Features of Bluetooth technology

1. Bluetooth Protocol Architecture

The whole Bluetooth protocol architecture can be divided into the bottom hardware module, the intermediate protocol layer and the high-end application layer. The Link Management layer (LMP), the baseband layer (BBP) and the Bluetooth radio channel form the underlying module of Bluetooth. The BBP layer is responsible for the transmission of frequency hopping and Bluetooth data and information frames. The LMP layer is responsible for the establishment and removal of connections and the safety and control of links, which provide different access to the upper software modules, but the message and data transfer between the two module interfaces must be interpreted by the Bluetooth host controller interface. In other words, the intermediate protocol layer includes the logic link control and the adaptation Protocol (L2CAP), the Service Discovery Protocol (SDP), the Serial Simulation Protocol (RFCOMM) and the Telephone Control Protocol specification (TCS). L2cap completes the data disassembly, the service quality control, the protocol multiplex and the group extraction function, is the other upper layer protocol Realization Foundation, therefore is also the Bluetooth protocol stack core part. SDP provides a mechanism for upper-level applications to discover services and their characteristics that are available on the network. At the top of the Bluetooth protocol stack is the high-end application layer, which corresponds to a cross-section of various application models and is part of the section. 13 sections are currently defined.

2. Bluetooth Low-level module

The lower-layer Bluetooth module is the core of Bluetooth technology and is part of any Bluetooth device that must be included.

Bluetooth works in the 2.4GHZ ISM band. The Bluetooth-terminated device says it can provide up to 720kbit/s data exchange rates.

Bluetooth supports both circuit-switched and packet-switched technologies, which define two link types, namely, connection-oriented synchronous link (SCO) and connectionless asynchronous link (ACL).

To enable Bluetooth devices to be connected in a very low power state, Bluetooth provides three energy-saving states, namely, Stop (park) status, Maintenance (Hold) status and Breathing (Sniff) status. These working modes are listed in ascending order according to energy efficiency: sniff mode, hold mode and park mode. (Computer science)

Bluetooth adopts three kinds of error correcting schemes: 1/3 forward error correction (FEC), 2/3 forward error correction and automatic re-sending (ARQ). The goal of forward error correction is to reduce the likelihood of a postback, but it also adds additional overhead. However, in a reasonable error-free rate environment, the redundant bids will reduce output, so the grouping definition itself is flexible, so it is feasible to define the FEC in the software. Generally speaking, the Bluetooth system uses the forward error correction scheme when the noise interference of the channel is large, in order to guarantee the quality of communication: For SCO links, 1/3 forward error correction is used; for ACL links, 2/3 forward error correction is used. In an AutoNumber automatic request restart scenario, a time slot data transmission must receive confirmation at the next time slot. Only when the data has passed the header error detection and the cyclic redundancy check (CRC) in the receiving end, the acknowledgement message is sent back to the originator, otherwise an error message is returned.

The mobility and openness of Bluetooth system make security problems become more and more important. Although the Bluetooth system used FM technology has provided a certain degree of security, but the Bluetooth system still needs the link layer and Application Layer Security management. In the link layer, the Bluetooth system provides authentication, encryption and key management functions. Each user has a personal identification number (PIN), which is translated into a 128bit link key (link key) for single two-way authentication. Once the certification is complete, the link will be encrypted with different lengths of password (Encryphon Key) to encrypt (this password is added to the shit, the maximum length is 128bit) The link Layer Security mechanism provides a large number of authentication schemes and a flexible encryption scheme (that is, allowing the length of the password to be negotiated). This mechanism is extremely important when equipment from different countries communicates with one another, because some countries specify the maximum password length. The Bluetooth system selects the minimum maximum allowable password length for each device in the Pico network. For example, the United States allows a 128bit password length, while Spain allows only 48bit, so that when the two devices are interoperable, 48bit is chosen to encrypt. The Bluetooth system also supports the special security mechanism of the different applications of the high level protocol stack. For example, when two computers are exchanging business card information, a computer can only access the business of another computer, but not the other business. Bluetooth security relies on a pin to establish trust between devices, and once this relationship is established, these pins can be stored in the device for quicker connection in the future.

3. Software module

The L2cap is part of the data link layer and is above the baseband protocol. L2CAP provides a connection-oriented and connectionless data service to the upper layer, which features: Protocol multiplexing, packet segmentation and reassembly (segmentation and reaassembly), and extraction (group abstraction). L2CAP allows high-level protocols and applications to send and receive data groupings up to 64K byte.

SDP provides a way for applications to discover the available protocols and determine the characteristics of these available protocols. The service discovery in the Bluetooth environment and the service discovery under the traditional network environment is very different, in the Bluetooth environment, the mobile RF environment changes very much, therefore the business parameter is also unceasingly transforms. SDP will emphasize the unique features of the Bluetooth environment. Bluetooth uses the client/server mechanism to define methods for discovering services based on the Bluetooth service type and attributes, and provides a way to browse services.

Rfcomm is a radio frequency communication protocol, it can simulate serial cable interface protocol, accord with ETSI0710 serial simulation protocol. Through Rfcomm, Bluetooth can be implemented in wireless environment for high-level protocols, such as PPP, TCP/IP, WAP and other support. In addition, Rfcomm can support the AT command set to enable wireless connectivity between mobile phones and fax machines and modems.

Bluetooth's support for voice is an important sign that distinguishes it from WLAN. Bluetooth Phone control specification is a bit-oriented laundry based on the ITU-T Recommendation Q.931, which defines a call control signaling for voice and data calls between Bluetooth devices and a mobility management process for handling Bluetooth TCS devices.