There are several HCI transport layer standards, each using a different hardware interface to transfer the same command, event and data packets. This standard allows the host stack or controller IC to be swapped with minimal adaptation. Standardized communication between the host stack (e.g., a PC or mobile phone OS) and the controller (the Bluetooth integrated circuit (IC)). Used for control of the radio link between two devices, highe, dmv, querying device abilities and power control. SCO packets may be sent every 1, 2, or 3 time slots.Įnhanced 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. There are no retransmissions, but forward error correction can be optionally applied. Each device transmits encoded voice data in the reserved timeslot. A SCO link is a set of reserved time slots on an existing ACL link. The type of radio link used for voice data. Synchronous Connection-Oriented (SCO) link 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.ĪCL 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. modulation ( Enhanced Data Rate packets allow up to triple data rate by using a different RF modulation for the payload)Ī connection must be explicitly set up and accepted between two devices before packets can be transferred.ĪCL packets are retransmitted automatically if unacknowledged, allowing for correction of a radio link that is subject to interference.Forward error correction (optionally reducing the data rate in favour of reliability).length (1, 3, or 5 time slots depending on required payload size).It can carry packets of several types, which are distinguished by: The normal type of radio link used for general data packets using a polling TDMA scheme to arbitrate access. 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.Ĭontroller stack Asynchronous Connection-Less (ACL) The host stack is generally implemented as part of an operating system, or as an installable package on top of an operating system. The controller stack is generally implemented in a low cost silicon device containing the Bluetooth radio and a microprocessor. The Bluetooth is split in two parts: a "controller stack" containing the timing critical radio interface, and a "host stack" dealing with high level data. This article gives an overview of the core protocols and those adopted protocols that are widely used. Additional protocols have been adopted from other standards bodies. Core protocols are defined by the trade organization Bluetooth SIG. The wireless data exchange standard Bluetooth uses a variety of protocols.
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