Data Synchronization in Mobile Computing Systems Lesson 05 Synchronization Engine and Mobile Agent for Synchronization

Transcription

1 Data Synchronization in Mobile Computing Systems Lesson 05 Synchronization Engine and Mobile Agent for Synchronization Oxford University Press All rights reserved. 1

2 Synchronizer (synchronization engine) Software tool for synchronization Resides at a host Called Synchronization server synchronizer at the server Oxford University Press All rights reserved. 2

3 Synchronizer Functions Configuring as per the specified domaindependent and conflict resolution rules Finds the data item or record appended at the data set(s) Discovers modifications with respect to the last action of synchronization of the specified data copies which have been deleted, added, or modified Oxford University Press All rights reserved. 3

4 Synchronizer Functions Makes changes in the copies accordingly In case of conflict, it resolves it as per resolution rule(s) Disseminates (propagates) the changes to other devices or systems so that others devices also incorporate the changes in their data copies Oxford University Press All rights reserved. 4

5 A Synchronizer adopted Method for performing synchronization task More efficient compared to one in which the synchronizer directly retrieves the changed records First logs in the information about the records which have been changed and then retrieves the changed records Oxford University Press All rights reserved. 5

6 Process of logging in the information about the changes Can be fast by just setting or resetting a flag called dirty or invalid flag Oxford University Press All rights reserved. 6

7 Synchronizer invalid flag When associated flag in set state (=1), record R state is modified or invalidated since previous synchronization When in reset state (=0), R is not modified or invalidated since previous synchronization Reduces the possibility of using conflicting entries at the server (or device) hosting the synchronizer Oxford University Press All rights reserved. 7

8 Example of Contact in a PIM data of a mobile phone device D Assume that a Contact with name N i exists A flag f nd associated with N i sets to 1 when N i and associated data are entered for the first time at D Another associated flag ef nd resets to 0 because data fields of contact N i are not empty now and the data is valid Oxford University Press All rights reserved. 8

9 Example of Contact in a PIM data of a mobile phone device D Additional data record containing personal information about office, home, mobile, default, and fax telephone numbers, address, address, and web address also associated with N i Oxford University Press All rights reserved. 9

10 Example of Contact in a PIM data of a mobile phone device D Assume that fax number, , and web fields in the records empty Further assume that a priority-based resolution adopted as the conflict resolution rule for the PIM data When the data at D and C are conflicting, the data at D has priority and is the dominant data Oxford University Press All rights reserved. 10

11 Synchronizer actions 1. Action 1 Assume that synchronizers Sy c and Sy d at a WAP computer C and D, respectively Both use the method of first logging in the information about the changed records Oxford University Press All rights reserved. 11

12 Synchronizer Action 1 When the device is placed on a cradle, connected to C, PIM data at the computer and the device synchronize at an instant t1 When Sy c synchronizes the N i at D, it looks for the flags f nd and ef nd at D If f nd = 1 and ef nd = 0, the Sy c synchronizes and replicates the N i and associated data at C Oxford University Press All rights reserved. 12

13 Synchronizer action 1 On the other hand, if f nd and ef nd are both 0, the Sy c ignores the synchronization of N i data and does not copy it at C After the synchronization completes at C using Sy c, the Sy d at D resets f nd to 0 Oxford University Press All rights reserved. 13

14 Synchronizer Action 2 2. Action 2: Now assume that device user at a later instant t2 has no changes in the contact Ni The N i is not dirty now because it has not been modified Therefore, the dirty flag f nd and invalidation flag ef nd at the device remain reset to 0. Oxford University Press All rights reserved. 14

15 Synchronizer Action 2 When the device is placed on the cradle next time, it connects to C at t2 The Sy c at C synchronizes the contact data for N i at D It looks for the flags f nd and ef nd at D Since both are found to be 0, the Sy c ignores the synchronization of N i data Oxford University Press All rights reserved. 15

16 Synchronizer Action 3 3. Action 3: Now assume that the device user at a later instant t3 enters the address at the contact Ni at D The N i is now called dirty because it has been modified, f nd at the device sets to 1 The ef nd still remains in the reset state, as data is not invalidated Oxford University Press All rights reserved. 16

17 Synchronizer Action 3 Again assume that when the device is placed on the cradle next time, it connects to C at the instant t3 The Sy c at C synchronizes the contact data for N i at D and looks for the flag f nd at D Oxford University Press All rights reserved. 17

18 Synchronizer Action 3 Since f nd is found to be 1, the Sy c synchronizes and copies the changes in N i and associated data at C The Sy d at D resets f nd to 0 after synchronization Oxford University Press All rights reserved. 18

19 Synchronizer Action 4 4. Action 4: Now assume that the device user at a later instant t4 deletes the contact Ni at D The Ni becomes empty because the data has been now invalidated Therefore, the invalid flag ef nd sets to 1 at D Oxford University Press All rights reserved. 19

20 Synchronizer Action 4 When the device is placed on the cradle next time, assume that it connects to C at the instant t4 The Sy c at C synchronizes the contact data for N i at D It looks for the flag ef nd at D Oxford University Press All rights reserved. 20

21 Synchronizer Action 4 Since ef nd is found 1, N i and its associated data at C are deleted The Sy d at D does not change ef nd to 0 after synchronization as long as contact Ni is not restored at D using the Restore option Oxford University Press All rights reserved. 21

22 Method Advantage Only the associated flags are retrieved by the synchronizers initially and, if necessary, the associated data record is retrieved later Thus the synchronization actions take very little time Oxford University Press All rights reserved. 22

23 Mobile Agents for Synchronization Deployed for synchronization Recognizes inconsistency and conflict in data received at a client from the connected remote server, local server, or a device using resolution rules Mobile agent is present at a host which can be the client, an intermediate node, or the server Oxford University Press All rights reserved. 23

24 Characteristic of mobile agent Can migrate from one node in a mobile computing system to another and if needed, to another host for data synchronization The host is one which is connected to the server The migrated mobile agent can function as proxy to a mobile device or computing system Oxford University Press All rights reserved. 24

25 Example Assume that A c is the agent for the synchronizer Sy c at a computer C It hosts at the device D but does the work for Sy c and Assume that a prioritybased resolution is adopted as the conflict resolution rule for the PIM data When the data at D and C are in conflict, the data at D has a higher priority and is dominant Oxford University Press All rights reserved. 25

26 Example of Agent A c The hosted at D logs in the information about the records which have been changed so that the Sy c can synchronize the changed records later whenever D connects to C The device connects to C for synchronization Oxford University Press All rights reserved. 26

27 Example of Agent A c The A c communicates the status of the modified and invalid flags to C for use by Sy c Oxford University Press All rights reserved. 27

28 Agent and Synchronizer Actions 1. Agent and Synchronizer Action 1: When the device is placed on a cradle, connected to WAP computer C, PIM data at the computer and the device synchronize at an instant t1 Oxford University Press All rights reserved. 28

29 Agent and Synchronizer Action 1 When C connects to D, the flag f nd is communicated as 1 and ef nd as 0 using A c Sy c synchronizes the contact data for N i at D and copies data for Ni at C Once the synchronization at C completes, A c at D resets the status of synchronization using Sy c and thus resets f nd to 0 Oxford University Press All rights reserved. 29

30 Agent and Synchronizer Action 2 2. Agent and Synchronizer Action 2: Now assume that device user has no changes at the contact Ni at a later instant t2. When the device is placed on the cradle next time, there is no communication from A c when the device again connects to C at t2 The Sy c at C does not initiate the synchronization Oxford University Press All rights reserved. 30

31 Agent and Synchronizer Action 3 3. Agent and Synchronizer Action 3: Now assume that device user enters the address at the contact N i at D at a later instant t3. When C connects to D, the flag f nd is communicated as 1 and ef nd as 0 using the A c Oxford University Press All rights reserved. 31

32 Agent and Synchronizer Action 3 The Sy c synchronizes the contact data for Ni at D Once the synchronization completes at C, A c at D resets the status of synchronization using Sy c making f nd 0 Oxford University Press All rights reserved. 32

33 Agent and Synchronizer Action 4 4. Agent and Synchronizer Action 4: Now assume that device user deletes the contact Ni at D at a later instant t4. When the device is placed on the cradle next time, it again connects to C at the instant t4 A c at D communicates ef nd as 1. Sy d deletes the record of contact N i at D. Oxford University Press All rights reserved. 33

34 Agent and Synchronizer Action 4 A c at D does not change ef nd to 0 after synchronization as long as contact N i is not restored at D using the Restore option Oxford University Press All rights reserved. 34

35 The agent A c not at host at the device D but at intermediate Bluetooth device Bluetooth device placed between the computer C and the device D It can also be present at the computer C itself which is the client in the present case Migration action is one of the advantages of an agent Oxford University Press All rights reserved. 35

36 The agent A c periodically seeking the status of the flags from D Sy c can then initiate the synchronization as per data state of A c The synchronizers initiate action as per the data state communicated by the agent and take no action in case no communication is received from it Oxford University Press All rights reserved. 36

37 An agent A c need not send only the status but changed data directly An agent A c need not send only the status as in the above actions 1 to 4 It can communicate the changed record directly from the server to the client That is, from D to C in the above example The use of agents for synchronization proves to be beneficial Oxford University Press All rights reserved. 37

38 Summary Synchronizer a software tool for synchronization Configurable Finds data Discover modifications Disseminate the changes to other devices Oxford University Press All rights reserved. 38

39 Summary A method that only the associated flags are retrieved by the synchronizers initially and, if necessary, the associated data record is retrieved later Synchronizer agent Characteristic of an agent is that it can migrate from one node in a mobile computing system to another Oxford University Press All rights reserved. 39

40 End of Lesson 05 Synchronization Engine and Mobile Agent for Synchronization Oxford University Press All rights reserved. 40