BT_540.pdf

 What is Bluetooth?  Goals  Requirements  Usage Models  Bluetooth Architecture  Security 2  Bluetooth is a new standard developed by a group of electronics manufacturers that will allow any sort of electronic equipment -- from computers an...

 What is Bluetooth?  Goals  Requirements  Usage Models  Bluetooth Architecture  Security 2  Bluetooth is a new standard developed by a group of electronics manufacturers that will allow any sort of electronic equipment -- 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 difference with other existing wireless technologies is that Bluetooth enables combined usability models based on functions provided by different devices. 3  The Bluetooth Special Interest Group comprises more than 1000 companies. The major companies who created the technology include  Intel  3com  Ericsson  IBM  Motorola  Nokia  Toshiba 4  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 5  Present wireless technology like infra red data communication has two problems  Line of Sight  One to One  Using data synchronizing– e.g. hot syn. on a PDA  problem of using the right cradle and cable.  BLUETOOTH OVERCOMES THESE PROBLEMS 6  It provides agreement at the physical level -- Bluetooth is a radio-frequency standard.  Provides agreement at the data link level where products have to agree on  when bits are sent  how many will be sent at a time  how the parties in a conversation can be sure that the message received is the same as the message sent 7  Bluetooth is a standard for a small , cheap radio chip to be plugged into computers, printers, mobile phones, etc  Bluetooth chip is designed to replace cabels. Information normally carried by the cable, is transmitted at a special frequency to a receiver Bluetooth chip.  These devices can form a quick ad-hoc secure “piconet” and start communication.  Connections in the “piconets” can occur even when mobile. 8  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. 9  Low cost as cables – chip $5  Secure as cables – must support authentication and encryption  Must support both data and voice.  Must connect to a variety of devices.  Must be able to function in a noisy environment.  Data rates – 721kbps , using the 2.45Ghz radio frequency band –I.S.M (Industrial, scientific and medical)  Must support many simultaneous and private “piconets”.  Must be low power, compact and global. 10  Connecting a computing device to a communicating device.  Allows any device with a Bluetooth chip to connect to the internet while located within the range of the access point.  Example- a notebook could link to the internet using a mobile phone as an access point.  Envisions public data access points 11  Standard peripheral devices like keyboard, mice, headsets etc working over a wireless link.  The same device can be used in multiple functions e.g a headset can access phones while in the office and can interface with a cellular phone when mobile. 12  Allows dynamic formation and breakdown of “PICONETS”--ad- hoc personal networks. 13  Core Specification - Deals with the lower layers of the architecture and describes how the technology works.  Profile Specification - Focuses on how to build interoperating devices using the core technology. 14 ► The Radio (layer) is the lowest defined layer of the Bluetooth specification. ► It defines the requirements of the Bluetooth transceiver device operating in the 2.4GHz ISM band. 15  In order to minimize interference the nominal antenna power is 1mW which can be extended to 100mW.  The low power limits the range to about 10 centimeters to 10 meters. With higher power of 100mW range of 100meters can be achieved.  It uses a packet switching protocol based on a technology called spread-spectrum frequency hopping to spread the energy across the ISM band. 16  A device will use 79 individual randomly chosen frequencies within a designated range, changing from one to another on a regular basis.  The designated range is from 2.402GHz to 2.480GHz, in steps of 1MHz.  The frequency hopping is done at a rate of 1600 times a second.  This allows more devices to use the limited time slice and secondly reduces the chance of two transmitters being on the same frequency at the same time. 17  Baseband layer – This layer defines the timing, framing, packets and flow control on the link.  Link Manager – Responsible for managing connection states(authentication & encryption), enforcing fairness among slaves & power management.  Logical Link Layer – Handles multiplexing, segmentation and reassembly of large packets and device discovery.  Audio – The audio data is directly mapped to the baseband layer. 18  Responsible for channel coding/decoding, timing and managing a Bluetooth link.  Master/slave  Devices in a connection are either master or slave.  Communication is only possible between a master and its slaves.  A master and the slaves are named piconets.  Scatternet; multiple piconets connected together.  Responsible for establishing, supervising and tear down connections and logical links.  Link controller states introduced to carry out these tasks.  States:  Standby  Inquiry / Inquiry Scan  Page / Page Scan  Connection  Inquiry  Used to detect all devcies in an unknown environment.  Page / Page Scan  Describes how connection is established.  Have to know the address of the other devices. Is usually achieved through inquiry.  Connection  Master and slaves are synchronized.  Connection is established. Source: Bluetooth Protocol Architecture v.1, white paper available at www.bluetooth.org  Each frame consists of a transmit packet and a receive packet.  Each packet may have either 1, 3 or 5 slots of 625s.  Single slot packet – max data rate of 172Kbps  Multi-slot frames support higher rates– 721Kbps or a max. of 3 voice channels. 23 LSB MSB ACCESS CODE HEADER PAYLOAD 68/72b 54b 0-2745b General basic rate packet format LSB MSB ACCESS CODE HEADER GUARD SYNC PAYLOAD 72b 54b 5 µs 11 µs 16-8200b 2FSK PSK General enhanced data rate packet format  All units have a unique global ID(BD_Addr) address( 48 bits)  The unit that initializes the connection is assigned as the master which controls the traffic of the connection.  A master can simultaneously connect up to seven slaves.  The master/slave roles can be swapped.  A device can be a master in only one “piconet” at a time. 25 26  Needs two parameters  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. 27  Devices not connected to a piconet are in STANDBY mode, using low power.  A connection is made by either a PAGE command if the address is known or by the INQUIRY command followed by a PAGE  When a radio sends an INQUIRY command, all the listening radios respond with their FHS packets, which tells the inquiring radio of all the radios in the area.  All listening radios perform a page scan and/or an inquiry scan every 1.25 seconds.  The master radio sends an FHS to the paged radio. 28  Shows a bunch of Bluetooth devices in proximity of each other.  Each device has its own ID and its clock offset 29  Radio A has become the master and has formed a piconet with B and C as the slaves.  Both B and C now share A’s ID and clock offset. 30 INQUIRY PAGE CONNECTION  Device in standby listens periodically  If a device wants to establish a piconet, it sends an inquiry, broadcast over all wake-up carriers  It will become the master of the piconet  If inquiry was successful, device enters page mode  Devices in standby may respond to the inquiry with its device address  It will become a slave to that master  After receiving a response from devices, the master can connect to each device individually  An AMA is assigned  Slaves synchronize to the hopping sequence established by the master  In active state, master and slaves listen, transmit and receive  A disconnect procedure allows devices to return to standby mode  standby disconnected Typical = 2s detach connecting inquiry page Typical = 0.6s Transmit Connected active AMA AMA Typical = 2ms Park Hold Sniff PMA AMA AMA low power AMA = Active Member Address PMA = Parked Member Address HOLD MODE  When data needs to be transmitted very infrequently, thus conserving power.  In this mode only an internal timer is running.  No data is transferred when in HOLD mode.  The master can put slaves on HOLD mode. SNIFF MODE ► A slave device listens to the piconet at a reduced rate. ► The SNIFF interval is programmable. ► In both the HOLD and SNIFF states the device retains its AMA. 35 PARK MODE  The device has given up the AMA and has become passive.  The parked device will occasionally listen to see if the master has sent any broadcast data asking it to become active. 36 Synchronous Connection Oriented(SCO)  Point to point full duplex link.  Typically used for voice data.  These packets do not use CRC and are not retransmitted.  Needs an asynchronous connectionless (ACL) type link to be first established. 37 Asynchronous Connectionless Link  This is a packet switched link between a master and slave.  Supports both isochronous(data must be delivered within certain time constraints) and asynchronous data. Error Correction Schemes  Forward error correction(1/3 and 2/3)  Automatic Repeat Request scheme. 38  SCO ACL ACL SCO ACL SCO SCO ACL MASTER SLAVE 1 SLAVE 2 SLAVE 3  Authentication and encryption is provided at the Link Manager layer.  The PIN is translated into a 128 bit link key which is used for authentication.  After authentication the radios will settle on a suitable length encryption key to be used.  Bluetooth relies on PIN codes to establish trusted relationships between devices. 40 41