Data Dissemination and Broadcasting Systems Lesson 05 Data Dissemination Broadcast-disk Models

Transcription

1 Data Dissemination and Broadcasting Systems Lesson 05 Data Dissemination Broadcast-disk Models Oxford University Press All rights reserved. 1

2 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. Oxford University Press All rights reserved. 2

3 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 Oxford University Press All rights reserved. 3

4 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 Oxford University Press All rights reserved. 4

5 Broadcast bandwidth Bandwidth means rate of bit transfer = (t s ) 1 = Number of bits (N) stored between 0 and 360 divided by T s T s = the time taken for one revolution of the disk t s = the time interval between successive bits transmitted from the disk Oxford University Press All rights reserved. 5

6 Broadcast Time interval between transmission of successive bits Each bit in each record repeatedly broadcast at successive time intervals (= N t s = T s ) Time interval between transmission of successive bits (T s /N) [= ts = reciprocal of bandwidth] Oxford University Press All rights reserved. 6

7 Number of adaptations and algorithms for broadcast 1. Circular Multi-disk Model 2. Flat Disk Model 3. Multi-disk Model with repetition rate proportional to priority 4. Skewed disk model Oxford University Press All rights reserved. 7

8 Circular multi-disk model Each block of records pushed with a repetition rate proportional to its hierarchical level Oxford University Press All rights reserved. 8

9 Circular multi-disk model Oxford University Press All rights reserved. 9

10 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) Oxford University Press All rights reserved. 10

11 Multi-disk model Entails multiple levels of records on the broadcast disk Oxford University Press All rights reserved. 11

12 Flat Disk model Oxford University Press All rights reserved. 12

13 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 Oxford University Press All rights reserved. 13

14 Multi-disk Model with repetition rate proportional to priority Oxford University Press All rights reserved. 14

15 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 Oxford University Press All rights reserved. 15

16 Multi-disk Model with repetition rate proportional to priority Oxford University Press All rights reserved. 16

17 Skewed-disk model Oxford University Press All rights reserved. 17

18 Skewed-disk model Oxford University Press All rights reserved. 18

19 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 Oxford University Press All rights reserved. 19

20 Skewed Disk Model High priority record blocks pushed more often than the low priority ones because these are repeated one after one more often Oxford University Press All rights reserved. 20

21 Push pull-based hybrid mechanism The server pushes the records through downlink and the devices send the requests to server through uplinks Oxford University Press All rights reserved. 21

22 Hybrid mechanism Responses Interleaved responses for devices p, q, and r interleaving High priority level 1 Low priority level 2 I p R 0,, R i 1 R 0,, R i 1 I q I r R i,, R n 1 m-level disk with p n/m records/level with interleaved responses Rotation Oxford University Press All rights reserved. 22

23 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 Oxford University Press All rights reserved. 23

24 Real-time environment Independent disk rotating at different speed Facilitates the delivery of data records within a deadline in a real-time environment Oxford University Press All rights reserved. 24

25 Broadcast Multi-disk Model for real time environment Oxford University Press All rights reserved. 25

26 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 Oxford University Press All rights reserved. 26

27 Summary Flat disk Skewed disk Hybrid data delivery [Interleaving of responses] Real time environment disks Oxford University Press All rights reserved. 27

28 End of Lesson 05 Data Dissemination Broadcast-disk Models Oxford University Press All rights reserved. 28