Low power Bluetooth connection process __ Bluetooth

(The article is a note about BLE connecting in Bluetooth Core spec V4.2) BLE connecting LE Generic Packet Structure (Vol. 1 part A, section 3.2.2)

The general structure of the link Layer Air interface packet closely reflects the architectural layers-found in the LE sys Tem. The LE packet structure is designed to optimal use in normal operation. It is shown in Figure 3.5.

The preamble is octet and the Access address is 4 octets. The PDU range is from 2 to 257 octets. The CRC is 3 octets.
All LE packets include theAccess Address. This is used to identify communications on a physical link, and to exclude or ignore packets on different links t Hat are using the same PHY channels in physical proximity. The Access address determines whether the packet was directed to the advertising physical link or the an active physical Li NK to a device. All LE Advertising physical links use a to fixed Access address. LE Active physical links use a randomly generated 32-bit value as their Access address. This provides a high number of the active devices that can is addressed in a LE piconet.
For advertising channel PDUs, thePDU HeaderContains the type of advertisement payload, the device address type for addresses contained in the advertisement and Adver Tising channel PDU payload length. Most Advertising ChannelPDU PayloadsContain The Advertiser ' s address and advertising data. One advertising channel PDU payload only contains the Advertiser ' s device address and the initiator ' s device address in WH Ich the advertisement is directed. Advertising channel PDUs with scan requests payloads the contain's scanner address and the device ' s advertiser device Ess. Advertising channel PDUs with scan responses contain, advertiser address and the device scan data. Advertising channel PDUs with connection request payloads contain the initiator's device address, Advertiser ' s device addr ESS and connection setup parameters.Access Address (vol. 6 part B section 2.1.2)

To mitigate the unwanted effects of the collision, each transmission on a physical channels starts and an Access It used as a correlation code by devices tuned to the physical channel. This Access is the physical channel. The Access address was present at the start of every transmitted packet.
The Link Layer used one physical channel at a given time.
Whenever the Link Layer is synchronized to the timing, frequency and Access address of a physical channel it are said to be ‘Connected' To-this channel (whether or not it are actively involved in communications over the channel).
The Access address to all advertising channel packets shall to 1000 1110 1000 1001 1011 1110 1101 0110b (0X8E89BED6).
The Access address in data channel packets shall is different for each Link Layer connection all between two with Certain restrictions as defined below. The Access address shall is a random32-bitValue, generated by the device in theinitiating Stateand sent in a connection the request as defined in the section 2.3.3.1. The initiator shall ensure this Access address meets the requirements.Initiating PDUs (vol. 6 part B 2.3.3)

The advertising channel PDU has a 16-bit header and a variable size payload. Its format is as shown in Figure 2.2. The bit Header field of the advertising channel PDU is as shown in Figure 2.3.


Connect_req Advertising channel PDU Type is called the initiating PDU which was sent by the Link Layer in the initiating St Ate and received by the Link Layer in the advertising state.
The Connect_req PDU has the Payload as shown in Figure 2.10. Txadd in the Advertising channel PDU header indicates whether the initiator ' s device to the field is public (Txadd = 0) or random (Txadd = 1). The Rxadd in the advertising channel PDU header indicates whether the Advertiser ' s device to the field is pub LIC (rxadd = 0) or random (Rxadd = 1).

The Payload field consists of Inita, Adva and Lldata fields. The Inita field shall contain the initiator ' s public or random-device address as indicated by Txadd. The Adva field shall contain The Advertiser ' s public or random-device address as indicated by Rxadd.
The format of the Lldata field is shown in Figure 2.11.

The lldata consists of fields:the AA field shall contain the Link Layer connection ' s Access address determined by the Link Layer Following the rules specified in section 2.1.2. ...LE Physical Channels (Vol. 1 part A, section 3.3)

The lowest architectural layer in the Bluetooth system is the physical channel. Two LE physical channels are defined.
The LE piconet Channel are used for communication between connected devices and are associated with a specific piconet. There are Notoginseng LE piconet channels.
The LE advertisement broadcast channel is used for broadcasting advertisements to LE devices. These advertisements can is used to discover, connect or send user data to scanner or initiator devices. The Le advertisement broadcast channel is a set of 3 fixed PHY channels spread evenly across the Le frequency spectrum.

In LE access address, hop index, and channel map are used to identify a physical channel. LE Physical Links (Vol. 1 part A, section 3.4)

A physical link represents a baseband connection between Bluetooth devices. A physical link is always associated with exactly one physical channel (although a physical channel could support more than One physical link). Within the Bluetooth system a physical link is a virtual concept that has no direct representation Within the structure of A transmitted packet.
The Le Piconet physical channels support an LE active physical link. The physical link is point-to-point link between the master and slave. It's always present when the slave was in a connection with the master.
The Le advertising physical channels support an LE advertising physical link. The physical link is a broadcast between The advertiser device and one or more scanner or initiator. It is always present then The Advertiser is broadcasting advertisement events.
For LE, there are no subsequent part of the packet that directly identifies the physical link. Instead the physical link may identified by association with the logical transport, as each logical transport are only R eceived on one physical link.LE Logical Transport (vol. 1 part A, section 3.5)

Logical Transport has a number of characteristics, including flow control, acknowledgement/repeat mechanisms, sequence num Bering and scheduling behavior. Logical transports are able to carry different types of Logical links (depending on the type of the Logical transport). In the case of some of the ' Bluetooth logical links These are multiplexed onto the same logical. Logical transports May is carried by active physical links on either the Basic or the adapted piconet physical.
Logical transport identification and real-time (link control signaling are carried in the packet header, and for some log The ical links identification is carried in the payload header.
The Le asynchronous connection (Le ACL) logical transport are used to carry LL and l2cap-control signaling and best effort Asynchronous user data. The default LE ACL is automatically created between the master and the slave when a device joins a piconet (connects to th e LE piconet physical channel). This default LE ACL is assigned a access channel number by the Piconet master. This access ' also used to identify ' active physical link when required.Connecting Procedure (Vol. 1 part A, section 4.2.2.5)

The procedure for forming connections is asymmetrical and requires this one Bluetooth device out the carries G procedure while the other Bluetooth device carries out the scanning procedure. The advertising procedure can be targeted and so this only one device would respond to the advertising. The scanning device can also target a advertising device by the-I discovering that advertising device be present in a connectable manner, and in the given area, and then scanning only connectable advertising events from that device using T He device filter. After receiving connectable advertising events from the targeted advertising device, it can initiate a connection< /strong> by sending the connection request to the targeted advertising device over the advertising broadcast physical Chan Nel. General Connection Establishment Procedure (vol. 3 part C 9.3.6)

The General Connection establishment procedure allows the Host to establish a connection with a set of known peer devices In the directed connectable mode or the undirected connectable mode.
Initiating a Connection (vol. 6 part D, section 5.1)

A device can initiate a connection to a advertiser. This is example shows a successful initiation, resulting in both devices to send able data (for the application 5.1).
initiating a Connection using directed advertising with Privacy (vol. 6 part D, section 5.4)

A device can initiate a connection to a advertiser The Who are using directed advertising. Privacy May is used during connection initiation to make it more difficult to track either device during-connection setup As as and as target a single initiator. The example shows a successful initiation, resulting in both devices-able to send application data (from Figure 5.4).
Connection State (vol. 6 part B, section 4.5)

The Link Layer enters the Connection state is initiator sends a connect_req PDU to a advertiser or a advertiser rec Eives a connect_req PDU from a initiator.
After entering the "Connection state", the Connection is considered to be created. The connection is isn't considered to being established at this point. A connection is only considered to being established once a data channel packet has been received from the peer. The only difference between a connection it is created and a connection this is established is the Link Layer connection Supervision timeout value is used (A/I 4.5.2).
When two devices are in a connection, the two devices act in different roles. A Link Layer in the master of is called a master. A Link Layer in the Slave role is called a Slave. The master controls the timing of a connection event. A connection event is a point of synchronization between the master and the slave. There shall is only one connection between two LE device. A initiator shall not send a connection the request to a advertiser it are already connected to.
If a advertiser receives a connection request from a initiator it are already to, it connected shall that request.Connected Mode (Vol. 1 part A, section 4.2.2.6)

After a successful connection procedure, the devices are physically to each of the other connected a within. This means so there is a piconet physical channel to which they are both, connected is a there link physical the Devices, and there are default Le-c and Le-u links.
Additional logical links are created using the Link Manager that exchanges LL Protocol messages with the remote Bluetooth Device to negotiate the creation and settings for these links.