Communication Switching Techniques

UNIT 5

P.M.Arun Kumar,Assistant Professor,

Department of IT,Sri Krishna College of Engineering and

Technology,Coimbatore.

Bluetooth Techniques

References

1. Wireless communication and networks –william stallings, Pearson education,2005

OverviewUniversal short-range wireless capabilityUses 2.4-GHz bandAvailable globally for unlicensed usersDevices within 10 m can share up to 720 kbps of capacitySupports open-ended list of applications

Data, audio, graphics, video

Bluetooth Application AreasData and voice access points

Real-time voice and data transmissionsCable replacement

Eliminates need for numerous cable attachments for connection

Ad hoc networkingDevice with Bluetooth radio can establish connection with another when in range

Bluetooth Standards DocumentsCore specifications

Details of various layers of Bluetooth protocol architecture

Profile specificationsUse of Bluetooth technology to support various applications

Protocol ArchitectureBluetooth is a layered protocol architecture

Core protocolsCable replacement and telephony control protocolsAdopted protocols

Core protocolsRadioBasebandLink manager protocol (LMP)Logical link control and adaptation protocol (L2CAP)Service discovery protocol (SDP)

Protocol ArchitectureCable replacement protocol

RFCOMMTelephony control protocol

Telephony control specification – binary (TCS BIN)Adopted protocols

PPPTCP/UDP/IPOBEXWAE/WAP

Bluetooth Protocol Stack

Usage ModelsFile transferInternet bridgeLAN accessSynchronizationThree-in-one phoneHeadset

Piconets and ScatternetsPiconet

Basic unit of Bluetooth networkingMaster and one to seven slave devicesMaster determines channel and phase

ScatternetDevice in one piconet may exist as master or slave in another piconetAllows many devices to share same areaMakes efficient use of bandwidth

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Master/Slave Relationships

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Wireless Network Configurations

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Wireless Network Configurations

Radio SpecificationClasses of transmitters

Class 1: Outputs 100 mW for maximum rangePower control mandatoryProvides greatest distance

Class 2: Outputs 2.4 mW at maximumPower control optional

Class 3: Nominal output is 1 mWLowest power

Baseband Specification

Frequency Hopping in BluetoothProvides resistance to interference and multipath effectsProvides a form of multiple access among co-located devices in different piconets

Frequency HoppingTotal bandwidth divided into 1MHz physical channelsFH occurs by jumping from one channel to another in pseudorandom sequenceHopping sequence shared with all devices on piconetPiconet access:

Bluetooth devices use time division duplex (TDD)Access technique is TDMAFH-TDD-TDMA

Frequency Hopping

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Baseband Specification (cont)

Physical Links between Master and Slave

Synchronous connection oriented (SCO)Allocates fixed bandwidth between point-to-point connection of master and slaveMaster maintains link using reserved slotsMaster can support three simultaneous links

Asynchronous connectionless (ACL)Point-to-multipoint link between master and all slavesOnly single ACL link can exist

Bluetooth Packet FieldsAccess code – used for timing synchronization, offset compensation, paging, and inquiryHeader – used to identify packet type and carry protocol control informationPayload – contains user voice or data and payload header, if present

Types of Access CodesChannel access code (CAC) – identifies a piconetDevice access code (DAC) – used for paging and subsequent responsesInquiry access code (IAC) – used for inquiry purposes

Access CodePreamble – used for DC compensation

0101 if LSB of sync word is 01010 if LSB of synch word is 1

Sync word – 64-bits, derived from:7-bit Barker sequenceLower address part (LAP)Pseudonoise (PN) sequence

Trailer0101 if MSB of sync word is 11010 if MSB of sync word is 0

Packet Header FieldsAM_ADDR – contains “active mode” address of one of the slavesType – identifies type of packetFlow – 1-bit flow controlARQN – 1-bit acknowledgmentSEQN – 1-bit sequential numbering schemesHeader error control (HEC) – 8-bit error detection code

Payload Format Payload header

L_CH field – identifies logical channelFlow field – used to control flow at L2CAP levelLength field – number of bytes of data

Payload body – contains user dataCRC – 16-bit CRC code

Error Correction Schemes1/3 rate FEC (forward error correction)

Used on 18-bit packet header, voice field in HV1 packet

2/3 rate FECUsed in DM packets, data fields of DV packet, FHS packet and HV2 packet

ARQUsed with DM and DH packets

ARQ Scheme ElementsError detection – destination detects errors, discards packetsPositive acknowledgment – destination returns positive acknowledgmentRetransmission after timeout – source retransmits if packet unacknowledgedNegative acknowledgment and retransmission –destination returns negative acknowledgement for packets with errors, source retransmits

Logical ChannelsLink control (LC)Link manager (LM)User asynchronous (UA)User isochronous (UI)Use synchronous (US)

Channel ControlStates of operation of a piconet during link establishment and maintenanceMajor states

Standby – default stateConnection – device connected

Channel ControlInterim substates for adding new slaves

Page – device issued a page (used by master)Page scan – device is listening for a pageMaster response – master receives a page response from slaveSlave response – slave responds to a page from masterInquiry – device has issued an inquiry for identity of devices within rangeInquiry scan – device is listening for an inquiryInquiry response – device receives an inquiry response

State Transition Diagram

Inquiry ProcedurePotential master identifies devices in range that wish to participate

Transmits ID packet with inquiry access code (IAC)Occurs in Inquiry state

Device receives inquiryEnter Inquiry Response stateReturns FHS packet with address and timing informationMoves to page scan state

Page ProcedureMaster uses devices address to calculate a page frequency-hopping sequenceMaster pages with ID packet and device access code (DAC) of specific slaveSlave responds with DAC ID packetMaster responds with its FHS packetSlave confirms receipt with DAC IDSlaves moves to Connection state

Slave Connection State ModesActive – participates in piconet

Listens, transmits and receives packetsSniff – only listens on specified slotsHold – does not support ACL packets

Reduced power statusMay still participate in SCO exchanges

Park – does not participate on piconetStill retained as part of piconet

Bluetooth AudioVoice encoding schemes:

Pulse code modulation (PCM) Continuously variable slope delta (CVSD) modulation

LINK MANAGER SPECIFICATION

LMP manages various aspects of the radio link between a master and slave

the protocol involves the exchange of messages in the form of LMP PDUs(protocol data units)

LMP PDUsGeneral responseSecurity Service

AuthenticationPairingChange link keyChange current link keyEncryption

LMP PDUsTime/synchronization

Clock offset requestSlot offset informationTiming accuracy information request

Station capabilityLMP versionSupported features

LMP PDUsMode control

Switch master/slave roleName requestDetachHold modeSniff modePark modePower control

LMP PDUsMode control (cont.)

Channel quality-driven change between DM and DHQuality of serviceControl of multislot packetsPaging schemeLink supervision

Logical link control and adaptation protocol L2CAP

Provides a link-layer protocol between entities with a number of servicesRelies on lower layer for flow and error controlMakes use of ACL links, does not support SCO linksProvides two alternative services to upper-layer protocols

Connectionless serviceConnection-mode service

L2CAP Logical ChannelsConnectionless

Supports connectionless serviceEach channel is unidirectionalUsed from master to multiple slaves

Connection-orientedSupports connection-oriented serviceEach channel is bidirectional

SignalingProvides for exchange of signaling messages between L2CAP entities

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L2CAP

L2CAP Packet Fields for Connectionless Service

Length – length of information payload, PSM fieldsChannel ID – 2, indicating connectionless channelProtocol/service multiplexer (PSM) – identifies higher-layer recipient for payload

Not included in connection-oriented packets

Information payload – higher-layer user data

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L2CAP Formats

Signaling Packet PayloadConsists of one or more L2CAP commands, each with four fields

Code – identifies type of commandIdentifier – used to match request with replyLength – length of data field for this commandData – additional data for command, if necessary

L2CAP Signaling Command Codes

L2CAP Signaling CommandsCommand reject command

Sent to reject any commandConnection commands

Used to establish new connectionsConfigure commands

Used to establish a logical link transmission contract between two L2CAP entities

L2CAP Signaling CommandsDisconnection commands

Used to terminate logical channelEcho commands

Used to solicit response from remote L2CAP entity

Information commandsUsed to solicit implementation-specific information from remote L2CAP entity

Flow Specification ParametersService typeToken rate (bytes/second)Token bucket size (bytes)Peak bandwidth (bytes/second)Latency (microseconds)Delay variation (microseconds)

References

1. Wireless communication and networks –william stallings, Pearson education,2005