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The RFCOMM Protocol

Serial interfaces are ubiquitous in computing and telecommunications devices, particularly those devices with a high affinity for Bluetooth communications. Notebook computers have serial ports, personal digital assistants typically have serial ports (often used to synchronize the PDA with some other device), many mobile telephones have serial ports (often used for a wired headset), many digital cameras use serial ports to transfer image data to another device, printers and other computer peripherals often use serial ports for communication, and so on. Moreover, infrared communication, which as previously established has some traits in common with Bluetooth wireless communication, normally uses a serial port to communicate with the IR transceiver.[1]

[1] In the PC domain, infrared communications are frequently tied to a COM port resource. In commonly used PC operating environments, these COM ports classically have been difficult to configure, especially for infrared communications. This drawback has led to a situation where, while many infrared ports are deployed in products, only a fraction of these ports are actually used, since many users lack the expertise or motivation to perform the necessary configuration process. The rise of infrared ports on PDAs and mobile phones, where the configuration process is much easier, seems to lead to a higher usage rate of infrared in peer-to-peer communications.

Because Bluetooth technology aims to replace cables, it seems clear that there is a large opportunity to replace serial cables. To do this effectively, the stack needs to support serial communication in the same manner as is done with cables, so that applications are presented with a familiar serial interface. This permits the cornucopia of legacy applications that are unaware of the Bluetooth technology to operate seamlessly over Bluetooth links. Furthermore, application software developers skilled in developing serial communication applications may still continue to do so, assured that their applications will operate over Bluetooth links. But the transport-layer protocols are not modeled after a serial port. L2CAP supports packet data structures, and while the air-interface may transmit bit patterns in a serial fashion, this is not the same as the common RS-232 types of serial interfaces used today with serial cables.


  

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