Basic Rate / Enhanced Data Rate (BR/EDR) radios operate in the 2.4 GHz ISM band.
The typical operation of the physical radio frequency layer is that a group of devices work on the same clock ( clock ) and frequency hopping pattern ( frequency hopping pattern ).
Among them, the device that provides the synchronization reference object is called the master device ( Master ).
Other devices to synchronize the master's clock and frequency hopping mode, these devices are called slave devices ( Slave ).
Such a group of devices forms a piconet .
This is the basis of device communication in BR/EDR technology.
Devices in the piconet use a specific frequency hopping pattern, determined by the algorithm from the master device's Bluetooth address and clock frequency.
The basic frequency hopping pattern is a pseudo-random sequence with 79 frequencies, separated by 1MHz, in the ISM band.
Frequency hopping mode is used for anti-interference and improved coexistence with non-frequency hopping Bluetooth.
A physical channel is divided into time units called time slots.
The data of the Bluetooth device is transmitted in these time slots.
Above the physical channel there is a layered link, channel and associated control protocol.
The layers are:
* physical channel (physical channel)
* physical link (physical link)
* logical transport (logical transport)
* logical link (logical link)
* L2CAP channel (L2CAP channel).
On the physical channel, a physical link ( physical link ) is formed between the master device and the slave device.
However, the physical channels of Inquiry scan and Page scan do not have associated physical links.
A physical link provides bidirectional packet transfer between a master and a slave, unless it is a connectionless slave physical link.
In this case, the physical link provides unidirectional data transmission capability for the master device.
In a piconet, a physical link is not allowed between slave devices, and a physical link is only allowed to be formed between a master device and a slave device.
This means that there is no direct communication between slave devices, only the communication between the master device and the slave device.
A logical link is based on a physical link.
A physical link will be used by one or more logical links.
Link Control Protocol, link manager protocol ( LMP ).
LMP is based on logical links and is used to control the baseband and physical layers.
Active devices in the piconet have a default connection-oriented asynchronous logical transport (asynchronous connection-oriented logical transport) used to transmit LMP protocol signals.
For historical reasons, this is called an ACL logical link.
For Connectionless Slave Broadcast devices, the ACL logical link is not required.
The Link Manager function uses the LMP to control the behavior of the device and provides services to manage the bottom layer (radio layer and baseband layer).
The LMP protocol is only carried on the primary ACL logical transport and the default broadcast logical transport
L2CAP , on top of the baseband layer, provides a channel-based abstraction for applications and services.
It performs segmentation and reassembly of application data and multiplexing and demultiplexing of multiple channels over shared logical links.
For more content reference: Bluetooth learning summary