Distribution Guide Device drivers Bluetooth: BlueZ and Obex HowTo Obex: HowTo and ussp-push

OBEX (abbreviation of OBject EXchange, also termed IrOBEX) is a communications protocol that facilitates the exchange of binary objects between devices. It is maintained by the Infrared Data Association but has also been adopted by the Bluetooth Special Interest Group and the SyncML wing of the Open Mobile Alliance (OMA). OBEX is similar in design and function to HTTP in that a client uses a reliable transport to connect to a server and may then request or provide objects. But OBEX differs in many important respects:
Transports: HTTP is normally layered above a TCP/IP port. OBEX is commonly implemented over an IrLAP/IrLMP/Tiny TP stack on an IrDA device. In Bluetooth, OBEX is implemented above Baseband/Link Manager/L2CAP/RFCOMM stack. Other such "bindings" of OBEX are possible.
Binary transmissions: HTTP uses human-readable text, but OBEX uses binary-formatted type-length-value triplets called "Headers" to exchange information about a request or an object. These are much easier to parse by devices with limited resources.
Session support: HTTP transactions are inherently stateless; generally an HTTP client opens a connection, makes a single request, receives its response, and closes the connection. 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 is the foundation for many Bluetooth higher-layer "profiles":

• Generic Object Exchange Profile
  
• Object Push Profile (phone to phone transfers)
  
• File Transfer Profile (phone to PC transfers)
  
• Synchronization Profile
  
• Basic Imaging Profile
  
• Basic Printing Profile
  

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The Obex packages

Before to use Obex for files exchanging via Bluetooth, you should install the following packages:

stlinux23-sh4-openobex-1.3-1.sh4.rpm stlinux23-sh4-obexserver-1.1-1.sh4.rpm stlinux23-sh4-ussp-push-0.9-1.sh4.rpm

The Openobex package is a free open source implementation of the Object Exchange (OBEX) protocol. The Obexserver is a Obex server for retrieving files from a Bluetooth device which is an Obex client as well.The ussp-push package is able to push files from an obex server device to a Bluetooth device (Obex client).

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Obex System: How to get files from a Bluetooth device

target% sdptool add --channel=CHANNEL_ID OPUSH

The field CHANNEL_ID can be obtained from the features previously got by the command sdptool browse as described in the related section (BlueZ HowTo). A typical value of this channel is 10. Finally, we can run the Obexserver as follow:

target% obexserver

In case of no errors, we get the following prompt:

target% obexserver Waiting for connection...

The system waits till the corresponding handled Bluetooth device will send a file (images, music, video, etc..) to the Obexserver. The file sent from the Bluetooth device will be available in the current directory.

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Obex System: How to send files to a Bluetooth device

target% rfcomm bind /dev/rfcomm0 MAC_ADDRESS CHANNELID

Typically, the used rfcomm is rfcomm0 but rfcommx with x>0 can be used. The MAC_ADDRESS is known and the CHANNEL_ID is the used channel for transmission and obtained from a simple "sdptool browse MAC_ADDRESS" command. For instance, using the hypothetical info above described and supposing a transmission channel equal to 9 (typical value), we can send the file "Image.jpeg" to the Bluetooth device (MAC_ADDRESS: 00:16:CF:DC:B9:81) using the following istructions:

target% rfcomm bind /dev/rfcomm0 00:16:CF:DC:B9:81 9 target% ussp-push /dev/rfcomm0 Image.jpeg Image_client.jpeg

Where Image_client.jpeg is the name of the sent file in the remote filesystem of the Bluetooth receiver.

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