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7/31/2019 Cnap Upgrade Davv 1 2

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Oxford University Press 2007. All rights reserved. 1

Data Dissemination and Broadcasting

Systems

Lesson 01

Communication Asymmetry and

Broadcast Architecture


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Communication Asymmetry

Intrinsically asymmetric Mobile

communication between the mobiledevice and static computer system

Device allocated a limited bandwidth Because of a large number of devices


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Communication Asymmetry

Bandwidth in the downstream from the

server to device much larger than theone in the upstream from the device toserver

Because mobile devices have limitedpower resources

Faster data transmission rates for long

intervals of time need greater powerdissipation from the devices


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Communication asymmetry in uplink

and downlink in a mobile network


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GSM networks data transmission

Rates go up to a maximum of 14.4 kbps

for both uplink and downlink

Symmetric communication

Only used for voice communication


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i-mode for many applications

Used for voice, multimedia transmission,

Internet access, voice communication

Base station provides downlink 384 kbps

Uplink from the devices restricted to 64kbps

Asymmetric communication


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The characteristics in wireless signals

Interference and time-dispersion

Signal distortion and transmission errors

at the receiver end

Lead to path loss and signal fading,which cause data loss

Greater access latency compared to

wired networks


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The characteristics in wireless signals

Data loss has to be taken care of by

repeat transmissions

Transmission errors have to be corrected

Taken care of by appending additionalbits, such as the forward error correction

bits


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The characteristics in Mobile

communication

Mobile devices also have low storage

capacity (memory)

Cannot hoard large databases

Accessing the data online not only has alatency period (is not instantaneous) but

also dissipates bandwidth resources of

the device


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Broadcasting

Corresponds to unidirectional (downlink

from the server to the devices)

Unicast communicationUnicast means

the transmission of data packets in acomputer network such that a single

destination receives the packets


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Broadcasting or application distribution

service

This destination generally the one which

has subscribed to the service

Mobile TVan example of unidirectional

unicast mode of broadcasting Each device receives broadcast data

packets from the service providers

application distribution system


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Broadcasting or application distribution

service

Applicationdistribution system

broadcasts data of text, audio, or videoservices


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A broadcasting architecture


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Summary

GSM symmetric and voice only

Mobile communication asymmetric in

general

Limited device capability Device memory, energy and uplink and

downlink bandwidths

Broadcast architecture


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End of Lesson 01

Communication Asymmetry and

Broadcast Architecture

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