Università degli Studi di Catania Dipartimento di Ingegneria Informatica e delle Telecomunicazioni Bluetooth Ing. A. Leonardi Università degli Studi di Catania Dipartimento di Ingegneria Informatica e delle Telecomunicazioni Bluetooth is a short range (10-100 m) and low-cost wireless network system to replace cables and give RF connection between consumer devices. 1 Università degli Studi di Catania Dipartimento di Ingegneria Informatica e delle Telecomunicazioni Scenarios Figure 2: Peripheral interconnects Figure 1: Personal Area Networking (PAN) Figure 3: Voice/Data Access Points Università degli Studi di Catania Dipartimento di Ingegneria Informatica e delle Telecomunicazioni Bluetooth Ad Hoc Networks (1) f Piconet The technology allows creation of small ad-hoc networks (piconets) consisting of at most 8 simultaneously active devices. f Scatternet Many different piconets may coexist and interoperate in the same physical area. 2 Università degli Studi di Catania Dipartimento di Ingegneria Informatica e delle Telecomunicazioni Bluetooth Ad Hoc Networks (2) fA piconet consists of one master and up to 7 slaves. fThe master is the central entity that decides transmit/receive resource allocation to different slaves and thus controls bandwidth usage among slaves. fTwo or more piconets can be linked together to form a scatternet. In this, one device in each piconet (either a master or a slave) acts like a bridge between them. Università degli Studi di Catania Dipartimento di Ingegneria Informatica e delle Telecomunicazioni Bluetooth Ad Hoc Networks (3) 3 Università degli Studi di Catania Dipartimento di Ingegneria Informatica e delle Telecomunicazioni Bluetooth Ad Hoc Networks (4) fA Bluetooth device can function as either a master as or a slave. fEach piconet can only have a single master, but a master in one piconet can be a slave in another piconet. fThis allows a dynamic topology construction of complex scatternet. Università degli Studi di Catania Dipartimento di Ingegneria Informatica e delle Telecomunicazioni Radio channel (1) fBluetooth operates in the unlicensed ISM band at 2.4 GHz. fA CDMA-FH/TDD system is used: 79 carriers spaced 1 MHz, in the band 2400-2483,5 MHz; the channel is divided into time slots where each slot corresponds to an RF hop frequency; consecutive slots correspond to different RF hop frequencies; all Bluetooth units participating in the piconet are time- and hop-synchronized to the channel; a TDD scheme is used where master and slave alternatively transmit. 4 Università degli Studi di Catania Dipartimento di Ingegneria Informatica e delle Telecomunicazioni Radio channel (2) fThe channel is divided into time slots, each 625 μs in lenght, thus the nominal hop rate is 1600 hops/s. Università degli Studi di Catania Dipartimento di Ingegneria Informatica e delle Telecomunicazioni Piconet channel (1) fThe piconet channel is represented by a pseudo-random hopping sequence hopping through the 79 RF channels. fThe hopping sequence is unique for the piconet and is determined by the Bluetooth device address of the master. fThe phase in the hopping sequence is determined by the Bluetooth clock of the master. 5 Università degli Studi di Catania Dipartimento di Ingegneria Informatica e delle Telecomunicazioni Piconet channel (2) Università degli Studi di Catania Dipartimento di Ingegneria Informatica e delle Telecomunicazioni Physical links (1) fBetween master and slave(s), different types of links can be established. Two link types have been defined: Synchronous Connection-Oriented (SCO) link Asynchronous Connection-Less (ACL) link fThe SCO link is a point-to-point link between a master and a single slave in the piconet. The master maintains the SCO link by using reserved slots at regular intervals. fThe SCO link reserves slots and can therefore be considered as a circuit-switched connection between the master and the slave. 6 Università degli Studi di Catania Dipartimento di Ingegneria Informatica e delle Telecomunicazioni Physical links (2) fThe ACL link is a point-to-multipoint link between the master and all the slaves participating on the piconet. fIn the slots not reserved for the SCO link(s), the master can establish an ACL link on a per-slot basis to any slave, including the slave(s) already engaged in an SCO link. fThe ACL link provides a packet-switched connection between the master and all active slaves participating in the piconet. Università degli Studi di Catania Dipartimento di Ingegneria Informatica e delle Telecomunicazioni Physical links (3) fA slave is permitted to return an ACL packet in the slave-to- master slot if and only if it has been addressed in the preceding master-to-slave slot. If the slave fails to decode the slave address in the packet header, it is not allowed to transmit. fACL packets not addressed to a specific slave are considered as broadcast packets and are read by every slave. 7 Università degli Studi di Catania Dipartimento di Ingegneria Informatica e delle Telecomunicazioni Example (1) fAn ACL link in a piconet with three devices: Università degli Studi di Catania Dipartimento di Ingegneria Informatica e delle Telecomunicazioni Example (2) fA mixed link in a piconet with four devices: 8 Università degli Studi di Catania Dipartimento di Ingegneria Informatica e delle Telecomunicazioni Multislot packet (1) fFor a multi-slot packet, the RF hop frequency to be used for the entire packet is derived from the Bluetooth clock value in the first slot of the packet. Università degli Studi di Catania Dipartimento di Ingegneria Informatica e delle Telecomunicazioni Multislot packet (2) fThe maximum throughput in an ACL link is obtainable with a piconet of two devices that use multislot packets of 5 slots: Maximum asymmetric throughput: 723.2 kb/s in one direction and 57.6 kb/s in the opposite direction; using 5-multislot packets in one direction and single slot packets in the other. Maximum symmetric throughput: 433.9 kb/s, using 5-multislot packets in both directions. 9 Università degli Studi di Catania Dipartimento di Ingegneria Informatica e delle Telecomunicazioni ARQ scheme in the ACL link fBluetooth uses a fast, unnumbered acknowledgment scheme: an ACK or a NAK is returned in response to the receipt of previously received packet. fThe slave will respond in the slave-to-master slot directly following the master-to-slave slot. fThe master will respond at the next event it will address the same slave (the master may have addressed other slaves between the last received packet from the considered slave and the master response to this packet). Università degli Studi di Catania Dipartimento di Ingegneria Informatica e delle Telecomunicazioni ARQ scheme in the ACL link Example 10 Università degli Studi di Catania Dipartimento di Ingegneria Informatica e delle Telecomunicazioni Bluetooth protocols stack Università degli Studi di Catania Dipartimento di Ingegneria Informatica e delle Telecomunicazioni Bluetooth protocols description (1) f Bluetooth Radio: defines the requirements of the Bluetooth transceiver device operating in the 2.4GHz ISM band f Baseband: fmanages physical channels and links apart from other services like error correction, data whitening, hop selection and Bluetooth security; fmanages asynchronous and synchronous links, handles packets and does paging and inquiry f LMP: Manager carries out link setup, authentication, link configuration and other protocols 11 Università degli Studi di Catania Dipartimento di Ingegneria Informatica e delle Telecomunicazioni Bluetooth protocols description (2) f HCI: provides a command interface to the baseband controller and link manager, and access to hardware status and control registers f L2CAP: provides connection-oriented and connectionless data services to upper layer protocols with protocol multiplexing capability, segmentation and reassembly operation, and group abstractions. f RFCOMM: provides emulation of serial ports over the L2CAP f SDP: provides a means for applications to discover which services are available and to determine the characteristics of those available services. Università degli Studi di Catania Dipartimento di Ingegneria Informatica e delle Telecomunicazioni Connection establishment fBy definition, the master is represented by the Bluetooth unit that initiates the connection (to one or more slave units). fOnce a piconet has been established, master-slave roles can be exchanged. fThere are two major states: STANDBY and CONNECTION; in addition, there are seven substates, page, page scan, inquiry, inquiry scan, master response, slave response, and inquiry response. 12 Università degli Studi di Catania Dipartimento di Ingegneria Informatica e delle Telecomunicazioni Connection establishment state diagram Università degli Studi di Catania Dipartimento di Ingegneria Informatica e delle Telecomunicazioni Inquiry procedures (1) fA device that want to discover other devices enters the inquiry state fA device that wants to be discovered enters the inquiry scan state fDuring an inquiry substate, the discovering unit collects the Bluetooth device addresses and clocks of all units that respond to the inquiry message. 13 Università degli Studi di Catania Dipartimento di Ingegneria Informatica e delle Telecomunicazioni Inquiry procedures (2) fThe inquiry message broadcast by the source does not contain any information about the source itself. However, it may indicate which class of devices should respond. fThe inquiry response is optional: a unit is not forced to respond to an inquiry message. fEvery devices during the inquiry procedure uses a well known inquiry hopping sequence of 32 dedicated frequencies. Università degli Studi di Catania Dipartimento di Ingegneria Informatica e delle Telecomunicazioni Page procedures (1) fThe page substate is used by the master (source) to activate and connect to a slave (destination) having the address known during inquiry phase. fThe master tries to capture the slave by repeatedly transmitting in different hop channels, according to the hopping sequence of the slave (obtained from its address). fThe slave enters periodically the page scan state. 14 Università degli Studi di Catania Dipartimento di Ingegneria Informatica e delle Telecomunicazioni Page procedures (2) fAlthough the master and the slave use the same hopping sequence, they surely use different phases Æ they may never meet each other. fTo compensate for the clock drifts, the master will send its page message twice per each TX slot on two different hop frequencies. Università degli Studi di Catania Dipartimento di Ingegneria Informatica e delle Telecomunicazioni Page procedures (3) fWhen a page message is successfully received by the slave, there is a coarse FH synchronization between the master and the slave. They enter a response routine to exchange information for a better synchronization. fThen the master and the slave changes to the channel (master’s) hopping sequence. fThe channel access code and channel hopping sequence are derived from the Bluetooth device address of the master. The timing is determined by the master clock. 15 Università degli Studi di Catania Dipartimento di Ingegneria Informatica e delle Telecomunicazioni Page procedures (4) Università degli Studi di Catania Dipartimento di Ingegneria Informatica e delle Telecomunicazioni Baseband Methods for Power Conservation (1) fSniff Mode is used when a slave shall participate in the piconet only in a sniff interval. fIn ACL link, keeping synchronization in a piconet at the connection establishment, it receives and transmits packets only in the time slots of the fixed interval called "sniff cycle". In other time slots, power consumption is saved by performing only the processing indispensable to maintain synchronization of a piconet. 16 Università degli Studi di Catania Dipartimento di Ingegneria Informatica e delle Telecomunicazioni Baseband Methods for Power Conservation (2) fHold Mode is useful when a BT Device doesn’t want to participate in the connection for a Hold Mode Length. fIn ACL link, keeping synchronization in a piconet at the connection establishment, a communication link is temporarily interrupted during a fixed period (defined as "hold time"). Power consumption is saved by performing only the processing indispensable to maintain synchronization of a piconet during hold time. If the hold time passes, it will return to the original ACL link and transmission and reception of a packet will be resumed. Università degli Studi di Catania Dipartimento di Ingegneria Informatica e delle Telecomunicazioni Baseband Methods for Power Conservation (3) fPark Mode is used to render the slaves inactive but still synchronized to the master using the beacon interval. fIt is low power consumption mode peculiar to a slave (a master does not become Park mode). Altough the synchronization of a piconet is maintained, the slave node can only receive packets but can not send packets. Except the receiving slot for every fixed interval called "beacon cycle", power consumption is saved by performing only the processing indispensable to maintain synchronization of a piconet. 17 Università degli Studi di Catania Dipartimento di Ingegneria Informatica e delle Telecomunicazioni Baseband Methods for Power Conservation (4) fEntry into sniff, hold or park mode requires an established ACL Connection. fThe following table summarizes the modes and the BT Role that can request, force, activate or exit the modes. 18
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