Computer Architecture
Lecture 29
Fasih
ur
Rehman
Last Class
•
Memories
•
Virtual memory
–
Address Translation
•
Memory Management
Today’s Agenda
•
Computer Communication
Analog Vs. Digital
Data Communication
•
Transmission of data (voice, video or text) via
electrical, optical or wireless link between
computers or network processors is referred
to as Data Communication
–
In computer communication, the data is generally
digital.
•
Mostly, the data that is required to be communicated
is in analog form.
•
So an analog to digital converter ADC will be required
to convert the analog data into digital data.
–
The link can be
•
Free space
•
Wires (twisted pair, coaxial cable, parallel conductors)
•
Optical fiber
Why Digital
•
Easy to mix signals and data using digital
techniques
•
Less
noise prone
•
Good
processing techniques are available for
digital
•
signals, such as
–
Data
compression (or source
coding)
–
Error
Correction (or channel coding)
–
Equalization
–
Security
Components of a Communication System
•
Source (Transmitter)
•
Medium (Communication Line)
•
Sink (Receiver)
•
Communication networks
•
Communication rules (protocols
)
–
Both source and sink act as node
History
•
Telegraph
•
Telephone
•
Computer
•
Transistor
•
Integrated Circuits (LSI, VLSI)
•
Satellites
Transmission Direction
•
Simplex
–
One way communication e.g. TV transmission
•
Half Duplex
–
Two way communication but not simultaneously
–
e.g.
walkie
talkie
•
Full Duplex
–
Simultaneous two way communication
–
telephone
Codes
•
Human Codes
–
Morse Code
•
Dots and Dashes
•
Machine Codes
–
Binary codes
•
use binary states
•
use same number of bits
•
so transmitted in same time
•
perfectly formed
•
alphanumeric
Common Codes
•
Baudot
code
•
ASCII
•
EBCDIC
•
Unicode
Some Commonly used Terms
•
Throughput
–
The number bits transferred per second.
–
Also called bandwidth
•
Latency
–
The that is elapsed between initiation of
transmission and earliest possible reception of a
give piece of information.
–
Also called delay
•
Network Topology
–
The way hosts are connected to the network
•
Star, ring topologies etc.
•
Main goal of topology is to have minimum latency with
high throughput
•
Some commonly used topologies are described as
Mesh
•
All nodes are connected to each other.
Bus Topology
•
All nodes are connected to a common bus
Star Topology
•
All nodes are connected to common hub.
Ring Topology
•
All computers are connected in a way that
they form a loop.
Hybrid Topology
•
Mix of the above topologies
Protocols
•
Set of rules to be followed in order to
communicate among the network nodes
Summary
•
Data Communication
–
Signals
–
Analog and Digital
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