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CS 635 Lecture 3, Part 3 Logical Link Control

(Note: Material for this page has been borrowed from http://gaia.cs.umass.edu/cs653-1997/notes/ch5/ch5-2.html)

Error Control

Go-Back-N ARQ

Go-Back-N continued

Go Back N: Example



 

Selective Repeat ARQ


As in go back-N:

Unlike Go-Back-N

Notes:

Selective Repeat ARQ: example:



 

How Big Can a Window Be?


Suppose sequence number space size is N

Fundamental problem: sender and receiver

Detecting Errors: checksums

Need to detect errors: bits in packet may be flipped while in transit or stored at intermediate notes.

Approach: add extra bits to packets that will aloow us to detect (possibly correct) bit errors

Simple example: parity

Forward Error Correction: FEC


ARQ protocols operate by detecting errors and retransmitting

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