Lectured By: Vivek Dimri Asst Professor CSE Deptt. SET

Introduction Bluetooth is a wireless protocol utilizing short-range communications technology facilitating data transmission over short distances from fixed and mobile devices, creating wireless personal area networks (PANs). Bluetooth uses a radio technology called frequency hopping spread spectrum. It chops up the data being sent and transmits chunks of it on up to 79 different frequencies.

Communication and Connection A master Bluetooth device can communicate with up to seven devices. This network group of up to eight devices is called a Piconet. A Piconet is an ad-hoc computer network, using Bluetooth technology protocols to allow one master device to interconnect with up to seven active devices. Up to 255 further devices can be inactive, or parked, which the master device can bring into active status at any time. At any given time, data can be transferred between the master and one other device.

Communication and Connection The Bluetooth specification allows connecting two or more piconets together to form a scatternet, with some devices acting as a bridge by simultaneously playing the master role in one piconet and the slave role in another. Peak transmission rate is 1 Mbps.

Communication and Connection

Bluetooth Channels The piconet channel is represented by a pseudo-random hopping sequence (through 79/23 RF frequencies) The hopping sequence is unique for the piconet and is determined by the device address of the master of the piconet. The phase is determined by the master clock. Channel is divided into time slots microsecs each. Each slot corresponds to a different hop frequency. Time Division Duplex - master and slave alternately transmit/listen. Packet start aligned with slot start

Bluetooth Channels m s1s1 625 sec f1 f2f3 f4

Physical Link Synchronous Connection Oriented (SCO) Link : symmetric point-to-point link between M and S reserved 2 consecutive slots at regular intervals master can support up to 3 simultaneous SCO links mainly for audio/voice never retransmitted Asynchronous Connection-less (ACL) Link symmetric/asymmetric point-to-multipoint between master and all slaves on a per-slot basis (polling scheme for control) only one ACL link per piconet packets retransmitted (ARQ)

Packets All data on the piconet channel is conveyed in packets 3 packet types are defined for the Baseband layer Control packets (ID, NULL, FHS, POLL) Voice packets (SCO) Data packets (ACL) Packet format - (68/72 bits) Access Code, (54 bits) Header, ( bits) Payload.

Packets Access code HeaderPayload Voice data header CRC SCO ACL 1/3/5 slot packets Unprotected/ 2/3 FEC ARQ scheme – retran- smit lost data pkts Single-slot packets 64 kbps Unprotected/ 1/3 or 2/3 FEC Never retransmitted Robust CVSD encoding used

Bluetooth Address Bluetooth Device Address (BD_ADDR) Unique 48 bit address Active Member Address (AM_ADDR) 3 bit address to identify active slave in a piconet MAC address of Bluetooth device All 0 is broadcast address Parked Member Address (PM_ADDR) 8 bit parked slave address

Setting up Connection Any Bluetooth device will transmit the following information on demand: Device name. Device class. List of services. Technical information, for example, device features, manufacturer, Bluetooth specification used, clock offset.

Bluetooth Architecture Bluetooth is both a hardware-based radio system and a software stack that specifies the linkages between layers. In this section, you’ll learn about: The Bluetooth protocol stack. The protocol stack is the core of the Bluetooth specification that defines how the technology works. The Bluetooth profiles. The profiles define how to use Bluetooth technology to accomplish specific tasks.

Bluetooth Architecture

Lower Layer Radio Layer Responsible for modulation/demodulation Define physical characteristics Baseband or Link Controller Layer Responsible for properly formatting of data for transmission. Handles synchronization of link Link Manager Protocol Translates HCI commands into baseband level operations Responsible for maintain and establish links and manage power change request. Host Control Interface Act as boundary between low layer protocol stack and upper layers

Bluetooth Architecture Upper Layer L2CAP (Logical Link Control and Adaptation Protocol) layer: Establishing connections across existing ACL links or requesting an ACL link if one does not already exist. Multiplexing between different higher layer protocols, such as RFCOMM and SDP, to allow many different applications to use a single ACL link. Repackaging the data packets it receives from the higher layers into the form expected by the lower layers. RFCOMM (Radio frequency communications) layer: It connects to the lower layers of the Bluetooth protocol stack through the L2CAP layer. RFCOMM is the cable replacement protocol used to create a virtual serial data stream. RFCOMM provides a simple reliable data stream to the user, similar to TCP.

Bluetooth Architecture Upper Layer SDP (Service Discovery Protocol): It defines actions for both servers and clients of Bluetooth services. Used to allow devices to discover what services each other support, and what parameters to use to connect to them. OBEX (object exchange): It is a transfer protocol that defines data objects and a communication protocol two devices can use to easily exchange those objects. Telephone control protocol-Binary (TCS-Bin): It’s a bit oriented protocol. It defines the call control signaling for the establishment of voice and data calls between Bluetooth devices. TCS BIN defines mobility management procedures for handling groups of Bluetooth TCS devices

Connection Establishment Two step process : Inquiry – to get device address. Paging – for Synchronization

Connection Establishment: Inquiry No master and slaves at this point Inquiry Inquiry Scan Inquiry Response Inquiry pkt FHS pkt Device A Device B

Connection Establishment: Pagging MasterSlave Page Page Scan Master Page Response Slave Page Response Connected Page pkt ID pkt FHS pkt ID pkt POLL NULL Uses FHS to get CAC and clk info Assigns active addr

Connection Establishment Time Connected PagingInquiry Typical Max 5.12 s s 0.64 s 7.38 s

Connection Modes Active Mode : Device actively participates on the piconet channel Power Saving modes Sniff Mode : Slave device listens to the piconet at a reduced rate. Least power efficient. Hold Mode : The ACL link to the slave is put on hold. SCO links are still supported. Frees capacity for inquiry, paging, participation in another piconet. Park Mode : The slave gives up its active member address. But remains synchronized (beacon channel). Listens to broadcasts. Most power efficient.