lecture computer networks - uni ulm
TRANSCRIPT
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LOMI Universität Ulm, 2002
LectureComputer Networks
Bluetooth
Prof. Dr. H. P. GroßmannDipl.-Ing. Andreas SchmeiserDepartment of Information Resource ManagementUniversity of Ulm, Germany
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LOMI Universität Ulm, 2002
What is Bluetooth?
Personal Area Network (PAN)
Short range wireless transmission for data and speech
Ad-hoc connections between notebooks, handheld devices, organizers, mobile phones, headsets, ...
Encrypted data transmissions
Replacement of several peripheral interfaces:parallel printer port, serial interface, network interface, IrDA
Harald Bluetooth the 10th century Viking king gaves the name to this technology
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Bluetooth Devices
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Special Interest Group (SIG)
5 companies founded the Bluetooth SIG at beginning of 1998: Ericsson Mobile Communications AB Nokia Mobile Phones IBM Corporation Toshiba Corporation Intel Corporation
Today more than 2100 SIG members 3COM Corporation Agere Systems, Inc. Microsoft Corporation Motorola, Inc.
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Key data
Transceiver operating frequency:2400 – 2483.5 MHz Industrial Scientific Medicine (ISM) band
Transmitter power: 1 mW, 2.5 mW, 100 mW Range: 10 m, up to 100 m (depending on transmitter power) Frequency hopping:
79 RF channels (USA, Europe and most other countries),23 RF channels (France) spaced 1 MHz, 1600 hops/s
Modulation: Gaussian Frequency Shift Keying (GFSK) Symbol Rate: 1 Ms/s Slotted Channel with 625 µs,
Full duplex transmission with Time-Division Duplex (TDD) Asynchronous Connection-Less (ACL) link
up to 433.9 kb/s (sym.), resp. 723.2 / 57.6 kb/s (asym.) Synchronous Connection-Oriented (SCO) link
64 kb/s (sym.), up to 3 links Authentication / Encryption
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Protocol Stack
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Protocol Stack
Bluetooth Core Protocols Baseband LMP (Link Manager Protocol) L2CAP (Logical Link Control and Adaption Protocol) SDP (Service Discovery Protocol)
Cable Replacement Protocol RFCOMM with TS 07.10 (Serial Port Emulation)
Telephony Control Protocol TCS Binary (Telephony Control protocol Specification) AT-Commands
Adopted Protocols PPP IP, TCP, UDP WAP OBEX ...
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Bluetooth Core Protocols I
Baseband Specification of the Bluetooth link controller which carries out the
baseband protocols and other low-level link routines
LMP (Link Manager Protocol) Used for link set-up and control Signals are interpreted and filtered out by the Link Manager on the
receiving side and are not propagated to higher layers.
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Bluetooth Core Protocols II
L2CAP (Logical Link Control and Adaption Protocol) Supports higher level protocol multiplexing, packet segmentation
and reassembly Conveying of quality of service information Protocol state machine, packet format and composition Test interface, required for Bluetooth test and certification program
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Bluetooth Core Protocols
SDP (Service Discovery Protocol) Protocol for locating services provided by or available through a
Bluetooth device Essential to find available services Access to located services takes place with other protocols
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Cable Replacement Protocol
RFCOMM with TS 07.10 (Serial Port Emulation) Emulation of a RS232 like interface Handles up to 60 simultaneous connections between 2 Bluetooth
devices
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Cable Replacement Protocol
RFCOMM with TS 07.10 (Serial Port Emulation) (continued)
RFCOMM Direct Connect
RFCOMM used with legacy COMM device
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Telephony Control Protocol
TCS (Telephony Control protocol Specification) Binary Call control signaling for the establishment of speech and data
calls between Bluetooth devices Uses a bit-oriented protocol
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Telephony Control Protocol
TCS (Telephony Control protocol Specification) Binary(continued)
Point-to-point signaling in a single-point environment
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Telephony Control Protocol
TCS (Telephony Control protocol Specification) Binary(continued)
Signaling in a multi-point environment
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Adopted Protocols
PPP (Point-to-Point Protocol) PPP over RFCOMM
TCP, UDP, IP Provides access to the Internet
WAP (Wireless Application Protocol) WAP over Bluetooth
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Adopted Protocols
OBEX (OBject EXchange Protocol) Provides exchange of data objects
OBEX in the protocol stack
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LectureComputer Networks
Bluetooth
Baseband Specification
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Topology
Point-to-point
Piconet(1 master,
up to 7 active slaves)
Scatternet(overlapped piconets)
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Physical Channel
Hopping sequence Nominal hop rate: 1600 hops/s Pseudo-random sequence Unique for each piconet Determined by device address of master
Time slots 625 µs in length Numbered according to the clock of the piconet master Cycle length: 227
Time Division Duplex (TDD) scheme Master transmits in even numbered slots Slaves in odd numbered slots Packets may extend over up to 5 slots
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TDD and timing
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Multi-slot packets
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Standard packet format
Access Code Header Payload
72 54 0 - 2745 Bit
LSB MSB
Least Significant Bit (LSB) corresponds to b0
LSB is the first bit sent over the air
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Access code format
Channel Access Code (CAC) Device Access Code (DAC) Inquiry Access Code (IAC)
General Inquiry Access Code (GIAC) Dedicated Inquiry Access Code (DIAC)
Access Code Header Payload
72 54 0 - 2745 Bit
Preamble Sync Word Trailer
4 64 4 Bit
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Packet header format
Access Code Header Payload
72 54 0 - 2745 Bit
AM_Addr HEC
3 4 1 Bit
Type Flow ARQN SEQN
81 1
AM_Addr: Active member addressType: Type code of packetFlow: Flow control – 0: Stop
ARQN: Acknowledge indicationSEQN: Sequence numberHEC: Header error check
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Packet Types
ACL packets
kbit/s
SCO packetsHigh-Quality Voice (64 kbit/s): HV1, HV2, HV3Combined Data Voice: DV
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Payload format - Data
Access Code Header Payload
72 54 0 - 2745 Bit
Payload-Header Body (Information) CRC
8 (single slot packet) or
16 (multi-slot packet)
0 - 2712 Bit
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Payload header format - Data
Access Code Header Payload
72 54 0 - 2745 Bit
Payload-Header Body (Information) CRC
8 or 16 0 - 2712 Bit
L_CH Flow Length
2 1 Bit
Res.
5 or 9 4
L_CH: Logical channelFlow: Flow control at L2CAP level – 0: Stop
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1/3 rate FEC (Forward Error Correction code)
Simple Repeat each bit 3 times
Used for Entire header Voice field in HV1 packet
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2/3 rate FEC (Forward Error Correction code)
(15,10) shortened Hamming code Code
corrects all single errors in each code-word detects all double errors in each code-word
LFSR generating the code
Used for Data Medium rate (DM) packets Data field in DV packet Frequency Hop Synchronization (FHS) packet High-Quality Voice HV2
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ARQ (Automatic Repeat reQuest) scheme for the data
Fast, unnumbered acknowledge scheme ACK (ARQN=1) or NAK (ARQN=0) is returned in response to
receipt of previously received packet Retransmission of previous packet till ARQN=1
Used for Data High rate (DH) Data Medium rate (DM) DV packet
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Error checking
Channel access code 64 bit sync word derived from 24 Bit master LAP Check of LAP prevents receiver from accepting packets of another
piconet
HEC, CRC Check both on errors and on wrong address Additional test of access code, because UAP normally included
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Logical channels
LC Channel (Link Control) Carries low level link control information like ARQ, flow control,
payload characterization Mapped onto packet header
LM Channel (Link Manager) Carries control information exchanged between the link managers
of master and slave(s) UA Channel (User Asynchronous)
Carries L2CAP transparent asynchronous user data Data may be transmitted in one or more baseband packets
UI Channel (User Isochronous) Like UA Channel Isochronous data channel supported by timing properly at higher
levels US Channel (User Synchronous)
Carries transparent synchronous user data Channel is carried over SCO link
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States
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States – Standby, Connection
Standby State Default state Low power mode Only native clock with accuracy of Low Power Oscillator (LPO) is
running
Connection State Active Mode – Unit actively participates on the channel
» Active Member Address (AM_ADDR) assigned Sniff Mode – Reduced duty cycle of slave‘s listen activity Hold Mode – Slave temporarily does not support ACL packets on
channel, frees capacity for other things like scanning, paging, inquiring, attending another piconet
Park Mode – Slave does not participate on channel, but still remains synchronized to the channel
» Parked Member Address (PM_ADDR) assigned» Access Request Address (AR_ADDR) assigned
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States – Paging
Device Access Code (DAC) is used to establish an actual connection Page Scan – Unit listens periodically for its own device access
code
Page – Master activates and connects to a slave» Master does not know when slave wakes up and on which hop
frequency» Therefore it transmits repeatedly a train of identical DACs on different
hop frequencies
Page Response – Procedure between master and slave to exchange vital information to continue connection setup
» Channel access code» Channel hopping sequence» Synchronized clocks
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States – Inquiry
Inquiry Access Code (IAC) is used to discover which other bluetooth devices are in range Inquiry Scan – Similar to the Page Scan substate, instead IAC is
used
Inquiry – Similar to Page substate, used by unit that wants to discover new devices
Inquiry Response – Recipient‘s address returned to master» FHS (Frequency Hop Synchronization) packet carries unit‘s
parameters (BD_ADDR)
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Bluetooth Addressing
Derived from IEEE 802 standard Unique for each device 48 Bit Bluetooth Device Address (BD_ADDR)
LAP: lower address part, 24 Bit UAP: upper address part, 8 Bit NAP: Non-significant address part, 16 Bit
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LectureComputer Networks
Bluetooth
Link Manager Protocol (LMP)
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Link Manager Protocol
LM messages have higher priority than user data Messages not acknowledged since Link Control (LC) channel
provides reliable link LM message timeout: 30 s
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LMP – Protocol Data Unit (PDU)
1 byte Header Transaction ID
0: Initiated by master1: Initiated by slave
7 bit OpCode
Content
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LMP Tasks
Authentication Encryption (start, stop, key size, mode, ...) Clock Offset Request Slot-Offset Supported Features Switch of Master-Slave role Change of Mode Power Control (TX-Power) Link attach and detach ...
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LectureComputer Networks
Bluetooth
Logical Link Control and Adaptation Protocol (L2CAP)
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L2CAP in Bluetooth Protocol Architecture
Provides connection-oriented and connectionless data services to upper layer protocols with multiplexing capability packet segmentation and reassembly Quality of Service group abstraction
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L2CAP protocol requirements
Simplicity Low overhead Applicable for devices with limited computational resources Low power consuption Minimum memory requirements
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References
The Official Bluetooth Websitehttp://www.bluetooth.com
Specification of the Bluetooth SystemVersion 1.1, 22 February 2001 Volume 1: Core Volume 2: Profiles
The Bluetooth SIG, Inc. Member Web Sitehttp://www.bluetooth.org