5. Protocols in Bluetooth Architecture
Bluetooth Core Protocols
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Figure 2 shows the Bluetooth protocol architecture. Bluetooth technology is designed for and optimized for use in mobile devices. Mobile computers, cellular handsets, network access points, printers, PDA’s, desktops, keyboards, joysticks and virtually any other device can have short range Bluetooth radios operating in the free 2.4GHz Industrial-Scientific-Medical (ISM) band integrated into them (single chip). It uses Frequency Hop (FH) spread spectrum, which divides the frequency band into a number of hop channels. Bluetooth radios use tiny radio-frequency transmitters, no larger than 1.0 by 0.5 inches, that can run off a watch battery for months. Power considerations are always important for battery-powered mobile devices, and Bluetooth’s low power modes meet those requirements with less than 0.1 W active power. And since Bluetooth is designed for both computing and communications applications, it is designed to support high quality simultaneous voice and data, with robust data transfer rates of up to 721 Kbps. IT supports both synchronous and asynchronous services and easy integration of TCP/IP for networking purposes.
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Figure 2: Simplistic Bluetooth Architecture View |
The complete Bluetooth protocol stack (Figure 3) has been designed to include the existing protocols as much as possible (like TCP, UDP, OBEX) as well as Bluetooth specific protocols like LMP and L2CAP. The protocol reuse ensures smooth interoperability between existing applications and hardware. The Specification is also open, thereby allowing vendors to build proprietary applications. Although different applications may run over different protocol stacks, they all use the Bluetooth data link and physical layers. The Applications layer lies on top of the vCard (internal object representation convention) layer.
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Figure 3: Complete Bluetooth protocol stack. |
| Topology | Supports up to 8 simultaneous links in a piconet |
| Flexibility | Goes through walls, bodies, clothes, ... |
| Data Rate | 1 MSPS, 721 Kbps |
| Power | 0.1 Watts active power |
| Size/Weight | 25 mm × 13 mm × 2 mm, several grams |
| Cost | Long term $5 per endpoint |
| Range | 10 meters or less; up to 100 meters with PA |
| Universal | Intended to work worldwide |
| Security | Very, link layer security, SS radio |
Table 1: Bluetooth features at a glance.
Baseband: The Baseband and Link Control Layer enables the RF link Bluetooth units in a piconet. This layer uses inquiry and paging procedures to synchronize the transmission between different Bluetooth devices.
Link Manager Protocol (LMP): The link manager protocol is responsible for setting up link channels between Bluetooth devices after performing security methods like authentication and encryption by generating, exchanging and verifying linking and encryption keys and negotiating baseband packet size.
Logical Link Control and Adaptation Protocol (L2CAP): L2CAP packets carry payloads which are carried to the upper layer protocols.
Service Discovery Protocol (SDP): Using SDP, device information, services allowed and characteristics of the services are queried between Bluetooth enabled devices.
Cable Replacement Protocol (RFCOMM): RFCOMM is a serial line emulation protocol.
Telephony Control Protocol: The Telephony Control - Binary (TCS Binary) and Telephony Control - AT Commands are used to establish speech and data calls between devices and control mobile phones and modems respectively.
Adopted Protocols: Bluetooth also supports PPP, TCP/UDP/IP, OBEX and WAP protocols to maximize interoperability.
For more details refer to the Bluetooth White Paper[7].