Models Systems - Devi Ahilya · PDF fileSystems Lesson 05 Data Dissemination Broadcast-disk Models © Oxford University Press 2007. All rights reserved. 2 Disk models for Broadcast

© Oxford University Press 2007. All rights reserved. 1

Data Dissemination and Broadcasting Systems

Lesson 05Data Dissemination Broadcast-disk

Models


Disk models for Broadcast

• Presumed that all the n records to be broadcast are stored on a circular disk from 0°to 360°

• A hypothetical disk revolves and the angle changes from 0° to 360°

• The entire N bits in n records get pushed through a hypothetical reading-head over the disk.


Broadcast Disk models

• The head continuously reads each bit of a record just beneath it and broadcasts it instantaneously on the wireless network

• During next revolution each bit in the records positioned from 0° to 360°broadcast once again in the same sequence as in earlier revolution


Classification of Data-Delivery Mechanisms

• In case a device misses a record in first revolution, it can cache the same in next or any of the successive revolutions


Broadcast bandwidth

• Bandwidth means rate of bit transfer = (ts)−−−−1 = Number of bits (N) stored between 0° and 360° divided by Ts

• Ts = the time taken for one revolution of the disk

• ts = the time interval between successive bits transmitted from the disk


Broadcast Time interval between transmission of successive bits

• Each bit in each record repeatedly broadcast at successive time intervals (= N × ts = Ts)

• Time interval between transmission of successive bits (Ts/N) [= ts = reciprocal of bandwidth]


Number of adaptations and algorithms for broadcast

1. Circular Multi-disk Model2. Flat Disk Model3. Multi-disk Model with repetition rate

proportional to priority4. Skewed disk model


Circular multi-disk model

• Each block of records pushed with a repetition rate proportional to its hierarchical level


Circular multi-disk model


Each rotating disk cycle

• Record blocks R0, R1, R2, R3, R0, R1, R2, R3, transmitted in a single broadcast cycle

• All record blocks have an equal priority level

• Using the flat-disk model, the server broadcasts the data as per cyclic requests (subscriptions)


Multi-disk model

• Entails multiple levels of records on the broadcast disk


Flat Disk model


Flat disk model

• The server broadcasts the data as per cyclic requests (subscriptions) without taking into account the number of devices that subscribe to a particular record


Multi-disk Model with repetition rate proportional to priority


Number of levels assigned to a block of records as per its priority

• Priority can be as per the number of users subscribing to it

• Assume that the transmission rate at each level is same but the repetition rate of a block of records is proportional to the record’s priority level


Multi-disk Model with repetition rate proportional to priority


Skewed-disk model


Skewed-disk model


Skewed Disk Model

• The block of records repeated as per their priorities for pushing or as per number of subscribers of a given record

• However, unlike the multi-disk model, the skewed-disk model entails consecutive repeated transmissions of a record block, followed by consecutive repeated transmissions of another record block, and so on


Skewed Disk Model

• High priority record blocks pushed more often than the low priority ones because these are repeated one after one more often


Push–pull-based hybrid mechanism

• The server pushes the records through downlink and the devices send the requests to server through uplinks


Hybrid mechanism Responses interleaving

High priority level 1

Ip R0,…, Ri −1 R0,…, Ri −1Iq Ir Ri,…, Rn −1

Low priority level 2

Rotationm-level disk with p × n/mrecords/level with interleaved responses

Interleaved responses for

devices p, q, and r


Real-time environment

• The records to be pushed in real time• The instants at which a record pushed

also matters• Each data record (or each set of data

records) represents an independent disk rotating at a speed inversely proportional to the time constraint associated with the record


Real-time environment

• Independent disk rotating at different speed

• Facilitates the delivery of data records within a deadline in a real-time environment


Broadcast Multi-disk Model for real time environment


Summary

• Broadcast disk models• A hypothetical disk (s) revolves and the

angle changes from 0° to 360°• The entire N bits in n records get pushed

through a hypothetical reading-head over the disk (s)

• Circular multi disk model…


… Summary

• Flat disk• Skewed disk• Hybrid data delivery [Interleaving of

responses] • Real time environment disks


End of Lesson 05Data Dissemination Broadcast-disk

Models

Documents

Models Systems - Devi Ahilya · PDF fileSystems Lesson 05 Data Dissemination Broadcast-disk Models © Oxford University Press 2007. All rights reserved. 2 Disk models for Broadcast