The magazine of the Melbourne PC User Group Bluetooth: Look Mum - No Wires Aman Kansal

Imagine walking into a hotel lobby and opening your laptop. It automatically connnects to the Internet without you having to search for a phone jack. You receive a meeting message on your mobile and it automatically updates your schedules in your PDA or your laptop. Walk into your client's office and your laptop has effortless access to his printer. Bluetooth promises all this and much more.
 
Over the past two years, Bluetooth has gained rapid attention and generated a lot of activity in both the computer and telecom industries. Touted initially as a cable replacement technology, it has now found a variety of other applications. This article explores the vision, architecture and the goals of this technology.

What Is Bluetooth?

Bluetooth is the name given to a new technology standard using short-range radio links, intended to replace the cables connecting portable and/or fixed electronic devices. The standard defines a uniform structure for a wide range of devices to communicate with each other, with minimal user effort. Its key features are robustness, low complexity, low power and low cost. The technology also offers wireless access to LANs, PSTN, the mobile phone network and the Internet for a host of home appliances and portable hand-held interfaces (Figure1).

The standard is aimed at achieving global acceptance such that any Bluetooth device, anywhere in the world, can connect to other Bluetooth devices in its proximity, regardless of brand. Bluetooth enabled electronic devices connect and communicate wirelessly via short-range, ad-hoc networks called piconets. Each unit can simultaneously communicate with up to seven other units per piconet. Moreover, each unit can simultaneously belong to several piconets. These piconets are established dynamically and automatically as Bluetooth devices enter and leave the radio proximity.
 
So Why Bluetooth?

First, there are the technology push kind of reasons that are making wireless connectivity not only feasible but also highly desirable. The ability to pack ever more transistors on a small area of silicon has made small embedded devices capable of running complex protocols. Embedded controllers in devices are now capable of being programmed, controlled and used in various smart ways. Thus intelligent devices can be embedded into the user's work and home areas. Various techniques are available to connect these embedded devices to the Internet, thus forming the so called "embedded Internet". Significant progress has been made in developing small and cheap sensors which can pick up useful signals from the user environment without user interaction or explicit command. 

New kinds of electronic tags, JINI (Java based service discovery) and Piano (which can be built over Bluetooth units, and specifies what sort of information they exchange) that enable interaction among dissimilar devices have become available. This has opened up the possibility for creating an "ubiquitous computing" environment. In this environment, the devices are controlled and activated by a combination of intelligent systems and strategically located sensors which work without explicit user support. The facility to automate depends heavily on the ability of devices to communicate wirelessly with each other, intelligent central servers, information repositories, sensors and actuators. Bluetooth can provide a solution to this requirement.
 
But the more immediate need comes from the desire to connect peripherals and devices without cables. The available technology-IrDA OBEX is based in infrared links that are limited to line-of-sight connections. Bluetooth is further fuelled by the demand for mobile and wireless access to LANs, internet over mobile and other networks, where the backbone is wired but the interface is free to move. A wide range of applications has been suggested for Bluetooth based devices. Some of these will be discussed in a later section.
 
History

The name Bluetooth may sound curious to the uninitiated. It comes from Harald Blatand "Bluetooth" II, king of Denmark 940-981 A.D. A runic stone has been erected in his capital city Jelling (Jutland) that depicts the chivalry of Harald and the "runes" say:

    1. Harald christenized the Danes.
    2. Harald controlled Denmark and Norway.
    3. Harald thinks notebooks and cellular phones should seamlessly communicate.

Bluetooth was invented in 1994 by L. M. Ericsson of Sweden. The Bluetooth Special Interest Group (SIG) was founded by Ericsson, IBM, Intel, Nokia and Toshiba in February 1998, to develop an open specification for short-range wireless connectivity. The group is now promoted by 3COM, Microsoft, Lucent and Motorola. More than 2000 companies have since joined the SIG.

Some Interesting Applications

The list of Bluetooth applications has exploded very rapidly. The standard is open and everybody is allowed to read it and use it. This has spurred a large number of startups and existing companies to develop Bluetooth based products leading to new ideas and rapid development. Some of the standardised applications are: 

1. Three-in-one phone: A single handset works as an intercom in the office (no call charges), as a PSTN phone whenever an access point to the PSTN is available, and as a mobile otherwise.

2. The Briefcase Trick: The RF link does not need line of sight. So a mobile could connect to a laptop even while it is in the briefcase and allow access to its facilities like e-mail.

3. The Automatic Synchroniser: Seamless connectivity between the user's PDAs, laptop and mobile will allow applications to automatically update and synchronise schedules and other data when modifications are made on one device.

4. Wireless headsets: These will allow access to user's mobiles and audio services even while the devices are in the user's pocket. Thus hands- free operation will be possible.

5. Car Kits: Hands-free devices will allow users to access their phones without letting their hands off the steering wheel.

6. E-payments: Using your mobile phone as your credit card. Many more have been suggested and are being developed. 

You can sure come up with your own. 

The Design

It may not seem all that difficult to set up a radio link. After all, RF communi-cation is nothing new and has existed for decades. But the requirements from the Bluetooth technology are very different. The design needs to meet a host of challenges: 

First, the technology should be such that a wide variety of devices-varying significantly in computation power and memory resources should be able to use it. These may include PDAs, computers and mobile phones on one hand and printers, mice and home appliances on the other. Unless a useful number of devices can connect, the use will stay limited. In the practical scenario all devices are not expected to be capable of all functionalities and users too may expect their familiar devices to perform their basic functions in the usual way. So Bluetooth must offer the facility for collaboration between devices, in the proximity of one another, where every device provides its inherent function based on its form, user interface, cost and power, but additional services emerge due to the synergy resulting out of the collaboration.

With this requirement in view, the Bluetooth protocol stack has been designed to be lightweight  and easily implementable in compact chips. Under US$5 implementations are soon expected. 

Second, the standard must enable the devices to establish ad-hoc connections. What this means is that the user should not need to feed the address of the device to connect, set up servers for each application and have to manually connect his devices each time she wishes to access a service. This is referred to as the "unconscious connectivity" paradigm. The devices connect on their own when in the proximity of each other if they need to.

For realising this, Bluetooth provides an automated device discovery service, so that the devices in proximity can detect each other's presence and start communications without having the user to explicitly give commands. 

Third, support for both data and voice is expected. These are the two types of data that are transmitted over networks today. So, if one of these is not provided, even on having connected to a network, the utility of the wireless link will be limited. Bluetooth provides asynchronous links for data and synchronous connection oriented links for voice calls. Support for Quality of Service (QOS) is also implemented to exploit the feature where the accessed network supports it. The requirement for video and streaming multimedia are being considered for the future versions of Bluetooth as these require bandwidths not easily realisable in the wireless links today. 

The fourth is the challenge of flexibility and expandability. A large number of users and service providers should be able to use the technology to custom design services based on it. This cannot be possible if each new application developed has to register through a central authority and users can access it only after reconfiguring their devices according to its requirements. The standard should allow an open means of incorporating new applications and services without having to make major changes in the device configurations or having to register with a central authority.

Bluetooth provides for this through its service discovery feature. An application running on one device can browse for similar applications on other devices and even exchange the application specific parameters for setting up a cooperative working environment for both the devices. 

There are also several other technical challenges that need to be met. The wireless environment has certain unique characteristics which make it much more hostile for digital communication than, say, a wireline. Further, as the wireless unit moves around, these characteristics change and the device  must adapt to these changing characteristics. The physical link uses robust modulation techniques to overcome these problems. Wireless devices can be truly wireless only if they are battery operated. This implies that the power consumption of the Bluetooth module should not be more than a small fraction of the host device into which the Bluetooth capability is to be introduced. Further, since Bluetooth devices will form part of people's personal usage, important data will be transferred over the wireless link when accessing other secure networks. So security considerations must be satisfied. Encryption facilities and authentication measures are part of the Bluetooth standard. 

The Bluetooth standard has made an attempt to meet these challenges at all layers of the protocol stack. The basic protocol stack is shown in Figure 2. The radio layer is the physical wireless connection. It uses the unlicensed Industrial Scientific and Medical band in the 2.4 GHz range. The modulation is based on fast frequency hopping to avoid interference with other communication units in this band. 

The technical details of the stack are not covered here and can be obtained from the specifications, available from http://www.bluetooth.com. 

Instead, a simplified description of the connection establishment process is given, to introduce the role of the various layers in the protocol stack. 

How Do Two Bluetooth Devices Connect?

Consider the following scenario: 
A person walks in to a hotel lobby and wants to access her e-mail over her Bluetooth enabled device, which could be a laptop or a Personal Digital Assistant. What would she have to do? Depending on the implementation, she would be clicking on a menu or an e-mail application icon. The rest is automatic. The Bluetooth unit would carry out the following procedures without requiring the user to do anything. 

Enquiry: The device on reaching a new environment would have automatically initiated an enquiry to find out what access points are within its range. (If not, it'll do so when the e-mail application asks for a link.) This will result in the following events:

• All nearby access points respond with their addresses.
• The device picks one out of the responding devices.

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