Figure 3: Bluetooth SIG Administrative Structure
In 1994, Ericsson Mobile Communications began to examine alternatives to cables linking accessories with their mobile phones. This study produced the initial specification for wireless technology, with the Bluetooth SIG founded in February 1998 by the core promoters:
Ericsson Mobile Communications AB.
Nokia Mobile Phones.
The core promoters announced the global SIG in May 1998 and invited other companies to join as Bluetooth adopters. In July 1999 the core promoters published version 1.0 of the specification and further enlarged the core promoter group in December 1998 with the inclusion of:
v Lucent (now Agere)
The responsibility for the various Bluetooth specifications is in the hands of the individual technical working groups. Once a specification reaches a version level 0.5 it is made visible to associate members. An associate members must be recommended by a promoter, and submit a fee. When a specification reaches version 1.0 it gets a higher level of visibility. Now adopters have visibility and any company can become an adopter by joining the SIG, signing and submitting the membership agreement (see Bluetooth).
The Bluetooth specifications are open specifications for wireless communications that are free to download and use; however to use it royalty free you do have to join the SIG. By joining the group you sign up to an adopters agreement sharing any patents essential for implementing Bluetooth. The specifications define minimum functionality allowing devices from different companies to communicate (see Bluetooth).
. They provide the following:
o Protocol definitions for interoperability
o Host controller interface
o Bearer services for higher layer protocols
o Production test
o Brand book
The Bluetooth specifications define the concept of a Personal Area Network (PAN), what they do not provide helps to position it in the ISM band. It is not focussed on Wide Area Networking (WAN) as it has a limited range and currently there is no hand over mechanism, though there is a working group. They do not provide implementation instructions at the application programming interfaces, user interfaces or a definition of hardware and software split. Although it could be argued there is guidance in the profiles specification. The rest of this section breaks down the specifications encompassing the key aspects of Bluetooth in order to explain the features (see Bluetooth).
A.2.1 The Protocol Stack
The Bluetooth specifications define not only a radio system but cover the underlying structure. The Core Specification contains a software protocol stack similar to the more familiar Open Systems Interconnect (OSI) standard reference model for communication protocol stacks. It permits applications to discover devices, the services they offer and permission to use these services. The stack is a sequence of layers with features crossing single or multiple layered boundaries. Figure 4 outlines the stack with each block corresponding to a Core Specification chapter. Other remaining chapters relate to compliance requirements, test modes and test control interface (see Bluetooth).
If we ascend the stack, we first come across the fundamental component, the radio. The radio modulates and demodulates data for transmitting and receiving over the air. The operating band of the radio is divided into 1 MHz spaced channels with a chosen modulation scheme of Gaussian Frequency Shift Keying (GFSK). Each channel is specified to signal at 1mega symbols per second, equivalent to 1 Mb/s. Above the radio are the Baseband and Link Controller, they are responsible for controlling the physical links via the radio, and assembling the packets and controlling the frequency hopping (see Bluetooth.
Progressing through the layers, the Link Manager (LM) controls and configures links to other devices. The Host Controller Interface (HCI) is above the LM layer and is probably one of the most important layers to consider as a designer. It handles communication between host and the module. The standard defines the HCI command packets that the host uses to control the module, the event packets used by the host to inform lower protocol layers of changes, the data packets for voice and data traffic between host and module and the transport layer used by the HCI packets. The transport layer can be USB (H2), RS232 (H3), UART (4) or a robust proprietary standard such as BCSP (BlueCore Serial Protocol).
The Logical Link Control and Adaptation (L2CAP) is a multiplexor, adapting data from higher layers and converting between different packet sizes. The next 4 layers could be loosely grouped as communication interfaces. These are RFCOMM (Radio Frequency COMMunication port) which provides an RS232 like serial interface. Wireless Application Protocol (WAP) and OBject EXchange (OBEX) are responsible for providing interfaces to other Communications Protocols. The final member of this rough grouping is the Telephony Control protocol Specification (TCS) providing telephony services. Service Discovery Protocol (SDP) lets devices discover the services available on another Bluetooth device (see Bluetooth).
Figure 4: The Bluetooth Protocol Stack
The application layer is probably obvious, but the standard provides Profiles laying out rules for how applications use the protocol stack, ensuring interoperability at application level (see Bluetooth).