In 1990, the IEEE 802 Executive Committee established the 802.11 Working Group to create a wireless local area network (WLAN) standard. The standard specified an operating frequency in the 2.4GHz ISM (Industrial, Scientific, and Medical) band. Seven years later, the group approved IEEE 802.11 as the world's first WLAN standard with data rates of 1 and 2 Mbps.

Afterwards, the committee began work on another 802.11 extension that would satisfy future needs. Within 24 months, the working group approved two higher rate physical layer extensions to 802.11. The two extensions were designed to work with the existing 802.11 MAC layer (Medium Access Control), with one being the IEEE 802.11a - 5.2GHz, and the other IEEE 802.11b - 2.4GHz.

The 802.11b protocol operates in the unlicensed 2.4GHz ISM band, using DSSS (direct-sequence spread-spectrum) transmission. Maximum data rate is about 11 Mbits/s with fallback rates of 5.5, 2 and 1 Mbits/s, depending on distance, noise and other factors. Range can be up to 100m, but this too is dependent on the environment.

ACL links are defined for burst data transmission, i.e. packet data primarily. They support symmetrical and asymmetrical, packet-switched, point-to-multipoint connections. Multi-slot packets use the ACL link type and can reach the maximum data rate 721 kbit/s in one direction and 57.6 kbit/s in the other direction if no error correction is used.

SCO links support symmetrical, circuit-switched, point-to-point connections and therefore is used primarily used for voice traffic. Two consecutive time slots, up and down, at fixed intervals are reserved for a SCO link. The data rate for SCO links is 64 kbit/s.

Data packets are protected by an Automatic Retransmission Query scheme. Every packet reception is checked for errors. If an error is detected, the receiving unit indicates this in the return packet and lost or faulty packets cause a one-slot delay. In this way, retransmission is in this way selective, only faulty packets are retransmitted.

Since retransmission is not optimal for voice transmissions due to its vulnerability for delays, a voice-encoding scheme is used. This scheme is highly resistant to bit errors. The errors that cannot be corrected result in an increasing background noise.

The Host Controller Interface, HCI, provides a uniform interface method for accessing the Bluetooth hardware capabilities. It contains a command interface to the Baseband controller and link manager and access to hardware status. Finally, it contains control and event registers.

L2CAP - Logical Link Control and Adaptation Protocol

The Bluetooth logical link control and adaptation protocol, L2CAP, is situated over the Baseband layer and beside the Link Manager Protocol in the Bluetooth protocol stack. The L2CAP layer provides connection-oriented and connectionless data services to upper layers.

The four main tasks for L2CAP are:

• Multiplexing – L2CAP must support protocol multiplexing since a number of protocols (e.g. SDP, RFCOMM and TCS Binary) can operate over L2CAP.
• Segmentation and Reassembly – Data packets exceeding the Maximum Transmission Unit, MTU, must be segmented before being transmitted. This and the reverse functionality, reassemble, is performed by L2CAP.
• Quality of Service – The establishment of an L2CAP connection allows the exchange of information regarding current Quality of Service for the connection between the two Bluetooth units.
• Groups – The L2CAP specification supports the mapping of groups on to a piconet.

LMP - Link Manager Protocol

The Link Manager Protocol, LMP, is responsible for link set-up between Bluetooth units. It handles the control and negotiation of packet sizes used when transmitting data. The Link Manager Protocol also handles management of power modes, power consumption, and state of a Bluetooth unit in a piconet. Finally, this layer handles generation, exchange and control of link and encryption keys for authentication and encryption.

OBEX Protocol

OBEX (Infra-red) is an optional application layer protocol designed to enable units supporting infrared communication to exchange a wide variety of data and commands in a resource-sensitive standardised fashion. RFCOMM is used as the main transport layer for OBEX

PDA (Pesronal Digital Assistant)

The Personal Digital Assistant is much like an electronic notebook which can carry out a multitude of tasks. Go to www.palm.com to get a better idea!

Point-to-Point Protocol (PPP)

Point-to-Point Protocol (PPP) in the Bluetooth technology is designed to run over RFCOMM to accomplish point-to-point connections.

RFCOMM

The RFCOMM protocol is a serial port emulation protocol. The protocol covers applications that make use of the serial ports of the unit and It provides transport capabilities for upper level services.

TCP, UDP + IP

The TCP, UDP + IP standards are defined to operate in Bluetooth units allowing them to communicate with other connected units, for instance, to the Internet. Hence, the Bluetooth unit can act as a bridge to the Internet.

Wireless Application Protocol (WAP)

The Wireless Application Protocol (WAP) is a wireless protocol specification that works across a variety of wide-area wireless network technologies bringing the Internet to mobile devices. Bluetooth can be used like other wireless networks with regard to WAP.