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Wireless LANs (cont)

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This comprehensive overview of Bluetooth technology covers its functioning with a focus on piconets and scatternets. We delve into Bluetooth's key features such as frequency hopping, data rates, and voice/data capabilities. The article explains the master-slave concept in piconets, how devices connect in ad-hoc networks, and the role of various packet types in communication. Additionally, it discusses Bluetooth's ability to manage multiple piconets and optimize network performance, providing insights for effective Bluetooth networking.

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Wireless LANs (cont)

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  1. WirelessLANs (cont) Bluetooth

  2. Landline Cable Replacement Data/Voice Access Points Personal Ad-hoc Networks What Is Bluetooth?

  3. Example...

  4. Some Bluetooth Facts…. • 2.4 GHz ISM Open band • Globally free available frequency, 89 MHz of spectrum available • FHSS radio (1600 hops/s and 79 frequencies) • 10 -100 m range • 8 active devices per piconet (share datarate) • Up to 10 piconets in bubble (full datarate) • 1 Mbps gross rate • Simultaneous voice/data capable • 432 Kbps (full duplex), 721/56 Kbps (asymmetric) or • 3 simultaneous full duplex voice channels per piconet or • a combination of data and voice

  5. Network Topology – Piconet • Piconets created ad-hoc • Master-Slave concept • Piconet defined by itsfrequency hopping sequence slave 3 slave1 master slave 2

  6. UnconnectedStandby ConnectingStates ActiveStates Low PowerModes master connecting slaves active slave parked slave standby Piconet establishment • Ad-hoc setup • Connection oriented • Power save modes

  7. or The piconet D • All devices in a piconet hop together • To form a piconet: master gives slaves its clock and device ID • Hopping pattern determined by device ID(48-bit) • Phase in hopping pattern determined by Clock • Non-piconet devices are in standby • Piconet Addressing • Active Member Address (AMA, 3-bits) • Parked Member Address (PMA, 8-bits) A E B C

  8. FH/TDD Channel f(k) f(k+1) f(k+2) master t slave t One slot: 625 ms One frame: 1250 ms

  9. 0-2745 72 54 access code packet header payload Packet Format

  10. Packet Types Access code Header Payload 72 bits 54bits 0-2475 bits Bluetooth Packet • Bluetooth Protocol supports 16 packet types, 15 types defined 4 Control packets common to both links POLL,NULL,FHS and ID 4 SCO packets used to carry voice with different payload lengths. HV1,HV2,HV3 and DV, where DV carries both voice and data 7 ACL packets with different payload lengths DM1,DM3,DM5,DH1,DH3,DH5 and AUX1 Carries data only

  11. 625 s f(k) f(k+1) f(k+2) f(k+3) f(k+4) f(k+5) f(k) f(k+3) f(k+4) f(k+5) f(k) f(k+5) Multi-slot Packets

  12. Error handling 72bits 0-2745bits 54bits • Forward-error correction (FEC) • headers are protected with 1/3 rate FEC and 8 bit CRC (HEC) • payloads may be FEC protected • 1/3 rate: simple bit repetition (SCO packets only) • 2/3 rate: (10,15) shortened Hamming code • 3/3 rate: no FEC • ARQ (ACL packets only) • 16-bit CRC (CRC-CCITT) & 1-bit ACK/NACK • 1-bit sequence number payload access code header

  13. Physical Link Definition • Synchronous Connection-Oriented (SCO) Link • circuit switching • symmetric, synchronous services • slot reservation at fixed intervals • Asynchronous Connection-Less (ACL) Link • packet switching • (a)symmetric, asynchronous services • polling access scheme

  14. SCO ACL SCO ACL ACL SCO SCO ACL Mixed Link Example MASTER SLAVE 1 SLAVE 2 SLAVE 3

  15. TYPE symmetric asymmetric DM1 108.8 108.8 108.8 DH1 172.8 172.8 172.8 DM3 256.0 384.0 54.4 DH3 384.0 576.0 86.4 DM5 286.7 477.8 36.3 DH5 432.6 721.0 57.6 Data Rates (kb/s)

  16. LAN access point access point mobile phone mobile phone headset headset printer printer laptop laptop master laptop laptop slave mouse mouse master/slave Multiple Piconets: A Scatternet

  17. Multiple Piconets: A Scatternet master slave master/slave

  18. Ad-hoc IP networking on Bluetooth (MANET) IP Hosts Bluetooth Link and Baseband Layer slave 3 slave 1 slave 5 slave 4 master master slave 2

  19. Some issues…. • Scatternet - A device present in more than one piconet • How to jump efficiently between piconets? • Delay sensitive applications? • Things happening in “sleeping” piconets? LAN access point

  20. Scatternet Forming/Reforming • “Optimal” scatternet configuration depends on • Connectivity and Node density • Traffic Distribution (Traffic matrix) • Mobility&Traffic dynamics - steady state ever reached? • Integration of connection establishment and (ad-hoc) routing? At t... At t+D t.

  21. s s s s s s s m s m s s m s s m ”Work” your Bluetooth Network • Bluetooth handles overlaid Piconets well • Overall capacity gained by setting up new piconets

  22. S-M 10 % of traffic S-M 55 % of traffic S-S 45 % of traffic S-S 90 % of traffic s s s s m s s s m s s s s s Smart Scatternet... • Move out large slave to slave traffic • Still part of old piconet - a scatternet P2 s s P1 P1 m s s s

  23. IP L2(Broadcast segment) Ad-hoc networking slave 3 slave 1 slave 5 slave 4 master master Bluetooth slave 2

  24. 2 2 1 1 3 3 2 2 1 1 3 3 Piconet scheduling slave 3 slave1 • Intra-piconet scheduling • Master controlled polling algorithm • Round Robin? • Inter-piconet scheduling • One transceiver • Different FHS master slave 2 master slave 3 slave 4 4 4

  25. A P2 s P1 s s s m2 s m1 s s s s s Inter-piconet Timing • Interpiconet communication may be “costly” • An interpiconet unit active in only one piconet at a time • SNIFF Mode - Periodic presence in each piconet INQUIRY Scan/PAGE Scan P1 P2

  26. SNIFF Mode • SNIFF Parameters • Tsniff • max(Nsniffattempt, Nsnifftimeout) = Wsniff • Approximately one frame lost per “Piconet switch” • Trade off: Delay vs. Throughput • Delay: Tsniff • Throughput: WsniffP2 TsniffP1 P1 P2 WsniffP2 TsniffP2

  27. Bluetooth Experiments Gerla, M et al,Tyrrenia Conf, sept 2000 • Experiment #!:TCP throughput in a single piconet. Throughput versus the no. of TCP connections. Each TCP connection starts from a different slave on the common piconet, and goes through the access point (BT master). • Experiment #2: TCP throughput when multiple piconets are used in parallel. Each piconet here supports a separate TCP connection. • Experiment #3: TCP and IP Telephony in a multiple piconet configuration. IP Telephony uses ACL channel. Question: can TCP and Telephony coexist?

  28. IP backbone IP backbone IP backbone IP router IP router IP router LAN LAN LAN M M S M 1 1 1 1 S M M M M M S M 3 3 2 3 2 2 2 3 S S (a) (b) (c) Fig. 4.

  29. Exp # 1:TCP throughput in Bluetooth (single piconet)

  30. Exp #2:TCP Throughput in WaveLAN vs BT (multiple piconets)

  31. Exp #2 (cont): Throughput of TCP flows

  32. TCP and IP Telephony • Voice carried on the ACL channel • Four piconets • In each piconet: 1 TCP and 6 Voice connections • TCP connections “always on” (file transfers) • Voice: ON-OFF model; 8Kbps coding rate • Voice packets: 20ms packetization -> 20 bytes • With header overhead: voice pkt = 30 bytes

  33. Exp #3: Bluetooth; TCP + VoIP

  34. Exp #3: Bluetooth; TCP + VoIP

  35. Exp #3: WaveLan 802.11: TCP + VoIP

  36. Exp #3: WaveLan 802.11: TCP + VoIP With 750 ms playout buffer, 5% packets lost

  37. Simulation: what have we learned? • Bluetooth performance predictable, dependable • Fairsharing across TCP connections (IEEE 802.11 is unfair, “capture”- prone) • BT aggregate throughput exceeds IEEE 802.11 • BT supports voice well even in heavy TCP load (IEEE 802.11 cannot deliver voice with TCP load) • BT not overly sensitive to microwave ovens Future work • BT load sensitive polling schedule • BT in low latency applications (sensors on walls) • BT scatternets (formation, schedules, routing etc) • BT vs UMTS comparison

  38. Bluetooth SIG2 - PAN WG • Personal Area Network • Ad-hoc Bluetooth work groups • QoS support (audio/video) • Possibly: “associated” members • opens up for academia • research oriented work

  39. Bluetooth Program Update • Final Specification published Monday 7/26/99 • Result of work from ~200 engineers • Updated Specification 1.0 B published 12/1/99 • SIG Membership Exceeds 1,700 Companies! • Becoming the choice for wireless connectivity • Membership list at www.bluetooth.com • Program on Track for Products in 2000 • Products announced • Next step is Qualification Program • Specification is basis for the proposed IEEE 802.15.1 standard

  40. PAN Impact on Internet Access for Mobile Devices • PAN allows sharing of “gateway” device • E.g., Only one cellular “modem” needed • E.g., Only one ADSL connection needed • PAN allows sharing of access “tariff” • All personal devices share same account • Allows multiple combinations of wireless and wired technology for Internet access with one or two communication interfaces

  41. PAN to Cellular Data Network • Available today using cables or IR • 2nd generation cellular better than analog • Cost and speed are still issues • RF value add is wireless connectivity without “line of sight” limitations • Also allows “unconscious” data reception PAN to WWAN

  42. PSTN, ISDN,HomePNA, xDSL PAN to Wired Infrastructure • Wireless “last hop” to the Internet • Public kiosks provide alternative to wireless wide-area networks PAN to LAN/WAN

  43. Summary • Bluetooth is a radio system (not a radio) • Building block for personal area networks • More information available at: http://www.bluetooth.com • PAN will improve the cost and convenience of achieving mobile Internet access

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