2.3.1 Bluetooth Wireless Technology
Basic Rate (BR) and Low Energy (LR) are the two types of Bluetooth wireless technology systems.
Some Bluetooth-enabled devices implement both systems. These devices can communicate with other devices implementing LR and BR and also with those implementing either LR or BR. Both types facilitate the device discovery, define connection mechanism, and enable device connection.
Basic Rate (BR) System
BR systems offer synchronous and asynchronous connections and operates at data transfer rate of 721.2 kb/s. The data transfer rate for Enhanced Data Rate (EDR) is 2.1 Mb/s and high-speed operation
system includes optional Enhanced Data Rate (EDR), Alternate Media Access Control (MAC), and Physical (PHY) layer extensions” (Bluetooth SIG,2020).
Low Energy (LE) System
LE supports an optional 2 Mb/s physical layer data rate. It also offers isochronous data transfer, both in the connectionless and connection-oriented mechanisms. LE system is designed to enable products that require low data transfer rates and with low duty cycles (Kabalchi & Kabalchi, 2019). LE con-sumes less power: it is cheap and less complex compared to BR and EDR (Bluetooth SIG, 2020).
2.3.2 Bluetooth Protocols
There are varieties of protocols used in data exchanges in a Bluetooth-enabled system, grouped as controller stack and host stack. The Bluetooth Core system comprises one or more controllers and a host. The host is the higher layer protocol of the Bluetooth stack, responsible for the communication between the controller and the applications. Bluetooth SIG defines Core protocols.
2.3.3 Controller Stack
The controller stack contains the critical radio interface of the Bluetooth protocol. It is usually a con-siderably cheap device enabled with Bluetooth radio and a microprocessor (Enrico & Quaglia, 2020).
Some of the protocols are the following:
• Asynchronous Connection-Less (ACL): ACL serves as a transmission link through which data is transferred in a Bluetooth-enabled system with an access code of 72-bit, packet header of 54 bit, payload, and CRC of 16 bit. It is a preferred choice when avoiding latency is not as crucial as data integrity. It can achieve a maximum data rate of 1306.9 kb/s in symmetric data transfer and 2178.1 kb/s and 177.1 kb/s for outgoing data and incoming data, respectively (Haataja, 2009).
• Synchronous Connection-Oriented (SCO): SCO links transfer voice data. Encoded voice data is transmitted in the reserved timeslot with packet sent every 1, 2, or 3 time slots. There is no retransmission. However, forward error correction is possible. The enhanced SCO (eSCO) provides much flexibility that improves radio availability for other links. (Bluetooth SIG, 2020). The maximum data transfer rate in both directions in a symmetric SCO links is 64 kb/s (Haataja, 2009).
• Link Management Protocol (LMP): LMP takes care of the management of Bluetooth link. It is implemented on controllers to manage radio links between two devices. It is responsible for negotiating features, monitoring device power, and administering connections. (Gehr-mann et al., 2004)
• Host Controller Interface (HCI): HCI standardizes interaction between controller and host.
In a hostless system, host stack and controller stack are implemented on the same micropro-cessor. The standard set by the HCI allows the swapping of host stack or controller, requiring minimum adaptation (Enrico & Quaglia, 2020). The use of HCI is optional, although it could function as a software interface.
• Low Energy Link Layer (LELL): LELL manages scanning, connection, advertisement, and security.
2.3.4 Host Stack
Host Stack is used in high-level data handling. It also facilitates the communications between appli-cations and controllers. In most cases, it is part of the operating system. Some of the protocols are the following:
• Logical Link Control and adaptation protocol (L2CAP): L2CAP present an interface for all data applications that use Asynchronous Connection-Less (ACL) links. It achieves large data packet transmission by segmenting and then re-assembling the packet at the receiver side (Gehrmann et al., 2004). Therefore, data can fit into the limits of lower layer data packets. It manages the Quality-of-Service (QoS) for higher layer protocol and the single path transmis-sion of multicast data to other Bluetooth devices (Ahmadi, 2016).
• Service Discovery Protocol (SDP): SDP plays a vital role in the Bluetooth ad-hoc networking capability enabling device discovery and connection. It also discovers and lists what service and support other devices can render. In the protocol stack, SDP is bound to L2CAP. Every support and services are identified by a Universally Unique Identifier (UUID) (Bluetooth SIG.
2020).
• Bluetooth Network Encapsulation Protocol (BNEP): BNEP is a protocol utilized by the per-sonal area network (PAN). It is part of L2CAP in the protocol stack. BNEP delivers network packets to L2CAP. Its functions are included into Subnetwork Access Protocol (SNAP) in wireless Local area networks (LAN). BNEP provides network capabilities to devices that use
• Radio Frequency Communication (RFCOMM): RFCOMM is a set of protocols bound to L2CAP in the protocol stack. It is responsible for ensuring that user has reliable access and simple data stream. RFCOMM API is readily available on most operating systems and this makes it a favored choice in Bluetooth devices.
• Telephony Control Protocol (TCS): TCS manages the setup and control of voice data (speech and calls) between Bluetooth devices. It is sometimes called telephony control protocol spec-ification binary.
• Audio/Video Control Transport Protocol (AVCTP): AVCTP is bound to L2CAP on the pro-tocol stack. It is used by the remote-control profile to transfer AV/C commands.
• Audio/Video Data Transport Protocol (AVDTP): It is bound to L2CAP on the protocol stack.
AVDTP is essential in video streaming and it is used in video distribution profile. (Bluetooth SIG, 2020)
• Low Energy Attribute Protocol (ATT): ATT is like SDP redesigned to be compatible with low-energy Bluetooth. ATT supports clients to write/read essential attributes revealed by the server in a simple, low-power-compatible format. (Ray & Agarwal, 2016)
• Low Energy Security Manager Protocol (SMP): In LE Bluetooth system, SMP implements pairing and manages the transport specific key distribution. It is bound to L2CAP in the pro-tocol stack.