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Wireless Networks - MAC layer

Wireless Networks - MAC layer

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Wireless Networks - MAC layer

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  1. Wireless Networks - MAC layer - Bluetooth

  2. What is Bluetooth? • Cable replacement technology primarily • Bluetooth wireless technology is an open specification for a low-cost, low-power, short-range radio technology for ad-hoc wireless communication of voice and data anywhere in the world. • Where does the name come from? • To honor a 10th century king Bluetooth in Denmark who united that country and established Christianity

  3. Bluetooth • Bluetooth Piconet: a polling/TDMA scheme • Bluetooth working group history • February 1998: The Bluetooth SIG is formed • promoter company group: Ericsson, IBM, Intel, Nokia, Toshiba • + 3Com, Lucent, Microsoft, Motorola • Bluetooth uses a frequency-hopping scheme in the unlicensed band at 2.4 GHz. • The major goal is to allow relatively cheap electronic devices to communicate directly in an ad-hoc fashion, Moreover, the Bluetooth equipped devices can also form networks– such a network of personal devices is often referred to as a personal area network (PAN).

  4. Landline Data/Voice Access Points …and combinations! Personal Ad-hoc Networks What does Bluetooth do for you? Cable Replacement - Synchronization - Cordless Headset It is reported that more than two billion Bluetooth-ready devices were shipped during 2012 – over 50 millions every day.

  5. Example...

  6. Bluetooth Technical Features: • 2.4 GHz ISM Open Band • Globally free available frequency • 79 channels (2400-2483.5 MHz ISM band) • Frequency Hopping & Time Division Duplex (1600 hops/second typically) • 10-100 Meter Range • Class I – 100 meter (300 feet) • Class II – 20 meter (60 feet) • Class III – 10 meter (30 feet) • Link Rate : 1 Mbps • Simultaneous Voice/Data Capable • SCO (Synchronous connection oriented) for voice • ACL (Asynchronous connectionless link) for data

  7. Frequency Hopping 1Mhz 79 83.5 Mhz • Divide Frequency band into 1 MHz hop channels • Radio hops from one channel to another in a pseudo-random manner as dictated by a hop sequence

  8. Frequency Hopping Map • Wireless channel is divided into time slots of 625μs • Frequency hopping sequence is defined by a pseudorandom number generator known to both transmitter and receiver • Packet transmission is aligned with the start of time slot

  9. Bluetooth Network Topology • PICONET —— Bluetooth LAN • Collection of devices connected in an ad hoc fashion • One unit acts as master and the others as slaves for the lifetime of the piconet • Master – device that initiates a data exchange • Slave – device that responds to the master • Master determines hopping pattern, slaves have to synchronize • There is one only one pattern in one piconet • 1600hops/sec • Devices in a piconet are synchronized to the same clock defined by master

  10. m s m s s s Bluetooth Network Topology • Point to point link • master - slave relationship • radios can function as masters or slaves • Assigning address • If (node -> node address==0) • MASTER • else • SLAVE • Piconet • Master can connect to 7 slaves • hopping pattern is determined by the master

  11. Connection Setup • Inquiry(查询消息) • Master 查找附近的蓝牙设备,以便通过收集来自从节点响应查询消息中得到该节点的设备地址(48b)和时钟 • Inquiry – scan(查询扫描) • Slave设备周期地监听来自其他设备的查询消息,以便自己能被发现,并在监听到后发送它的地址和时钟信息。

  12. Master Active Slave • Parked Slave • Connected • Not in Pico Standby Connection Setup • Page (寻呼) • Master 通过在不同的跳频序列发送消息,来激活一个从节点, 并建立连接。调频序列由slaver的地址码计算出 • Page – scan(寻呼扫描) • Slaver 周期性地在扫描窗间隔时间内唤醒自己,并监听自己的访问码, Slaver节点每隔1.28s在这个扫描窗上根据寻呼跳频序列选择一个扫描频率

  13. Packet Types Data/voice packets Control packets Voice data ID* Null Poll FHS DM1 HV1 HV2 HV3 DV DH1 DH3 DH5 DM1 DM3 DM5 FHS – Frequency Hop Synchronization DM – Data Medium rate HV – High quality Voice DV – Data Voice DH – Data High rate

  14. Packet Format 54 bits 72 bits 0 - 2744 bits • Access code • used for timing synchronization, offset compensation, paging, and inquiry Access code Header Payload header Data Voice CRC No CRC No retries ARQ FEC (optional) FEC (optional) 625 µs master slave

  15. m Max 7 active slaves s s s Packet Header 54 bits • Addressing (3) • Packet type (4) • Flow control (1) • 1-bit ARQ (1) • Sequencing (1) • HEC (8) Access code Payload Header Purpose 16 packet types (some unused) Broadcast packets are not ACKed For filtering retransmitted packets Verify header integrity total 18 bits Encode with 1/3 FEC to get 54 bits

  16. Cordless headset mouse Cell phone Inter piconet communication Cordless headset Cell phone Cell phone Cordless headset

  17. Scatternet- Gateway node participates in more than one piconet on a time-division basis Not implemented in COTS equipment

  18. Scatternet, scenario 2 How to schedule presence in two piconets? Forwarding delay ? Missed traffic? Not implemented in COTS equipment

  19. Applications IP SDP RFCOMM Control Data Audio L2CAP Link Manager Baseband RF Bluetooth Protocol Stack Composed of protocols to allow Bluetooth devices to locate each other and to create, configure and manage both physical and logical links that allow higher layer protocols and applications to pass data through these transport protocols Transport Protocol Group

  20. Applications IP SDP RFCOMM Control Data Audio L2CAP Link Manager Baseband RF Bluetooth Protocol Stack Additional transport protocols to allow existing and new applications to operate over Bluetooth. Packet based telephony control signaling protocol also present. Also includes Service Discovery Protocol. Middleware Protocol Group

  21. Applications IP SDP RFCOMM Control Data Audio L2CAP Link Manager Baseband RF Bluetooth Protocol Stack Consists of Bluetooth aware as well as un-aware applications. Application Group

  22. Applications IP SDP RFCOMM Control Data Audio L2CAP LMP Link Manager Baseband RF Link Manager Protocol • Setup and management • of Baseband connections • Piconet Management • Link Configuration • Security

  23. IP L2CAP Applications L2CAP - Logical Link Control and Adaptation Protocol SDP RFCOMM Data • L2CAP provides • Protocol multiplexing • Segmentation and • Re-assembly • Quality of service negotiation Audio L2CAP Link Manager Baseband RF

  24. IP RFCOMM (Radio Frequency Communication)-- Serial Port Emulation using RFCOMM Applications SDP Serial Port RFCOMM Data • Serial Port emulation on top of a packet oriented link • Similar to HDLC (High level • Data Link Control protocol) • RS232 • For supporting legacy apps Audio L2CAP Link Manager Baseband RF

  25. IP IP over Bluetooth V 1.0 • Internet access using cell phones • Connect PDA devices & laptop computers to the Internet via LAN access points Applications SDP GOALS RFCOMM Data Audio L2CAP Link Manager Baseband RF

  26. Bluetooth Personal Area Networks- Ad Hoc and extend to Mesh • PANs extend the Internet to the user personal domain • 3G (2.5G) networks will give Internet access to PANs • PANs will generate more traffic than a single device • Utilize an aggregate of access networks (WLAN, 3G, DSL)

  27. IP Bluetooth Networking - Conclusions Bluetooth IP networking opens up new possibilities ---- Mesh networks • Enables spontaneous Ad Hocnetworking • Between people, • Between machines, • Mainly small, short range ad-hoc networks • Solves your “personal problems”... • Limited complexity and security risks • Sharing 3G traffic in current mobile internet???? • The enabler for PANs! • Gives a natural extension of Internet into the PAN via 3G • Enables stepwise upgrading of devices -- not tied to one multimedia terminal! • Makes use of the 3G bandwidth immediately • QoS ~ Bluetooth ?