L2CAP(Logical Link Control and Adaptation Layer Protocol)

참고자료: https://www.bluetooth.com/specifications/specs/core-specification-5-3/

 

* Bluetooth 전체 Architecture Layer는 "블루투스 아키텍처 계층" 참고

* Channel, Link, Transport 개념은 "Bluetooth Channel, Transport, Link" 참고

 

1. L2CAP 개요

- Upper layer의 Protocol Multiplexer 담당

- SAR(Segmentation and reassembly) 담당

- SDU(Service Data Units): Upper layer의 data packet을 64 Kbyte까지 수신 가능

- CID(Channel Identifier)를 사용하여 Baseband Logical Link와 연결됨

- CID(Channel Identifier)를 사용하여 Logical Channel 구분

- Host layer에 위치 ("Bluetooth Architecture Layer" 참고)

 

2. L2CAP Channel에서 CID(Channel Identifier)

- CID(Channel Identifier)를 사용하여 Logical Channel 구분

L2CAP Channel에서 CID

 

3. L2CAP Architecture

- L2CAP SAR(Segmentation and reassembly), Fragmentation 기능

L2CAP architecture block

 

4. Baseband Logical Link에 따라 할당된 CID(Channel Identifier)

- Baseband Logical Link는 "Bluetooth Baseband Architecture Layer" 참고

 

4-1. ACL-U Baseband Logical Link에서 CID(Channel Identifier)

CID	Description	Channel Characteristics
0x0000	Null identifier	Not allowed
0x0001	L2CAP Signaling channel
0x0002	Connectionless channel
0x0003	Previously used	Not applicable
0x0007	BR/EDR Security Manager
0x003F	Previously used	Not applicable
0x0040 ~ 0xFFFF	Dynamically allocated	L2CAP configuration mechanism를 사용하여 통신 L2CAP credit based create connection mechanism를 사용하여 통신
All other values	Reserved for future use	Not applicable

 

4-2. APB-U Baseband Logical Link에서 CID(Channel Identifier)

CID	Description	Channel Characteristics
0x0000	Null identifier	Not allowed
0x0002	Connectionless channel

 

4-3. LE-U Baseband Logical Link에서 CID(Channel Identifier)

CID	Description	Channel Characteristics
0x0000	Null identifier	Not allowed
0x0004	Attribute protocol
0x0005	L2CAP LE Signaling channel
0x0006	LE Security Manager protocol	Not applicable
0x0020 ~ 0x003E	Assigned Numbers	https://www.bluetooth.com/specifications/assigned-numbers/
0x0040 ~ 0xFFFF	Dynamically allocated	L2CAP configuration mechanism를 사용하여 통신 L2CAP credit based create connection mechanism를 사용하여 통신
All other values	Reserved for future use	Not applicable