# Critique Of Osi Model-Data Communication-Lecture Notes, Study notes for Data Communication. Agra University

## Data Communication

Description: Data Communication is exchange of data between two devices. In computers data exchange is in form of 0 and 1. This course discuss how computer communicate, what is medium and what are expenses. This handout includes: Critique, Osi, Model, Widespread, Implementations, Empty, Presentation, Apocalype, Standards
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LECTURE # 8
Critique of OSI Model
Reasoning for OSI not getting Widespread
¾Bad Timing(slide) (Apocalypse of Two Elephants)
–David Clarke of MIT
–If standards are written too early: subject is badly understood and bad standards
–If standards are written too late so many companies may have already made
investments in doing the same thing with different other ways
–Flow control, error control, addressing is multiple
–Session and Presentation(EMPTY), Network and DL(Full)
Apocalypse of Two Elephants
Physical (Layer 1)
oCoordinates the functions required to transmit a bit stream over a physical medium
oDeals with mechanical and electrical specifications of Tx. Medium and Interface
oAlso defines procedures and functions that physical devices and interfaces need to
perform for TX. To occur (Figure)
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Figure
xFunctions of Physical Layer
oPhysical Characteristics of Interface & Media
¾Defines characteristics of Interface b/w device and Tx Medium
¾Interface is a plug gable connector that joins one or more signal conductors
¾Also defines the type of transmission medium
oRepresentation of Bits/Encoding
¾The physical layer data consists of a stream of bits (sequence of 1’s and 0’s)
¾To be transmitted the bits must be ENCODED into signals: Electrical or
Optical
¾Physical layer decides the type of ENCODING
oData Rate / Transmission Rate
¾Date Rate ( Bits per second) also decided by the Physical Layer
¾So , Physical layer defines the Duration of a Bit
¾Means how long will a bit last
oSynchronization of Bits
¾Sender and Receiver must be synchronized at the bit level
¾Sender and Receiver clocks must be synchronized
¾It is done by Physical layer
oLine Configuration
¾Physical Layer is also concerned with Line Configuration
¾Line Configuration represents the connection of device with the Medium
¾Point-To-Point or Multipoint
oPhysical Topology
¾Mesh, Star, Ring, Bus etc.
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