Bluetooth Techniques.ppt

1、Bluetooth Techniques,Chapter 15,Overview,Universal short-range wireless capability Uses 2.4-GHz band Available globally for unlicensed users Devices within 10 m can share up to 720 kbps of capacity Supports open-ended list of applications Data, audio, graphics, video,Bluetooth Application Areas,Data

2、 and voice access points Real-time voice and data transmissions Cable replacement Eliminates need for numerous cable attachments for connection Ad hoc networking Device with Bluetooth radio can establish connection with another when in range,Bluetooth Standards Documents,Core specifications Details

3、of various layers of Bluetooth protocol architecture Profile specifications Use of Bluetooth technology to support various applications,Protocol Architecture,Bluetooth is a layered protocol architecture Core protocols Cable replacement and telephony control protocols Adopted protocols Core protocols

4、 Radio Baseband Link manager protocol (LMP) Logical link control and adaptation protocol (L2CAP) Service discovery protocol (SDP),Protocol Architecture,Cable replacement protocol RFCOMM Telephony control protocol Telephony control specification binary (TCS BIN) Adopted protocols PPP TCP/UDP/IP OBEX

5、WAE/WAP,Usage Models,File transfer Internet bridge LAN access Synchronization Three-in-one phone Headset,Piconets and Scatternets,Piconet Basic unit of Bluetooth networking Master and one to seven slave devices Master determines channel and phase Scatternet Device in one piconet may exist as master

6、or slave in another piconet Allows many devices to share same area Makes efficient use of bandwidth,Wireless Network Configurations,Radio Specification,Classes of transmitters Class 1: Outputs 100 mW for maximum range Power control mandatory Provides greatest distance Class 2: Outputs 2.4 mW at maxi

7、mum Power control optional Class 3: Nominal output is 1 mW Lowest power,Frequency Hopping in Bluetooth,Provides resistance to interference and multipath effects Provides a form of multiple access among co-located devices in different piconets,Frequency Hopping,Total bandwidth divided into 1MHz physi

8、cal channels FH occurs by jumping from one channel to another in pseudorandom sequence Hopping sequence shared with all devices on piconet Piconet access: Bluetooth devices use time division duplex (TDD) Access technique is TDMA FH-TDD-TDMA,Frequency Hopping,Physical Links between Master and Slave,S

9、ynchronous connection oriented (SCO) Allocates fixed bandwidth between point-to-point connection of master and slave Master maintains link using reserved slots Master can support three simultaneous links Asynchronous connectionless (ACL) Point-to-multipoint link between master and all slaves Only si

10、ngle ACL link can exist,Bluetooth Packet Fields,Access code used for timing synchronization, offset compensation, paging, and inquiry Header used to identify packet type and carry protocol control information Payload contains user voice or data and payload header, if present,Types of Access Codes,Ch

11、annel access code (CAC) identifies a piconet Device access code (DAC) used for paging and subsequent responses Inquiry access code (IAC) used for inquiry purposes,Access Code,Preamble used for DC compensation 0101 if LSB of sync word is 0 1010 if LSB of synch word is 1 Sync word 64-bits, derived fro

12、m: 7-bit Barker sequence Lower address part (LAP) Pseudonoise (PN) sequence Trailer 0101 if MSB of sync word is 1 1010 if MSB of sync word is 0,Packet Header Fields,AM_ADDR contains “active mode” address of one of the slaves Type identifies type of packet Flow 1-bit flow control ARQN 1-bit acknowled

13、gment SEQN 1-bit sequential numbering schemes Header error control (HEC) 8-bit error detection code,Payload Format,Payload header L_CH field identifies logical channel Flow field used to control flow at L2CAP level Length field number of bytes of data Payload body contains user data CRC 16-bit CRC c

14、ode,Error Correction Schemes,1/3 rate FEC (forward error correction) Used on 18-bit packet header, voice field in HV1 packet 2/3 rate FEC Used in DM packets, data fields of DV packet, FHS packet and HV2 packet ARQ Used with DM and DH packets,ARQ Scheme Elements,Error detection destination detects er

15、rors, discards packets Positive acknowledgment destination returns positive acknowledgment Retransmission after timeout source retransmits if packet unacknowledged Negative acknowledgment and retransmission destination returns negative acknowledgement for packets with errors, source retransmits,Logi

16、cal Channels,Link control (LC) Link manager (LM) User asynchronous (UA) User isochronous (UI) Use synchronous (US),Channel Control,States of operation of a piconet during link establishment and maintenance Major states Standby default state Connection device connected,Channel Control,Interim substat

17、es for adding new slaves Page device issued a page (used by master) Page scan device is listening for a page Master response master receives a page response from slave Slave response slave responds to a page from master Inquiry device has issued an inquiry for identity of devices within range Inquir

18、y scan device is listening for an inquiry Inquiry response device receives an inquiry response,State Transition Diagram,Inquiry Procedure,Potential master identifies devices in range that wish to participate Transmits ID packet with inquiry access code (IAC) Occurs in Inquiry state Device receives i

19、nquiry Enter Inquiry Response state Returns FHS packet with address and timing information Moves to page scan state,Page Procedure,Master uses devices address to calculate a page frequency-hopping sequence Master pages with ID packet and device access code (DAC) of specific slave Slave responds with

20、 DAC ID packet Master responds with its FHS packet Slave confirms receipt with DAC ID Slaves moves to Connection state,Slave Connection State Modes,Active participates in piconet Listens, transmits and receives packets Sniff only listens on specified slots Hold does not support ACL packets Reduced p

21、ower status May still participate in SCO exchanges Park does not participate on piconet Still retained as part of piconet,Bluetooth Audio,Voice encoding schemes: Pulse code modulation (PCM) Continuously variable slope delta (CVSD) modulation Choice of scheme made by link manager Negotiates most appr

22、opriate scheme for application,Bluetooth Link Security,Elements: Authentication verify claimed identity Encryption privacy Key management and usage Security algorithm parameters: Unit address Secret authentication key Secret privacy key Random number,LMP PDUs,General response Security Service Authen

23、tication Pairing Change link key Change current link key Encryption,LMP PDUs,Time/synchronization Clock offset request Slot offset information Timing accuracy information request Station capability LMP version Supported features,LMP PDUs,Mode control Switch master/slave role Name request Detach Hold

24、 mode Sniff mode Park mode Power control,LMP PDUs,Mode control (cont.) Channel quality-driven change between DM and DH Quality of service Control of multislot packets Paging scheme Link supervision,L2CAP,Provides a link-layer protocol between entities with a number of services Relies on lower layer

25、for flow and error control Makes use of ACL links, does not support SCO links Provides two alternative services to upper-layer protocols Connection service Connection-mode service,L2CAP Logical Channels,Connectionless Supports connectionless service Each channel is unidirectional Used from master to

26、 multiple slaves Connection-oriented Supports connection-oriented service Each channel is bidirectional Signaling Provides for exchange of signaling messages between L2CAP entities,L2CAP Packet Fields for Connectionless Service,Length length of information payload, PSM fields Channel ID 2, indicatin

27、g connectionless channel Protocol/service multiplexer (PSM) identifies higher-layer recipient for payload Not included in connection-oriented packets Information payload higher-layer user data,Signaling Packet Payload,Consists of one or more L2CAP commands, each with four fields Code identifies type

28、 of command Identifier used to match request with reply Length length of data field for this command Data additional data for command, if necessary,L2CAP Signaling Command Codes,L2CAP Signaling Commands,Command reject command Sent to reject any command Connection commands Used to establish new conne

29、ctions Configure commands Used to establish a logical link transmission contract between two L2CAP entities,L2CAP Signaling Commands,Disconnection commands Used to terminate logical channel Echo commands Used to solicit response from remote L2CAP entity Information commands Used to solicit implementation-specific information from remote L2CAP entity,Flow Specification Parameters,Service type Token rate (bytes/second) Token bucket size (bytes) Peak bandwidth (bytes/second) Latency (microseconds) Delay variation (microseconds),