Bluetooth LMP Introduction

LMP is the link management protocol used for link establishment and control.

1. Introduction

The entities based on this layer are called Link Manager (LM: link managers)
Lm converts the command to the baseband layer (including the following)
~ Add slaves to piconet and assign them active member addresss
~ Detach disconnected slaves from piconet
~ Configure master and slaves switching links
~ Create an ACL and an SCO Link
~ Set the connection to low power mode: Hold, sniff and Park
~ Control Test Mode

LMP consists of a series of messages (ACL-C logical links transmitted at the ACL logical Transport Layer)
These messages are interpreted and executed by LM and cannot be transmitted to high-level protocols.

2. packet format)

The lmp pdu can be in two formats (opcode = 7/15 bit)
Detailed format reference Vol2-Park C-5

LMP messages are transmitted in the form of transaction. The same group of dialogs have the same transaction ID.
The identification parameter is transaction ID:
-0: The Master initiates transaction.
-1: slave initiates transaction

LMP messages use a DM1 package. If the hv1 SCO link is used and the payload length is less than 9 bytes, A dv can also be used.

 

3. Procedure Rules

Use the following symbol in a sequence chart:

Pdu1: A-> B
Pdu2: B->
Pdu3: A-> B (optional)
Pdu4: B-> A (optional)
Pdu5: A <-> B

The vertical line indicates that multiple PDUS can be sent selectively.

4. General Response Message)

Lmp_accepted and lmp_not_accepted are used when opcode is 7 bit.
Lmp_accepted_ext and lmp_not_accepted_ext are used when opcode is 15 bit.

5. device features)

Bluetooth settings define many features that LMP messages need to determine whether both parties support these features during transmission (Vol2-Park C-3.2)
These features are reflected in the form of bit mask in LMP messages (Vol2-Park C-3.3)
-1: supported
-0: not supported

6. Procedure

LMP detailed process includes seven categories (Vol2-Park C-4)
-Connection Control
-Security
-Information requests
-Role switch
-Modes of operation
-Logical transports
-Test Mode

For more information, see <Link Management Protocol>