List of Bluetooth protocols
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The wireless data exchange standard Bluetooth uses a variety of protocols. Core protocols are defined by the trade organization Bluetooth SIG. Additional protocols have been adopted from other standards bodies. This article gives an overview of the core protocols and those adopted protocols that are widely used.
The Bluetooth protocol stack is split in two parts: a "controller stack" containing the timing critical radio interface, and a "host stack" dealing with high level data. The controller stack is generally implemented in a low cost silicon device containing the Bluetooth radio and a microprocessor. The host stack is generally implemented as part of an operating system, or as an installable package on top of an operating system. For integrated devices such as Bluetooth headsets, the host stack and controller stack can be run on the same microprocessor to reduce mass production costs; this is known as a hostless system.
Controller stack
Asynchronous Connection-Less [logical transport] (ACL)
The normal type of radio link used for general data packets using a polling TDMA scheme to arbitrate access. It can carry packets of several types, which are distinguished by:
- length (1, 3, or 5 time slots depending on required payload size)
- Forward error correction (optionally reducing the data rate in favour of reliability)
- modulation (Enhanced Data Rate packets allow up to triple data rate by using a different RF modulation for the payload)
A connection must be explicitly set up and accepted between two devices before packets can be transferred.
ACL packets are retransmitted automatically if unacknowledged, allowing for correction of a radio link that is subject to interference. For isochronous data, the number of retransmissions can be limited by a flush timeout; but without using L2PLAY retransmission and flow control mode or EL2CAP, a higher layer must handle the packet loss.
ACL links are disconnected if there is nothing received for the supervision timeout period; the default timeout is 20 seconds, but this may be modified by the master.
Synchronous Connection-Oriented (SCO) link
The type of radio link used for voice data. A SCO link is a set of reserved time slots on an existing ACL link. Each device transmits encoded voice data in the reserved timeslot. There are no retransmissions, but forward error correction can be optionally applied. SCO packets may be sent every 1, 2, or 3 time slots.
Enhanced SCO (eSCO) links allow greater flexibility in setting up links: they may use retransmissions to achieve reliability, allow for a wider variety of packet types and for greater intervals between packets than SCO, thus increasing radio availability for other links(.)
Link Management Protocol (LMP)
Used for control of the radio link between two devices, highe, dmv, querying device abilities and power control. Implemented on the controller.
Host Controller Interface (HCI)
Standardized communication between the host stack (e.g., a PC or mobile phone OS) and the controller (the Bluetooth integrated circuit (IC)). This standard allows the host stack or controller IC to be swapped with minimal adaptation.
There are several HCI transport layer standards, each using a different hardware interface to transfer the same command, event and data packets. The most commonly used are USB (in PCs) and UART (in mobile phones and PDAs).
In Bluetooth devices with simple functionality (e.g., headsets), the host stack and controller can be implemented on the same microprocessor. In this case the HCI is optional, although often implemented as an internal software interface.
Low Energy Link Layer (LE LL)
This is the LMP equivalent for Bluetooth Low Energy (LE), but is simpler. It is implemented on the controller and manages advertisement, scanning, connection and security from a low-level, close to the hardware point of view from Bluetooth perspective.
Host stack
== null el2caps null all Bluetooth null el2csps