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Bluetooth Link Manager Protocol (LMP) structure

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  • Time of issue:2018-02-01 00:00
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Bluetooth Link Manager Protocol (LMP) structure

Information

General description

The Link Manager Protocol (LMP) controls and coordinates all aspects of the operation of the Bluetooth® connection between two devices. This includes setting up and controlling logical transmission and logical link and physical link control. The link manager protocol carry protocol is used for communication between the link manager (LM) of two devices connected through ACL logical transmission.

General rules

LMP information is exchanged through the ACL-C logical link, and this logical link is transmitted through the default ACL logical transmission (see Bluetooth specification baseband section 4.4 for details). The difference between ACL-C logical link and ACL-U (transmitting L2CAP and user data) lies in the logical link identifier (LLID) field transmitted in the payload header of a variable-length packet. ACL-C has a higher priority than other communications.

The LMP information is carried through the ACL-C logical link, which does not guarantee delivery or inform the time when the data packet has been received. The LMP program takes this issue into account when synchronizing the status changes of the two devices. For example, the formulated standard specifies that a reusable logical transfer address (LT_ADDR) appears due to the device leaving the piconet or entering the dormant state. Other LMP programs (such as standby and role switching) list the Bluetooth clock as a parameter to define a fixed synchronization point. Switching in or out of sniffing mode is protected by switching mode.

LMP operates according to transactions. Transaction refers to a collection of coherent information exchanges that achieve a specific purpose.

Equipment function

All functions added after the 1.1 version specification have corresponding LMP function bits. Supporting these functions in the qualification process may become "mandatory", but LM will still make these functions optional because it must interoperate with older devices that do not support these functions.

These functions are represented by bit masks when transmitting LMP information. Any version of the link manager will read the LMP function mask and use the lowest common function subset to interpret.

Rules of procedure

The link manager protocol contains the PDU (Protocol Data Unit) enabling the following information

Connection control

1. Establish a connection

2. Separation

3. Power Control

4. Adaptation frequency hopping

5. Channel quality drives data rate changes (CQDDR)

6. Quality of Service (QoS)

7. Call plan parameters

8. Control multi-slot packets

9. Enhanced data rate

10. Packet LMP PDU

Safety

1. Certification

2. Pairing

3. Change the link key

4. Change the current link key type

5. Encryption

6. Apply for the supported encryption key length

7. Safe and simple pairing

Information request

1. Time accuracy

2. Clock skew

3. LMP version

4. Supported features

5. Name request

Role switching

1. Time slot deviation

2. Role switching

Operating mode

1. Standby mode

2. Sleep mode

3. Sniffing mode

Logical transmission

1. SCO logic transmission

2. eSCO logical transmission

Test mode

1. Activation and deactivation test

2. Control test mode

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