DATA COMMUNICATION (ELA…)
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Transcript of DATA COMMUNICATION (ELA…)
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DATA COMMUNICATION(ELA…)
PROTOCOLS AND ARCHITECTURE1
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PROTOCOLS
Used for communications between entities in different systems
Must speak the same language
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KEY ELEMENTS OF A PROTOCOL Syntax
Data formatsSignal levels
SemanticsControl informationError handling
TimingSpeed matchingSequencing
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SERVER
RFLINK
PC
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EXAMPLE: THREE-LAYER MODEL Communications can be said to involve
three agents:`
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EXAMPLE: THREE-LAYER MODEL Makes sense to organize the
communication task into three, relatively independent layers
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CommTask
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EXAMPLE: THREE-LAYER MODEL Network Access Layer Functions
Exchange of data between the computer and the network
Sending computer provides address of destination to help in determining routing options
May invoke levels of service (i.e., priority) Software used in this layer depends on type of
network used
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EXAMPLE: THREE-LAYER MODEL Computer-Transport Layer Functions
Reliable data exchange Data arrive at destination application Same order in which they were sent
Independent of network being used Independent of application
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EXAMPLE: THREE-LAYER MODEL Application Layer Functions
Support for different user applications User applications refer to network applications Examples
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EXAMPLE: THREE-LAYER MODEL Addressing Requirements
Two levels of addressing required Each computer needs unique network address Each application on a multi-tasking computer needs a
unique address within the computerService Access Point (SAP)
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PROTOCOL ARCHITECTURES AND NETWORKS
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PROTOCOL DATA UNITS
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OSI – THE MODEL
Open Systems Interconnection (OSI) Developed by the International
Organization for Standardization (ISO) Seven layers A theoretical system delivered too late! TCP/IP is the de facto standard
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OSI – THE MODELLayering is the key! Each layer performs a subset of the
required communication functions Each layer relies on the next lower
layer to perform more primitive functions
Each layer provides services to the next higher layer
Changes in one layer should not require changes in other layers
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THE OSI ENVIRONMENT
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STANDARDIZATION WITHIN THE OSI FRAMEWORK
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ELEMENTS OF STANDARDIZATION
Protocol specificationOperates between the same layer on two
systemsMay involve different operating systemProtocol specification must be precise
Format of data units Semantics of all fields Allowable sequence of PDUs
Service definitionFunctional description of what is provided
AddressingReferenced by SAPs
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LAYER SPECIFIC STANDARDS
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ISO OSI REFERENCE MODEL
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Application Layer (7)
Presentation Layer (6)
Session Layer (5) Transport Layer (4)
Network Layer (3) Data Link Layer
(2) Physical Layer (1)
Application orientedNetwork oriented
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NETWORK-DEPENDENT LAYERS
Physical LayerConcerned with the physical and electrical
interfaces b/w the user equipment and the network equipment
Responsible for the transmission of bitsAlways implemented using hardwarePhysical layer standards
RS-232-C RS-449 RS-422-A RS-423-A
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NETWORK-DEPENDENT LAYERS
Data Link LayerAssembles data bits into a block, or frameResponsible for ensuring error-free, reliable
transmission of dataRequests retransmission or correction if any
errors occurExample protocols
BSC SDLC HDLC PPP
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NETWORK-DEPENDENT LAYERS Network Layer
Responsible for appropriate routing of messages across a network
Only layer concerned with types of switching networks used to route data
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USE OF A RELAY
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APPLICATION-ORIENTED LAYERS Transport Layer
Responsible for: Monitoring the quality of the communications channel Selecting the most cost-efficient communication
service based on reliability required for a particular transmission
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APPLICATION-ORIENTED LAYERS
Session Layer Requests that a logical connection be established
based on the end user’s request Transfer a file
File location File destination
Controls any necessary log-ons and passwords Responsible for terminating connection
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APPLICATION-ORIENTED LAYERS
Presentation Layer Provides format and code conversion services
Printing operations Concerned with syntax and semantics of the
information transmitted File transfers b/w heterogeneous hosts
Data compression Data encryption
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APPLICATION-ORIENTED LAYERS Application layer
Provides access to the network for the end user Remote terminal access File transfer
Network management statistics and diagnostics can also be implemented in this layer
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TCP/IP PROTOCOL SUITE Dominant commercial protocol architecture Specified and extensively used before OSI Developed through the US Department of
Defense Used by the Internet
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TCP/IP LAYERS Physical Layer Network Access Layer Internet Layer Transport Layer (a.k.a., Host-to-host) Application Layer
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PHYSICAL LAYER Physical interface between data transmission
device (e.g. computer) and transmission medium or network Characteristics of transmission medium Signal levels Data rates
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NETWORK ACCESS LAYER Exchange of data between end system and
network Destination address provision Invoking services like priority Software depends on type of network
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INTERNET LAYER (IP) Systems may be attached to different
networks Routing functions across multiple networks Implemented in end systems and routers
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TRANSPORT LAYER Reliable delivery of data Ordering of delivery Uses Transmission Control Protocol (TCP)
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APPLICATION LAYER Support for user applications
HTTP Simple Mail Transfer Protocol (SMTP) Telnet FTP
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OPERATION OF TCP AND IP
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PDUS IN TCP/IP
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SOME PROTOCOLS IN TCP/IP SUITE
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OSI VS. TCP/IP
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STANDARDS
Required to allow for interoperability between equipment
AdvantagesEnsures a large market for equipment and
softwareAllows products from different vendors to
communicate Disadvantages
Freeze technologyMay be multiple standards for the same
thing e.g., military vs. commercial
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STANDARDS ORGANIZATIONS
Internet Society ISO International Telecommunications Union –
Telecommunications Sector (ITU-T) ATM forum
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