What is Bluetooth supposed to do? In a nutshell, Bluetooth can provide users with the ability to easily interact with a wide range of network applications that include voice and data applications. The equipment used to access the network can include PDAs, voice headsets, and cellular phones. The equipment that the users will be accessing with these devices could include other similar devices (point-to-point exchanges), LAN access units, or other access units designed to provide connectivity to an assortment of facilities.

To be viable, applications built on the Bluetooth interface must be easy to use and must operate efficiently. Furthermore, as a wireless application that can be used in public spaces, some degree of security must be provided. Users are likely to be sharing some form of private information over the links. When in reasonable proximity of network services, user equipment should require no more than a minimum essential set of user actions to activate the applications. The system must automatically detect all available devices, discover available services, and make it as easy as possible for the end users to access the services that they are seeking.

The types of information exchanged over the Bluetooth interface can include a broad range of voice and data applications. If you think for a moment about the types of applications that are handled in a home, an office, or in the domain of mobility, almost all are included in the set of Bluetooth applications.

The SIG has identified several applications that are used as reference applications. Additionally, the standards specification includes a comprehensive set of application profiles that describe the specific protocol operating modes that apply to each application. The application scenarios identified by the SIG include:

• File transfer. Several types of information can be exchanged between devices. Information that can be exchanged can range from small objects (such as vCards between PDAs) to larger files between computers.

• Internet bridge. The Internet bridge model is based on the use of a mobile telephone or cordless modem device that provides modem services to a PC, to enable cordless access for dial-up networking services. At the interface point between the computer and the access device, AT-style commands can be used to control the network access. Once the connection is made, either point-to-point protocol (PPP) for data or other fax signaling can take control of the link.

• LAN access. Somewhat similar to the Internet bridge scenario, the LAN access mode is based on the use of a device that acts as a LAN access point (LAP) providing Bluetooth access services to one or more data terminals (DT).

• Synchronization. Synchronization refers to the ability to exchange and synchronize information between devices that handle personal information management (PIM) data, which can include phone book, calendar, and task information.

• Three-in-one phone. Basically, telephones can be developed to operate in up to three different modes, which can include making voice calls through a basestation (as in the case of cordless phones), connecting directly between two phones in the same area (walkie-talkie mode), and finally in accessing the cellular phone network (obviously not using the Bluetooth interface)

• “Ultimate headset.” This is a case where Bluetooth can be used to provide the standard wireless audio headset services, enabling the additional security services afforded by the Bluetooth protocol.

This is a standard that is intended to address a full range of voice and data user access services, with the added attraction of being easy to integrate into next generation consumer electronics, communication, and computing devices. Where the Infrared Data Association (IrDA) standards focused on very close distance, line of sight (actually directed) interfaces, Bluetooth offers a broader range of services that are in-line with the convergence of information transfer into a single point of interface.

So, what does the Bluetooth architecture look like? It is a layered set of interfaces that operate over the 2.4-GHz Industrial, Scientific, and Medical (ISM) frequency band. Some of the fundamentals of the Bluetooth access suite include:

• Physical operating range. Normal mode is up to 10 meters. There are also extended reach capabilities in the specification that increase the transmit power to reach up to 100 meters.

• Concurrent device operations. Bluetooth networks include the concept of a piconet, which is essentially the set of elements that can directly communicate with one another. Up to eight devices can be included in a single piconet.

• Power consumption. Many of the devices that participate in Bluetooth communications are small and intended to be portable. With one of the major considerations in portable device weight being power consumption, the system has been designed to operate using only small amounts of power. In the case of Bluetooth, interface power consumption ranges from 30 mA (sleeping), to 300 mA (standby), and a maximum of 800 mA while transmitting information.

• Voice networking. Up to three users can participate on a piconet at any one time. Voice services are high-quality, being carried over 64-kbps transport with a range of encodings that can include pulse coded modulation (PCM) (either A-Law or m-Law) and continuous variable slope delta (CVSD) modulation.

• Data transport. Data transport can operate in either symmetric or asymmetric modes. Depending on the mode of operation, the transfer rate can be 721 kbps downstream and 56 kbps upstream (asymmetric), or 432 kbps bidirectional (symmetric).

• Cost. Cost is an extremely important factor. The Bluetooth SIG has targeted interface component prices to start at $20 for the interface, with a final target of $5. Given that the Bluetooth interface is intended to be included in many consumer devices, one of the keys to its success will be the fact that it is inexpensive.

This has been a concerted effort on the part of several companies to develop a set of standards that can meet the needs of a broad range of users. The information is widely available, with a set of publicly available standards and large participation in the Bluetooth SIG.

One of the important lessons that the Bluetooth SIG has learned is that there’s not much point in reinventing the wheel. Wherever possible, they’ve pointed developers to using standard protocols and mechanisms that include the PPP, AT-style commands, the IrDA object exchange (OBEX) protocol, and others. The Bluetooth SIG has defined the specific protocols necessary to provide the link services, service discovery, and link management germane to the specific RF interface.

The full suite of protocols included in the Bluetooth domain is shown in Figure 1 . Some of these protocols may look familiar to you from other application domains, such as IrDA, the Internet, or the Wireless Applications Forum. There are others, particularly the physical and link layer services, that are specific to the Bluetooth interface.

These protocols can be logically separated into four groups, which are:

• Bluetooth core protocols. These are the protocols that define and provide secure RF, frequency-hopped data transfer (the baseband protocol), link management (the Link Management Protocol [LMP]), logical link control and adaptation protocol (L2CAP), and service discovery (through the Service Discovery Protocol [SDP]).

• Cable Replacement Protocol. This is the RFComm protocol as defined within Bluetooth.

• Telephony Control Protocols. These are the service protocols that control the signaling required to control voice and data services. For voice services, the Telephony Control Protocol Specification (TCS) Binary protocol provides call control. Data services are managed through the de facto AT command set

• Adapted protocols. These are the user protocols that can be transported over the Bluetooth interface. Following the Bluetooth strategy of inventing only necessary protocols, this set of protocols is largely derived from protocols defined by other standards bodies. Some examples of the protocols that are adapted include OBEX, TCP/IP, and PPP.

As more equipment supports Bluetooth, this list is likely to grow. Bluetooth is designed to provide the types of data transport service associated with a broad range of applications. Over the next several months of this column, the core protocols, cable replacement protocol, and TCS protocols will be the topic of discussion.

Mike Rodbell is director of embedded software development for CIENA Communications, Inc. He has developed voice and data communication systems for a wide range of commercial and military systems. He holds a BSCS from Trinity College in Hartford, CT, and MSSE from Loyola College of Baltimore, MD. He can be reached at mrodbell@ciena.com or http://www.ciena.com .