Bluetooth physical link type: SCO and ACL Link

The Bluetooth physical link ACL (asynchronous connectionless), and the other link is SCO (synchronous connection oriented), which is mainly used to transmit data communication with high time requirements.
The Bluetooth baseband technology supports two connection types: Synchronous and targeted connections (SCO) and asynchronous connectionless connections (ACL. The former is mainly used for Synchronous voice transmission, and the latter is mainly used for grouped data transmission.
The SCO connection is a symmetric connection that uses the reserved time slot to transmit data packets. After the connection is established, the main device and the slave device can send SCO packets without being selected. SCO data packets can send both voice and data, but are only used to resend the damaged part of the data during data transmission.
An ACL link is used to send data packets in a targeted manner. It supports both symmetric and asymmetric connections (either one-to-one or one-to-multiple ). The master device is responsible for controlling the link bandwidth and deciding the bandwidth that each slave device in the micronetwork can occupy and the symmetry of the connection. Data can be transferred from a device only when it is selected. The ACL link also supports receiving broadcast messages from the master device to all slave devices in the micro-network.
Different types of links can be determined between the master and slave units. Two link classes are defined as follows: ● synchronous SCO ing (SCO, synchronous connection oritened) ● asynchronous ing (ACL, asynchronous Connection Less) (you can refer to the TCP connection and UDP connection of the TCP/IP protocol. Of course, there are more than two TCP/IP connection methods, and sctp; to understand the Bluetooth protocol, refer to the TCP/IP protocol)
The synchronous targeted link (SCO) is a point-to-point link between the master unit and slave unit in the Peer network. The Main Unit maintains the SCO link through regular use of the reserved time slot. The ACL link is a one-point multi-access connection between the master unit and all slave units in the Peer network. In this connection mode, the master unit does not retain the SCO link by time slot. The Master Unit establishes an ACL link to any other slave unit on each time slot base. This includes the slave units that are scheduled to use SCO links.
A) the SCO link is a point-to-point synchronous connection between the master unit and the specified slave unit. SCO connections use reserved time slots for transmission and grouping. Therefore, this mode can be seen as implementing circuit exchange connections between the master and slave units. SCO links are mainly used to support time-limit information such as voice. From the perspective of the master unit, it supports up to three SCO links of the same slave unit or different slave unit. In terms of units, it supports up to three SCO links for the same master unit. If the link comes from different master units, only two SCO links are supported for the slave unit. In this case, the SCO group cannot be transmitted (the difference between the SCO group and the ACL group ). The main unit sends the group at regular intervals. Therefore, in the reserved master-slave time slot, the SCO interval from the master unit to the slave unit is tsco ). In the master-slave time slot, the SCO slave unit always allows the response to the SCO group for transmission. However, if the original master-slave time slot uses different addressing addresses, this transmission cannot be used. In the group header, if an error occurs when the SCO slave unit decodes the address code of the slave unit, the SCO group can still be returned in the reserved SCO time slot. The SCO link is established by the main unit to send the SCO message, and is established by the LM protocol. The message group contains scheduled parameters (for example, the SCO interval tsco and the reserved time slot compensation dsco. To prevent clock hiding, set the initialization flag of information in LMP to indicate that initialization Mode 1 or initialization Mode 2 is used, and the slave unit will use the initialization flag to indicate the initialization mode. If the MSB of the current master clock (clk27) is 0, the master unit uses initialization Mode 1. When the MSB of the current main clock (clk27) is 1, the main unit uses the initialization Mode 2. The master is retained by the master and slave-since the SCO time slot is initialized based on the time slots that meet the following equations.
Clk27-1 mod tsco = dsco. Initialization Method 1 (clk27-1, clk26-1) mod tsco = dsco. Initialization Method 2
The master-slave SCO time slot directly follows the master-slave SCO time slot. After initialization, the clock value CLK (k + 1) from the SCO time slot is established as the next master by adding a fixed interval tsco to the current master-the clock value from the SCO time slot. CLK (k + 1) = CLK (k) + tsco.
B) ACL Link
When the SCO link is not retained, the main unit can be grouped and exchanged with any slave unit in each time slot base. The ACL Link provides a group exchange link between the master unit and all the active units in the gram network. Both asynchronous and other service modes can be used. If only a single ACL link exists between the master and slave nodes, packet retransmission is performed for most ACL groups to ensure data integrity. In the slave-Primary time slot, if the master-slave time slot before the master-only time slot has been edited, an ACL group is allowed to be returned from the slave unit. If the unit address in the group header fails to be decoded, it cannot be transmitted.
The ACL group is not configured as the specified slave unit of the broadcast group and is read by each slave unit. If no data is transmitted on the ACL link and no polling request is made, the transfer process does not exist on the ACL link.