Bluetooth Core Technology Overview (5): Bluetooth protocol specifications (irobex, bnep, avdtp, avctp)

Keywords: Bluetooth Core Technology protocol IrDA bnep avdtp avctp

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Download link:Bluetooth profile specifications(Basically covering all Bluetooth protocols ),Buletooth core 2.1-4.0 specification(Core Protocol V2.1 \ V3.0 \ v4.0 of the three Bluetooth versions ),Core Bluetooth Technology and Application(For more information about the Bluetooth protocol, see)

Bluetooth Core Technology Overview (I): Bluetooth Overview
Core Bluetooth Technology Overview (II): Bluetooth application scenarios
Bluetooth Core Technology Overview (III): Bluetooth protocol specifications (RF, baseband Link Control, Link Management)

I. IrDA Interoperability Protocol
Irobex infrared object interaction protocol (obex) enables high-level protocols to operate simultaneously on wireless links of Bluetooth and infrared.

Main Operation Commands include: Connection operation, disconnection operation, put operation, and get operation.

1. Connection operation, Operation Code 0x80

Byte 0	Byte 1, 2	Byte 3	Byte 4	Bytes 5, 6	Byte 7 ~ N
0x80	Connection Request group Length	Obex version	Flag	Maximum length of the obex group that the client can receive	Optional Header

Byte 0	Byte 1, 2	Byte 3	Byte 4	Bytes 5, 6	Byte 7 ~ N
0x80 connect command	7	0x10	Flag	65534	Optional Header

Connection response

2. DisconnectThe operation code is 0x81.

3. Put operationThe operation code is 0x02.

After the connection is successful, the client uses the put request to "push" the object to the server. If the object is large, the put request can be grouped by multiple put requests.

4. Get operationThe operation code is 0x03.

Ii. Audio and telephone control protocols

1. Framework

Bluetooth Audio is shown in the Protocol Stack: audio is synchronized through baseband transmission and is implemented for connection groups. It is not provided in a standard form and is not part of the protocol stack.
Tcs_binary is a binary encoding instruction set based on group calls. It is located on top of L2CAP. Implement Bluetooth cordless phones and walkie talkie functions.
RFCOMM is used for AT commands. dial-up Internet access, Bluetooth headsets, headsets, and faxes are controlled by sending AT commands.
2. Audio part
64 Kbps carrier-level language quality audio streams
CVSD Continuous Variable Slope Delta Continuous Variable Slope increment.
PCM pulse code modulation.
PCM has a slope effect. CVSD uses the syllable compression algorithm and the encoding step size is automatically adjusted according to the signal slope change. It is a good coding solution to improve the language's anti-interference ability.
3. Telephone Control
TCS-binary Telephone Control Section.
(1) telephone call
Call Control, call establishment, and call removal;
(2) Group Management
Access permission requests, distributed configuration, and quick internal Member access.
Iii. Network Encapsulation Protocol bnep
Bnep ipvthnetworkencapsulation protocol network encapsulation protocol.
To exchange information with network devices such as computers, telephones, PDAs, and household appliances integrated with Bluetooth technology, a unified data group at the network layer is required. The Network Encapsulation Protocol re-encapsulates data groups from different networks and transmits data through L2CAP. This part of the protocol seems to be of little use in reality, and there are more simple and convenient ways to implement network functions.
Bnep supports IPv4, IPv6, and IPX

Iv. audio and video distribution protocol avdtp
Avdtpaudio/video distribution transport protocol audio and video distribution and transmission protocol

Protocols for A/V avdtp, avctp, gavdp, a2dp, and AVCRP
1. Basic concepts and terminologies
Stream:Stream is the form of audio/video transmission data. It is unidirectional transmission and is divided into media groups in avdtp. The stream is identified with a uniform HS handle.

2. Signaling
Avdtp signaling list

Command	Signaling identifier	Description
Avdtp_discover	0x01	Discover the stream endpoint in the device
Avdtp_get_capabilities	0x02	Ability to obtain stream endpoint Information
Avdtp_set_configuration	0x03	Configure Sep
Avdtp_get_configuration	0x04	Obtain the current Sep Configuration
Avdtp_reconfigure	0x05	Reconfigure Sep
Avdtp_open	0x06	After successfully configuring SEP, open the stream
Avdtp_start	0x07	Stream opened: Used to start forming a stream; when the stream is paused: used to form a new stream.
Avdtp_close	0x08	Disable Sep
Avdtp_suspend	0x09	Request Sep to suspend
Avdtp_security_control	0x0a	Set Content Protection for devices, or request device status information
Avdtp_abort	0x0b	The process of interruption being established or transmitted
Avdtp_get_all_capabilities
Avdtp_delayreport

This part of signaling achieves Bluetooth a2dp data stream control;
(1) stream signaling management process

(2) Get capabilities to obtain supported features

(3) set configuration to configure audio Parameters

Other commands are similar to the above two operations.
V. audio and video control transmission protocol avctp

Avctp allows audio and video devices to support multiple application frameworks. Each application framework defines the corresponding message formats and rules.
This part of the operation is also insufficient in practical applications. The amount of data transmitted by Bluetooth is limited, and the implementation of these functions is insufficient. With the development of science and technology, the advantages and disadvantages of Bluetooth in wireless communication are highlighted, and the right direction to find is a reasonable direction of development.