BLE L2CAP Connection Oriented Channels (CoC)

[中文]

Supported Socs

ESP32

ESP32-C2

ESP32-C3

ESP32-S3

L2CAP Connection Oriented Channels (CoC) is a BLE feature that enables reliable, stream-oriented data transfer between BLE devices. Unlike GATT, which is based on attribute protocol, L2CAP CoC provides a connection-oriented channel model similar to TCP, allowing for larger data transfers with flow control.

Key features of L2CAP CoC:

  • Connection-oriented: Establishes dedicated channels between devices

  • Flow control: Prevents data loss by controlling transmission rate

  • Larger MTU: Supports MTU sizes up to 512 bytes (configurable)

  • Bidirectional: Full-duplex communication on established channels

  • Multiple channels: Support for multiple concurrent CoC channels

L2CAP CoC is particularly useful for applications that require:

  • Large file transfers

  • Audio/video streaming

  • Bulk data synchronization

  • Any application needing reliable, stream-oriented communication

Application Example

The PSM (Protocol/Service Multiplexer) value can be configured via Kconfig. In the example projects, it can be set in Example Configuration → L2CAP CoC PSM menu. Valid range: 0x0001-0x00FF (1-255).

  • 0x0001-0x007F: Fixed Bluetooth SIG-defined services

  • 0x0080-0x00FF: Dynamic custom services

Both central and peripheral devices must use the same PSM value to establish a connection.

// PSM value is configured via Kconfig (CONFIG_EXAMPLE_L2CAP_COC_PSM)
// Default value: 0x00EF (239)
#define L2CAP_COC_PSM CONFIG_EXAMPLE_L2CAP_COC_PSM
#define L2CAP_COC_MTU CONFIG_BLE_CONN_MGR_L2CAP_COC_MTU  // Maximum Transmission Unit

// Initialize L2CAP CoC memory pool
ESP_ERROR_CHECK(esp_ble_conn_l2cap_coc_mem_init());

// Create L2CAP CoC server
// app_ble_conn_l2cap_coc_event_handler is your callback function
esp_err_t rc = esp_ble_conn_l2cap_coc_create_server(
    L2CAP_COC_PSM, L2CAP_COC_MTU,
    app_ble_conn_l2cap_coc_event_handler, NULL);

Examples

  1. BLE L2CAP CoC Central example: bluetooth/ble_l2cap_coc/l2cap_coc_central.

  2. BLE L2CAP CoC Peripheral example: bluetooth/ble_l2cap_coc/l2cap_coc_peripheral.

API Reference

See BLE Connection Management for the L2CAP CoC API reference.

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