Bluetooth basics and Applications & protocols used by Bluetooth headsets

A very important feature of Bluetooth is that all Bluetooth products do not need to implement all Bluetooth specifications. To make it easier to maintain compatibility between bluetooth devices, the profile is defined in the Bluetooth specification. Profile defines how a device implements a connection or application. You can understand profile as a connection layer or application layer protocol.
(1) The Bluetooth host controller module, as the underlying layer of Bluetooth, is a typical hardware implementation and cannot be directly controlled by applications (or services added on Bluetooth. Bluetooth HCI has two types: uart and USB, because the former is simple and efficient, so the former is mostly. The diagram is as follows:

(2) The Bluetooth Host module allows applications to send/receive data through a Bluetooth connection, or Configure connection parameters:
· RFCOMM allows applications to simulate a Bluetooth connection as a serial port. This supports traditional protocols.
· Logical Connection Control and Adaptation Protocol the Logical Link Control and Adaptation Protocol (L2CAP) is used to control multi-user connections and process packet segmentation and combination. This is a common choice for applications.
· Service Discovery Protocol the Service Discovery Protocol (SDP) is used to locate and describe the services provided or available by bluetooth devices. The application is mainly used when it is set to communicate with another bluetooth device.
· The Host Control Interface the Host Controller Interface (HCI) driver encapsulates high-level modules for communication with hardware.

(3) Bluetooth profile: for example, if a company wants their Bluetooth chip to support all Bluetooth headsets, it only needs to support headset profile, the communication and compatibility between the chip and other Bluetooth devices do not need to be considered. If you want to buy a Bluetooth Product, You should know which profiles are required for your application and make sure that your Bluetooth Product supports these profiles.

Four of all profiles are basic ones, which will be used by other profiles. They are:

Gap profile: Generic Access Profile, which ensures that different Bluetooth products can discover each other and establish a connection.
Sdap profile: service discovery application profile through which a bluetooth device can find services provided by other Bluetooth devices and query related information.
SPP Profile: Serial Port profile, simulating serial communication.
Goep profile: Generic Object Exchange profile, Common Object Exchange. The profile name is confusing. It defines data transmission, including synchronization, file transmission, or pushing other data. You can understand it as a content-independent transport layer protocol, which can be used by any application to transmit Custom Data Objects.

In addition, Bluetooth also defines nine application (usage) profiles.
CTP profile: Cordless Telephone profile, cordless phone.
IP profile: intercom profile, which establishes a voice connection between two devices. In other words, it turns two expensive Bluetooth devices into inexpensive walkie talkie devices.
HS profile: headset profile, used to connect the headset.
DNP profile: dial-up networking profile, used to provide the dial-up network function for the PC.
FP profile: Fax profile, fax function.
Lap profile: LAN Access Profile, which uses the PPP protocol to establish a LAN.
OPP profile: Object push profile, used to transmit data objects between devices.
FTP profile: File Transfer profile, used for file transfer.

SP profile: Synchronization Profile, used for synchronization between different Bluetooth devices to maintain data consistency.

A2dp: The full name is the Advanced Audio distribution profile Bluetooth audio transmission model agreement! A2dp uses a chip in the headset to stack data to achieve high sound definition. A headset with a2dp is a Bluetooth stereo headset.

========================================================== ========================================================== ==============================

In Bluetooth, The HFP, MK, and a2dp protocols are often used to connect to Bluetooth headsets for communication and music-related operations. What are the relationships and differences between them? In the android Bluetooth menu, the description of the headset device is divided into mobile phone audio and Media Audio. What are their meanings and corresponding Bluetooth protocols?

(1) Both HFP (hands-free profile) and MK (headset profile) are designed to implement Bluetooth calls. The functions implemented are related to Bluetooth calls. Basically all Bluetooth headsets and on-board Bluetooth support these two protocols.

Only the most basic call operations are performed on the phone, the phone is closed, the volume is adjusted, and the voice is switched between the mobile phone and the Bluetooth headset.
In addition to the above features, HFP also includes advanced features such as control of third-party calls, rejected calls, and powered display on the headset, for example, the at cmd used for control is completely different.
In Android design, the two protocols are not displayed separately, but both are expressed as "Mobile Phone audio". HFP is preferentially connected during use, the target user can only attempt to connect to the target user if the target user fails to connect to the target user.
(2) While a2dp (Advanced Audio distribution profile) is only used for stereo music transmission. For example, a2dp is used when playing MP3 in a music player. Generally, dual-ears Bluetooth headsets and on-board Bluetooth support a2dp, and a few single-ears headphones may also implement a2dp. Compared with heat/HFP, a2dp delivers fast transmission speed and sound quality, but is slightly less real-time (theoretically, users cannot feel it ). In Android, it is expressed as "Media Audio"
 

Reference: http://blog.csdn.net/btooth/archive/2006/07/15/924542.aspx