Data Synchronization in Mobile Computing Systems Lesson 10 SyncML Protocols

Transcription

1 Data Synchronization in Mobile Computing Systems Lesson 10 SyncML Protocols Oxford University Press All rights reserved. 1

2 SyncML provisions for an open standard Representation protocol Synchronization protocol Ways of formatting the document Ways of description of architecture for synchronization Ways for binding an application with the well known transport protocols Oxford University Press All rights reserved. 2

3 Ways of binding SyncML codes bind the WAP, Bluetooth, or IrDA protocols and a mobile application run for synchronization and synchronize with Bluetooth, WAP 2.0, or IrDA level 5 connection using a SyncML client and engine Oxford University Press All rights reserved. 3

4 SyncML provisions for an open standard Interfaces for binding the programming languages which are very common, for example, Java, C, and C++. Prototype implementation for using the SyncML Oxford University Press All rights reserved. 4

5 SyncML programming Based on two protocols the SyncML representation protocol and the SyncML synchronization protocol The SyncML representation protocol defines the representation format of SyncML messages which are in XML It gives details about the inner working of the SyncML framework Oxford University Press All rights reserved. 5

6 SyncML Message SyncML protocol specifies that a message has SyncHdr and SyncBody, with meta info as well as device info present within SyncHdr Meta info is placed between the start and end tags <MetInf> and </MetInf> and device info between <DevInfo> and </DevInfo> Oxford University Press All rights reserved. 6

7 Universal Resource Identifier (URI) A full path specification for a device resource Assume a PIM data structured like a tree Oxford University Press All rights reserved. 7

8 Universal Resource Identifier (URI) The parent PIM data object is the root object At the branches of the root object, there are objects called daughter data record copies, these are calendar, address_book, and tasks_to_do Oxford University Press All rights reserved. 8

9 Address_book object Has the branches having the contacts. Each of the contacts object has branches and daughter objects which may be leaves The leaves are name, office, home, mobile and fax numbers, home and office addresses, web addresses, and IDs Oxford University Press All rights reserved. 9

10 Root object of device PIM data dev_pim_data Assume that the root object of device PIM data dev_pim_data Server PIM data PIM_data The root PIM_data hierarchy at the server PIM_data address_book contacts Raj Kamal telnum_rk Oxford University Press All rights reserved. 10

11 PIM data object address_book branches Further has the object Contacts Contacts has the object Raj Kamal Raj Kamal object has a leaf, the resource telephone number, telnum_rk Oxford University Press All rights reserved. 11

12 PIM data object address_book telnum_rk contains the telephone number data in digits, where resource refers to an entity used in the computations or for synchronization For an API, the resource is at the leaf during computations using the telnum_rk Oxford University Press All rights reserved. 12

13 Protocol specification of the URI Used to identify any resource at the object PIM_data/address_book/contacts/Raj Kamal is URI for identifying a resource at the Contacts at the server PIM_data/address_book/contacts/Raj Kamal/telNumRK is URI for the resource at the leaf telnum_rk Oxford University Press All rights reserved. 13

14 Protocol specification of the URI If the object Raj Kamal has two branches, telnum_rk and address_rk, then the URI for the leaf object address_rk will be PIM_data/contacts/Raj Kamal/address_RK, where address_rk has the text of address Oxford University Press All rights reserved. 14

15 Commands Create, Delete, Add, Update, Sync, Alert, Atomic, Search, Read, Get, Exec, Put, Copy, Results, Map, and Status Refer Table 9.1 for the meaning of the commands Alert command is a special SyncML feature by which the server alerts the client Oxford University Press All rights reserved. 15

16 Sample Code <SyncBody> <Status> <Cmd>SyncHdr</Cmd> <CmdRef>0</CmdRef> <MsgRef>1</MsgRef> <TargetRef> IMEI:49 800</TargetRef> <SourceRef> </SourceRef> <Data>212</Data> </Status> Oxford University Press All rights reserved. 16

17 Sample Code <Status> <Cmd>Alert</Cmd> <CmdRef>1</CmdRef> <MsgRef>1</MsgRef> <!- - Assume that Device contact data object at the device is dev_contacts, which was the target defined at the header and assume that new contact added at the server is URI./contacts/Raj Kamal and Alert is sent to client device - - > Oxford University Press All rights reserved. 17

18 Sample Code <TargetRef>./dev_contacts</TargetRef> <SourceRef>./contacts/ Raj Kamal </SourceRef> <Data>200</Data> </Status> </SyncBody> Oxford University Press All rights reserved. 18

19 Security For secure synchronization of messages between source and destination, a message M sent from a source to destination needs verification of its integrity and authenticity of the source Oxford University Press All rights reserved. 19

20 keyed hash message authentication code (HMAC) HMAC source of message M sent along with M Generated after computations at the source At the destination, the HMAC dest is regenerated Oxford University Press All rights reserved. 20

21 Keyed hash message authentication code (HMAC) If the HMAC dest computed at the destination matches with the received HMAC source, the integrity of M stands verified Oxford University Press All rights reserved. 21

22 Computations for HMAC Done using M, a secret key S and an iterative hash function Iterative function is a function repeatedly operated on the operand Two of the several iterative hash functions can be used SHA-1 (secure hash algorithm-1) and MD-5 (message digest algorithm-5) Oxford University Press All rights reserved. 22

23 Handling Large Objects Using <MoreData> tag Wireless transmission, there are interruptions Therefore, a large data object should be broken into many chunks <MoreData> tag for transmitting large object data in chunks Oxford University Press All rights reserved. 23

24 Handling Large Objects Using <MoreData> tag Using <MoreData> tag, a large object can be exchanged by dividing it into data chunks. Each chunk has a start tag <MoreData> and an end tag </Moredata> Oxford University Press All rights reserved. 24

25 Handling Large Objects Using <MoreData> tag This indicates that next chunk expected in next session The receiving objects join the chucks to recreate a large object Oxford University Press All rights reserved. 25

26 Use of status codes in case of Errors SyncML protocol defines error codes in the event of data conflict, incomplete document, and other errors that occur during synchronization Status codes between 500 and 599 are received for response from the receiver For example,code 511 which implies server failure Oxford University Press All rights reserved. 26

27 Example of status codes For example, assume that a status code sent by the receiver of SyncML message is error code 501 This implies that the command could not be implemented at the receiver because the SyncML client or server did not support it for any of the resources Oxford University Press All rights reserved. 27

28 Setup and Synchronization phases SyncML DM protocol specifies a standard method for set up and synchronization Device management one-way synchronization of the device from the server Oxford University Press All rights reserved. 28

29 Setup and Synchronization phases The server sets and updates the data on the client device It also requests for the device data, for example, data for enabling device authentication by it Oxford University Press All rights reserved. 29

30 Setup and Synchronization phases Data exchange occurs in phases using packages 0 4 A package is a SyncML message containing XML document Phases of data exchanges in packages 0 2 are called setup phases Phases of data exchanges in packages 3 and 4 are called synchronization or management phases Oxford University Press All rights reserved. 30

31 Setup and Synchronization phases Oxford University Press All rights reserved. 31

32 Summary Representation protocol Synchronization protocol Ways of formatting the document Ways of description of architecture for synchronization Interfaces for Binding Prototype implementation Oxford University Press All rights reserved. 32

33 Summary Universal resource Identifier by full path from root to leaf Commands for message exchanges for synchronization and client-server exchanges HMAC security Oxford University Press All rights reserved. 33

34 Summary <MoreData> for handling large objects Four phases for set-up and synchronization Oxford University Press All rights reserved. 34

35 End of Lesson 10 SyncML Protocol Oxford University Press All rights reserved. 35