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OBEX (abbreviation ofOBject EXchange, also termedIrOBEX) is acommunication protocol that facilitates the exchange of binary objects between devices. It is maintained by theInfrared Data Association but has also been adopted by theBluetooth Special Interest Group and theSyncML wing of theOpen Mobile Alliance (OMA). One of OBEX's earliest popular applications was in thePalm III. ThisPDA and its many successors use OBEX to exchange business cards, data, even applications.

Although OBEX was initially designed for infrared, it has now been adopted byBluetooth, and is also used overRS-232,USB,WAP and in devices such asLivescribe smartpens.

OBEX is similar in design and function toHTTP in providing the client with a reliable transport for connecting to a server and may then request or provide objects. But OBEX differs in many important respects:

• HTTP is normally layered above aTCP/IP link. OBEX can also be, but is commonly implemented on anIrLAP/IrLMP/Tiny TP stack on anIrDA device. InBluetooth, OBEX is implemented on aBaseband/ACL/L2CAP (and, for legacy uses,RFCOMM) stack. Other such "bindings" of OBEX are possible, such as overUSB.
• HTTP uses human-readable text, but OBEX uses binary-formattedtype–length–value triplets named "Headers" to exchange information about a request or an object. These are much easier to parse by resource-limited devices.
• HTTP transactions are inherently stateless; generally an HTTP client opens a connection, makes a single request, receives its response, and either closes the connection ormakes other unrelated requests. In OBEX, a single transport connection may bear many related operations. In fact, recent additions to the OBEX specification allow an abruptly closed transaction to be resumed with all state information intact.

OBEX works by exchangingobjects, which are used for a variety of purposes: establishing the parameters of a connection, sending and requesting data, changing the current path or the attributes of a file.

Objects arefields andheaders. As an example, the following may be the object used for requesting the phonebook from a mobile:

This object contains two fields (command and length) and two headers. The first field (command) specifies that it is a request for data (GET). The second field is the total size of the object, including the two fields.

This object also contains two headers, specifically a "Connection ID" and a "Name". The first byte of each header is the header's name and its content type. In this case:

• 0xCB means that this header is a "Connection ID", a number obtained previously; the two highest-order bits of0xCB are11, and this pair specifies that this as a 4-byte quantity;
• the first byte of the second header is0x01; this byte identifies this header as a "Name" one; the first two bits of0x01 are00, meaning that the content of this header is a null-terminatedUnicode string (inUCS-2 form), prefixed by the number of bytes it is made of (0x00 0x1e).

A possible response, containing the requested data, could be:

In this example, the phonebook is assumed short enough to be contained in a single response object. The only header has0x49 as its identifier, meaning that it is an "End of Body", the last chunk of information (also the only one, in this case). The first two bits of0x49 are01, meaning that the content of this header is length-prefixed data: the two next bytes0x00 0x2F tells the length of this data (in decimal, 47), the succeeding ones are the data, in this case a phonebook comprising only an emptyvCard of 47 bytes.

This example shows a singleGET command and its response, the only headers involved being connection id, name and end-of-body. Before issuing it, aCONNECT command should have been sent for establishing some parameters of the connection, including the connection id. Other commands arePUT,SETPATH,ACTION,ABORT, andDISCONNECT. Some other notable headers includetype,time,description,target.

After the client (e.g., computer) connects to the server (e.g., mobile), a typical session consists in the client sending a number of objects and getting their responses from the server. As an example:

• CONNECT: one of the fields specifies the largest size of packets the client can receive; aTARGET header specifies the kind of service the client is expecting (file-browsing,Sync, phonebook access); the server answer with its maximal packet length, the connection id, and other data
• GET: the client requests a file, specifying the connection id, the file name and/or its type; the server answer with the file content, or just a part of it; in the latter case, the client has to send otherGET objects to obtain the rest of the file
• SETPATH: the client tells the server to switch to a different file folder, specifying the connection id and the folder name in two headers
• GET: the client requests a listing of the folder content by sending an object with the connection id and an appropriateTYPE header (e.g.,x-obex/folder-listing for file transfer,x-bt/vcard-listing for phonebook access)
• PUT: the client sends a file to the server; if it is too large to fit into a single packet, the server will request the next part with a CONTINUE response
• DISCONNECT: the client informs the server that it is closing the session

The exchange may differ significantly depending on the service. For example,SyncML does not useSETPATH, while an OBEX push is made of justCONNECT (without a TARGET header),PUT and an optionalDISCONNECT.

The following protocols runs over OBEX, or have bindings to do so:

OBEX Push

Transfers a file from the originator of the request to the recipient; a CONNECTION object containing no target is sent, then PUT is used to transfer the file

OBEX File Transfer Protocol

Stores and retrieves files, similar toFTP. The target header of the CONNECTION object is{0xF9, 0xEC, 0x7B, 0xC4, 0x95, 0x3C, 0x11, 0xD2, 0x98, 0x4E, 0x52, 0x54, 0x00, 0xDC, 0x9E, 0x09}; the response contains the connection id to use in subsequentGET,PUT,SETPATH andACTION object.

Phonebook Access

Similar to file transfer, but uses a target{0x79, 0x61, 0x35, 0xF0, 0xF0, 0xC5, 0x11, 0xD8, 0x09, 0x66, 0x08, 0x00, 0x20, 0x0C, 0x9A, 0x66}; phonebook entries can be listed (with various possible orderings and filters) and retrieved from certain directories undertelecom/ usingGET andSETPATH

IrMC

IrMC was designed for the exchange of phonebook entries, calendar entries, digital business cards, andto-do lists. In its connectionless form, a singlePUT is used to transfer data; otherwise, various files and folders within telecom/ can be retrieved or pushed; a target header{'I', 'R', 'M', 'C', '-', 'S', 'Y', 'N', 'C'} may be used inGET requests to differentiate the kind of indexing used

SyncML

SyncML can synchronize phonebooks, calendars, notes, and other data. In its OBEX binding, the target of theCONNECT object is{'S', 'Y', 'N', 'C', 'M', 'L', '-', 'S', 'Y', 'N', 'C'}; a session then consists in a sequence ofPUT-GET pairs where namelessXML orWBXML files are sent and received, in turn.

Optional package javax.obex inJava APIs for Bluetooth provides an implementation of OBEX inJava.^[1]

OpenObex is an open-source implementation of OBEX inC. It provides functions for connecting overIrDA,Bluetooth,USB andTCP/IP, building objects and handling received data. An example schema of a client application is:

voidcallback_function(...){/* process received data */}intmain(){OBEX_Init(...,callback_function);OBEX_TransportConnect(...);object=OBEX_ObjectNew(...);OBEX_ObjectAddHeader(object,...);OBEX_ObjectAddHeader(object,...);OBEX_Request(...,object);while(...)OBEX_HandleInput(...)object=OBEX_ObjectNew(...);OBEX_ObjectAddHeader(object,...);OBEX_Request(...,object);while(...)OBEX_HandleInput(...)/* ... */OBEX_TransportDisconnect(handle);OBEX_Cleanup(handle);}

Objects are sent byOBEX_Request. After callingOBEX_HandleInput, received data is processed in the callback function (which was specified when callingOBEX_Init). The callback function can determine whether the response has been completely received, and therefore whether the main program can exit from thewhile loop it is executing.

PyOBEX provides partial support for OBEX inPython.^[2] nOBEX is a fork of PyOBEX with more complete OBEX support, and support for the BluetoothHands Free Profile to facilitate OBEX testing on automotive infotainment systems.^[3]

OBEX is the foundation for many higher-layer "profiles":

• Android devices in version2.1 “Eclair” and above
• AllPalms sincePalm III, except webOS devices: the Palm Pre, Palm Pre Plus, Palm Pixi and Palm Pixi Plus.
• Most non-AndroidSharp,Motorola,Samsung,Sony Ericsson,HTC andNokia phones withinfrared orBluetooth port. Android devices are supported but this is supposed to be saying that they are supported as well.
• LG enV Touch (VX11000)
• Many otherPDAs since 2003, until their decline due to being replaced by smartphones
• Many other phones withinfrared orBluetooth port
• Windows Phone 7.8 and 8 devices (limited to the transferring of pictures, music and videos via a 'Bluetooth Share' app).

• Shared file access
• List of Bluetooth profiles

• OBEX specification at IrDA.org
• Bluetooth profilesArchived 2013-12-31 at theWayback Machine, including specifications for OBEX and OBEX-based protocols (GOEP, FTP, OBEX push, SYNC)
• OpenOBEX an open source implementation of the OBEX protocol

• Infrared Data Association
• Bluetooth

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