syncml protocols lesson 10 - devi ahilya vishwavidyalaya · syncml message • syncml protocol ......

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Data Synchronization in Mobile Computing Systems

Lesson 10SyncML Protocols


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


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


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


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


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>


Universal Resource Identifier (URI)

• A full path specification for a device resource

• Assume a PIM data structured like a tree


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


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 email IDs


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


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


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


Protocol specification of the URI

• Used to identify any resource at the object

• PIM_data/address_book/contacts/RajKamal is URI for identifying a resource at the Contacts at the server

• PIM_data/address_book/contacts/RajKamal/telNumRK is URI for the resource at the leaf telNum_RK


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_RKhas the text of address


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


Sample Code

<SyncBody><Status><Cmd>SyncHdr</Cmd> <CmdRef>0</CmdRef>

<MsgRef>1</MsgRef><TargetRef> IMEI:49…………800</TargetRef><SourceRef> http://www.syncml.org/sync-server

</SourceRef><Data>212</Data> </Status>


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 - - >


Sample Code

<TargetRef>./dev_contacts</TargetRef><SourceRef>./contacts/ Raj Kamal

</SourceRef><Data>200</Data></Status>

</SyncBody>


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


keyed hash message authentication code (HMAC)

• HMACsource of message M sent along with M

• Generated after computations at the source

• At the destination, the HMACdest is regenerated


Keyed hash message authentication code (HMAC)

• If the HMACdest computed at the destination matches with the received HMACsource, the integrity of M stands verified


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)


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



• 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>



• This indicates that next chunk expected in next session

• The receiving objects join the chucks to recreate a large object


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


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


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



• 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



• 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


Summary

• Representation protocol • Synchronization protocol• Ways of formatting the document • Ways of description of architecture for

synchronization• Interfaces for Binding• Prototype implementation

…


… Summary

• Universal resource Identifier by full path from root to leaf

• Commands for message exchanges for synchronization and client-server exchanges

• HMAC security…


… Summary

• <MoreData> for handling large objects• Four phases for set-up and

synchronization


End of Lesson 10SyncML Protocol

syncml protocols lesson 10 - devi ahilya vishwavidyalaya · syncml message • syncml protocol ......

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