Bluetooth.ppt

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1、Bluetooth,Owen Garmire and Seila Kheang CSE 466 Fall 2001 http:/www.cs.washington.edu/homes/seila/bluetooth.ppt,Bluetooth Overview,Wireless technology for short-range voice and data communication Low-cost and low-power Provides a communication platform between a wide range of “smart” devices Not lim

2、ited to “line of sight” communication,Motivation,Computer,Bluetooth Applications,Automatic synchronization between mobile and stationary devices Connecting mobile users to the internet using bluetooth-enabled wire-bound connection ports Dynamic creation of private networks,Synchronization,Keep data

3、on different devices synchronized without using a cable Example: Walk into office and have your PDA synch with your laptop on your desk without even taking your PDA out of your briefcase,Connecting to Internet,Being able to gain access to the Internet by using “Bluetooth access points” Access point

4、is used as a gateway to the internet Both the access point and the device are Bluetooth-enabled An example of Service Discovery Protocol Access point provides a service to the device,Ad Hoc Networks,Up to 8 devices can be actively connected in master/slave configuration Piconets can be combined to f

5、orm scatternets providing unlimited device connectivity,Protocol Stack,Bluetooth Radio,Uses 2.4 GHz ISM band spread spectrum radio (2400 2483.5 MHz) Advantages Free Open to everyone worldwide Disadvantages Can be noisy (microwaves, cordless phones, garage door openers),Frequency Hopping,In order to

6、mitigate interference, Bluetooth implements frequency hopping 1600 hops per second through 79 1MHz channels Spreads Bluetooth traffic over the entire ISM band All slaves in piconet follow the master for frequency hop sequence,Frequency Hopping (cont.),Hops every packet Packets can be 1, 3, or 5 slot

7、s long (a slot is 625s) Packets are pretty short,Baseband Layer,Provides in-order delivery of byte streams Handles Frequency Hop Sequences for Synchronization and Transmission Establishes Links Synchronous Connection Oriented (SCO) Asynchronous Connection-Less (ACL) Provides functionality to determi

8、ne nearby Bluetooth devices,Connection (Inquiry and Paging),Link controller states during connection process,Bluetooth: Hello, Anyone Around?,Inquiry Procedure Sends out an inquire, which is a request for nearby devices (within 10 meters) Devices that allow themselves to be discoverable issue an inq

9、uiry response Can take up to 10.24 seconds, after which the inquiring device should know everyone within 10 meters of itself,Device Discovery Illustrated,D,A,10 meters,H,M,N,L,P,O,Q,B,C,F,K,J,G,I,E,After inquiry procedure, A knows about others within range,Issues with Inquire Messages,Are the inquir

10、er transmitting and the receiver listening on the same frequency? Since they are not yet connected, they are on totally different hop sequences, and most likely on different channels If they are on the same frequency, what if they are on a noisy channel? Bluetooth provides the capability for receive

11、rs to issue multiple inquiry responses,Main Idea Behind Inquire,Inquiring device sends out an inquire on 16 different frequencies (16 channel train) Receiver (device in standby mode), performs an inquire scan long enough for an inquiring device to send the inquire on 16 frequencies Receiver does an

12、inquire scan frequent enough so that it is guaranteed to wake up during a 16 channel train,Inquiry Hop Train,The Numbers Behind Inquire,Each full scan of a 16 channel train takes about 1.28 seconds 16 channels * 625us * 128 trains = 1.28 seconds One full 16 channel train takes 10ms. Receiver enters

13、inquiry scan state at least once every 1.28 seconds, and stays in that state for 10ms.,What about noise?,Devices always reply to received inquiry messages with an inquiry response An inquirer is allowed to received multiple responses from one device In order to account for the fact that channels can

14、 be noisy and transmissions can get lost, the 128 train scan is repeated up to 4 times for each train (10.24 seconds) Designed to successfully communicate at least once with all devices within range,Inquiry,Uses 32 inquire channels to send out inquiry messages Send out inquiry on 32 channels, broken

15、 up into 2 inquiry hop trains (16 different channels to transmit packets) Intended to catch a device in inquiry scan mode on one of the 32 inquire channels,Inquiry Scan,A device periodically listens for inquiry packets at a single frequency chosen out of 16 frequencies Inquiry hop sequence depends o

16、n device address Stays in the state long enough for a inquiring device to cover 16 frequencies Will re-enter inquiry scan state even after responding to an inquire,Inquiry Response,When radio receives inquire, it will wait between 0 and .32 seconds before sending an FHS packet as a response This is

17、done to avoid collision with another radio that also wants to send an FHS packet FHS Packet contains: Device ID Clock After inquiring radio is done with inquiring procedure, it knows all of the radios (that are discoverable) within range,Paging: Will you connect to me?,Very similar to inquire Still

18、have not synchronized clocks or frequencies Establishes actual Piconet connection with a device that it knows about Connection process involves a 6 steps of communication between the the master and the slave,Paging Illustrated,D,E,F,H,G,I,K,J,C,M,N,L,P,O,Q,B,B,A,A,A,10 meters,Step 1: The Page Comman

19、d,Device broadcasts a page message out to the device that it wants to set up a connection with Does this in a similar manner as inquire messages (on 2 frequency trains of 16 frequencies each) Once the device receives a page response, it will stop paging and move on to step 2,Paging: Steps 2 & 3,Step

20、 2: In the page response, an acknowledgement is sent back to the master containing the slave ID Step 3: In the master response, the frequency hopping generator is stopped and the master issues an FHS packet to the slave,Paging: Step 4,The slave issues a final slave response transmission that is alig

21、ned to the slaves native clock Using the data from the FHS packet, the slave calculates adopts the masters frequency hopping pattern and synchronizes to its clock,Paging: Step 5,When the master receives the packet, it jumps back to its frequency hopping pattern and assigns the slave an Active Member

22、 Address (AMA) for the piconet Master sends out a poll packet to ensure that the slave is on its frequency hopping pattern,Paging: Step 6,Once the slave receives the poll packet, the slave replies with any kind of packet to ensure that it is on the right channel The acknowledgement must be received

23、by the Master within the timeout period At the conclusion of step 6, a new synchronized connection is established between the master and the slave,Link Manager,Performs all link creation, management, and termination operations Responsible for all the physical link resources in the system Handles the

24、 control and negotiation of packet sizes used when transmitting data Controls Operation Modes for devices in a piconet Sets up, terminates, and manages baseband connections between devices Establishes different types of links dependent on requests from the L2CAP layer Synchronous Connection-Oriented

25、 (SCO) Asynchronous Connection-Less (ACL),Asynchronous Connection-Less (ACL),Designed for data traffic Packet switched connection where data is exchanged sporadically as and when data is available from higher up the stack Data integrity is checked through error checking and retransmission One ACL li

26、nk between a master and a slave,Synchronous Connection Oriented (SCO),Intended for use with time-bounded information such as audio or video Provides a circuit-switched connection where data is regularly exchanged Retransmission is not necessary, since data is real-time Up to 3 SCO links per piconet,

27、ACL Links vs. SCO Links,ACL Setup Under LMP,Establishing Piconets,Whenever there is a connection between two Bluetooth devices, a piconet is formed Always 1 master and up to 7 active slaves Any Bluetooth device can be either a master or a slave Can be a master of one piconet and a slave of another p

28、iconet at the same time (scatternet) All devices have the same timing and frequency hopping sequence,Scatternets,Formed by two or more Piconets Master of one piconet can participate as a slave in another connected piconet No time or frequency synchronization between piconets,Link Manager Operation,D

29、evices operate in standby mode by default until they become connected to a piconet 4 Connection Modes Active Hold Park Sniff Modes allow devices to adjust power consumption, performance, and the number/role of participants in a piconet,Active Mode,Limited to 7 Active slaves for each master Three bit

30、 address (AM_ADDR) given to each active slave Unit actively participates on channel Can receive communications in any given frame Active slaves are polled by master for transmissions Unit operates on high-power,Hold Mode,Frees slave to Attend another Piconet Perform scanning, paging, or inquiry oper

31、ations Move into low-power sleep Unit keeps active member address Unit does not support ACL packets on the channel but may support SCO packets Master and slave agree on a one time hold duration after which the slave revives and synchronizes with channel traffic Unit operates on low-power,Sniff Mode,

32、Very similar to hold mode Slave is freed for reoccurring fixed time intervals Master can only communicate during arranged “sniff” time slots,Park Mode,Parked unit gives up active member address and is assigned 8 bit Parked member address (PM_ADDR) allows master to unpark slave 8 bit Access request a

33、ddress (AR_ADDR) allows slave to ask master to unpark it Unit stays synchronized to channel Operates in very low-power sleep,Park Mode (cont.),Provides the ability to connect more than 7 devices to a master (8 bit PM_ADDR allows 255 parked devices) Active and Parked slaves can be switched in and out

34、 to allow many connections to a single piconet,Park Mode (cont.),Master establishes a beacon channel and beacon interval when a slave is parked Parked slave wakes up at regular beacon interval to Maintain synchronization Listen for “broadcast” messages (packets with all zero AM_ADDR) Potentially mak

35、e access request to master through (AR_ADDR),Park Mode (cont.),Beacon slots must have at least “null” master-to-slave traffic Master-to-slave transmissions may extend over multiple beacon slots,Security,Link manager provides mechanism used by devices at either end of a link for Negotiating encryptio

36、n mode Coordinating encryption keys Baseband handles encryption and key generation,Host Controller Interface (HCI),Most Bluetooth systems consist of two processors: The higher layers of the protocol stack (L2CAP, SDP, RFCOMM) are run on the host devices processor The lower layers of the protocol sta

37、ck (Baseband and radio) are run on specific Bluetooth hardware HCI provides an interface between the higher and the lower layers of the protocol stack,HCI Flow Control,Main function of the Host Controller Interface Many times higher layer protocols have data rates much larger than data rate across B

38、luetooth radio and air interfaces Also need to handle the reverse situation when the host cannot accept data as fast as the Bluetooth module can send it,Two Pieces of HCI,Host controller resides on Bluetooth hardware accepting communications over the physical bus (radio and air) HCI Driver resides o

39、n the host accepting communications from higher layer protocols,The basic structure showing how the host controller layers are fitted into the protocol stack,RFCOMM,Cable replacement protocol allowing applications built to interface with serial port to function seamlessly with bluetooth Emulates ser

40、ial port over the L2CAP protocol by specifying how a data stream can be emulated RFCOMM actually handles parallel data,Emulating the Serial Port,Typically, the receive and transmit lines are connected to a UART (Universal Asynchronous Receiver Transmitter) Job of the UART is to convert between seria

41、l data sent down cables and the parallel data processing which devices use Since software that deals with serial ports view the data after it has been through UART, it only sees the parallel data RFCOMM protocol only works with parallel data by connecting to the lower layers via L2CAP,Service Discov

42、ery Protocol (SDP),Idea: Traditional LANs: Find a connection to a printer (or other resource) and keep that connection for a long time Bluetooth: Walk into an area, find a printer (or other resource), use it, then walk away forgetting any details of the connection,SDP Client/Server Model,SDP Server

43、is any Bluetooth device that offers services to other Bluetooth device (ex. Bluetooth-enabled printer, etc.) Each SDP Server maintains its own database that contains information about the services that it offers SDP Client is any Bluetooth device that uses the services offered by an SDP Server,SDP i

44、n the Bluetooth Protocol Stack,SDP Query,The SDP client queries an SDP server to find out what services are available Uses the L2CAP link that is set up between the client and the server L2CAP link provides information on services but doesnt handle any connection to services Need to specify a class

45、of services that the client wants to use (e.g. printing services),SDP Database,SDP Database is a set of records that describes the different services that the server can provide to another Bluetooth device When the SDP server gets a query, it looks up the service that the client is requesting and re

46、turns information to the client on how to connect to the service,Using the Services,The SDP client establishes a separate (non-SDP) connection to use the service SDP connection is only used to determine service availability The L2CAP connection uses to get information for the service can be dropped

47、(if no more services are needed) or retained (if the client still needs more services from the server),Logical Link Control and Application Protocol (L2CAP),Performs 4 major functions Managing the creation and termination of logical links for each connection through “channel” structures Enforcing an

48、d defining QoS requirements Adapting Data, for each connection, between application (APIs) and Bluetooth Baseband formats through Segmentation and Reassembly (SAR) Performing Multiplexing to support multiple concurrent connections over a single common radio interface (multiple apps. using link betwe

49、en two devices simultaneously),Segmentation/Reassembly,Baseband packet size is limited Can handle payload of 2745 bits L2CAP accepts packet size up to 64kb L2CAP segments large packets into smaller baseband manageable packets Smaller received baseband packets are reassembled coming back up the proto

50、col stack,Quality of Service,Applications may demand QoS on specific parameters Peak bandwidth Latency Delay variation Token rate Token bucket size L2CAP provides requested QoS if possible and notifies application if link can not support demands,Protocol Multiplexing,Applications may access L2CAP through different support protocols Service Discovery Protocol (SDP) RFCOMM Telephony Control Protocol Specification (TCS) Baseband is not concerned with operation protocols meaning L2CAP must distinguish between them,