data dissemination n broadcasting

8/12/2019 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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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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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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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

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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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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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.

data dissemination n broadcasting

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