Introduction to bluetooth

outline Why bluetooth History Bluetooth stack and technology Reference

bluetooth Why bluetooth?  Cable replacement between devices  Open Specification  Low power consumption  Connection can be initiated without user interaction  Devices can be connected to multiple devices at the same time

history The technology was born in 1994 Standardized by the Bluetooth Special Interest Group (SIG),a consortium founded in spring 1998 by Ericsson,Intel,IBM,Nokia,and Toshiba The first version was released July 1999

stack

Bluetooth stack and OSI layers

stack Bluetooth Stack  Transport Protocol group Radio,Baseband, L2CAP and HCI  Middleware Protocol group PPP, IP, TCP,WAP, OBEX, IrDA RFCOMM, TCS, SDP  Application group

stack

Transport Protocol group  Allow Bluetooth devices to locate each other  manage physical and logical links with higher layer protocols and applications  support both asynchronous and synchronous transmission

stack Middleware Protocol group  includes third-party and industry-standard protocols as well as Bluetooth SIG developed protocols  These protocols allow existing and new applications to operate over Bluetooth links

stack Application group  Consists of actual applications that use Bluetooth links  They can include legacy applications as well as Bluetooth-aware applications

radio Primarily concerned with the design of the Bluetooth transceivers Bluetooth devices operate on 2.4 GHz Industrial Scientific Medical band (ISM band) Unlicensed in most countries

radio Techniques to minimize packet loss:  Frequency Hopping  Adaptive power control  Short data packets

radio TDD (Time Division Duplex)  The channel is divided into time slots, each 625 μs in lenght, thus the nominal hop rate is 1600 hops/s  When in inquiry or page mode, it hops at 3200 hops/s with a residence time of μ sec

radio Master only transmits in odd slots Slaves only transmit in even slots

radio FHSS (Frequency Hopping Spread Spectrum)  Divides the ISM-band into 79 1-Mhz channels Channel 0: 2402 MHz … channel 78: 2480 MHz  Communication between devices switches between available channels

radio 625 μs

radio Three power classes defined with max output power from 1 mW (Class 1) to 100 mW (Class 3)  power class 1 : long range (~100m,~100mW)  power class 2 : mid range (~10m,~2.5mW)  power class 3 : short range (~1m,~1mW)

radio Packet

radio Access Code  Channel Access Code (CAC)  Device Access Code (DAC)  Inquiry Access Code (IAC) GIAC ( Global IAC) DIAC ( Discovery IAC )

radio Packet Header  AM_ADDR : the active member address in piconet  TYPE : kind of code  FLOW : flow control  ARQN : ACK,NAK  SEQN : discriminate duplication of ARQN  HEC : Header verify Payload  Data header, data and CRC

radio Kind of code  Normal ID,NULL,POLL,FHS,DM1  SCO HV1,HV2,HV3,DV  ACL DM1,DH1,DM3,DH3,DM5,DH5,AUX1

radio

Error Control  1/3FEC(Forward Error Correction)  2/3FEC(Forward Error Correction)  ARQ(Automatic Repeat Request)

radio ARQ scheme in the ACL link

baseband Defines how Bluetooth devices search for and connect to other devices Responsible for channel coding/decoding, timing and managing a Bluetooth link

baseband Master/slave  Piconet : A master and the slaves piconet

baseband  Scatternet : multiple piconets connected together scatternet

baseband  Communication is only possible between a master and its slaves.  Master determines hopping pattern, slaves have to synchronize  Each piconet has a unique hopping pattern  Participation in a piconet = synchronization to hopping sequence  Each piconet has one master and up to 7 simultaneous slaves  The maximum number of “parked” slaves is 255 per piconet

baseband Device connection states

baseband Inquire and Page

baseband 3 power saving modes  sniff : slave listens to the channel at a reduced rate (decreasing of duty cycle)-least power efficient  Hold : data transfer is held for a specific time period - medium power efficient  park : synchronized to the piconet but does not participate in traffic

baseband link types  Voice link – SCO (Synchronous Connection Oriented) FEC (forward error correction), no retransmission, 64 kbit/s duplex, point-to-point, single-slot packet size  Data link – ACL (Asynchronous ConnectionLess) Asynchronous, point-to-multipoint, up to kbit/s symmetric or 723.2/57.6 kbit/s asymmetric, Variable packet size (1,3,5 slots)

baseband

The Link Manager Protocol(LMP) LMP manages  bandwidth allocation for general data  bandwidth reservation for audio traffic  trust relationships between devices  encryption of data  control of power usage

Host Controller Interface (HCI) This layer is not a required part of the specification Defines a standard interface for upper level applications to access the lower layers of the stack Its purpose is to enable interoperability among devices and the use of existing higherlevel protocols and applications

Logical Link Control and Adaption (L2CAP) Deals with  multiplexing of different services RFCOMM, SDP, telephony control  segmentation, reassembling of packets  Quality of Service  Group abstraction Create/close group, add/remove member  only support ACL connection

Service Discovery Protocol (SDP) Inquiry/response protocol for discovering services  Searching for and browsing services in radio proximity  Adapted to the highly dynamic environment  Defines discovery only, not the usage of services  Caching of discovered services

Reference Praktikum Mobile und Verteilte Systeme im Sommersemester 2006  Prof. Dr. C. Linnhoff-Popien, Peter Ruppel, Georg Treu Bluetooth  Steffen Witt and Tobias Julius Neubert Bluetooth  Alessandro Leonardi Bluetooth  Dr.-Ing. H. Ritter, “What is Bluetooth”  Patricia McDermott-Wells