Bluetooth revealed

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Strictly speaking, these technologies are not limited to the WPAN domain, although they can be considered part of it. IrDA is relevant for comparison to Bluetooth wireless communications because the two technologies share some similar usage models and protocols. HomeRF, like Bluetooth wireless technology, is a relatively short-range RF communications scheme that operates in the 2. These technologies are described next, with the objective of providing a context in which Bluetooth wireless communications as a WPAN technology can be better understood.

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Understanding this emerging technology can benefit not only industry professionals but also consumers who can use and obtain value from it. The Bluetooth Special Interest Group As described above, Bluetooth wireless communication is embodied as a technology specification. This specification is a result of the cooperation of many companies within an organization called the Bluetooth Special Interest Group, or SIG. There is no "Bluetooth headquarters" nor is there any "Bluetooth corporation" nor any sort of legally incorporated entity. The SIG is governed by legal agreements among the member parties but it is not a company unto itself.

The SIG should not be construed as a formal standards body; rather it is an organization chartered to define and promote the technology. In fulfilling this charter the SIG is dependent upon the contributions and participation of its member companies. Clearly a major task of the SIG has been to develop the specification, but other SIG activities include joint work with other consortia and standards and regulatory bodies, educational and promotional events such as developers conferences and the definition of a testing and certification process.

In Ericsson had begun a project to study the feasibility of a low-power and low-cost radio interface to eliminate cables between mobile phones and their accessories. In today's computing and communications industries, proprietary new technologies rarely succeed; customers clearly prefer to purchase and deploy technologies based upon industry standards. By creating a level playing field, standards give customers greater freedom to choose from among competing platforms and solutions, to protect their investments as technologies evolve and to leverage and in some cases, also influence multicompany skills and organizations devoted to developing the standards.

In this industry environment, the Ericsson inventors understood that the technology was more likely to be widely accepted, and thus could be more powerful, if it was adopted and refined by an industry group that could produce an open, common specification. In early , leading companies in the computing and telecommunication industries formed the Bluetooth SIG to focus on developing exactly such an open specification.

These companies formed the original core group known as promoter companies of the SIG. The SIG was publicly announced in May with a charter to produce an open specification for hardware and software that would promote interoperable, cross-platform implementations for all kinds of devices.

While open standards can be quite advantageous, one potential disadvantage of standards bodies, consortia, special interest groups and similar organizations is that they tend toward inherent inefficiencies as compared to single-company efforts. Within a single company there is often one overriding objective for developing new technology; in a multi-company effort each participant may have different, perhaps even competing goals. Even with modern ways to exchange information, such as electronic mail, group interactions are still likely to be more efficient within a single organization than throughout a group composed of many organizations especially when those organizations are geographically diverse, as is the case for the members of the SIG—telephone calls, for example, have to take into account the fact that the people involved reside in time zones with little or no overlap of typical working [or even waking] hours.

To overcome some of these potential drawbacks, the SIG intentionally was created with a small number of companies committed to the rapid development of the specification who were willing to expend the resources necessary to accomplish this. SIG Progression As the specification evolved and awareness of the technology and the SIG increased, many other companies joined the SIG as adopters; adopters are entitled to a royalty-free license to produce products with Bluetooth wireless communication based upon the specification and can receive and comment upon early versions of SIG publications.

Today there are over 1, adopter members of the SIG, representing academia and industries such as consumer electronics, automotive, silicon manufacturing, consulting, telecommunications and many others. The original SIG's objective was to develop, as rapidly as possible, an open specification that was sufficiently complete to enable implementations. By carefully organizing the SIG and making use of frequent in-person meetings supplemented by even more frequent conference calls and e-mail exchanges, the SIG produced a thorough specification together, the volume 1 core specification and volume 2 profiles number over 1, pages in about one and one-half years version 1.

These working groups included:. Some of the larger working groups, such as the software working group, were further divided into task forces focusing on a particular layer of the Bluetooth protocol stack. Coordinating all of these working groups and governing the overall SIG was a program management committee composed of voting representatives from each of the promoter companies. During the one and one-half years that the SIG was developing the specification, working groups and task forces met and conducted their business both together and separately. Most working groups and task forces also held weekly conference calls.

In addition, e- mail distribution lists were used liberally and in fact were a primary method for conducting working group business. Because of the geographic diversity of the people involved, it was difficult to find mutually convenient times for frequent voice conversations;[3] thus electronic mail quickly became a convenient and heavily used means of communication in many respects it allowed specification development around the clock. Indeed, the official ratification of the final versions of the specification, profiles and errata was conducted using the e-mail reflectors. The group remains very active today in maintaining the existing documentation and in creating enhancements to the specification, along with new profiles.

This work is discussed in further detail in Part 4 of this book. It easily can be seen that it took an enormous effort to develop over 1, pages of complex and detailed information in just over a year's time.

Bluetooth Demystified

For many in the SIG this became their full-time job or at least a primary responsibility. Issues, both technical and non-technical, inevitably arose and were handled through discussion and voting when necessary, but in general the development and refinement of specifications and profiles progressed in an exemplary manner. A spirit of cooperation, fostered by the common objective of producing an open specification for this important new technology, usually carried the day at least in the authors' experience in the software and interoperability working groups.

The Bluetooth Name and History Bluetooth is notable in the high-technology industry in several respects, but in particular its name garners much attention. Most new industry initiatives are known by a name which describes their. The answer lies in the heritage and perhaps the whimsy of the original inventors. There are numerous histories and accounts of the Bluetooth namesake and how that name came to be chosen; the generally accepted story and facts are cited here. During his reign King Harald is reported to have united Denmark and Norway and to have brought Christianity to Scandinavia.

For a technology with its origins in Scandinavia, it seemed appropriate to the SIG founders to name the organization that was intended to unify multinational companies after a Scandinavian king who united countries. Thus was born the Bluetooth name, which initially was an unofficial code name for the project but today has become the trademark name see footnote 1 on page 3 of the technology and the special interest group. Figure 1. Bluetooth wireless communication has engendered tremendous interest since the SIG's formation was announced.

Articles in many leading computer-industry trade press publications and in quite a few of the mainstream media have appeared with some frequency. The SIG-sponsored conference in December in Los Angeles attracted over 2, developers from diverse geographies and industries. Reader's Guide to This Book This chapter has introduced the Bluetooth Special Interest Group, the technology, its chief characteristics and the history of its development. The remaining chapters of Part 1 provide additional background intended to aid in understanding the technology and what it can do.

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Chapter 2 discusses wireless communication technologies in general and the Bluetooth radio frequency wireless solution in particular, including requirements and design choices for use of the. Chapter 3 describes the significance of developing usage models for Bluetooth wireless communication and how these usage models relate to Bluetooth profiles. Each of the usage models is described, focusing on the benefits and value for a product's end user. Distinctions are drawn between those usage models enabled with version 1. Chapter 4 briefly explains the purpose, scope, structure and relationships of the Bluetooth specification and profiles, serving as an introduction to Parts 2 and 3 where these topics are covered in detail.

In Chapter 5 the relationships among the various layers of the stack are examined, and each of the remaining chapters in Part 2 then covers one or more of these layers in detail. The intent is not just to reiterate information already available in the specification but rather to provide information that supplements the specification and aids in its understanding.

Wherever possible we include information about the history, rationale and justification of the technical contents of the specification based upon our participation in its development. Chapter 6 describes the radio hardware, link controller, baseband, and link manager layers of the protocol stack. Together these layers comprise the lower layers of the transport group of the protocol stack.

Topics covered include the motivation and design tradeoffs behind the radio and baseband specifications, including the choice of the 2. Chapter 7 describes the logical link control and adaptation protocol L2CAP and host controller interface HCI layers of the protocol stack. We call these the upper layers of the transport group of the protocol stack, and they form the basis for the remainder of the software stack, including any new protocols that may be introduced in the future.

Topics covered include the motivation and design tradeoffs leading to the development of the HCI and the situations in which this layer is relevant; issues with flow control and its architectural placement within the stack; and how higher-layer elements of the stack can use and benefit from L2CAP.

These are middleware layers that provide abstractions in the form of logical interfaces and message transactions that can be used by application layers. Topics covered include the motivation and design tradeoffs for specifying a logical serial interface and its resulting benefits; how legacy applications could use Bluetooth wireless communication via RFCOMM; the motivation and design tradeoffs for specifying a new discovery protocol; and how SDP maps to other discovery protocols.

These are layers of the protocol stack that incorporate protocols and object formats specified by the Infrared Data Association IrDA into the Bluetooth specification. Topics covered include the motivation and design tradeoffs for reusing existing IrDA protocols and object formats; how existing IrDA applications could use Bluetooth wireless communications; and similarities and differences between IrDA and Bluetooth wireless communications. Chapter 10 discusses the telephony control specification TCS layer of the protocol stack and also describes how voice and audio communications are managed.

Topics covered include the motivation and design tradeoffs for specifying separate voice and data channels; reasons for the selection of voice encoding techniques, including tradeoffs of quality and efficiency; and alternative forms of telephony control protocols and why TCS was chosen.

In "Part 3. The Bluetooth Profiles Examined" we look into volume 2 of the Bluetooth specification, commonly known as the Bluetooth profiles, in the same manner in which we covered the core specification in Part 2. Chapter 11 examines the motivation for, development of and relationships among the various profiles, which define how to use the protocol stack to achieve interoperable solutions. Each of the remaining chapters in Part 3 then covers one or more of these profiles in detail. Just as in Part 2, the intent of these chapters is not simply to reiterate information already available in the profile specification but rather to provide information to supplement the specification and aid in its understanding.

These profiles define fundamental principles used to establish connections among devices with Bluetooth wireless communication capability and provide a basis upon which the remaining profiles are built. Topics covered include the motivation and design tradeoffs for security features such as pairing and encryption; the various possibilities for devices to be discovered; and how applications could access and make use of the service discovery protocol for service location and browsing.

Chapter 13 discusses the telephony class of profiles, including cordless telephony, intercom and headset. These profiles define various ways to use voice communication and call control for telephony applications. Topics covered include the motivation and design tradeoffs for selection of the version 1. Chapter 14 presents the serial port-based class of profiles, including generic object exchange, object push, file transfer and synchronization in addition to the common serial port profile itself.

These profiles all define ways to use the RFCOMM virtual serial port to exchange and synchronize data between two peer devices. Topics covered include the serial port profile "family tree"; configuration of the serial port profile and the relevance of typical serial parameters in Bluetooth wireless communications; why the distinction between object exchange, object push and file transfer is important; and current and future possibilities for data synchronization.

Chapter 15 describes the networking class of profiles that includes dial-up networking, LAN access and fax. These profiles all deal with some variation on data networking between two or more peer devices. Topics covered include limitations of Bluetooth wireless communications relative to some fax requirements; the relevance and value of audio feedback for dial-up networking; and the many possibilities for networking with Bluetooth wireless communications and why LAN Access using PPP was chosen for version 1.

The Future of Bluetooth Wireless Communications" looks at where the technology is headed.

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Chapter 16 discusses future possibilities for the technology, including those that the SIG is currently developing: automotive, imaging, printing, extended service discovery, association with the IEEE This chapter discusses how new usage cases might be realized using Bluetooth wireless communication and how industry innovators might go about developing new Bluetooth wireless communication solutions.

In addition, the product landscape for Bluetooth wireless technology is explored, including the current and projected marketplace. Chapter 17 summarizes the book and offers concluding remarks about the future of Bluetooth wireless communication, including a short discussion of interoperability and the opportunities that the technology presents. Technology Basics Communication can take many forms—audio, visual, written, electronic and so on. In the realm of electronics, analog and digital communications are so pervasive in modern society that they are largely taken for granted.

The exchange of data using these forms of communication has led to the use of terms such as "the information industry" and "the information age. We begin with a brief general discussion of wireless communications and then progress through more specific forms relevant to the Bluetooth technology. There are many other types of wireless communication; our intent here is to touch upon those that provide background for the Bluetooth technology rather than to provide a primer on wireless technologies in general.

Wired and Wireless Communications A great deal of data is carried over wired networks—many telephones, coaxial cable systems, local area networks and parts of the Internet communicate via wires and cables. Many televisions are connected to cable systems, most networked computers are connected to telephone lines or wired networks such as Ethernet networks, and even cordless and mobile telephones rely on wired "landline" telephone systems to carry and route calls between endpoints.

Communicating without wires is not a new concept. Broadcast radio and television are two common examples of wireless communications; others include satellites, cordless and cellular telephones and remotely controlled televisions, garage door openers and automobile door locks. While most of these examples employ communication via radio waves, the use of infrared, a nonvisible spectrum of light, is also relatively common. Bluetooth wireless communication employs radio frequency or RF technology, using radio waves to communicate through the air in a manner fundamentally similar to broadcast radio or television.

Radio Frequency Wireless Communications RF technologies employ transmitters and receivers tuned to produce and consume, respectively, radio waves of a given frequency range. The transmitter's power and the receiver's sensitivity help to determine the distance over which they can communicate. High transmission power output is used for long-range communications such as broadcast television while short-range communications generally require much less power; thus technologies that are designed to communicate across only a few meters could be employed in small, mobile battery powered devices.

Another characteristic that is relevant for communication applications is the ability of radio waves to penetrate many objects. Obstacles reflect light waves used in technologies such as infrared, but radio waves used in RF technologies in general can with certain limitations penetrate many obstacles although in some cases radio waves can diffract or go around objects too. Thus RF technologies can permeate many obstacles such as clothing, bodies, walls, doors and the like.

This means that there is no requirement for a "line of sight" between the transmitter and the receiver. RF technologies use frequency modulation to generate radio waves within a certain frequency spectrum, which encode information and can be intercepted by receivers tuned to the corresponding frequency. FM radio broadcasts, for example, operate in the 88 megahertz MHz to MHz frequency spectrum; some cordless telephones operate in the MHz frequency spectrum; Bluetooth wireless communications and other technologies operate in the 2.

Because the usable radio frequency space is finite, most governments regulate its use, partitioning frequency ranges and granting licenses to transmit at those frequencies at specified power levels. In the United States, for example, a federal license is required to transmit in the FM radio frequency spectrum except at extremely low power levels that limit the range to no more than about 30 meters.

Some frequencies are reserved for use without a license under certain conditions. For example, in the United States unlicensed operation is permitted, with some restrictions, in the MHz and 2. In fact, through multinational agreement, the 2. In general the chosen frequency spectrum can be used globally without license so long as the rules for operating within this spectrum are followed. RF Communications in the 2.

These include:. Japan began using all 79 channels in Microwave ovens also operate within this frequency range. Because this spectrum is unlicensed, new uses for it are to be expected for example, a new generation of cordless telephones also uses the 2. Thus the requirement to anticipate and address interference in the 2.

Each technology using this spectrum has made design choices within the spectrum's constraints that optimize that technology for particular applications or domains. Bluetooth wireless communication is designed to take maximum advantage of the available channel bandwidth and to minimize RF interference and its effects while operating at very low power. Spread Spectrum RF Communications Within RF communications, spread spectrum refers to dividing the available spectrum based upon frequency, time, a coding scheme or some other method. Messages to be sent are then divided into various parts packets that are transmitted across the divided spectrum.

Frequency division spread spectrum or frequency hopping , which is the method employed with Bluetooth wireless communication, divides the spectrum into different frequencies, or channels. Each technology specifies its own method for establishing the frequency hopping pattern.

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Obviously the receiver s of the message must know the hopping pattern to tune to the correct channels in succession to receive each packet and assemble the complete message. This process is called frequency hopping spread spectrum, or FHSS. Direct sequence is another form of spread spectrum RF communication employed in other technologies such as wireless LANs and is outside the scope of this book.

FHSS introduces additional complexity as compared to using a single statically selected frequency, yet it also supplies some benefits. First, RF interference can be reduced since all radios hop often randomly or at least pseudorandomly, and often rapidly from one frequency to another. When all of the participants in the spectrum employ FHSS, interference caused by colliding transmissions on the same frequency is less likely than it would be if each radio used a single channel for a long duration. In addition, when collisions do occur, their effects are lessened, since only a single packet is lost and that packet could be retransmitted at a new frequency, where again it is less likely to encounter interference.

Second, FHSS can provide a degree of security for communications in that only a receiver that knows the frequency hopping pattern can receive and assemble all the packets of a message. Because the hopping pattern for a given spectrum could be constructed in a number of ways, it could be difficult to deduce and follow an unknown hopping pattern, especially when the spectrum is heavily utilized with many radios.

Thus FHSS can be employed to hinder eavesdropping. In fact, this latter characteristic led to the invention of FHSS, usually attributed to George Antheil and Hedy Lamarr the latter is more famous as an American actress. Their patent of the frequency hopping concept was motivated by an attempt to find a "secret communication system" using radio waves to control torpedoes during World War II. Interested readers are referred to, for example, [IAL99] or other accounts easily found via World Wide Web search engines.

Furthermore, any rationale or implications of the choice of naming the Bluetooth technology after a Danish king rather than an American actress are not explored here. As previously noted, the use of spread spectrum is required in the 2. The design for Bluetooth wireless communication employs relatively rapid frequency hopping nominally 1, times per second and is described more fully below and in Chapter 6.

Infrared Wireless Communication RF is not the only form of wireless communication. Infrared technology is used with devices such as notebook computers, personal digital assistants and electronic remote controls. Infrared wireless communication makes use of the invisible spectrum of light just beyond red in the visible spectrum. IrDA technology is relevant when discussing Bluetooth technology because IrDA is also designed for short-range, low-power unlicensed communications.

IrDA also defines a physical layer and a software protocol stack designed to promote interoperable communications, as does the Bluetooth specification.

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Despite the differences between IrDA and Bluetooth wireless communications, such as data transmission speeds and signal paths infrared largely requires line-of-sight paths while RF can penetrate many objects , the similarities are such that the SIG worked with the IrDA in. Because there is overlap in the application spaces of IrDA and Bluetooth wireless communications, the specification includes an IrDA interoperability layer in which some protocols defined by IrDA are incorporated.

This helps to promote interoperability among wireless applications no matter which communications transport is being used. IrDA interoperability in the Bluetooth specification is further detailed in Chapter 9. The result is a wireless communication technology that is especially appropriate for cable replacement and for use with portable devices in pervasive computing applications. Some of the fundamental principles for Bluetooth RF communication are described here; details of the radio and baseband operation are given in Chapter 6.

Master and Slave Roles At the baseband level, when two devices establish a Bluetooth link, one acts in the role of master and the other in the role of slave. The specification permits any Bluetooth radio to assume either role, and a device may act as a master for one communication link and as a slave for another link.

The master device determines the frequency hopping pattern based upon its Bluetooth device address and the phase for the hopping sequence based upon its clock. All slaves communicating with a given master hop together in unison with the master. The master role generally is assumed by the device that initiates the communication. A given master may communicate with multiple slaves—up to 7 active slaves and up to parked slaves[6] active and parked slaves are described more fully below ; all slaves communicating with a single master form what the specification calls a piconet also described more fully below.

There can be only one master in a single piconet.

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The Bluetooth specification defines "direct" addressing for up to parked slaves via a parked slave address but also permits "indirect" addressing of parked slaves by their specific Bluetooth device address, thus effectively allowing any number of parked slaves, although from a practical perspective it would be unusual to have more than devices in a single piconet. This topic is explored more fully in Chapter 6. The master-slave relationship is necessary in Bluetooth low level communications but in general devices operate as peers.

When one device establishes a point-to-point link with another device, the role that each device assumes master or slave is often unimportant and is irrelevant to higher-level protocols and to the user of the device. In some usage scenarios it may be advantageous or even necessary for a given device to assume a particular role, but in many cases it is not critical to establish a single specific role for each device; some scenarios work.

It is important to understand the master-slave relationship for low-level communications while at the same time understanding that in general devices operate as peers to each other. Figure 2. Baseband Modes and Energy-Conserving Features As noted above, a piconet can include up to seven active slaves and many more parked slaves. The specification includes a definition for this parked baseband mode, as well as for other modes called sniff and hold.

The various baseband modes facilitate energy conservation by allowing the radios to enter low-power states. These low-power modes are really just three different methods for entering and exiting a low-power state, and the mode applies to a given Bluetooth connection rather than to the device as a whole. These baseband modes also permit a greater number of devices to be co-located in the same proximity sphere, since not all devices need to have active communication links at the same time.

All four of these baseband modes active, sniff, hold and park apply when the baseband is in a connection state; when not connected, the baseband is in a standby state, which should not be confused with any of the connected state modes. That is, the baseband states are connected and standby; within the connected state there are four modes active, sniff, hold and parked.

These states and modes are described in more detail in Chapter 6. In active mode a slave essentially always listens for transmissions from the master. Active slaves receive packets that enable them to remain synchronized with the master and that inform them when they can transmit packets back to the master. The active state typically provides the fastest response time but also typically consumes the most power, since it is always receiving packets and is always prepared to transmit packets.

Sniff mode is one method for reducing power consumption. In sniff mode a slave essentially becomes active periodically. The master agrees to transmit packets destined for a particular slave only at certain regular intervals although it may not transmit packets at every interval. The slave then needs to listen for packets from the master only at the start of each interval subject to some timing tolerances.

If the slave receives packets at the start of the interval it continues to listen and receive packets; otherwise it can "sleep" until the next interval. Sniff mode could permit reduced power consumption by reducing the average duty cycle of the radio but is likely to be less responsive than active mode. The power consumption and responsiveness in sniff mode depend upon the length of the sniff interval. In hold mode a slave may stop listening for packets entirely for a specified time interval.

During the hold time the slave need not listen for packets from the master and could be doing other things such as establishing links to other devices, or the slave could just sleep during the hold time.

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At the end of the hold period the slave resumes listening for packets from the master. Hold mode may be less responsive than sniff mode and could permit greater power savings than sniff mode, although this depends upon the hold time duration and upon what the slave does during the hold time sleeps versus communicates on other links. Since packet types have not yet been introduced, this section describes the fundamental concept of hold mode. A more complete description can be found in Chapter 6. In parked mode a slave maintains synchronization with the master but is no longer considered active slaves in active, sniff and hold modes are considered active.

Since there can be only seven active slaves in a piconet at one time, the use of parked mode allows the master to orchestrate communications within a piconet of more than seven devices by exchanging active and parked slaves to maintain up to seven active connections while the remaining slaves in the piconet are parked.

A parked slave still needs to maintain synchronization with the master and does so by listening to the master periodically, using a beaconing scheme described in Chapter 6. Parked mode is typically the least responsive of the connected modes, since the slave must make the transition to become an active member of the piconet before resuming general communications, but parked mode may permit greater power conservation.

However, both power consumption and responsiveness in these modes is highly dependent upon factors such as the amount of communications traffic and the hold and sniff periods, which can affect the duty cycle of the radios. As a general rule, active slaves will consume the most power but will be the most responsive, while parked slaves will typically be the least responsive.

The figure illustrates the general trend, although these relationships may vary in specific cases. Typical relative responsiveness versus power consumption for connected state baseband modes generalized; may not apply in all cases. In addition to the baseband modes which permit energy conservation, another power-saving feature is adaptive transmission power.

This feature allows slaves to inform the master when the master's transmission power is not appropriate, so that the master can adjust its transmission power. This is accomplished through the use of a received signal strength indicator RSSI. When the RSSI value is outside some determined boundaries, the slave can ask the master to adjust the power. This is especially useful when two devices are in close proximity and maximum transmission power is not required analogous to two people standing next to each other, with one person shouting and the second person asking the shouter to speak more quietly.

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Of course the converse is also true: transmission power increases also could be requested when the RSSI value indicates too weak a signal but the primary motivation for adaptive transmission power is to reduce power consumption when a lower transmission power is sufficient. The master maintains transmission power settings for each slave so that a change in transmission power for one slave does not affect other slaves in the piconet.

Like other energy-conservation features, adaptive transmission power could also allow a greater number of devices to be co-located in the same proximity sphere, since it could further reduce the possibility of RF interference with other devices. Communications Topology The Bluetooth network model is one of peer-to-peer communications based upon proximity networking. When two devices come within range of each other,[8] they could automatically establish a communications link.