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목 차

목 차. L2CAP 정의 및 역할 2. Layer 구성 및 interface 개요 3. Bluetooth usage models 4. L2CAP process 5. Example 6. Terminology 7. Summary. 1. L2CAP 정의 및 역할. - L2CAP : L ogical L ink C ontrol and A daptation P rotocol Adapts higher-layer protocols to the lower-layer protocol

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목 차

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  1. 목 차 • L2CAP 정의 및 역할 • 2. Layer 구성 및 interface 개요 • 3. Bluetooth usage models • 4. L2CAP process • 5. Example • 6. Terminology • 7. Summary + C1 Bluetooth +

  2. 1. L2CAP 정의 및 역할 - L2CAP : Logical Link Controland Adaptation Protocol Adapts higher-layer protocols to the lower-layer protocol : handle MUX of higher-layer protocols and segmentation/re-assembly of large packets. *higher-layer protocols : RFCOMM, SDP, PPP, TCP/IP, WAP … *lower-layer protocol : HCI, Baseband (concerned with connection establishment, addressing, timing, etc…) + C1 Bluetooth +

  3. 2. Layer 구성 및 interface 개요 Applications SDP TCS RFCOMM Audio MUX L2CAP process L2CAP HCI Baseband RF ↑ Higher Lower ↓ + C1 Bluetooth +

  4. 2. Layer 구성 및 interface 개요 (continued) 1) Multiplexing Baseband didn’t know/support the every protocol type ☞ L2CAP CAN ! 2) Fragmentation/Recombination L2CAP segmentation과 HCI/BB에서 처리할 수 있는 packet size가 다르므로 HCI/BB가 처리할 수 있게 packet control 3) Flow control, error control (optional) Baseband can’t detect or it’s hard to detect ☞ L2CAP CAN ! 4) Segmentation/Reassembly (only used in retransmission, flow control) Memory management, error correction by retransmission + C1 Bluetooth +

  5. 2. Layer 구성 및 interface 개요 (continued) Transmitter Receiver L2CAP L2CAP HCI HCI e.g) RFCOMM SDU 생성 Segmentation Reassembly L2CAP * Fragmentation/Recombination PDU 생성 PDU 생성 HCI가 알아듣게 packet 구성 L2CAP이 알아듣게 packet 구성 <Fragmentation> <Recombination> * Segmentation/Reassembly : Only retransmission, flow control SDU 가 여러 개의 segmentation으로 조각남 여러 개의 segmentation이 SDU로 합쳐짐 + C1 Bluetooth +

  6. 3. Bluetooth usage models SDP RFCOMM File transfer application OBEX RFCOMM Audio TCS BIN Cordless phone application SDP AT commands Modem emulation AT commands Headset application Audio SDP SDP RFCOMM PPP L2CAP L2CAP L2CAP L2CAP (1) File transfer (2) Dial-up networking (4) Cordless phone (3) Headset + C1 Bluetooth +

  7. 4. L2CAP process Length Length Length *PSM CID CID CID Data ≥1 command(s) Data Makes use of ACL links (not support for *SCO links) e.g) comparison text with audio transmission L2CAP channel (3 types of logical channels) - Connectionless : unidirectional. half-duplex. Broadcast data. - Connection-oriented : bidirectional. Full-duplex. QoS is assigned. - Signaling : signaling messages 2 byte 2 ≥ 2 0 ~ 65533 Connectionless PDU 0x0002 2 2 0 ~ 65535 Connection-oriented PDU 0x0040~0xFFFF 2 2 Signaling PDU 0x0001 *SCO packets are never retransmitted. *PSM(Protocol/Service Multiplexer) : identify the higher-layer recipient for the data in packet + C1 Bluetooth +

  8. 4. L2CAP process (continued) * CID : Local에서만 의미가 있는 ID로, 다수의 connection-oriented channels을 구분하고자 할 때 쓰임 0x0041 0x0041 0x0001 0x0042 0x0050 0x0002 0x0002 + C1 Bluetooth +

  9. 5. Example * JPG filetransmission Conditions ) 1. JPGbinary data transmission and reception 2. 전반적인 흐름 이해를 목적 3. Higher layer : OBEX protocol 4. Connection-oriented channel 사용 5. Prototype 6. Master : transmit the binary file Slave : receive the binary file + C1 Bluetooth +

  10. 5. Example (continued) Transmit .jpg file Receive .jpg file OBEX File transfer App. RFCOMM RFCOMM File transfer App. OBEX size : 353 KB mux Length : 353 KB, CID : 0x0040, Data : 0x9CCB … L2CAP L2CAP 0x0161 0x0040 0xFFD8FFE0 … Fragmentation Length CID Data Recombination Baseband Baseband HCI RF HCI RF Connection handle PB flag BC flag Length L2CAP data Master Slave + C1 Bluetooth +

  11. 6. Terminology * ACL(Asynchronous Connectionless) : Point-to-multipoint link. Master exchange packets with any slave. Retransmission is applied. * Channel : logical connection between two endpoints in peer devices * CID(Channel ID) : local name that indicates channel endpoint * Fragmentation : lower layer와의 transmission을 위해 만들어짐. HCI가 처리하도록 조각냄 (Recombination과 반대) * L2CAP : Logical Link Control and Adaptation Protocol * LMP(Link Manager Protocol) : responsible for link setup between bluetooth devices * OBEX(Object Exchange protocol) : binary transmission. similar to HTTP * PDU(Protocol Data Unit) : L2CAP packet data * PSM(Protocol/Service Multiplexer) : identify the higher-layer recipient for the data in packet * Reassembly : segment are assembled. Only used in retransmission, flow control (Segmentation과 반대) * Recombination : HCI는 L2CAP가 처리할 수 있도록 조합함(Fragmentation과 반대) * RFCOMM(Radio Frequency Communications) : cable replacement protocol * SCO(Synchronous Connection Oriented) : Point-to-point link. allocate a fixed bandwidth. SCO packets are never retransmitted. * SDU(Service Data Unit) : upper layer에서 생성된 data. SDU는 1개 이상의 segment로 구성된다. * SDP(Service Discovery Protocol) : query device information, services, etc to enable connection between two or more bluetooth devices * Segmentation : SDU is split into several segmentations. Only used in Retransmission, flow control (Reassembly와 반대) * TCS BIN : Telephony Control Specification-Binary + C1 Bluetooth +

  12. 7. Summary + C1 Bluetooth +

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