Download - Data Dissemination n Broadcasting
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Data Dissemination andBroadcasting system
Prof. Jayesh Patel
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Content
Communication AsymmetryData delivery mechanism
Push based , Pull based and Hybrid mechanism.
Broadcast disk models for cyclic repetition of
data.
Indexing techniques for selective tuning.
Digital audio and video broadcasting.
Mobile TV.
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Communication Asymmetry
Intrinsically asymmetric Mobile communicationbetween the mobile device and static computer
system.
Device allocated a limited bandwidth.
Because of a large number of devices.
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Communication Asymmetry (cont..)Bandwidth in the downstream from the server to
device much larger than the one in the upstream from
the device to server
Because mobile devices have limited power resources.
Faster data transmission rates for long intervals of
time need greater power dissipation from the devices.
GSM
Rates go up to a maximum of 14.4 kbps for both uplink
and downlink.
Symmetric communication and used for voice
communication
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Communication Asymmetry (cont..)i- Mode
Used for voice, multimedia transmission, Internet
access, voice communication.
Base station provides down link 384 kbps and Up link
from the devices restricted to 64 kbps.
Asymmetric communication
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Communication Asymmetry Architecture
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Characteristics of Mobile communication
Wireless signalsInterference and time dispersion.
Signal distortion and transmission error.
Path loss and signal fading results data loss
Latency issue.
Low storage capacity of mobile device.
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Broadcasting
Corresponds to unidirectional (down link fromthe server to the devices).
Unicast communication Unicast means
the transmission of data packets in a computer
network such that a single destination receives
the packets.
This destination generally the one which has
subscribed to the service.
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Broadcasting (cont..)
Mobile TV an 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 Architecture
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Classification of Data- Delivery Mechanism
Push-based mechanisms (publish subscribe
mode).
Pull-based mechanisms (on-demand mode).
Hybrid mechanisms (hybrid mode).
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Push-based Mechanism
Server pushes data records from a set of
distributed computing systems.
Examples of distributed computing:
advertisers or generators of traffic congestion,
weather reports, stock quotes, and news
reports.
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Push-based Mechanism (cont..)
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Push-based Mechanism (cont..)
Data pushed as per the subscription for a push
service by a user.
Pushing Algorithm
The structure of data records to be pushed isselected.
Data is pushed at selected time intervals using adaptive
algorithm.
Bandwidths adapted for downlink (for pushes) using an
algorithm.
A mechanism also adopted to stop pushes when a device
is handed over to another cell.
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Push-based Mechanism (cont..)
Advantages:
Enable broadcast of data services to multiple devices.
Server is not interrupted frequently by requests fromthe mobile devices.
Best option for the server as they prevent serveroverload, which may occur due to flooding of devicerequests
Disadvantages:
Dissemination of unsolicited, irrelevant, or out-of-context data.
User may not be interested in the disseminated dataand may be inconvenienced.
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Pull-based Mechanism
User-device or computing system pulls the data
records from the service providers application
database server or from a set of distributed
computing systems.
On-demand mode from a set of distributed
computing systems, music album server, ringtones server, video clips server, or bank account
activity server.
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Pull-based Mechanism (cont..)
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Pull-based Mechanism (cont..)
Selective response from server:
Records pulled and selective response to
demand.
Server transmits data packets as response
selectively.
After client-authentication, verification, orsubscription account check.
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Pull-based Mechanism (cont..)
Pull based Mechanism
Used for the uplink channel depends upon the number
of pull requests.
Threshold limits the number of pull requests in a given
period of time. Controls the number of server
interruptions.
A mechanism adopted to prevent access when handed
over to another cell. On device hand off, thesubscription canceled or passed on to the new service
provider system.
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Pull-based Mechanism (cont..)
Advantages:
No unsolicited or irrelevant data arrives at the device
Relevant data disseminated only when the user asksfor it.
Best option when the server has very little contentionand is able to respond to many device requests withinexpected time intervals.
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Pull-based Mechanism (cont..)
Disadvantages:
Server faces frequent interruptions and queues ofrequests at the server may cause congestion in cases ofsudden rise in demand for certain data record (s).
The energy and bandwidth required for On-demandmode when sending the requests for hot items andtemporal records (records changing with time) large.
A large number of devices making requests to theservice provider choke the network.
The server is flooded with interruptions.