_(data)http://en.wikipedia.org/wiki/Symbol_(data)http://en.wikipedia.org/wiki/Symbol_(data)http://en.wikipedia.org/wiki/Transmission_mediahttp://en.wikipedia.org/wiki/Transmission_mediahttp://en.wikipedia.org/wiki/Transmission_mediahttp://en.wikipedia.org/wiki/Electrical_connectorhttp://en.wikipedia.org/wiki/Electrical_connectorhttp://en.wikipedia.org/wiki/Electrical_connectorhttp://en.wikipedia.org/wiki/Cablehttp://en.wikipedia.org/wiki/Cablehttp://en.wikipedia.org/wiki/Cablehttp://en.wikipedia.org/wiki/Transmission_linehttp://en.wikipedia.org/wiki/Transmission_linehttp://en.wikipedia.org/wiki/Signal_levelhttp://en.wikipedia.org/wiki/Signal_levelhttp://en.wikipedia.org/wiki/Signal_levelhttp://en.wikipedia.org/wiki/Electrical_impedancehttp://en.wikipedia.org/wiki/Electrical_impedancehttp://en.wikipedia.org/wiki/Electrical_impedancehttp://en.wikipedia.org/wiki/Electromagnetic_spectrumhttp://en.wikipedia.org/wiki/Electromagnetic_spectrumhttp://en.wikipedia.org/wiki/Frequency_allocationhttp://en.wikipedia.org/wiki/Frequency_allocationhttp://en.wikipedia.org/wiki/Frequency_allocationhttp://en.wikipedia.org/wiki/Signal_strengthhttp://en.wikipedia.org/wiki/Signal_strengthhttp://en.wikipedia.org/wiki/Signal_strengthhttp://en.wikipedia.org/wiki/Bandwidth_(signal_processing)http://en.wikipedia.org/wiki/Bandwidth_(signal_processing)http://en.wikipedia.org/wiki/Bandwidth_(signal_processing)http://en.wikipedia.org/wiki/Infrared_radiationhttp://en.wikipedia.org/wiki/Infrared_radiationhttp://en.wikipedia.org/wiki/Infrared_radiationhttp://en.wikipedia.org/wiki/Optical_fiberhttp://en.wikipedia.org/wiki/Optical_fiberhttp://en.wikipedia.org/wiki/Optical_fiberhttp://en.wikipedia.org/wiki/Modulationhttp://en.wikipedia.org/wiki/Modulationhttp://en.wikipedia.org/wiki/Line_codinghttp://en.wikipedia.org/wiki/Line_codinghttp://en.wikipedia.org/wiki/Bit_synchronizationhttp://en.wikipedia.org/wiki/Bit_synchronizationhttp://en.wikipedia.org/wiki/Serial_communicationhttp://en.wikipedia.org/wiki/Serial_communicationhttp://en.wikipedia.org/wiki/Serial_communicationhttp://en.wikipedia.org/wiki/Start-stop_signallinghttp://en.wikipedia.org/wiki/Start-stop_signallinghttp://en.wikipedia.org/wiki/Flow_control_(data)http://en.wikipedia.org/wiki/Flow_control_(data)http://en.wikipedia.org/wiki/Flow_control_(data)http://en.wikipedia.org/wiki/Asynchronous_serial_communicationhttp://en.wikipedia.org/wiki/Asynchronous_serial_communicationhttp://en.wikipedia.org/wiki/Asynchronous_serial_communicationhttp://en.wikipedia.org/wiki/Circuit_switchinghttp://en.wikipedia.org/wiki/Circuit_switchinghttp://en.wikipedia.org/wiki/Multiplexinghttp://en.wikipedia.org/wiki/Multiplexinghttp://en.wikipedia.org/wiki/Circuit_switchedhttp://en.wikipedia.org/wiki/Circuit_switchedhttp://en.wikipedia.org/wiki/Circuit_switchedhttp://en.wikipedia.org/wiki/Carrier_sensehttp://en.wikipedia.org/wiki/Carrier_sensehttp://en.wikipedia.org/wiki/CSMA/CDhttp://en.wikipedia.org/wiki/CSMA/CDhttp://en.wikipedia.org/wiki/CSMA/CDhttp://en.wikipedia.org/wiki/Multiple_access_protocolhttp://en.wikipedia.org/wiki/Multiple_access_protocolhttp://en.wikipedia.org/wiki/Multiple_access_protocolhttp://en.wikipedia.org/wiki/Equalizationhttp://en.wikipedia.org/wiki/Equalizationhttp://en.wikipedia.org/wiki/Training_sequencehttp://en.wikipedia.org/wiki/Training_sequencehttp://en.wikipedia.org/wiki/Training_sequencehttp://en.wikipedia.org/wiki/Pulse_shapinghttp://en.wikipedia.org/wiki/Pulse_shapinghttp://en.wikipedia.org/wiki/Pulse_shapinghttp://en.wikipedia.org/wiki/Signal_processinghttp://en.wikipedia.org/wiki/Signal_processinghttp://en.wikipedia.org/wiki/Signal_processinghttp://en.wikipedia.org/wiki/Forward_error_correctionhttp://en.wikipedia.org/wiki/Forward_error_correctionhttp://en.wikipedia.org/wiki/Forward_error_correctionhttp://en.wikipedia.org/wiki/Bit-interleavinghttp://en.wikipedia.org/wiki/Bit-interleavinghttp://en.wikipedia.org/wiki/Channel_codinghttp://en.wikipedia.org/wiki/Channel_codinghttp://en.wikipedia.org/wiki/Channel_codinghttp://en.wikipedia.org/wiki/Bit_ratehttp://en.wikipedia.org/wiki/Bit_ratehttp://en.wikipedia.org/wiki/Point-to-point_(telecommunications)http://en.wikipedia.org/wiki/Point-to-point_(telecommunications)http://en.wikipedia.org/wiki/Point-to-multipointhttp://en.wikipedia.org/wiki/Point-to-multipointhttp://en.wikipedia.org/wiki/Point-to-multipointhttp://en.wikipedia.org/wiki/Network_topologyhttp://en.wikipedia.org/wiki/Network_topologyhttp://en.wikipedia.org/wiki/Network_topologyhttp://en.wikipedia.org/wiki/Bus_networkhttp://en.wikipedia.org/wiki/Bus_networkhttp://en.wikipedia.org/wiki/Bus_networkhttp://en.wikipedia.org/wiki/Ring_networkhttp://en.wikipedia.org/wiki/Ring_networkhttp://en.wikipedia.org/wiki/Ring_networkhttp://en.wikipedia.org/wiki/Mesh_networkhttp://en.wikipedia.org/wiki/Mesh_networkhttp://en.wikipedia.org/wiki/Mesh_networkhttp://en.wikipedia.org/wiki/Star_networkhttp://en.wikipedia.org/wiki/Star_networkhttp://en.wikipedia.org/wiki/Star_networkhttp://en.wikipedia.org/wiki/Serial_communicationhttp://en.wikipedia.org/wiki/Serial_communicationhttp://en.wikipedia.org/wiki/Parallel_communicationhttp://en.wikipedia.org/wiki/Parallel_communicationhttp://en.wikipedia.org/wiki/Parallel_communicationhttp://en.wikipedia.org/wiki/Simplex_communicationhttp://en.wikipedia.org/wiki/Simplex_communicationhttp://en.wikipedia.org/wiki/Duplex_(telecommunications)#Half-duplexhttp://en.wikipedia.org/wiki/Duplex_(telecommunications)#Half-duplexhttp://en.wikipedia.org/wiki/Duplex_(telecommunications)#Half-duplexhttp://en.wikipedia.org/wiki/Duplex_(telecommunications)#Full-duplexhttp://en.wikipedia.org/wiki/Duplex_(telecommunications)#Full-duplexhttp://en.wikipedia.org/wiki/Duplex_(telecommunications)#Full-duplexhttp://en.wikipedia.org/wiki/Autonegotiationhttp://en.wikipedia.org/wiki/Autonegotiationhttp://en.wikipedia.org/wiki/Modemshttp://en.wikipedia.org/wiki/Modemshttp://en.wikipedia.org/wiki/Modemshttp://en.wikipedia.org/wiki/V.92http://en.wikipedia.org/wiki/V.92http://en.wikipedia.org/wiki/V.92http://en.wikipedia.org/wiki/Infrared_Data_Associationhttp://en.wikipedia.org/wiki/Infrared_Data_Associationhttp://en.wikipedia.org/wiki/USBhttp://en.wikipedia.org/wiki/USBhttp://en.wikipedia.org/wiki/Electronic_Industries_Alliancehttp://en.wikipedia.org/wiki/RS-232http://en.wikipedia.org/wiki/RS-232http://en.wikipedia.org/wiki/RS-232http://en.wikipedia.org/wiki/EIA-422http://en.wikipedia.org/wiki/EIA-422http://en.wikipedia.org/wiki/EIA-422http://en.wikipedia.org/wiki/RS-423http://en.wikipedia.org/wiki/RS-423http://en.wikipedia.org/wiki/RS-423http://en.wikipedia.org/wiki/RS-449http://en.wikipedia.org/wiki/RS-449http://en.wikipedia.org/wiki/RS-449http://en.wikipedia.org/wiki/RS-485http://en.wikipedia.org/wiki/RS-485http://en.wikipedia.org/wiki/RS-485http://en.wikipedia.org/wiki/Ethernet_physical_layerhttp://en.wikipedia.org/wiki/Ethernet_physical_layerhttp://en.wikipedia.org/wiki/10BASE-Thttp://en.wikipedia.org/wiki/10BASE-Thttp://en.wikipedia.org/wiki/10BASE-Thttp://en.wikipedia.org/wiki/10BASE2http://en.wikipedia.org/wiki/10BASE2http://en.wikipedia.org/wiki/10BASE2http://en.wikipedia.org/wiki/10BASE5http://en.wikipedia.org/wiki/10BASE5http://en.wikipedia.org/wiki/10BASE5http://en.wikipedia.org/wiki/100BASE-TXhttp://en.wikipedia.org/wiki/100BASE-TXhttp://en.wikipedia.org/wiki/100BASE-TXhttp://en.wikipedia.org/wiki/100BASE-TXhttp://en.wikipedia.org/wiki/100BASE-FXhttp://en.wikipedia.org/wiki/100BASE-FXhttp://en.wikipedia.org/wiki/100BASE-FXhttp://en.wikipedia.org/wiki/100BASE-Thttp://en.wikipedia.org/wiki/100BASE-Thttp://en.wikipedia.org/wiki/100BASE-Thttp://en.wikipedia.org/wiki/1000BASE-Thttp://en.wikipedia.org/wiki/1000BASE-Thttp://en.wikipedia.org/wiki/1000BASE-SXhttp://en.wikipedia.org/wiki/1000BASE-SXhttp://en.wikipedia.org/wiki/1000BASE-SXhttp://en.wikipedia.org/wiki/802.11http://en.wikipedia.org/wiki/Wi-Fihttp://en.wikipedia.org/wiki/Wi-Fihttp://en.wikipedia.org/wiki/Wi-Fihttp://en.wikipedia.org/wiki/Digital_subscriber_linehttp://en.wikipedia.org/wiki/Digital_subscriber_linehttp://en.wikipedia.org/wiki/Integrated_Services_Digital_Networkhttp://en.wikipedia.org/wiki/Integrated_Services_Digital_Networkhttp://en.wikipedia.org/wiki/T-carrierhttp://en.wikipedia.org/wiki/T-carrierhttp://en.wikipedia.org/wiki/T-carrierhttp://en.wikipedia.org/wiki/E-carrierhttp://en.wikipedia.org/wiki/E-carrierhttp://en.wikipedia.org/wiki/E-carrierhttp://en.wikipedia.org/wiki/Synchronous_optical_networkhttp://en.wikipedia.org/wiki/Synchronous_optical_networkhttp://en.wikipedia.org/wiki/Optical_Transport_Networkhttp://en.wikipedia.org/wiki/Optical_Transport_Networkhttp://en.wikipedia.org/wiki/GSMhttp://en.wikipedia.org/wiki/Um_air_interfacehttp://en.wikipedia.org/wiki/Um_air_interfacehttp://en.wikipedia.org/wiki/Um_air_interfacehttp://en.wikipedia.org/wiki/Bluetoothhttp://en.wikipedia.org/wiki/Bluetoothhttp://en.wikipedia.org/wiki/International_Telecommunication_Unionhttp://en.wikipedia.org/wiki/International_Telecommunication_Unionhttp://en.wikipedia.org/wiki/ITU-Thttp://en.wikipedia.org/wiki/ITU-Thttp://en.wikipedia.org/wiki/ITU-Thttp://en.wikipedia.org/wiki/IEEE_1394_interfacehttp://en.wikipedia.org/wiki/IEEE_1394_interfacehttp://en.wikipedia.org/wiki/IEEE_1394_interfacehttp://en.wikipedia.org/wiki/ITU-Thttp://en.wikipedia.org/wiki/International_Telecommunication_Unionhttp://en.wikipedia.org/wiki/Bluetoothhttp://en.wikipedia.org/wiki/Um_air_interfacehttp://en.wikipedia.org/wiki/GSMhttp://en.wikipedia.org/wiki/Optical_Transport_Networkhttp://en.wikipedia.org/wiki/Synchronous_optical_networkhttp://en.wikipedia.org/wiki/E-carrierhttp://en.wikipedia.org/wiki/T-carrierhttp://en.wikipedia.org/wiki/Integrated_Services_Digital_Networkhttp://en.wikipedia.org/wiki/Digital_subscriber_linehttp://en.wikipedia.org/wiki/Wi-Fihttp://en.wikipedia.org/wiki/802.11http://en.wikipedia.org/wiki/1000BASE-SXhttp://en.wikipedia.org/wiki/1000BASE-Thttp://en.wikipedia.org/wiki/100BASE-Thttp://en.wikipedia.org/wiki/100BASE-FXhttp://en.wikipedia.org/wiki/100BASE-TXhttp://en.wikipedia.org/wiki/100BASE-TXhttp://en.wikipedia.org/wiki/10BASE5http://en.wikipedia.org/wiki/10BASE2http://en.wikipedia.org/wiki/10BASE-Thttp://en.wikipedia.org/wiki/Ethernet_physical_layerhttp://en.wikipedia.org/wiki/RS-485http://en.wikipedia.org/wiki/RS-449http://en.wikipedia.org/wiki/RS-423http://en.wikipedia.org/wiki/EIA-422http://en.wikipedia.org/wiki/RS-232http://en.wikipedia.org/wiki/Electronic_Industries_Alliancehttp://en.wikipedia.org/wiki/USBhttp://en.wikipedia.org/wiki/Infrared_Data_Associationhttp://en.wikipedia.org/wiki/V.92http://en.wikipedia.org/wiki/Modemshttp://en.wikipedia.org/wiki/Autonegotiationhttp://en.wikipedia.org/wiki/Duplex_(telecommunications)#Full-duplexhttp://en.wikipedia.org/wiki/Duplex_(telecommunications)#Half-duplexhttp://en.wikipedia.org/wiki/Simplex_communicationhttp://en.wikipedia.org/wiki/Parallel_communicationhttp://en.wikipedia.org/wiki/Serial_communicationhttp://en.wikipedia.org/wiki/Star_networkhttp://en.wikipedia.org/wiki/Mesh_networkhttp://en.wikipedia.org/wiki/Ring_networkhttp://en.wikipedia.org/wiki/Bus_networkhttp://en.wikipedia.org/wiki/Network_topologyhttp://en.wikipedia.org/wiki/Point-to-multipointhttp://en.wikipedia.org/wiki/Point-to-point_(telecommunications)http://en.wikipedia.org/wiki/Bit_ratehttp://en.wikipedia.org/wiki/Channel_codinghttp://en.wikipedia.org/wiki/Bit-interleavinghttp://en.wikipedia.org/wiki/Forward_error_correctionhttp://en.wikipedia.org/wiki/Forward_error_correctionhttp://en.wikipedia.org/wiki/Signal_processinghttp://en.wikipedia.org/wiki/Pulse_shapinghttp://en.wikipedia.org/wiki/Training_sequencehttp://en.wikipedia.org/wiki/Equalizationhttp://en.wikipedia.org/wiki/Multiple_access_protocolhttp://en.wikipedia.org/wiki/CSMA/CDhttp://en.wikipedia.org/wiki/Carrier_sensehttp://en.wikipedia.org/wiki/Circuit_switchedhttp://en.wikipedia.org/wiki/Multiplexinghttp://en.wikipedia.org/wiki/Circuit_switchinghttp://en.wikipedia.org/wiki/Asynchronous_serial_communicationhttp://en.wikipedia.org/wiki/Flow_control_(data)http://en.wikipedia.org/wiki/Start-stop_signallinghttp://en.wikipedia.org/wiki/Serial_communicationhttp://en.wikipedia.org/wiki/Bit_synchronizationhttp://en.wikipedia.org/wiki/Line_codinghttp://en.wikipedia.org/wiki/Modulationhttp://en.wikipedia.org/wiki/Optical_fiberhttp://en.wikipedia.org/wiki/Infrared_radiationhttp://en.wikipedia.org/wiki/Bandwidth_(signal_processing)http://en.wikipedia.org/wiki/Signal_strengthhttp://en.wikipedia.org/wiki/Frequency_allocationhttp://en.wikipedia.org/wiki/Electromagnetic_spectrumhttp://en.wikipedia.org/wiki/Electrical_impedancehttp://en.wikipedia.org/wiki/Signal_levelhttp://en.wikipedia.org/wiki/Transmission_linehttp://en.wikipedia.org/wiki/Cablehttp://en.wikipedia.org/wiki/Electrical_connectorhttp://en.wikipedia.org/wiki/Transmission_mediahttp://en.wikipedia.org/wiki/Symbol_(data)


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TransferJetphysical layer

Etherloop

ARINC 818Avionics Digital Video Bus

G.hn/G.9960physical layer

CAN bus(controller area network) physical layer

Mobile Industry Processor Interfacephysical layer

Hardware equipment (network node) examples

Network adapter

Repeater

Network hub

Modem

Fiber Media Converter

Relation to TCP/IP modelTheTCP/IP model,defined inRFC 1122andRFC 1123,is a high-level networking description

used for the Internet and similar networks. It does not define an equivalent layer that deals

exclusively with hardware-level specifications and interfaces, as this model does not concern

itself directly with physical interfaces. SeveralRFCsmention a physical layer and data link layer,

but that is in context ofIEEEprotocols.RFC 1122and 1123 do not mention any physical layer

functionality or physical layer standards.

Data link layer

In the seven-layerOSI modelofcomputer networking,the data link layeris layer 2; in

theTCP/IP reference model,it is part of thelink layer.The data link layer is the protocol layer

that transfers data between adjacent network nodes in awide area networkor between nodes

on the samelocal area networksegment.[1]The data link layer provides the functional and

procedural means totransferdata between network entities and might provide the means to

detect and possibly correct errors that may occur in thephysical layer.

Examples of data link protocols areEthernetfor local area networks (multi-node), thePoint-to-

Point Protocol(PPP),HDLCandADCCPfor point-to-point (dual-node) connections.

The data link layer is concerned with local delivery offramesbetween devices on the same

LAN. Data-link frames, as theseprotocol data unitsare called, do not cross the boundaries of a

local network. Inter-network routing and global addressing are higher layer functions, allowing

data-link protocols to focus on local delivery, addressing, and media arbitration. In this way, the

data link layer is analogous to a neighborhood traffic cop; it endeavors to arbitrate between

parties contending for access to a medium, without concern for their ultimate destination.

When devices attempt to use a medium simultaneously, frame collisions occur. Data-linkprotocols specify how devices detect and recover from such collisions, and may provide

mechanisms to reduce or prevent them.
http://en.wikipedia.org/wiki/TransferJethttp://en.wikipedia.org/wiki/TransferJethttp://en.wikipedia.org/wiki/Etherloophttp://en.wikipedia.org/wiki/Etherloophttp://en.wikipedia.org/wiki/ARINC_818http://en.wikipedia.org/wiki/ARINC_818http://en.wikipedia.org/wiki/G.hnhttp://en.wikipedia.org/wiki/G.9960http://en.wikipedia.org/wiki/G.9960http://en.wikipedia.org/wiki/G.9960http://en.wikipedia.org/wiki/CAN_bushttp://en.wikipedia.org/wiki/CAN_bushttp://en.wikipedia.org/wiki/Mobile_Industry_Processor_Interfacehttp://en.wikipedia.org/wiki/Mobile_Industry_Processor_Interfacehttp://en.wikipedia.org/wiki/Network_adapterhttp://en.wikipedia.org/wiki/Network_adapterhttp://en.wikipedia.org/wiki/Repeaterhttp://en.wikipedia.org/wiki/Repeaterhttp://en.wikipedia.org/wiki/Network_hubhttp://en.wikipedia.org/wiki/Network_hubhttp://en.wikipedia.org/wiki/Modemhttp://en.wikipedia.org/wiki/Modemhttp://en.wikipedia.org/wiki/Fiber_Media_Converterhttp://en.wikipedia.org/wiki/Fiber_Media_Converterhttp://en.wikipedia.org/wiki/TCP/IP_modelhttp://en.wikipedia.org/wiki/TCP/IP_modelhttp://en.wikipedia.org/wiki/TCP/IP_modelhttp://tools.ietf.org/html/rfc1122http://tools.ietf.org/html/rfc1122http://tools.ietf.org/html/rfc1122http://tools.ietf.org/html/rfc1123http://tools.ietf.org/html/rfc1123http://tools.ietf.org/html/rfc1123http://en.wikipedia.org/wiki/Request_for_Commentshttp://en.wikipedia.org/wiki/Request_for_Commentshttp://en.wikipedia.org/wiki/Request_for_Commentshttp://en.wikipedia.org/wiki/IEEEhttp://en.wikipedia.org/wiki/IEEEhttp://en.wikipedia.org/wiki/IEEEhttp://tools.ietf.org/html/rfc1122http://tools.ietf.org/html/rfc1122http://tools.ietf.org/html/rfc1122http://en.wikipedia.org/wiki/OSI_modelhttp://en.wikipedia.org/wiki/OSI_modelhttp://en.wikipedia.org/wiki/OSI_modelhttp://en.wikipedia.org/wiki/Computer_networkhttp://en.wikipedia.org/wiki/Computer_networkhttp://en.wikipedia.org/wiki/Computer_networkhttp://en.wikipedia.org/wiki/TCP/IP_reference_modelhttp://en.wikipedia.org/wiki/TCP/IP_reference_modelhttp://en.wikipedia.org/wiki/Link_layerhttp://en.wikipedia.org/wiki/Link_layerhttp://en.wikipedia.org/wiki/Link_layerhttp://en.wikipedia.org/wiki/Wide_area_networkhttp://en.wikipedia.org/wiki/Wide_area_networkhttp://en.wikipedia.org/wiki/Wide_area_networkhttp://en.wikipedia.org/wiki/Local_area_networkhttp://en.wikipedia.org/wiki/Local_area_networkhttp://en.wikipedia.org/wiki/Network_segmenthttp://en.wikipedia.org/wiki/Network_segmenthttp://en.wikipedia.org/wiki/Data_link_layer#cite_note-1http://en.wikipedia.org/wiki/Data_link_layer#cite_note-1http://en.wikipedia.org/wiki/Data_link_layer#cite_note-1http://en.wikipedia.org/wiki/Transfer_(computing)http://en.wikipedia.org/wiki/Transfer_(computing)http://en.wikipedia.org/wiki/Transfer_(computing)http://en.wikipedia.org/wiki/Physical_layerhttp://en.wikipedia.org/wiki/Physical_layerhttp://en.wikipedia.org/wiki/Physical_layerhttp://en.wikipedia.org/wiki/Ethernethttp://en.wikipedia.org/wiki/Ethernethttp://en.wikipedia.org/wiki/Ethernethttp://en.wikipedia.org/wiki/Point-to-Point_Protocolhttp://en.wikipedia.org/wiki/Point-to-Point_Protocolhttp://en.wikipedia.org/wiki/Point-to-Point_Protocolhttp://en.wikipedia.org/wiki/HDLChttp://en.wikipedia.org/wiki/HDLChttp://en.wikipedia.org/wiki/HDLChttp://en.wikipedia.org/wiki/ADCCPhttp://en.wikipedia.org/wiki/ADCCPhttp://en.wikipedia.org/wiki/ADCCPhttp://en.wikipedia.org/wiki/Frame_(networking)http://en.wikipedia.org/wiki/Frame_(networking)http://en.wikipedia.org/wiki/Frame_(networking)http://en.wikipedia.org/wiki/Protocol_data_unitshttp://en.wikipedia.org/wiki/Protocol_data_unitshttp://en.wikipedia.org/wiki/Protocol_data_unitshttp://en.wikipedia.org/wiki/Protocol_data_unitshttp://en.wikipedia.org/wiki/Frame_(networking)http://en.wikipedia.org/wiki/ADCCPhttp://en.wikipedia.org/wiki/HDLChttp://en.wikipedia.org/wiki/Point-to-Point_Protocolhttp://en.wikipedia.org/wiki/Point-to-Point_Protocolhttp://en.wikipedia.org/wiki/Ethernethttp://en.wikipedia.org/wiki/Physical_layerhttp://en.wikipedia.org/wiki/Transfer_(computing)http://en.wikipedia.org/wiki/Data_link_layer#cite_note-1http://en.wikipedia.org/wiki/Network_segmenthttp://en.wikipedia.org/wiki/Local_area_networkhttp://en.wikipedia.org/wiki/Wide_area_networkhttp://en.wikipedia.org/wiki/Link_layerhttp://en.wikipedia.org/wiki/TCP/IP_reference_modelhttp://en.wikipedia.org/wiki/Computer_networkhttp://en.wikipedia.org/wiki/OSI_modelhttp://tools.ietf.org/html/rfc1122http://en.wikipedia.org/wiki/IEEEhttp://en.wikipedia.org/wiki/Request_for_Commentshttp://tools.ietf.org/html/rfc1123http://tools.ietf.org/html/rfc1122http://en.wikipedia.org/wiki/TCP/IP_modelhttp://en.wikipedia.org/wiki/Fiber_Media_Converterhttp://en.wikipedia.org/wiki/Modemhttp://en.wikipedia.org/wiki/Network_hubhttp://en.wikipedia.org/wiki/Repeaterhttp://en.wikipedia.org/wiki/Network_adapterhttp://en.wikipedia.org/wiki/Mobile_Industry_Processor_Interfacehttp://en.wikipedia.org/wiki/CAN_bushttp://en.wikipedia.org/wiki/G.9960http://en.wikipedia.org/wiki/G.hnh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Contents

[hide]

1 Overview

2 Sublayers of the data link layer

o 2.1 Logical link control sublayer

o 2.2 Media access control sublayer

3 Data link layer services

4 Error detection and correction

5 Protocol examples

6 Software interfaces


8 See also

9 References

10 External links

OverviewDelivery of frames by layer 2 devices is effected through the use of unambiguous hardware

addresses. A frame's header contains source and destination addresses that indicate which

device originated the frame and which device is expected to receive and process it. In contrast

to the hierarchical and routable addresses of the network layer, layer-2 addresses are flat,

meaning that no part of the address can be used to identify the logical or physical group to

which the address belongs.

The data link thus provides data transfer across the physical link. That transfer can be reliable

or unreliable; many data-link protocols do not have acknowledgments of

successful framereception and acceptance, and some data-link protocols might not even haveany form of checksum to check for transmission errors. In those cases, higher-level protocols

must provideflow control,error checking, and acknowledgments and retransmission.

In some networks, such asIEEE 802local area networks, the data link layer is described in

more detail withmedia access control(MAC) andlogical link control(LLC) sublayers; this means

that theIEEE 802.2LLC protocol can be used with all of the IEEE 802 MAC layers, such as

Ethernet,token ring,IEEE 802.11,etc., as well as with some non-802 MAC layers such

asFDDI.Other data-link-layer protocols, such asHDLC,are specified to include both sublayers,

although some other protocols, such asCisco HDLC,use HDLC's low-level framing as a MAC

layer in combination with a different LLC layer. In theITU-TG.hnstandard, which provides a

way to create a high-speed (up to 1 Gigabit/s)local area networkusing existing home wiring(power lines,phone lines andcoaxial cables), the data link layer is divided into three sub-layers

(application protocol convergence, logical link control and medium access control).

Within the semantics of the OSI network architecture, the data-link-layer protocols respond to

service requests from thenetwork layerand they perform their function by issuing service

requests to thephysical layer.

Sublayers of the data link layer

The data link layer has two sublayers:logical link control(LLC) andmedia access

control(MAC).[2]

Logical link control sublayer
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rg/wiki/Token_ringhttp://en.wikipedia.org/wiki/IEEE_802.2http://en.wikipedia.org/wiki/Logical_link_controlhttp://en.wikipedia.org/wiki/Media_access_controlhttp://en.wikipedia.org/wiki/IEEE_802http://en.wikipedia.org/wiki/Flow_control_(data)http://en.wikipedia.org/wiki/Data_framehttp://en.wikipedia.org/wiki/Data_link_layer#External_linkshttp://en.wikipedia.org/wiki/Data_link_layer#Referenceshttp://en.wikipedia.org/wiki/Data_link_layer#See_alsohttp://en.wikipedia.org/wiki/Data_link_layer#Relation_to_TCP.2FIP_modelhttp://en.wikipedia.org/wiki/Data_link_layer#Software_interfaceshttp://en.wikipedia.org/wiki/Data_link_layer#Protocol_exampleshttp://en.wikipedia.org/wiki/Data_link_layer#Error_detection_and_correctionhttp://en.wikipedia.org/wiki/Data_link_layer#Data_link_layer_serviceshttp://en.wikipedia.org/wiki/Data_link_layer#Media_access_control_sublayerhttp://en.wikipedia.org/wiki/Data_link_layer#Logical_link_control_sublayerhttp://en.wikipedia.org/wiki/Data_link_layer#Sublayers_of_the_data_link_layerhttp://en.wikipedia.org/wiki/Data_link_layer#Overviewhttp://en.wikipedia.org/wiki/Data_link_layer


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The uppermost sublayer, LLC,multiplexesprotocols running atop the data link layer, and

optionally provides flow control, acknowledgment, and error notification. The LLC provides

addressing and control of the data link. It specifies which mechanisms are to be used for

addressing stations over the transmission medium and for controlling the data exchanged

between the originator and recipient machines.

Media access control sublayer

MAC may refer to the sublayer that determines who is allowed to access the media at any one

time (e.g.CSMA/CD). Other times it refers to aframestructure delivered based onMAC

addressesinside.

There are generally two forms of media access control: distributed and centralized. Both of

these may be compared to communication between people. In a network made up of people

speaking, i.e. a conversation, we look for clues from our fellow talkers to see if any of them

appear to be about to speak. If two people speak at the same time, they will each pause a

random amount of time and then attempt to speak again, effectively establishing a long and

elaborate game of saying "no, you first".

The Media Access Control sublayer also determines where oneframeof data ends and the next

one starts frame synchronization.There are four means of frame synchronization: time based,

character counting, byte stuffing and bit stuffing.

The time basedapproach simply puts a specified amount of time between frames. The

major drawback of this is that new gaps can be introduced or old gaps can be lost due to

external influences.

Character countingsimply notes the count of remaining characters in the frame's header.

This method, however, is easily disturbed if this field gets faulty in some way, thus making it

hard to keep up synchronization. Byte stuffingprecedes the frame with a special byte sequence such asDLESTXand

succeeds it with DLEETX.Appearances of DLE (byte value 0x10) have to beescapedwith

another DLE. The start and stop marks are detected at the receiver and removed as well as

the inserted DLE characters.

Similarly,bit stuffingreplaces these start and end marks with flag consisting of a special bit

pattern (e.g. a 0, six 1 bits and a 0). Occurrences of this bit pattern in the data to be

transmitted are avoided by inserting a bit. To use the example where the flag is 01111110, a

0 is inserted after 5 consecutive 1's in the data stream. The flags and the inserted 0's are

removed at the receiving end. This makes for arbitrary long frames and easy

synchronization for the recipient. Note that this stuffed bit is added even if the following data

bit is 0, which could not be mistaken for a sync sequence, so that the receiver canunambiguously distinguish stuffed bits from normal bits.

Data link layer services

Encapsulation ofnetwork layerdata packets intoframes

Frame synchronization

Logical link control(LLC) sublayer:

Error control(automatic repeat request,ARQ), in addition to ARQ provided bysometransport-layerprotocols, toforward error correction(FEC) techniques provided

on thephysical layer,and to error-detection and packet canceling provided at all layers,including the network layer.Data-link-layer error control (i.e. retransmission oferroneous packets) is provided in wireless networks andV.42 telephone network
http://en.wikipedia.org/wiki/Multiplexeshttp://en.wikipedia.org/wiki/Multiplexeshttp://en.wikipedia.org/wiki/Multiplexeshttp://en.wikipedia.org/wiki/CSMA/CDhttp://en.wikipedia.org/wiki/CSMA/CDhttp://en.wikipedia.org/wiki/CSMA/CDhttp://en.wikipedia.org/wiki/Frame_(networking)http://en.wikipedia.org/wiki/Frame_(networking)http://en.wikipedia.org/wiki/Frame_(networking)http://en.wikipedia.org/wiki/MAC_addresshttp://en.wikipedia.org/wiki/MAC_addresshttp://en.wikipedia.org/wiki/MAC_addresshttp://en.wikipedia.org/wiki/MAC_addresshttp://en.wikipedia.org/wiki/Frame_(networking)http://en.wikipedia.org/wiki/Frame_(networking)http://en.wikipedia.org/wiki/Frame_(networking)http://en.wikipedia.org/wiki/Frame_synchronizationhttp://en.wikipedia.org/wiki/Frame_synchronizationhttp://en.wikipedia.org/wiki/Frame_synchronizationhttp://en.wikipedia.org/wiki/Data_Link_Escapehttp://en.wikipedia.org/wiki/Data_Link_Escapehttp://en.wikipedia.org/wiki/Start_Of_Texthttp://en.wikipedia.org/wiki/Start_Of_Texthttp://en.wikipedia.org/wiki/Start_Of_Texthttp://en.wikipedia.org/wiki/End_Of_Texthttp://en.wikipedia.org/wiki/End_Of_Texthttp://en.wikipedia.org/wiki/End_Of_Texthttp://en.wikipedia.org/wiki/Escape_sequencehttp://en.wikipedia.org/wiki/Escape_sequencehttp://en.wikipedia.org/wiki/Escape_sequencehttp://en.wikipedia.org/wiki/Bit_stuffinghttp://en.wikipedia.org/wiki/Bit_stuffinghttp://en.wikipedia.org/wiki/Bit_stuffinghttp://en.wikipedia.org/wiki/Network_layerhttp://en.wikipedia.org/wiki/Network_layerhttp://en.wikipedia.org/wiki/Network_layerhttp://en.wikipedia.org/wiki/Frame_(telecommunications)http://en.wikipedia.org/wiki/Frame_(telecommunications)http://en.wikipedia.org/wiki/Frame_(telecommunications)http://en.wikipedia.org/wiki/Frame_synchronizationhttp://en.wikipedia.org/wiki/Frame_synchronizationhttp://en.wikipedia.org/wiki/Logical_link_controlhttp://en.wikipedia.org/wiki/Logical_link_controlhttp://en.wikipedia.org/wiki/Error_controlhttp://en.wikipedia.org/wiki/Error_controlhttp://en.wikipedia.org/wiki/Automatic_repeat_requesthttp://en.wikipedia.org/wiki/Automatic_repeat_requesthttp://en.wikipedia.org/wiki/Transport-layerhttp://en.wikipedia.org/wiki/Transport-layerhttp://en.wikipedia.org/wiki/Transport-layerhttp://en.wikipedia.org/wiki/Forward_error_correctionhttp://en.wikipedia.org/wiki/Forward_error_correctionhttp://en.wikipedia.org/wiki/Forward_error_correctionhttp://en.wikipedia.org/wiki/Physical_layerhttp://en.wikipedia.org/wiki/Physical_layerhttp://en.wikipedia.org/wiki/Physical_layerhttp://en.wikipedia.org/wiki/Network_layerhttp://en.wikipedia.org/wiki/Network_layerhttp://en.wikipedia.org/wiki/V.42#Error_control_and_data_compressionhttp://en.wikipedia.org/wiki/V.42#Error_control_and_data_compressionhttp://en.wikipedia.org/wiki/V.42#Error_control_and_data_compressionhttp://en.wikipedia.org/wiki/Network_layerhttp://en.wikipedia.org/wiki/Physical_layerhttp://en.wikipedia.org/wiki/Forward_error_correctionhttp://en.wikipedia.org/wiki/Transport-layerhttp://en.wikipedia.org/wiki/Automatic_repeat_requesthttp://en.wikipedia.org/wiki/Error_controlhttp://en.wikipedia.org/wiki/Logical_link_controlhttp://en.wikipedia.org/wiki/Frame_synchronizationhttp://en.wikipedia.org/wiki/Frame_(telecommunications)http://en.wikipedia.org/wiki/Network_layerhttp://en.wikipedia.org/wiki/Bit_stuffinghttp://en.wikipedia.org/wiki/Escape_sequencehttp://en.wikipedia.org/wiki/End_Of_Texthttp://en.wikipedia.org/wiki/Start_Of_Texthttp://en.wikipedia.org/wiki/Data_Link_Escapehttp://en.wikipedia.org/wiki/Frame_synchronizationhttp://en.wikipedia.org/wiki/Frame_(networking)http://en.wikipedia.org/wiki/MAC_addresshttp://en.wikipedia.org/wiki/MAC_addresshttp://en.wikipedia.org/wiki/Frame_(networking)http://en.wikipedia.org/wiki/CSMA/CDhttp://en.wikipedia.org/wiki/Multiplexes


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modems,but not in LAN protocols such asEthernet,since bit errors are so uncommonin short wires. In that case, onlyerror detectionand canceling of erroneous packets areprovided.

Flow control,in addition to the one provided on thetransport layer.Data-link-layer errorcontrol is not used in LAN protocols such as Ethernet, but in modems and wirelessnetworks.

Media access control(MAC) sublayer:

Multiple access protocolsfor channel-access control, for exampleCSMA/CDprotocolsforcollision detectionand re-transmission inEthernetbus networks and hub networks,or theCSMA/CAprotocol forcollision avoidancein wireless networks.

Physical addressing (MAC addressing)

LAN switching(packet switching)including MAC filtering andspanning tree protocol

Data packet queuing orscheduling

Store-and-forwardswitching orcut-through switching

Quality of Service(QoS) control

Virtual LANs(VLAN)

Error detection and correction Besides framing, data link layers also include mechanisms to detect and even recover from

transmission errors.

For a receiver to detect transmission error, the sender must add redundant information (in

the form of bits) as anerror detectioncode to the frame sent.

When the receiver obtains a frame with an error detection code it recomputes it andverifies whether the received error detection code matches the computed error detectioncode. If they match theframeis considered to be valid.

An error detection code can be defined as a function that computes the r (amount of

redundant bits) corresponding to each string of N total number of bits.

The simplest error detection code is theParity bit.

The parity bit allows a receiver to detect transmission errors that have affected a singlebit among the transmitted N+r bits. If there are two or more bits in error, the receivermay not be able to detect the transmission error.

A simple example of how this works by usingmeta-data.Say we want to transmit the word

'HELLO'. To keep things simple we will change each letter in the alphabet as its position in the

alphabet. Thus, the letter A is coded as 1, B as 2, and so on:

HELLO

85121215

Adding the digits 8 + 5 + 12 + 12 + 15 = 52. Then we add 5 + 2 = 7 to get the meta-data. We

then transmit:

851212157

If there are no errors, the receiver will get 8 5 12 12 15 7. The receiver knows that the last

number received is the error-detecting meta-data and that all data before is the message. It can
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recalculate the above math and if it comes to the same meta-data answer, it can be concluded

that the data was received without errors. If it receives something like 7 5 12 12 15 it can run the

check by: 7 + 5 + 12 + 12 + 15 = 51 and 5 + 1 = 6, Since 6 does not equal 7 the receiver can

discard the received data as defective.

Protocol examples

Address Resolution Protocol(ARP)

ARCnet

ATM

Cisco Discovery Protocol(CDP)

Controller Area Network(CAN)

Econet

Ethernet

Ethernet Automatic Protection Switching(EAPS)

Fiber Distributed Data Interface(FDDI)

Frame Relay

High-Level Data Link Control(HDLC)

IEEE 802.2(provides LLC functions to IEEE 802 MAC layers)

IEEE 802.11wireless LAN

LattisNet

Link Access Procedures, D channel(LAPD)

LocalTalk

Multiprotocol Label Switching(MPLS)

Nortel Discovery Protocol(NDP)

OpenFlow(SDN)

Split multi-link trunking(SMLT)

Point-to-Point Protocol(PPP) Serial Line Internet Protocol (SLIP)(obsolete)

IEEE 802.1aq-Shortest Path Bridging

Spanning Tree Protocol

StarLan

Token ring

Unidirectional Link Detection(UDLD)

and most forms ofserial communication.

Software interfaces

Data link layer implementations may be in software only, simulating a network interface.

Relation to TCP/IP model

In theTCP/IP(Internet Protocol Suite)model, OSI's data link layer (in addition to other

components) is contained within the TCP/IP's lowest layer, thelink layer.The Internet Protocol's

link layer only concerns itself with hardware issues to the point of obtaining hardware addresses

for locating hosts on a physical network link and transmitting data frames onto the link. Thus,

the link layer is broader in scope and encompasses all methods that affect the local link, which

is the group of connections that are limited in scope to other nodes on the local access network.

The TCP/IP model is not a top/down comprehensive design reference for networks. It was

formulated for the purpose of illustrating the logical groups and scopes of functions needed in
http://en.wikipedia.org/wiki/Address_Resolution_Protocolhttp://en.wikipedia.org/wiki/Address_Resolution_Protocolhttp://en.wikipedia.org/wiki/ARCnethttp://en.wikipedia.org/wiki/ARCnethttp://en.wikipedia.org/wiki/Asynchronous_Transfer_Modehttp://en.wikipedia.org/wiki/Asynchronous_Transfer_Modehttp://en.wikipedia.org/wiki/Cisco_Discovery_Protocolhttp://en.wikipedia.org/wiki/Cisco_Discovery_Protocolhttp://en.wikipedia.org/wiki/Controller_Area_Networkhttp://en.wikipedia.org/wiki/Controller_Area_Networkhttp://en.wikipedia.org/wiki/Econethttp://en.wikipedia.org/wiki/Econethttp://en.wikipedia.org/wiki/Ethernethttp://en.wikipedia.org/wiki/Ethernethttp://en.wikipedia.org/wiki/Ethernet_Automatic_Protection_Switchinghttp://en.wikipedia.org/wiki/Ethernet_Automatic_Protection_Switchinghttp://en.wikipedia.org/wiki/Fiber_Distributed_Data_Interfacehttp://en.wikipedia.org/wiki/Fiber_Distributed_Data_Interfacehttp://en.wikipedia.org/wiki/Frame_Relayhttp://en.wikipedia.org/wiki/Frame_Relayhttp://en.wikipedia.org/wiki/High-Level_Data_Link_Controlhttp://en.wikipedia.org/wiki/High-Level_Data_Link_Controlhttp://en.wikipedia.org/wiki/IEEE_802.2http://en.wikipedia.org/wiki/IEEE_802.2http://en.wikipedia.org/wiki/IEEE_802.11http://en.wikipedia.org/wiki/Wireless_LANhttp://en.wikipedia.org/wiki/Wireless_LANhttp://en.wikipedia.org/wiki/Wireless_LANhttp://en.wikipedia.org/wiki/LattisNethttp://en.wikipedia.org/wiki/LattisNethttp://en.wikipedia.org/wiki/Link_Access_Procedures,_D_channelhttp://en.wikipedia.org/wiki/Link_Access_Procedures,_D_channelhttp://en.wikipedia.org/wiki/LocalTalkhttp://en.wikipedia.org/wiki/LocalTalkhttp://en.wikipedia.org/wiki/Multiprotocol_Label_Switchinghttp://en.wikipedia.org/wiki/Multiprotocol_Label_Switchinghttp://en.wikipedia.org/wiki/Nortel_Discovery_Protocolhttp://en.wikipedia.org/wiki/Nortel_Discovery_Protocolhttp://en.wikipedia.org/wiki/OpenFlowhttp://en.wikipedia.org/wiki/OpenFlowhttp://en.wikipedia.org/wiki/Split_multi-link_trunkinghttp://en.wikipedia.org/wiki/Split_multi-link_trunkinghttp://en.wikipedia.org/wiki/Point-to-Point_Protocolhttp://en.wikipedia.org/wiki/Point-to-Point_Protocolhttp://en.wikipedia.org/wiki/SLIPhttp://en.wikipedia.org/wiki/SLIPhttp://en.wikipedia.org/wiki/SLIPhttp://en.wikipedia.org/wiki/IEEE_802.1aqhttp://en.wikipedia.org/wiki/IEEE_802.1aqhttp://en.wikipedia.org/wiki/Shortest_Path_Bridginghttp://en.wikipedia.org/wiki/Shortest_Path_Bridginghttp://en.wikipedia.org/wiki/Shortest_Path_Bridginghttp://en.wikipedia.org/wiki/Spanning_Tree_Protocolhttp://en.wikipedia.org/wiki/Spanning_Tree_Protocolhttp://en.wikipedia.org/wiki/StarLanhttp://en.wikipedia.org/wiki/StarLanhttp://en.wikipedia.org/wiki/Token_ringhttp://en.wikipedia.org/wiki/Token_ringhttp://en.wikipedia.org/wiki/UDLDhttp://en.wikipedia.org/wiki/UDLDhttp://en.wikipedia.org/wiki/Serial_communicationhttp://en.wikipedia.org/wiki/Serial_communicationhttp://en.wikipedia.org/wiki/Serial_communicationhttp://en.wikipedia.org/wiki/TCP/IP_modelhttp://en.wikipedia.org/wiki/TCP/IP_modelhttp://en.wikipedia.org/wiki/TCP/IP_modelhttp://en.wikipedia.org/wiki/Internet_Protocol_Suitehttp://en.wikipedia.org/wiki/Internet_Protocol_Suitehttp://en.wikipedia.org/wiki/Internet_Protocol_Suitehttp://en.wikipedia.org/wiki/Link_layerhttp://en.wikipedia.org/wiki/Link_layerhttp://en.wikipedia.org/wiki/Link_layerhttp://en.wikipedia.org/wiki/Link_layerhttp://en.wikipedia.org/wiki/Internet_Protocol_Suitehttp://en.wikipedia.org/wiki/TCP/IP_modelhttp://en.wikipedia.org/wiki/Serial_communicationhttp://en.wikipedia.org/wiki/UDLDhttp://en.wikipedia.org/wiki/Token_ringhttp://en.wikipedia.org/wiki/StarLanhttp://en.wikipedia.org/wiki/Spanning_Tree_Protocolhttp://en.wikipedia.org/wiki/Shortest_Path_Bridginghttp://en.wikipedia.org/wiki/IEEE_802.1aqhttp://en.wikipedia.org/wiki/SLIPhttp://en.wikipedia.org/wiki/Point-to-Point_Protocolhttp://en.wikipedia.org/wiki/Split_multi-link_trunkinghttp://en.wikipedia.org/wiki/OpenFlowhttp://en.wikipedia.org/wiki/Nortel_Discovery_Protocolhttp://en.wikipedia.org/wiki/Multiprotocol_Label_Switchinghttp://en.wikipedia.org/wiki/LocalTalkhttp://en.wikipedia.org/wiki/Link_Access_Procedures,_D_channelhttp://en.wikipedia.org/wiki/LattisNethttp://en.wikipedia.org/wiki/Wireless_LANhttp://en.wikipedia.org/wiki/IEEE_802.11http://en.wikipedia.org/wiki/IEEE_802.2http://en.wikipedia.org/wiki/High-Level_Data_Link_Controlhttp://en.wikipedia.org/wiki/Frame_Relayhttp://en.wikipedia.org/wiki/Fiber_Distributed_Data_Interfacehttp://en.wikipedia.org/wiki/Ethernet_Automatic_Protection_Switchinghttp://en.wikipedia.org/wiki/Ethernethttp://en.wikipedia.org/wiki/Econethttp://en.wikipedia.org/wiki/Controller_Area_Networkhttp://en.wikipedia.org/wiki/Cisco_Discovery_Protocolhttp://en.wikipedia.org/wiki/Asynchronous_Transfer_Modehttp://en.wikipedia.org/wiki/ARCnethttp://en.wikipedia.org/wiki/Address_Resolution_Protocol


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the design of the suite of internetworking protocols of TCP/IP, as needed for the operation of the

Internet. In general, direct or strict comparisons of the OSI and TCP/IP models should be

avoided, because the layering in TCP/IP is not a principal design criterion and in general

considered to be "harmful" (RFC 3439). In particular, TCP/IP does not dictate a strict

hierarchical sequence of encapsulation requirements, as is attributed to OSI protocols.

Network layerIn the seven-layerOSI modelofcomputer networking,the network layeris layer 3. The

network layer is responsible forpacket forwardingincludingroutingthrough intermediate

routers, whereas thedata link layeris responsible for media access control, flow control and

error checking.

Contents

[hide]

1 Functions

2 Protocols


4 See also

5 References

6 External links

Functions

The network layer provides the functional and procedural means of transferring variable-

lengthdatasequences from a source to a destination host via one or more networks, whilemaintaining thequality of servicefunctions.

Functions of the network layer include:

Connection model:connectionlesscommunication

For example,IPis connectionless, in that a datagram can travel from a sender to arecipient without the recipient having to send an acknowledgement. Connection-orientedprotocols exist at other, higher layers of the OSI model.

Host addressing

Every host in the network must have a unique address that determines where it is. Thisaddress is normally assigned from a hierarchical system. For example, you can be "FredMurphy" to people in your house, "Fred Murphy, 1 Main Street" to Dubliners, or "FredMurphy, 1 Main Street, Dublin" to people in Ireland, or "Fred Murphy, 1 Main Street,Dublin, Ireland" to people anywhere in the world. On the Internet, addresses are knownasInternet Protocol (IP) addresses.

Message forwarding

Since many networks are partitioned into subnetworks and connect to other networks forwide-area communications, networks use specialized hosts, called gateways orrouters,to forward packets between networks. This is also of interest to mobile applications,where a user may move from one location to another, and it must be arranged that hismessages follow him. Version 4 of theInternet Protocol(IPv4)was not designed with thisfeature in mind, although mobility extensions exist.IPv6has a better designed solution.
http://tools.ietf.org/html/rfc3439http://tools.ietf.org/html/rfc3439http://tools.ietf.org/html/rfc3439http://en.wikipedia.org/wiki/OSI_modelhttp://en.wikipedia.org/wiki/OSI_modelhttp://en.wikipedia.org/wiki/OSI_modelhttp://en.wikipedia.org/wiki/Computer_networkinghttp://en.wikipedia.org/wiki/Computer_networkinghttp://en.wikipedia.org/wiki/Computer_networkinghttp://en.wikipedia.org/wiki/Packet_forwardinghttp://en.wikipedia.org/wiki/Packet_forwardinghttp://en.wikipedia.org/wiki/Packet_forwardinghttp://en.wikipedia.org/wiki/Routinghttp://en.wikipedia.org/wiki/Routinghttp://en.wikipedia.org/wiki/Routinghttp://en.wikipedia.org/wiki/Data_link_layerhttp://en.wikipedia.org/wiki/Data_link_layerhttp://en.wikipedia.org/wiki/Data_link_layerhttp://en.wikipedia.org/wiki/Network_layerhttp://en.wikipedia.org/wiki/Network_layerhttp://en.wikipedia.org/wiki/Network_layerhttp://en.wikipedia.org/wiki/Network_layer#Functionshttp://en.wikipedia.org/wiki/Network_layer#Functionshttp://en.wikipedia.org/wiki/Network_layer#Protocolshttp://en.wikipedia.org/wiki/Network_layer#Protocolshttp://en.wikipedia.org/wiki/Network_layer#Relation_to_TCP.2FIP_modelhttp://en.wikipedia.org/wiki/Network_layer#Relation_to_TCP.2FIP_modelhttp://en.wikipedia.org/wiki/Network_layer#See_alsohttp://en.wikipedia.org/wiki/Network_layer#See_alsohttp://en.wikipedia.org/wiki/Network_layer#Referenceshttp://en.wikipedia.org/wiki/Network_layer#Referenceshttp://en.wikipedia.org/wiki/Network_layer#External_linkshttp://en.wikipedia.org/wiki/Network_layer#External_linkshttp://en.wikipedia.org/wiki/Datahttp://en.wikipedia.org/wiki/Datahttp://en.wikipedia.org/wiki/Datahttp://en.wikipedia.org/wiki/Quality_of_servicehttp://en.wikipedia.org/wiki/Quality_of_servicehttp://en.wikipedia.org/wiki/Quality_of_servicehttp://en.wikipedia.org/wiki/Connectionlesshttp://en.wikipedia.org/wiki/Connectionlesshttp://en.wikipedia.org/wiki/Connectionlesshttp://en.wikipedia.org/wiki/Internet_Protocolhttp://en.wikipedia.org/wiki/Internet_Protocolhttp://en.wikipedia.org/wiki/Internet_Protocolhttp://en.wikipedia.org/wiki/IP_addresshttp://en.wikipedia.org/wiki/IP_addresshttp://en.wikipedia.org/wiki/IP_addresshttp://en.wikipedia.org/wiki/Router_(computing)http://en.wikipedia.org/wiki/Router_(computing)http://en.wikipedia.org/wiki/Router_(computing)http://en.wikipedia.org/wiki/Internet_Protocolhttp://en.wikipedia.org/wiki/Internet_Protocolhttp://en.wikipedia.org/wiki/IPv4http://en.wikipedia.org/wiki/IPv4http://en.wikipedia.org/wiki/IPv4http://en.wikipedia.org/wiki/IPv6http://en.wikipedia.org/wiki/IPv6http://en.wikipedia.org/wiki/IPv6http://en.wikipedia.org/wiki/IPv6http://en.wikipedia.org/wiki/IPv4http://en.wikipedia.org/wiki/Internet_Protocolhttp://en.wikipedia.org/wiki/Router_(computing)http://en.wikipedia.org/wiki/IP_addresshttp://en.wikipedia.org/wiki/Internet_Protocolhttp://en.wikipedia.org/wiki/Connectionlesshttp://en.wikipedia.org/wiki/Quality_of_servicehttp://en.wikipedia.org/wiki/Datahttp://en.wikipedia.org/wiki/Network_layer#External_linkshttp://en.wikipedia.org/wiki/Network_layer#Referenceshttp://en.wikipedia.org/wiki/Network_layer#See_alsohttp://en.wikipedia.org/wiki/Network_layer#Relation_to_TCP.2FIP_modelhttp://en.wikipedia.org/wiki/Network_layer#Protocolshttp://en.wikipedia.org/wiki/Network_layer#Functionshttp://en.wikipedia.org/wiki/Network_layerhttp://en.wikipedia.org/wiki/Data_link_layerhttp://en.wikipedia.org/wiki/Routinghttp://en.wikipedia.org/wiki/Packet_forwardinghttp://en.wikipedia.org/wiki/Computer_networkinghttp://en.wikipedia.org/wiki/OSI_modelhttp://tools.ietf.org/html/rfc3439


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Within the service layering semantics of the OSI network architecture, the network

layer responds to service requests from thetransport layerand issues service

requests to thedata link layer.

Protocols

IPv4/IPv6,Internet Protocol

DVMRP,Distance Vector Multicast Routing Protocol

ICMP,Internet Control Message Protocol

IGMP,Internet Group Management Protocol

PIM-SM,Protocol Independent Multicast Sparse Mode

PIM-DM,Protocol Independent Multicast Dense Mode

IPsec,Internet Protocol Security

IPX,Internetwork Packet Exchange

RIP,Routing Information Protocol

DDP,Datagram Delivery Protocol

RSMLTRouted-SMLT ARP,Address Resolution Protocol

Shortest Path Bridging

Relation to TCP/IP model

TheTCP/IP modeldescribes the protocols used by the Internet.[1]The TCP/IP model

has a layer called theInternet layer,located above thelink layer.In many textbooks

and other secondary references, the TCP/IP Internet layer is equated with the OSI

network layer. However, this comparison is misleading, as the allowed

characteristics of protocols (e.g., whether they are connection-oriented orconnection-less) placed into these layers are different in the two models. The

TCP/IP Internet layer is in fact only a subset of functionality of the network layer. It

describes only one type of network architecture, the Internet.

In general, direct or strict comparisons between these models should be avoided,

since the layering in TCP/IP is not a principal design criterion and the Internet

Engineering Task Force(IETF) considers it "harmful".[2]

Transport layer

Incomputer networking,a transport layerprovides end-to-end or host-to-host communication

services for applications within a layered architecture of network components and

protocols.[1]The transport layer provides services such asconnection-orienteddata

streamsupport,reliability,flow control,andmultiplexing.

Transport layer implementations are contained in both theTCP/IP model(RFC 1122),[2]which is

the foundation of theInternet,and theOpen Systems Interconnection(OSI) modelof general

networking, however, the definitions of details of the transport layer are different in these

models. In theOpen Systems Interconnectionmodel the transport layer is most often referred to

as Layer 4.

The best-known transport protocol is theTransmission Control Protocol(TCP). It lent its name

to the title of the entireInternet Protocol Suite,TCP/IP. It is used for connection-oriented
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nsmission_Control_Protocolhttp://en.wikipedia.org/wiki/Internet_Protocol_Suitehttp://en.wikipedia.org/wiki/Internet_Protocol_Suitehttp://en.wikipedia.org/wiki/Internet_Protocol_Suitehttp://en.wikipedia.org/wiki/Internet_Protocol_Suitehttp://en.wikipedia.org/wiki/Transmission_Control_Protocolhttp://en.wikipedia.org/wiki/Open_Systems_Interconnectionhttp://en.wikipedia.org/wiki/OSI_modelhttp://en.wikipedia.org/wiki/Open_Systems_Interconnectionhttp://en.wikipedia.org/wiki/Internethttp://en.wikipedia.org/wiki/Transport_layer#cite_note-2http://tools.ietf.org/html/rfc1122http://en.wikipedia.org/wiki/TCP/IP_modelhttp://en.wikipedia.org/wiki/Multiplexinghttp://en.wikipedia.org/wiki/Flow_control_(data)http://en.wikipedia.org/wiki/Reliability_(computer_networking)http://en.wikipedia.org/wiki/Data_streamhttp://en.wikipedia.org/wiki/Data_streamhttp://en.wikipedia.org/wiki/Connection-oriented_communicationhttp://en.wikipedia.org/wiki/Transport_layer#cite_note-1http://en.wikipedia.org/wiki/Computer_networkinghttp://en.wikipedia.org/wiki/Network_layer#cite_note-2http://en.wikipedia.org/wiki/Internet_Engineering_Task_Forcehttp://en.wikipedia.org/wiki/Internet_Engineering_Task_Forcehttp://en.wikipedia.org/wiki/Link_layerhttp://en.wikipedia.org/wiki/Internet_layerhttp://en.wikipedia.org/wiki/Network_layer#cite_note-1http://en.wikipedia.org/wiki/TCP/IP_modelhttp://en.wikipedia.org/wiki/Shortest_Path_Bridginghttp://en.wikipedia.org/wiki/Address_Resolution_Protocolhttp://en.wikipedia.org/wiki/Routed-SMLThttp://en.wikipedia.org/wiki/Datagram_Delivery_Protocolhttp://en.wikipedia.org/wiki/Routing_Information_Protocolhttp://en.wikipedia.org/wiki/IPXhttp://en.wikipedia.org/wiki/IPsechttp://en.wikipedia.org/wiki/Protocol_Independent_Multicasthttp://en.wikipedia.org/wiki/Protocol_Independent_Multicasthttp://en.wikipedia.org/wiki/IGMPhttp://en.wikipedia.org/wiki/Internet_Control_Message_Protocolhttp://en.wikipedia.org/wiki/DVMRPhttp://en.wikipedia.org/wiki/Internet_Protocolhttp://en.wikipedia.org/wiki/Data_link_layerhttp://en.wikipedia.org/wiki/Transport_layer


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transmissions, whereas the connectionlessUser Datagram Protocol(UDP) is used for simpler

messaging transmissions. TCP is the more complex protocol, due to its stateful design

incorporating reliable transmission and data stream services. Other prominent protocols in this

group are theDatagram Congestion Control Protocol(DCCP) and theStream Control

Transmission Protocol(SCTP).

Contents

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1 Services

2 Analysis

3 Protocols

4 Comparison of transport layer protocols

5 Comparison of OSI transport protocols

6 References

7 External links

Services

Transport layer services are conveyed to an application via a programming interface to the

transport layer protocols. The services may include the following features:

Connection-oriented communication:It is normally easier for an application to interpret a

connection as adata streamrather than having to deal with the underlying connection-less

models, such as thedatagrammodel of theUser Datagram Protocol(UDP) and of

theInternet Protocol(IP).

Same order delivery: The network layer doesn't generally guarantee that packets of data will

arrive in the same order that they were sent, but often this is a desirable feature. This isusually done through the use of segment numbering, with the receiver passing them to the

application in order. This can causehead-of-line blocking.

Reliability:Packets may be lost during transport due tonetwork congestionand errors. By

means of anerror detection code,such as achecksum,the transport protocol may check

that the data is not corrupted, and verify correct receipt by sending

anACKorNACKmessage to the sender.Automatic repeat requestschemes may be used

to retransmit lost or corrupted data.

Flow control:The rate of data transmission between two nodes must sometimes be

managed to prevent a fast sender from transmitting more data than can be supported by the

receivingdata buffer,causing a buffer overrun. This can also be used to improve efficiency

by reducingbuffer underrun. Congestion avoidance:Congestion controlcan control traffic entry into a

telecommunications network, so as to avoidcongestive collapseby attempting to avoid

oversubscription of any of the processing orlinkcapabilities of the intermediate nodes and

networks and taking resource reducing steps, such as reducing the rate of sendingpackets.

For example,automatic repeat requestsmay keep the network in a congested state; this

situation can be avoided by adding congestion avoidance to the flow control, includingslow-

start.This keeps the bandwidth consumption at a low level in the beginning of the

transmission, or after packet retransmission.

Multiplexing:Portscan provide multiple endpoints on a single node. For example, the name

on a postal address is a kind of multiplexing, and distinguishes between different recipients

of the same location. Computer applications will each listen for information on their own

ports, which enables the use of more than onenetwork serviceat the same time. It is part of

the transport layer in theTCP/IP model,but of thesession layerin the OSI model.
http://en.wikipedia.org/wiki/User_Datagram_Protocolhttp://en.wikipedia.org/wiki/User_Datagram_Protocolhttp://en.wikipedia.org/wiki/User_Datagram_Protocolhttp://en.wikipedia.org/wiki/Datagram_Congestion_Control_Protocolhttp://en.wikipedia.org/wiki/Datagram_Congestion_Control_Protocolhttp://en.wikipedia.org/wiki/Datagram_Congestion_Control_Protocolhttp://en.wikipedia.org/wiki/Stream_Control_Transmission_Protocolhttp://en.wikipedia.org/wiki/Stream_Control_Transmission_Protocolhttp://en.wikipedia.org/wiki/Stream_Control_Transmission_Protocolhttp://en.wikipedia.org/wiki/Stream_Control_Transmission_Protocolhttp://en.wikipedia.org/wiki/Transport_layerhttp://en.wikipedia.org/wiki/Transport_layerhttp://en.wikipedia.org/wiki/Transport_layerhttp://en.wikipedia.org/wiki/Transport_layer#Serviceshttp://en.wikipedia.org/wiki/Transport_layer#Serviceshttp://en.wikipedia.org/wiki/Transport_layer#Analysishttp://en.wikipedia.org/wiki/Transport_layer#Analysishttp://en.wikipedia.org/wiki/Transport_layer#Protocolshttp://en.wikipedia.org/wiki/Transport_layer#Protocolshttp://en.wikipedia.org/wiki/Transport_layer#Comparison_of_transport_layer_protocolshttp://en.wikipedia.org/wiki/Transport_layer#Comparison_of_transport_layer_protocolshttp://en.wikipedia.org/wiki/Transport_layer#Comparison_of_OSI_transport_protocolshttp://en.wikipedia.org/wiki/Transport_layer#Comparison_of_OSI_transport_protocolshttp://en.wikipedia.org/wiki/Transport_layer#Referenceshttp://en.wikipedia.org/wiki/Transport_layer#Referenceshttp://en.wikipedia.org/wiki/Transport_layer#External_linkshttp://en.wikipedia.org/wiki/Transport_layer#External_linkshttp://en.wikipedia.org/wiki/Connection-oriented_communicationhttp://en.wikipedia.org/wiki/Connection-oriented_communicationhttp://en.wikipedia.org/wiki/Data_streamhttp://en.wikipedia.org/wiki/Data_streamhttp://en.wikipedia.org/wiki/Data_streamhttp://en.wikipedia.org/wiki/Datagramhttp://en.wikipedia.org/wiki/Datagramhttp://en.wikipedia.org/wiki/Datagramhttp://en.wikipedia.org/wiki/User_Datagram_Protocolhttp://en.wikipedia.org/wiki/User_Datagram_Protocolhttp://en.wikipedia.org/wiki/User_Datagram_Protocolhttp://en.wikipedia.org/wiki/Internet_Protocolhttp://en.wikipedia.org/wiki/Internet_Protocolhttp://en.wikipedia.org/wiki/Internet_Protocolhttp://en.wikipedia.org/wiki/Head-of-line_blockinghttp://en.wikipedia.org/wiki/Head-of-line_blockinghttp://en.wikipedia.org/wiki/Head-of-line_blockinghttp://en.wikipedia.org/wiki/Reliability_(computer_networking)http://en.wikipedia.org/wiki/Reliability_(computer_networking)http://en.wikipedia.org/wiki/Network_congestionhttp://en.wikipedia.org/wiki/Network_congestionhttp://en.wikipedia.org/wiki/Network_congestionhttp://en.wikipedia.org/wiki/Error_detection_codehttp://en.wikipedia.org/wiki/Error_detection_codehttp://en.wikipedia.org/wiki/Error_detection_codehttp://en.wikipedia.org/wiki/Checksumhttp://en.wikipedia.org/wiki/Checksumhttp://en.wikipedia.org/wiki/Checksumhttp://en.wikipedia.org/wiki/Acknowledgement_(data_networks)http://en.wikipedia.org/wiki/Acknowledgement_(data_networks)http://en.wikipedia.org/wiki/Acknowledgement_(data_networks)http://en.wikipedia.org/wiki/Negative-acknowledge_characterhttp://en.wikipedia.org/wiki/Negative-acknowledge_characterhttp://en.wikipedia.org/wiki/Negative-acknowledge_characterhttp://en.wikipedia.org/wiki/Automatic_repeat_requesthttp://en.wikipedia.org/wiki/Automatic_repeat_requesthttp://en.wikipedia.org/wiki/Automatic_repeat_requesthttp://en.wikipedia.org/wiki/Flow_control_(data)http://en.wikipedia.org/wiki/Flow_control_(data)http://en.wikipedia.org/wiki/Data_bufferhttp://en.wikipedia.org/wiki/Data_bufferhttp://en.wikipedia.org/wiki/Data_bufferhttp://en.wikipedia.org/wiki/Buffer_underrunhttp://en.wikipedia.org/wiki/Buffer_underrunhttp://en.wikipedia.org/wiki/Buffer_underrunhttp://en.wikipedia.org/wiki/Congestion_avoidancehttp://en.wikipedia.org/wiki/Congestion_avoidancehttp://en.wikipedia.org/wiki/Congestion_controlhttp://en.wikipedia.org/wiki/Congestion_controlhttp://en.wikipedia.org/wiki/Congestion_controlhttp://en.wikipedia.org/wiki/Congestive_collapsehttp://en.wikipedia.org/wiki/Congestive_collapsehttp://en.wikipedia.org/wiki/Congestive_collapsehttp://en.wikipedia.org/wiki/Data_linkhttp://en.wikipedia.org/wiki/Data_linkhttp://en.wikipedia.org/wiki/Data_linkhttp://en.wikipedia.org/wiki/Packet_(information_technology)http://en.wikipedia.org/wiki/Packet_(information_technology)http://en.wikipedia.org/wiki/Packet_(information_technology)http://en.wikipedia.org/wiki/Automatic_repeat_requesthttp://en.wikipedia.org/wiki/Automatic_repeat_requesthttp://en.wikipedia.org/wiki/Automatic_repeat_requesthttp://en.wikipedia.org/wiki/Slow-starthttp://en.wikipedia.org/wiki/Slow-starthttp://en.wikipedia.org/wiki/Slow-starthttp://en.wikipedia.org/wiki/Slow-starthttp://en.wikipedia.org/wiki/Multiplexinghttp://en.wikipedia.org/wiki/Multiplexinghttp://en.wikipedia.org/wiki/TCP_and_UDP_porthttp://en.wikipedia.org/wiki/TCP_and_UDP_porthttp://en.wikipedia.org/wiki/TCP_and_UDP_porthttp://en.wikipedia.org/wiki/Network_servicehttp://en.wikipedia.org/wiki/Network_servicehttp://en.wikipedia.org/wiki/Network_servicehttp://en.wikipedia.org/wiki/TCP/IP_modelhttp://en.wikipedia.org/wiki/TCP/IP_modelhttp://en.wikipedia.org/wiki/TCP/IP_modelhttp://en.wikipedia.org/wiki/Session_layerhttp://en.wikipedia.org/wiki/Session_layerhttp://en.wikipedia.org/wiki/Session_layerhttp://en.wikipedia.org/wiki/Session_layerhttp://en.wikipedia.org/wiki/TCP/IP_modelhttp://en.wikipedia.org/wiki/Network_servicehttp://en.wikipedia.org/wiki/TCP_and_UDP_porthttp://en.wikipedia.org/wiki/Multiplexinghttp://en.wikipedia.org/wiki/Slow-starthttp://en.wikipedia.org/wiki/Slow-starthttp://en.wikipedia.org/wiki/Automatic_repeat_requesthttp://en.wikipedia.org/wiki/Packet_(information_technology)http://en.wikipedia.org/wiki/Data_linkhttp://en.wikipedia.org/wiki/Congestive_collapsehttp://en.wikipedia.org/wiki/Congestion_controlhttp://en.wikipedia.org/wiki/Congestion_avoidancehttp://en.wikipedia.org/wiki/Buffer_underrunhttp://en.wikipedia.org/wiki/Data_bufferhttp://en.wikipedia.org/wiki/Flow_control_(data)http://en.wikipedia.org/wiki/Automatic_repeat_requesthttp://en.wikipedia.org/wiki/Negative-acknowledge_characterhttp://en.wikipedia.org/wiki/Acknowledgement_(data_networks)http://en.wikipedia.org/wiki/Checksumhttp://en.wikipedia.org/wiki/Error_detection_codehttp://en.wikipedia.org/wiki/Network_congestionhttp://en.wikipedia.org/wiki/Reliability_(computer_networking)http://en.wikipedia.org/wiki/Head-of-line_blockinghttp://en.wikipedia.org/wiki/Internet_Protocolhttp://en.wikipedia.org/wiki/User_Datagram_Protocolhttp://en.wikipedia.org/wiki/Datagramhttp://en.wikipedia.org/wiki/Data_streamhttp://en.wikipedia.org/wiki/Connection-oriented_communicationhttp://en.wikipedia.org/wiki/Transport_layer#External_linkshttp://en.wikipedia.org/wiki/Transport_layer#Referenceshttp://en.wikipedia.org/wiki/Transport_layer#Comparison_of_OSI_transport_protocolshttp://en.wikipedia.org/wiki/Transport_layer#Comparison_of_transport_layer_protocolshttp://en.wikipedia.org/wiki/Transport_layer#Protocolshttp://en.wikipedia.org/wiki/Transport_layer#Analysishttp://en.wikipedia.org/wiki/Transport_layer#Serviceshttp://en.wikipedia.org/wiki/Transport_layerhttp://en.wikipedia.org/wiki/Stream_Control_Transmission_Protocolhttp://en.wikipedia.org/wiki/Stream_Control_Transmission_Protocolhttp://en.wikipedia.org/wiki/Datagram_Congestion_Control_Protocolhttp://en.wikipedia.org/wiki/User_Datagram_Protocol


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Analysis

The transport layer is responsible for delivering data to the appropriate application process on

the host computers. This involvesstatistical multiplexingof data from different application

processes, i.e. forming data packets, and adding source and destination port numbers in the

header of each transport layer data packet. Together with the source and destination IP

address, the port numbers constitutes anetwork socket,i.e. an identification address of theprocess-to-pro

open systems interconnection model (osi).pdf

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