Bluetooth

BLUETOOTH

INTRODUCTION

Bluetooth is a wireless technology standard for exchanging data over short distances (using short-wavelength radio transmissions in the ISM band from 2400–2480 MHz) from fixed and mobile devices, creating personal area networks (PANs) with high levels of security. Different type of network is needed to connect different small devices in close proximity (about 10 m) without expensive wiring or the need for a wireless infrastructure .Bluetooth is a new standard suggested by a group of electronics manufacturers that will allow any sort of electronic tools from computers and cell phones to keyboards and headphones to make its own connections, without wires, cables or any direct action from a user. A key distinction with other offered wireless technologies is that bluetooth enables combined usability models based on functions provided by different devices. Bluetooth was invented in1994 by L.M.Ericson of Sweden. The name is attributed to Harald Bluetooth was king of Denmark around the turn of the last millennium. Choosing this name for the standard indicates how important companies from the Baltic region (nations including Denmark, Sweden, Norway and Finland) are to the communications industry.

As famous as the name is the bluetooth symbol. Bluetooth icon can be recognized by all. The main strength of bluetooth is its ability to simultaneously handle both data and voice transmissions. It is capable of supporting one asynchronous data channel and up to three synchronous voice channels, or one channel sup-porting both voice and data. This ability combined with ad hoc device connection and automatic service discovery make it a superior solution for mobile devices and Internet applications. This grouping allows such novel solutions as a mobile hands-free headset for voice calls, print to fax capability, and automatically synchronizing PDA, laptop, and cell phone address book applications.

BLUETOOTH FEATURE:

It is Wireless and automatic

Bluetooth is inexpensive (< $5 per unit) It Handles both data and voice

Signals are omni-directional and can pass through walls and briefcases Bluetooth uses frequency hopping at rate of 1600 Lops/sec

It operates on 79 channels in 2.4GHZ band with 1MHZ carrier spacing Pi-conet is the important terminology

NETWORK TOPOLOGY

Piconet:

A set of bluetooth devices sharing a common channel is called piconet. A piconet is a collection of devices connected via Bluetooth technology in an ad hoc fashion. A piconet starts with two connected devices, and may grow to eight connected devices. All Bluetooth devices are peer units and have identical implementations. However, when establishing a piconet, one unit will act as a Master and the other(s) as slave(s) for the duration of the piconet connection. Master is a Bluetooth device that sets the frequency hopping sequence. The Slave synchronizes to the Masters in time and frequency by following the Master‘s frequency hoping sequence. Every Bluetooth device has a unique

Bluetooth device address and a 28-bit Bluetooth clock. The baseband part of the Bluetooth System uses a special algorithm, which calculates the frequency hop sequence from the masters clock and device address. In addition to controlling the frequency hop sequence, the Master controls when Slaves are to transmit using Time Division Multiplexing (TDM).

When there is just one Master and one Slave the system is called a Point to Point connection. When many Slaves are connected to one Master, the system is called a Point to Multipoint. Both these types are referred to as a Piconet and all follow the frequency hopping sequence of the Master. The Slaves in the Piconet only have links to the Master and no direct links between Slaves.

Formation of piconet:

Two parameters are needed for the formation of piconet

Hopping pattern of the radio it wishes to connect.

Phase within the pattern i.e. the clock offset of the hops.

The global ID defines the hopping pattern. The master shares its global ID and its clock offset with the other radios which become slaves. The global ID and the clock parameters are exchanged using a FHS (Frequency Hoping Synchronization) packet.

There is no difference between terminals and base stations, two or more devices can form a piconet. The unit establishing the piconet repeatedly becomes the master, all other devices will be slaves. The hopping pattern is determined by the device ID, a 48-bit worldwide unique identifier. The phase in the hopping pattern is determined by the master‘s clock. After altering the interior clock according to the master a device may take part in the piconet. All active devices are assigned a 3-bit active member address (AMA). All parked devices use an 8-bit parked member address (PMA). Devices in stand-by do not need any address. All users within one piconet have the same hopping sequence and share the same 1 MHz channel. As more users join the piconet, the throughput per user drops quickly.

Scatternet :

Bluetooth defines a structure called scatternet to facilitate inter piconet communication. A scatternet is formed by interconnecting multiple piconet. A group of piconet is called scatternet.

If a device wants to take part in more than one piconet, it has to coordinate to the hopping sequence of the piconet it wants to take part in. If a device acts as slave in one piconet, it just starts to synchronize with the hopping sequence of the piconet it wants to join. After synchronization, it acts as a slave in this piconet and no longer participates in its former piconet. To permit synchronization, a slave has to know the uniqueness of the master that determines the hopping sequence of a piconet. Before leaving one piconet, a slave informs the current master that it will be unavailable for a certain amount of time.

The left over devices in the piconet continue to communicate normal.

A master can also go away from its piconet and act as a slave in another piconet. It is obviously not possible for a master of one piconet to act as the master of another piconet as this would direct to identical behavior. As soon as a master leaves a piconet, all traffic within this piconet is balanced until the master returns. Communication between different piconets takes place by devices jumping back and forth between these nets. If this is done occasionally, for instance, isochronous data streams can be forwarded from one piconet to another. On the other hand, scatternets are not yet supported by all piconet.

BLUETOOTH PROTOCOL STACK

The Bluetooth protocol stack can be divided into:

Core Specification -Deals with the lower layers of the architecture and describes how the technology works. It describe the protocol from physical to data link layer along with management functions.

Profile Specification -Focuses on how to build interoperating devices using the core technology.

Bluetooth Radio : specifics details of the air interface, including frequency, frequency hopping, modulation scheme, and transmission power.

Baseband: concerned with connection establishment within a piconet, addressing, packet format, timing and power control.

Link manager protocol (LMP): establishes the link setup between Bluetooth devices and manages ongoing links, including security aspects (e.g. authentication and encryption), and control and negotiation of baseband packet size

Logical link control and adaptation protocol (L2CAP): adapts upper layer protocols to the baseband layer. Provides both connectionless and connection-oriented services.

Service discovery protocol (SDP): handles device information, services, and queries for service characteristics between two or more Bluetooth devices.

Host Controller Interface (HCI): provides an interface method for accessing the Bluetooth hardware capabilities. It contains a command interface, which acts between the Baseband controller and link manager

TCS BIN (Telephony Control Service): bit-oriented protocol that defines the call control signaling for the establishment of voice and data calls between Bluetooth devices.

OBEX(OBject EXchange) : Session-layer protocol for the exchange of objects, providing a model for object and operation representation

RFCOMM: a reliable transport protocol, which provides emulation of RS232 serial ports over the L2CAP protocol

WAE/WAP: Bluetooth incorporates the wireless application environment and the wireless application protocol into its architecture.

Physical links

Different types of links can be established between master and slave. Two link types have been defined they are:

Synchronous Connection-Oriented (SCO) link. Asynchronous Connection-Less (ACL) link.

1.Synchronous Connection Oriented (SCO): It Support symmetrical, circuit-switched, point-to-point connections . It is typically used for voice traffic. The Data rate is 64 kbit/s.

2.Asynchronous Connection-Less (ACL): It Support symmetrical and asymmetrical, packet-switched, point-to-multipoint connections. It is typically used for data transmission .Up to 433.9 kbit/s are used in symmetric or 723.2/57.6 kbit/s are used in asymmetric. The master uses polling. A slave may answer if it has used the preceeding slot.

Connection establishment states:

Standby : The State in which Bluetooth device is inactive, radio not switched on, enable low power operation.

Page : The Master enters page state and starts transmitting paging messages to Slave using earlier gained access code and timing information.

Page Scan : The Device periodically enters page state to allow paging devices to establish connections.

Inquiry: The State in which device tries to discover all Bluetooth enabled devices in the close vicinity.

Inquiry scan : Most devices periodically enter the inquiry scan state to make themselves available to inquiring devices.

Slave connection state modes:

Active –It participates in piconet It Listens, transmits and receives frames

Sniff – It only listens on specified slots

Hold –It does not support ACL frames. It has reduced power status. It May still participate in SCO exchanges

Park – It does not participate on piconet and it Still retained as part of piconet

Bluetooth security:

There are three modes of security for Bluetooth access between two devices.

                Non-secure  

                        Service level enforced security   Link level enforced security

The following are the three basic security services specified in the Bluetooth standard:

Authentication : It verify the identity of communicating devices. User authentication is not provided natively by Bluetooth.

Confidentiality : It prevent information compromise caused by eavesdropping by ensuring that only authorized devices can access and view data.

Authorization :It allow the control of resources by ensuring that a device is authorized to use a service before permitting it to do so.