Bluetooth Protocols

by Ken Burnside Google

    Bluetooth is a wireless standard for personal-area networks. It uses low-frequency radio broadcasts to transmit data between electronic devices, in a set of frequencies that won't penetrate most construction and that don't reliably extend past about 6 feet. First introduced with prototypes in 2000, Bluetooth has gone through multiple generations of the basic protocol and gained ancillary functions which might well be protocols of their own.

    Controller Stack Protocols

    There are five core protocols in the Bluetooth Controller Stack. This is the subset of the Bluetooth standard that describes low-level functionality underlying device communications. The first two protocols are the Asynchronous Connection Logical Transport link and the Synchronous Connection Oriented link. These protocols determine the type and format of data transmitted between devices. Broadly speaking, ACL uses automatic retransmission if a reception acknowledgement is not received, while SCO uses a reserved portion of the packets on each transmission layer. SCO is critical for voice transmission, while ACL is used for data shared between devices. The other three controller stack protocols are the Link Management Protocol, which helps identify devices in the same Bluetooth network, the Host/Controller Interface (HCI) protocol, which is the heart of device pairing in Bluetooth, and the Low Energy Link Layer (LE LL), which manages connection security between devices.

    Logical Link Control and Adaptation Protocol

    This protocol, abbreviated L2CAP, is the protocol that translates data between the low level Bluetooth protocols in the controller stack (which deal primarily with radio frequency management and signaling between devices) and the networking layers that various Bluetooth devices use for file sharing, transmitting keystrokes from a keyboard to a computer. It also provides quality of service management and monitoring, so that when a Bluetooth connection fails, it fails in ways that trigger error messages and notifications.

    Networking Analog Protocols

    While many Bluetooth devices use the same TCP/IP protocols that Internet devices do, there are Bluetooth-specific networking protocols that encapsulate data for the vagaries of intermittent radio frequency networking. Bluetooth supports several specialized networking transport protocols, including Telephony Control Protocol, also known as TCP -- which, it should be noted, is not the same as the "TCP" in the well-known TCP/IP. Others include Audio/Video Control Transport Protocol and Audio/Video Data Transport Protocols, which support audio and video data transmission, including buffering and reprioritization of packets to reduce communications lag; they also form a large part of speech recognition for Bluetooth headsets.

    Other Supported Protocols

    Bluetooth also supports a number of standard Internet protocols and protocols from other standards organizations, such as PPP, used for fetching mail over a point-to-point TCP/IP connection, TCP/IP itself, the fundamental communications protocol of the Internet, along with its UDP extension, and Wireless Application Protocol (WAP), as an interface for telephony protocols. It also supports Object Exchange (OBEX), which is a protocol for maintaining object-oriented commands and shared objects and their modification on the Bluetooth network. OBEX is derived from the protocols used for infrared transmission between PDAs.

    About the Author

    Ken Burnside has been writing freelance since 1990, contributing to publications as diverse as "Pyramid" and "Training & Simulations Journal." A Microsoft MVP in Excel, he holds a Bachelor of Arts in English from the University of Alaska. He won the Origins Award for Attack Vector: Tactical, a board game about space combat.

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