Introduction to Bluetooth

Bluetooth is an always-on, short-range radio hookup that resides on a microchip. It was initially developed by Swedish mobile phone maker Ericsson in 1994 as a way to let laptop computers make calls over a mobile phone. Since then, several thousand companies have signed on to make Bluetooth the low-power short-range wireless standard for a wide range of devices. Industry observers expect Bluetooth to be installed in billions of devices by 2005.

The Bluetooth standards are published by an industry consortium known as the Bluetooth SIG (special interest group).

The concept behind Bluetooth is to provide a universal short-range wireless capability. Using the 2.4 GHz band, available globally for unlicensed low-power uses, two Bluetooth devices within 10 m of each other can share up to 720 Kbps of capacity. Bluetooth is intended to support an open-ended list of applications, including data (such as schedules and telephone numbers), audio, graphics, and even video. For example, audio devices can include headsets, cordless and standard phones, home stereos, and digital MP3 players. Following are some examples of the capabilities that Bluetooth can provide consumers:

Bluetooth Applications

Bluetooth is designed to operate in an environment of many users. Up to eight devices can communicate in a small network called a piconet. Ten of these piconets can coexist in the same coverage range of the Bluetooth radio. To provide security, each link is encoded and protected against eavesdropping and interference.

Bluetooth provides support for three general application areas using short-range wireless connectivity:

Bluetooth Standards Documents

The Bluetooth standards present a formidable bulkwell over 1,500 pages, divided into two groups: core and profile. The core specifications describe the details of the various layers of the Bluetooth protocol architecture, from the radio interface to link control. Related topics are also covered, such as interoperability with related technologies, testing requirements, and a definition of various Bluetooth timers and their associated values.

The profile specifications are concerned with the use of Bluetooth technology to support various applications. Each profile specification discusses the use of the technology defined in the core specifications to implement a particular usage model. The profile specification includes a description of which aspects of the core specifications are mandatory, optional, and not applicable. The purpose of a profile specification is to define a standard of interoperability, so that products from different vendors that claim to support a given usage model will work together. In general terms, profile specifications fall into one of two categories: cable replacement or wireless audio. The cable replacement profiles provide a convenient means for logically connecting devices in proximity to one another and for exchanging data. For example, when two devices first come within range of one another, they can automatically query each other for a common profile. This might then cause the end users of the device to be alerted, or cause some automatic data exchange to take place. The wireless audio profiles are concerned with establishing short-range voice connections.

The Bluetooth developer must wade through the many documents with a particular application in mind. The reading list begins with coverage of some essential core specifications plus the general access profile. This profile is one of a number of profiles that serve as a foundation for other profiles and don't specify independently usable functionality. The general access profile specifies how the Bluetooth baseband architecture, defined in the core specifications, is to be used between devices that implement one or multiple profiles. Following a basic set of documents, the reading list splits along two lines, depending on whether the reader's interest is in cable replacement or wireless audio.

Protocol Architecture

Bluetooth is defined as a layered protocol architecture consisting of core protocols, cable replacement and telephony control protocols, and adopted protocols.

The core protocols form a five-layer stack consisting of the following elements:

Protocol Architecture

Bluetooth is defined as a layered protocol architecture consisting of core protocols, cable replacement and telephony control protocols, and adopted protocols.

The core protocols form a five-layer stack consisting of the following elements:

RFCOMM is the cable replacement protocol included in the Bluetooth specification. RFCOMM presents a virtual serial port that is designed to make replacement of cable technologies as transparent as possible. Serial ports are one of the most common types of communications interfaces used with computing and communications devices. Hence, RFCOMM enables the replacement of serial port cables with the minimum of modification of existing devices. RFCOMM provides for binary data transport and emulates EIA-232 control signals over the Bluetooth baseband layer. EIA-232 (formerly known as RS-232) is a widely used serial port interface standard.

Bluetooth specifies a telephony control protocol. TCS BIN (telephony control specificationbinary) is a bit-oriented protocol that defines the call control signaling for the establishment of speech and data calls between Bluetooth devices. In addition, it defines mobility-management procedures for handling groups of Bluetooth TCS devices.

The adopted protocols are defined in specifications issued by other standards-making organizations and incorporated into the overall Bluetooth architecture. The Bluetooth strategy is to invent only necessary protocols and use existing standards whenever possible. These are the adopted protocols:

Usage Models

A number of usage models are defined in Bluetooth profile documents. In essence, a usage model is a set of protocols that implement a particular Bluetooth-based application. Each profile defines the protocols and protocol features supporting a particular usage model. Following are the highest-priority usage models: