Personal Area Networking over Bluetooth

Personal Area Networking over Bluetooth Pravin Bhagwat Networking Research Group AT&T Labs - Research pravin@acm.org ACM Mobicom 2000 Half day tutorial Aug 06, 2000 Boston, MA Bluetooth A cable replacement technology 1 Mb/s symbol rate Range 10+ meters Single chip radio + baseband at low power & low price point Why not use Wireless LANs? - power - cost Pravin Bhagwat (AT&T Labs) 2 Tutorial 3: Bluetooth 1

Value proposition of Bluetooth Cordless headset Cell phone mouse Data access point Cable replacement Internet access Ad hoc networking Pravin Bhagwat (AT&T Labs) 3 Bluetooth working group history February 1998: The Bluetooth SIG is formed promoter company group: Ericsson, IBM, Intel, Nokia, Toshiba May 1998: Public announcement of the Bluetooth SIG July 1999: 1.0A spec (>1,500 pages) is published December 1999: ver. 1.0B is released December 1999: The promoter group increases to 9 3Com, Lucent, Microsoft, Motorola February 2000: There are 1,800+ adopters Pravin Bhagwat (AT&T Labs) 4 Tutorial 3: Bluetooth 2

New Applications Pravin Bhagwat (AT&T Labs) 5 Synchronization User benefits Automatic synchronization of calendars, address books, business cards Push button synchronization Proximity operation Pravin Bhagwat (AT&T Labs) 6 Tutorial 3: Bluetooth 3

Cordless Headset Cordless headset User benefits Multiple device access Cordless phone benefits Hands free operation Pravin Bhagwat (AT&T Labs) 7 Usage scenarios examples Data Access Points Synchronization Headset Conference Table Cordless Computer Business Card Exchange Instant Postcard Computer Speakerphone Pravin Bhagwat (AT&T Labs) 8 Tutorial 3: Bluetooth 4

Bluetooth Specifications Pravin Bhagwat (AT&T Labs) 9 Bluetooth Specifications Applications SDP IP RFCOMM Data Control L2CAP Audio Link Manager Baseband RF Single chip with RS-232, USB, or PC card interface A hardware/software/protocol description An application framework Pravin Bhagwat (AT&T Labs) 10 Tutorial 3: Bluetooth 5

Interoperability & Profiles Represents default solution for a usage model Vertical slice through the protocol stack Basis for interoperability and logo requirements Each Bluetooth device supports one or more profiles Protocols Applications Profiles Pravin Bhagwat (AT&T Labs) 11 Technical Overview Pravin Bhagwat (AT&T Labs) 12 Tutorial 3: Bluetooth 6

Bluetooth Radio Specification Applications SDP IP RFCOMM Data Control L2CAP Audio Link Manager Baseband RF Pravin Bhagwat (AT&T Labs) 13 Design considerations power Noise, interference Data signal x(t) spectrum Recovered data signal cost Goal high bandwidth conserve battery power cost < $10 Pravin Bhagwat (AT&T Labs) 14 Tutorial 3: Bluetooth 7

EM Spectrum AM radio S/W radio TV TV FM radio cellular ISM band 902 928 Mhz 2.4 2.4835 Ghz 5.725 5.785 Ghz LF MF HF VHF UHF SHF EHF 30kHz 300kHz 3MHz 30MHz 300MHz 3GHz 30GHz 300GHz 10km 1km 100m 10m 1m 10cm 1cm 100mm infrared visible UV X rays 1 khz 1 MHz 1 GHz 1 THz 1 PHz 1 EHz Gamma rays Propagation characteristics are different in each frequency band Pravin Bhagwat (AT&T Labs) 15 Unlicensed Radio Spectrum 33cm 12cm 5cm 26 Mhz 83.5 Mhz 125 Mhz 902 Mhz 928 Mhz 2.4 Ghz 2.4835 Ghz 5.725 Ghz 5.785 Ghz cordless phones baby monitors Wireless LANs 802.11 Bluetooth Microwave oven unused Pravin Bhagwat (AT&T Labs) 16 Tutorial 3: Bluetooth 8

Bluetooth radio link 1Mhz... 1 2 3 79 83.5 Mhz frequency hopping spread spectrum 2.402 GHz + k MHz, k=0,, 78 1,600 hops per second GFSK modulation 1 Mb/s symbol rate transmit power 0 dbm (up to 20dbm with power control) Pravin Bhagwat (AT&T Labs) 17 Review of basic concepts Pravin Bhagwat (AT&T Labs) 18 Tutorial 3: Bluetooth 9

db (relative measure) 10 11 $ 100B db = 10 log (times) Net worth 10,000 times 40 db 10,000 * 1,000 times = 10,000,000 times 40 db + 30 db = 70dB 10 7 10 4 Bill $ 10M 1,000 times 30 db $ 10K Steve Grad Pravin Bhagwat (AT&T Labs) 19 Path loss in db 10 1 10 W P db = 10 log (----) 1 P 2 Power Path loss from source to d2 = 70dB 10-3 1 mw 10-6 source 10,000 times 1,000 times 40 db 30 db 1 µw d1 d2 Pravin Bhagwat (AT&T Labs) 20 Tutorial 3: Bluetooth 10

dbm ( absolute measure of power) 10 1 10 W = 40 dbm P dbm = 10 log (-------) 1 1mW Power + 10,000 times 10-3 1 mw = 0 dbm 10-6 source - 1,000 times 1 µw = -30 dbm d1 d2 Pravin Bhagwat (AT&T Labs) 21 Radio propagation: path loss near field P r path loss in 2.4 Ghz band P t r 8m r > 8m r P r near field r 2 far field r 3.3 path loss = 10 log (4πr 2 /λ) r 8m = 58.3 + 10 log (r 3.3 /8) r > 8m Pravin Bhagwat (AT&T Labs) 22 Tutorial 3: Bluetooth 11

Fading and multipath Fading: rapid fluctuation of the amplitude of a radio signal over a short period of time or travel distance Tx Rx Effects of multipath Fading Varying doppler shifts on different multipath signals Time dispersion (causing inter symbol interference) Pravin Bhagwat (AT&T Labs) 23 Bandwidth of digital data Time domain Fourier transform Frequency domain Signal amplitude baseband signal (1 Mbs) 0.5 MKhz 1 Mhz 1.5 Mhz Baseband signal cannot directly be transmitted on the wireless medium Need to translate the baseband signal to a new frequency so that it can be transmitted easily and accurately over a communication channel Pravin Bhagwat (AT&T Labs) 24 Tutorial 3: Bluetooth 12

Channel coding and modulation low Q modulation demodulation high Q channel coding channel decoding baseband signal baseband signal Challenges Modulation of 1Mhz baseband signal into 2.4Ghz band is difficult to achieve in one step CMOS transistors do not operate at those frequencies Difficult to build filters with high Q factor Pravin Bhagwat (AT&T Labs) 25 Radio architecture: typical design Intermediate Frequency mixing modulation mixing Intermediate Frequency demodulation channel coding baseband signal channel decoding baseband signal Pravin Bhagwat (AT&T Labs) 26 Tutorial 3: Bluetooth 13

Mixing The process of translating the information signal to a different position in the frequency spectrum F lo F c Transmitted signal at 2.4 Ghz Modulated signal at Intermediate Frequency (IF) F c Mixer F c - F lo F c - F lo F lo F c + F lo Low pass filter Pravin Bhagwat (AT&T Labs) 27 Image rejection Image appears like a co-channel jammer F lo F c RF pre-selector filter IF 80 Mhz Signal at 2.4 Ghz IF = 280 Mhz Good image rejection performance when F lo is sufficiently far away from F c That is, when IF frequency is high To allow single chip integrated radio, IF should be moved down to lower frequency Pravin Bhagwat (AT&T Labs) 28 Tutorial 3: Bluetooth 14

Image rejection with Low IF In-band image F lo F c IF 80 Mhz Signal at 2.4 Ghz IF = 3 Mhz To allow single chip integrated radio, IF is moved down to 3 Mhz which allows construction of the filter on-chip with low power It is impossible to build a RF pre-selector filter to remove the inband image So a special RF architecture is used called image-reject mixer to suppress in-band interference arising from the image. Pravin Bhagwat (AT&T Labs) 29 Radio architecture: typical design Analog IF D/A mixing modulation oscillators, PA filters oscillators, LNA filters mixing A/D demodulation IF DSP channel coding CMOS baseband signal channel decoding baseband signal Pravin Bhagwat (AT&T Labs) 30 Tutorial 3: Bluetooth 15

Radio architecture: Bluetooth Analog IF D/A mixing modulation CMOS oscillators, LNA, filters mixing A/D demodulation IF DSP channel coding CMOS baseband signal channel decoding baseband signal Pravin Bhagwat (AT&T Labs) 31 Single chip radio: challenges Analog DSP IF channel coding CMOS D/A mixing modulation baseband signal Integrating a low-noise on chip synthesizer Handling the wide dynamic range of input interference signals Low power draw Cross talk between analog/analog and analog/digital circuits Achieving good linearity in an integrated filter Dealing with very low-level input signals (10v ) in the presence of IC substrate noise Dealing with high-level ( -5dBm) input signals while keeping a low voltage power supply Achieving desired design performance in the presence of 15-20% component variations for R & C Pravin Bhagwat (AT&T Labs) 32 Tutorial 3: Bluetooth 16

Bluetooth Radio Low Cost Single chip radio (minimize external components) Today s technology Time division duplex Pravin Bhagwat (AT&T Labs) 33 Bluetooth Radio Low Power Standby modes Low voltage RF Sniff, Hold, Park Pravin Bhagwat (AT&T Labs) 34 Tutorial 3: Bluetooth 17

Bluetooth Radio Robust operation Fast frequency hopping Strong interference protection Fast ARQ Robust access code Forward header correction 1600 hops/sec Pravin Bhagwat (AT&T Labs) 35 Transmit power & receiver sensitivity 0 dbm Tx power -20 Rx power @ 10 cm -70-91 Rx power @ 10m Noise floor C/I = 21 db Pravin Bhagwat (AT&T Labs) 36 Tutorial 3: Bluetooth 18

Radio: design rationale Allow low cost low IF Trade sensitivity for integration One chip radio is possible Pravin Bhagwat (AT&T Labs) 37 Baseband Applications IP SDP RFCOMM Data L2CAP Audio Link Manager Baseband RF Control Pravin Bhagwat (AT&T Labs) 38 Tutorial 3: Bluetooth 19

Bluetooth Physical link Point to point link master - slave relationship radios can function as masters or slaves Piconet Master can connect to 7 slaves Each piconet has max capacity (1 Mbps) hopping pattern is determined by the master Pravin Bhagwat (AT&T Labs) 39 Connection Setup Inquiry - scan protocol to lean about the clock offset and device address of other nodes in proximity Pravin Bhagwat (AT&T Labs) 40 Tutorial 3: Bluetooth 20

Inquiry on time axis Slave1 f1 f2 Master Inquiry hopping sequence Slave2 Pravin Bhagwat (AT&T Labs) 41 Piconet formation Page - scan protocol to establish links with nodes in proximity Master Active Slave Parked Slave Standby Pravin Bhagwat (AT&T Labs) 42 Tutorial 3: Bluetooth 21

Addressing Bluetooth device address (BD_ADDR) 48 bit IEEE MAC address Active Member address (AM_ADDR) 3 bits active slave address all zero broadcast address Parked Member address (PM_ADDR) 8 bit parked slave address Pravin Bhagwat (AT&T Labs) 43 Piconet channel FH/TDD f1 f2 f3 f4 f5 f6 625 sec 1600 hops/sec Pravin Bhagwat (AT&T Labs) 44 Tutorial 3: Bluetooth 22

Multi slot packets FH/TDD f1 f4 f5 f6 625 µsec Data rate depends on type of packet Pravin Bhagwat (AT&T Labs) 45 Physical Link Types Synchronous Connection Oriented (SCO) Link slot reservation at fixed intervals Asynchronous Connection-less (ACL) Link Polling access method SCO ACL ACL SCO ACL ACL SCO ACL ACL Pravin Bhagwat (AT&T Labs) 46 Tutorial 3: Bluetooth 23

Packet Types Control packets Data/voice packets ID* Null Poll FHS DM1 Voice HV1 HV2 HV3 DV DM1 DM3 DM5 data DH1 DH3 DH5 Pravin Bhagwat (AT&T Labs) 47 Packet Format 72 bits 54 bits 0-2744 bits Access code Header Payload Voice header Data CRC No CRC No retries FEC (optional) ARQ FEC (optional) 625 µs master slave Pravin Bhagwat (AT&T Labs) 48 Tutorial 3: Bluetooth 24

Access Code 72 bits Access code Header Payload Purpose Synchronization DC offset compensation Identification Signaling Types Channel Access Code (CAC) Device Access Code (DAC) Inquiry Access Code (IAC) X Pravin Bhagwat (AT&T Labs) 49 Packet Header 54 bits Access code Header Payload Purpose Addressing (3) Packet type (4) Flow control (1) 1-bit ARQ (1) Sequencing (1) HEC (8) total 18 bits Encode with 1/3 FEC to get 54 bits Max 7 active slaves 16 packet types (some unused) Broadcast packets are not ACKed For filtering retransmitted packets Verify header integrity Pravin Bhagwat (AT&T Labs) 50 Tutorial 3: Bluetooth 25

Voice Packets (HV1, HV2, HV3) 72 bits 54 bits 240 bits Access Header code 30 bytes Payload = 366 bits HV1 10 bytes + 1/3 FEC HV2 20 bytes + 2/3 FEC HV3 2.5ms 1.25ms (HV1) 3.75ms (HV2) 30 bytes (HV3) Pravin Bhagwat (AT&T Labs) 51 Data rate calculation: DM1 and DH1 625 µs 72 bits 54 bits 240 bits Access code Header 30 bytes = 366 bits Payload Dir Size 17 Freq 1600/2 Rate 108.8 DM1 1 17 2 2/3 FEC 17 108.8 DH1 1 27 2 27 27 172.8 172.8 625 µs 1 2 Pravin Bhagwat (AT&T Labs) 52 Tutorial 3: Bluetooth 26

Data rate calculation: DM3 and DH3 1875 µs 72 bits 54 bits Access code Header 1500 bits 187 bytes = 1626 bits DM3 Payload 2 121 2 2/3 FEC Dir Size 121 17 Freq 1600/4 Rate 387.2 54.4 DH3 2 183 2 183 27 585.6 86.4 1875 µs 1 2 3 4 Pravin Bhagwat (AT&T Labs) 53 Data rate calculation: DM5 and DH5 3125 µs 72 bits 54 bits Access Code Header 2744 bits 343 bytes = 2870 bits DM5 Payload 2 224 2 2/3 FEC Dir Size 224 17 Freq 1600/6 Rate 477.8 36.3 DH5 2 339 2 339 27 723.2 57.6 3125 µs 625 µs 1 2 3 4 5 6 Pravin Bhagwat (AT&T Labs) 54 Tutorial 3: Bluetooth 27

Data Packet Types DM1 Symmetric 108.8 Asymmetric 108.8 108.8 DM3 258.1 387.2 54.4 2/3 FEC DM5 286.7 477.8 36.3 Symmetric Asymmetric No FEC DH1 DH3 DH5 172.8 390.4 433.9 172.8 585.6 723.2 172.8 86.4 57.6 Pravin Bhagwat (AT&T Labs) 55 Inter piconet communication Cordless headset mouse Cordless headset Cell phone Cell phone Cell phone Cordless headset Pravin Bhagwat (AT&T Labs) 56 Tutorial 3: Bluetooth 28

Scatternet Pravin Bhagwat (AT&T Labs) 57 Scatternet, scenario 2 How to schedule presence in two piconets? Forwarding delay? Missed traffic? Pravin Bhagwat (AT&T Labs) 58 Tutorial 3: Bluetooth 29

Baseband: Summary Device 1 Device 2 LMP L2CAP Data link L2CAP LMP Baseband Physical Baseband TDD, frequency hopping physical layer Device inquiry and paging Two types of links SCO and ACL links Multiple packet types (multiple data rates with and without FEC) Pravin Bhagwat (AT&T Labs) 59 Link Manager Protocol Applications IP SDP RFCOMM Data L2CAP Audio Link Manager Control LMP Setup and management of Baseband connections Baseband RF Piconet Management Link Configuration Security Pravin Bhagwat (AT&T Labs) 60 Tutorial 3: Bluetooth 30

Piconet Management Attach and detach slaves Master-slave switch Establishing SCO links Handling of low power modes ( Sniff, Hold, Park) Paging Master req response Slave Pravin Bhagwat (AT&T Labs) 61 Low power mode (hold) Hold offset Slave Master Hold duration Pravin Bhagwat (AT&T Labs) 62 Tutorial 3: Bluetooth 31

Low power mode (Sniff) Sniff offset Sniff duration Slave Sniff period Master Traffic reduced to periodic sniff slots Pravin Bhagwat (AT&T Labs) 63 Low power mode (Park) Slave Beacon instant Master Beacon interval Power saving + keep more than 7 slaves in a piconet Give up active member address, yet maintain synchronization Communication via broadcast LMP messages Pravin Bhagwat (AT&T Labs) 64 Tutorial 3: Bluetooth 32

Link Configuration Quality of service Polling interval Broadcast repetition Power control Packet type negotiation Multi-slot packets Paging Master LMP_quality_of_se rvice LMP_not_Accepted Slave Pravin Bhagwat (AT&T Labs) 65 Connection establishment & Security Goals Authenticated access Only accept connections from trusted devices Privacy of communication prevent eavesdropping Paging Constraints Processing and memory limitations $10 headsets, joysticks Cannot rely on PKI Simple user experience Master LMP_host_conn_req LMP Accepted Security procedure LMP_setup_complete Slave LMP_setup_complete Pravin Bhagwat (AT&T Labs) 66 Tutorial 3: Bluetooth 33

Authentication Authentication is based on link key (128 bit shared secret between two devices) How can link keys be distributed securely? challenge Verifier response accepted Claimant Link key Link key Pravin Bhagwat (AT&T Labs) 67 Pairing (key distribution) Pairing is a process of establishing a trusted secret channel between two devices (construction of initialization key K init ) K init is then used to distribute unit keys or combination keys PIN + Claimant address Verifier Random number challenge Claimant PIN + Claimant address Random number response Random number Kinit accepted Kinit Pravin Bhagwat (AT&T Labs) 68 Tutorial 3: Bluetooth 34

Encryption Encryption Key ( 8 128 bits) Derived from the Link key Encryption mode Key size Start encryption Encrypted traffic Stop encryption Pravin Bhagwat (AT&T Labs) 69 Link Manager Protocol Summary Device 1 Device 2 LMP L2CAP Data link L2CAP LMP Baseband Physical Baseband Piconet management Link configuration Low power modes QoS Packet type selection Security: authentication and encryption Pravin Bhagwat (AT&T Labs) 70 Tutorial 3: Bluetooth 35

L2CAP Applications IP SDP RFCOMM Logical Link Control and Adaptation Protocol Data L2CAP Audio Link Manager Baseband RF L2CAP provides Protocol multiplexing Segmentation and Re-assembly Quality of service negotiation Pravin Bhagwat (AT&T Labs) 71 Why baseband isn t sufficient IP RFCOMM IP RFCOMM MTU Multiplexing demultiplexing Baseband reliable*, flow controlled in-sequence, asynchronous link with possible duplication Baseband packet size is very small (17min, 339 max) No protocol-id field in the baseband header Pravin Bhagwat (AT&T Labs) 72 Tutorial 3: Bluetooth 36

Need a multiprotocol encapsulation layer IP RFCOMM IP RFCOMM unreliable, no integrity reliable*, in-order, flow controlled, ACL link with possible duplication Desired features Protocol multiplexing Segmentation and re-assembly Quality of service What about Reliability? Connection oriented or connectionless? integrity checks? Pravin Bhagwat (AT&T Labs) 73 Segmentation and reassembly Length Payload Baseband packets start of L2CAP CRC CRC CRC continuation of L2CAP continuation of L2CAP cannot cope with re-ordering or loss mixing of multiple L2CAP fragments not allowed If the start of L2CAP packet is not acked, the rest should be discarded min MTU = 48 672 default Pravin Bhagwat (AT&T Labs) 74 Tutorial 3: Bluetooth 37

Multiplexing and Demultiplexing IP RFCOMM IP RFCOMM Circuit or connection-less? Why is L2CAP connection oriented? Baseband is polling based Bandwidth efficiency - carry state in each packet Vs. maintain it at end-points Need ability for logical link configuration - MTU - reliability (Flush timeout option) - QoS (token bucket parameter negotiation) Pravin Bhagwat (AT&T Labs) 75 L2CAP Channels Length CID Payload Slave #1 01 CID CID 01 CID CID master 01 CID CID 01 signaling channel data channel 01 CID Slave #3 Signaling channel for 1) connection establishment 2) channel configuration 3) disconnection CID Slave #2 01 Signaling channel CID does not uniquely determine the identity of the source L2CAP entity Pravin Bhagwat (AT&T Labs) 76 Tutorial 3: Bluetooth 38

L2CAP connection: an example Establishment Initiator Target L2CAP_ConnectReq L2CAP_ConnectRsp Configuration MTU, QoS reliability L2CAP_ConfigReq L2CAP_ConfigRsp L2CAP_ConfigReq L2CAP_ConfigRsp Data transfer Termination L2CAP_DisconnectRsp L2CAP_DisconnectReq Pravin Bhagwat (AT&T Labs) 77 L2CAP Packet Format (Connectionless) 2 2 2+ 0 64K Length DCID PSM Payload Not fully developed yet. Pravin Bhagwat (AT&T Labs) 78 Tutorial 3: Bluetooth 39

L2CAP: Summary Design constraints: Simplicity Low overhead Limited computation and memory Power efficient Assumptions about the lower layer Reliable, in-order delivery of fragments Integrity checks on each fragment Asynchronous, best effort point-to-point link No duplication Full duplex Service provided to the higher layer Protocol multiplexing and demultiplexing Larger MTU than baseband Point to point communication Pravin Bhagwat (AT&T Labs) 79 Bluetooth Service Discovery Protocol SDP Applications IP RFCOMM Data L2CAP Audio Link Manager Baseband RF Pravin Bhagwat (AT&T Labs) 80 Tutorial 3: Bluetooth 40

Example usage of SDP Establish L2CAP connection to remote device Query for services search for specific class of service, or browse for services Retrieve attributes that detail how to connect to the service Establish a separate (non-sdp) connection to user the service Pravin Bhagwat (AT&T Labs) 81 Serial Port Emulation using RFCOMM Applications SDP IP RFCOMM Data L2CAP Audio Link Manager Baseband RF Serial Port emulation on top of a packet oriented link Similar to HDLC For supporting legacy apps Pravin Bhagwat (AT&T Labs) 82 Tutorial 3: Bluetooth 41

Serial line emulation over packet based MAC RFCOMM L2CAP RFCOMM L2CAP Design considerations framing: assemble bit stream into bytes and, subsequently, into packets transport: in-sequence, reliable delivery of serial stream control signals: RTS, CTS, DTR Options collect MTU bytes and then send wait until a timeout send whatever is available Pravin Bhagwat (AT&T Labs) 83 IP over Bluetooth V 1.0 Applications IP SDP RFCOMM Data L2CAP Audio Link Manager Baseband RF GOALS Internet access using cell phones Connect PDA devices & laptop computers to the Internet via LAN access points Pravin Bhagwat (AT&T Labs) 84 Tutorial 3: Bluetooth 42

LAN access point profile Access Point IP PPP Why use PPP? Security Authentication Access control Efficiency header and data compression Auto-configuration Lower barrier for deployment RFCOMM L2CAP LMP Baseband Pravin Bhagwat (AT&T Labs) 85 Inefficiency of layering Palmtop IP PPP rfc 1662 RFCOMM L2CAP packet oriented byte oriented packet oriented LAN access point IP PPP rfc 1662 RFCOMM L2CAP Emulation of RS-232 over the Bluetooth radio link could be eliminated Pravin Bhagwat (AT&T Labs) 86 Tutorial 3: Bluetooth 43

Terminate PPP at LAN access point Palmtop Access Point IP IP PPP PPP ethernet RFCOMM RFCOMM Bluetooth Bluetooth PPP server function at each access point management of user name/password is an issue roaming is not seamless Pravin Bhagwat (AT&T Labs) 87 L2TP style tunneling Palmtop Access Point PPP server IP PPP IP PPP RFCOMM Bluetooth RFCOMM Bluetooth UDP IP ethernet UDP IP ethernet Tunneling PPP traffic from access points to the PPP server 1) centralized management of user name/password 2) reduction of processing and state maintenance at each access point 3) seamless roaming Pravin Bhagwat (AT&T Labs) 88 Tutorial 3: Bluetooth 44

Seamless roaming with PPP REQ 1 Server 2 REQ 3 RPL RPL 4 CLR 5 MAC level registration MAC level handoff palmtop Pravin Bhagwat (AT&T Labs) 89 IP over Bluetooth Next steps IP based network connectivity peer-to-peer connectivity Internet connectivity for non-pc devices IP over wireless media Decentralized techniques for link formulation, naming, addressing, and routing Investigation of the right design point for running IP over toasters, light switches, & fire alarms Pravin Bhagwat (AT&T Labs) 90 Tutorial 3: Bluetooth 45

Research challenges &%! " # $!% ' $" Plug-n-play applications Resource Discovery Routing over scatternets Techniques for link formation Will the current solutions for each layer work in this environment? Pravin Bhagwat (AT&T Labs) 91 What is different in this scenario?,% &*!"+ # $!% Connection oriented, lowpower link technology " %-% %! ( ) Small, multi-hop networks Simple devices Isolated network Dynamic network Applications ---> services ----> routing ----> link creation Pravin Bhagwat (AT&T Labs) 92 Tutorial 3: Bluetooth 46

Link Formation The problem does not exist in most wired/wireless networks Proximity Link Low power modes require careful use of broadcast Maintaining connectivity in absence of application traffic seems wasteful Hints from higher layer are needed Pravin Bhagwat (AT&T Labs) 93 Routing over Scatternets Nodes must co-operate to forward packets (MANET style protocols) Forwarding at Layer 2 or Layer 3? Bridging or routing? What interface should be exported to the layer above? Better coupling with the service discovery layer is needed Pravin Bhagwat (AT&T Labs) 94 Tutorial 3: Bluetooth 47

Service discovery &*!"+ # $!%,% " %-% %! ( ) Need solutions for address allocation, name resolution, service discovery Existing solutions in the Internet depend on infrastructure Judicious use of Multicast/broadcast is needed These goals are similar to what Zero-conf WG is already working on Pravin Bhagwat (AT&T Labs) 95 Point to ponder Zero-conf Will Zero-conf on top of MANET on top of scatternet construction algorithm solve our problem? Layered and simple, but potential inefficiencies MANET Cross-layer optimizations are worth considering Scatternet formation Pravin Bhagwat (AT&T Labs) 96 Tutorial 3: Bluetooth 48

Mobicom 2000 Aug 6, 2000 Scatternet enumeration Problem: given N Bluetooth nodes how many different ways can scatternets be formed? node type constraint master slave bridge degree constraint degree (master) <= 7 degree (bridge ) >= 2, <= max connectivity constraint no slave to slave link no master to master link (makes it a bi-partite graph) Pravin Bhagwat (AT&T Labs) 97 Graph enumeration Assign a label x i to each node x 1 x 22 x 32 x 4 x 54 x 63 x 73 x 84 x 9 x 1 deg. seq. d = (1,2,2,1,4,3,3,3,4,1,1) d i = 2 * edges N ji=1 j=1 = n(d) x d1 1... x dn n How to cope with the combinatorial explosion? E.g., for n = 10, the product has 2 45 terms Pravin Bhagwat (AT&T Labs) 98 Tutorial 3: Bluetooth 49

Mobicom 2000 Aug 6, 2000 Scatternet topology space Pravin Bhagwat (AT&T Labs) 99 Modeling Bluetooth constraints: an example 5 slaves (d = 1) 2 bridges (d = 2, 3) 3 masters slave = ( y 1 + y 2 + y 3 ) bridge 1 = (y 1 y 2 + y 1 y 3 + y 2 y 3 ) bridge 2 = (y 1 y 2 y 3 ) P = (y 1 + y 2 + y 3 ) 5 (y 1 y 2 + y 1 y 3 + y 2 y 3 ) 1 (y 1 y 2 y 3 ) 1 there are 56 possible choices of bridge nodes, so total number of ways = 56.3 5.3.1 Pravin Bhagwat (AT&T Labs) 100 Tutorial 3: Bluetooth 50

Mobicom 2000 Aug 6, 2000 Modeling Bluetooth constraints In general q1 slaves (d = 1) q2 bridges (d = 2)... qk bridges (d = k) slave = ( y 1 + y 2 + y 3.. ) bridge 1 = (y 1 y 2 + y 1 y 3 + y 2 y 3.. ) bridge 2 = (y 1 y 2 y 3 + y 1 y 2 y 3.. ).. bridge k = (y 1 y 2 y 3... + y 2 y 3 y 4.. ) P = 1 (y) q1 2 (y) q2 3 (y) q3... k (y) qk Pravin Bhagwat (AT&T Labs) 101 Managing combinatorial explosion Elementary symmetric functions can be expressed in terms of power sums, e.g. 2 (y) = y 1 y 2 + y 1 y 3.. + y m-1 y m = 1 / 2 (( y i ) 2 - ( y i2 )) P = 1 (y) q1 2 (y) q2 3 (y) q3... k (y) qk - Expand in terms of power sums - compute modulo w.r.t. a high degree polynomial, e.g., y 7 Pravin Bhagwat (AT&T Labs) 102 Tutorial 3: Bluetooth 51

Scatternet topology space Pravin Bhagwat (AT&T Labs) 103 Open problems Estimation of the traffic carrying capacity of Scatternets Enumeration of large size ad hoc networks Decentralized algorithms for network construction Dynamics of information propagation in large size ad hoc networks A killer application Pravin Bhagwat (AT&T Labs) 104 Tutorial 3: Bluetooth 52

References Bluetooth The universal radio interface for ad hoc, wireless connectivity, Jaap Haartsen. Ericsson review 03, 1998. (http://www.ericsson.com/review/issues.taf ) Bluetooth version 1.0 specifications http://www.bluetooth.com/developer/specification/core.asp Part A, Radio Specification Part B, Baseband Part C, Link Manager Protocol Part D, Logical Link Control and Adaption Protocol Specification Part E, Service Discovery Protocol (SDP) Bluetooth version 1.0 profiles http://www.bluetooth.com/developer/specification/profiles.asp Part K:9, LAN access profile Future updates will be posted at: http://www.research.att.com/~pravinb/bluetooth/ Pravin Bhagwat (AT&T Labs) 105 Thank you Pravin Bhagwat (AT&T Labs) 106 Tutorial 3: Bluetooth 53