cmpe 257 - wireless and mobile networking 1 cmpe 257 spring 2006 bluetooth wireless and mobile...

1CMPE 257 - Wireless and Mobile Networking

CMPE 257

Spring 2006Bluetooth

Wireless and Mobile Networks


Announcements

• Access to QualNet.– Two options:

• Get a CD from the helpdesk (BE 240).– Contains license and necessary instructions.

• Or, remote access via ssh.


Today

• Bluetooth.


Bluetooth


Overview

• Cable replacement technology.– Connect devices such as phone handsets,

headsets, computer peripherals, etc.

• Industry standard.– Allows wireless communication between

devices.


Applications: Cable Replacement

1 Mb/s.• Range ~10 meters.• PANs• Single chip radio.

– Low power & low cost.

Why not use Wireless LANs?- power- cost


Applications: Synchronization

• Automatic synchronization of calendars, address books, business cards.


Applications: Cordless Headset

• Multiple device access.

• Hands-free operation.

Cordlessheadset


More applications…

• Conference table.• Cordless computer.• Instant photo transmission.• Cordless phone.


Bluetooth Origins• Study by Ericsson Mobile Communications in

1994.– Alternatives to cables connecting mobile

phones to accessories.– Use of radio links instead of infrared.

• Why?– Transmission of data and voice.

• Result: Bluetooth spec.– Named after Harald Blatand (Danish for

Bluetooth).– 10th century Viking king who united Denmark

and Norway.


Bluetooth SIG History

• Early 1998: Bluetooth SIG is formed.– Promoter company group: Ericsson, IBM,

Intel, Nokia, Toshiba.

– Goal: develop license-free technology for universal wireless connectivity.

– Target: handheld market.

– Bluetooth spec: defines RF wireless communication interface and protocols.


Bluetooth SIG History

• May 1998: Public announcement of Bluetooth SIG.• July 1999: 1.0A spec (>1,500 pages) published.• December 1999: version 1.0B released.• December 1999: promoters increases to 9.

– 3Com, Lucent, Microsoft, Motorola• February 2000: 1,800+ adopters.• February 2001: version 1.1 out.


More History…

• Recently, IEEE 803.15.1 standard for Wireless PANs (WPANs)– Only MAC and PHY.


Goals• Open spec.• Low cost.

– In order to replace cables, should have similar cost.

– Cell phone cable is ~ $10.

• Power efficiency.• Lightweight and small form factor.• Easy to use.• Reliable and resilient to failures.


The Bluetooth Standard

• Defines a protocol stack to enable heterogeneous devices to communicate.

• The Bluetooth stack includes protocols for the radio layer all the way up to device discovery, service discovery, etc.


Bluetooth Protocol Stack

RF

Baseband

Link Manager

L2CAP

RFCOMM/SDP

Applications

Link Controller

Host Controller Interface

PHY

Data Link Layer

Network Layer

Transport Layer

Session LayerPresentation Layer

Application

OSI/ISO


Bluetooth Layers

• Radio: physically transmits/receives data.• Baseband/Link Controller: controls PHY.• Link Manager: controls links to other devices.• Host Controller:e2e communication. • Logical Link Control:

multiplexes/demultiplexes data from higher layers.

• RFCOMM: RS323-like serial interface.• SDP: allows service discovery among

Bluetooth devices.


The Bluetooth PHY


Radio Band

• 2.4 GHz license-free ISM band.• Available worldwide.• Industrial, Scientific, Medical (ISM) band.

– Unlicensed, globally available.

– Centered around 2.4 GHz.

• Resilient to interference.• Frequency hopping.• Range: 10, 20, and 100m.• 1MB/s.


Unlicensed Radio Spectrum

902 Mhz

928 Mhz

26 Mhz 83.5 Mhz 125 Mhz

2.4 Ghz

2.4835 Ghz5.725 Ghz

5.785 Ghz

cordless phonesbaby monitorsWireless LANs

802.11BluetoothMicrowave oven

unused

33cm 12cm 5cm


Bluetooth Radio Link

• MA scheme: Frequency hopping spread spectrum.– 2.402 GHz + k MHz, k=0, …, 78– 1,600 hops per second.– 1 Mb/s data rate.

. . .

1Mhz

1 2 3 79

83.5 Mhz


BT Radio Link (Cont’d)

• Time-division duplex (TDD)– Separation of Xmission and reception in time.– Units alternate transmits and receives.

• Gaussian Frequency Shift Keying (G-FSK) modulation.– ‘1’s as positive frequency deviations from

carrier frequency; ‘0’s as negative deviations.


Multiple Access

• BT targets large number of independent communications active in the same area at the same time.

• Single FH channel: 1 Mb/s.• Each 1Mb/s channel shared by limited number of

participants.– In target user scenarios, it’s unlikely that all units in-

range will share data among all of them.– 1 MB/s is reasonable. (is it?)

• Theoretically, total bandwidth is 79 Mb/s.– In practice, < 79 Mb/s since codes are non-orthogonal.


Baseband

Carries out MACfunctions.

RF

Baseband

Link Manager

L2CAP

RFCOMM/SDP

Applications

Link Controller


Control end of baseband+link controller=Data link layer


Master and Slaves

• Communicating devices must agree on hopping sequence.

• BT devices can operate as masters or slaves.• Master node defines sequence to be used.• Slave units use master id to pick sequence.• Master also controls when devices are

allowed to transmit.– Master allocates slots to slaves.– Allocates total available bandwidth among

slaves.


Piconets

• BT communication takes place over piconets.• Piconet formation initiated by master.• All other participants are slaves.• Number of participants limited to 8 (1 master and 7

slaves).– Channel capacity and addressing overhead.– Each slave assigned a locally unique ID.

• Master/slave roles last for the duration of the piconet.


More on Piconets

• On a piconet, slaves only have direct links to master.

• Point-to-point or point-to-multipoint connections.


Piconets: Considerations

• Most target applications involve local communication among small group of devices.

• Piconets with up to 8 nodes match well.• If many groups of devices active

simultaneously, each group as separate piconet.

• Overlapping piconets can coexist.


Contention-Free MA

• Master and slaves.• Master performs medium access control.

– Schedules traffic through polling.• Time slots alternate between master and slave

transmission.– Master-slave: master includes slave address.– Slave-master: only slave chosen by master in previous

master-slave slot allowed to transmit.– If master has data to send to a slave, slave polled

implicitly; otherwise, explicit poll.


BT States

Standby

Inquiry Page

Transmit Connected

Park Hold Sniff

Unconnected

Connecting

Active

Low power

. Initially, all nodes in standby.. Node (master) can begininquiry to find nearbydevices.. Piconet is then formed.. Devices join by paging.


Inquiry

• Device discovery• Listeners respond with

their address.


PagingMaster

Active Slave

Parked Slave

Standby

• Device enters paging to invite others to join its piconet.

• Establishes links with nodes in proximity.• Paging message unicast to selected receiver.• Receiver sends ACK.• Sender becomes master, receiver slave.


Piconet New Node Admission

• Master can actively try to discover new nodes or wait (in scan/listen mode) to be discovered.

• Communication in the current piconet suspended.

• Admission latency versus piconet capacity tradeoff.


Bluetooth Link Formation

• Point-to-point link:– Master-slave relationship. m s

ss

m

s

• Piconet:– 8 units: channel capacity.– Master (establishes piconet) can connect to up to 7 slaves.– Master/slave relationship lasts while link/piconet lasts.– No slave-to-slave communication.


Link Types

• 2 types of links:– Synchronous (SCO) links:

• Point-to-point between master and slave.• Link established by reserving slots in either direction

periodically.• Used to carry real-time traffic (voice).

– Asynchronous (ACL) links:• Point-to-multipoint between master and slaves.• Use remaining slots on channel.• Traffic scheduled by master.


Error Control

• Supports both FEC and retransmission.• FEC for SCO packets.• ARQ for ACL traffic.

– If no ACKs, retransmit.

– Stop-and-wait ARQ.• Fast-ARQ: ACK included in RX slot

immediately following the TX slot in which packet was sent.

– CRC to check for errors.


Packet Format

72 bits 54 bits 0 - 2744 bitsAccess code

Header Payload

DataVoice CRCNo CRCNo retries

625 µs

master

slave

header

ARQFEC (optional)

FEC (optional)


Access Code

• Address of piconet master.

Access code

Header Payload

72 bits


Packet Header

• Addressing (3)• Packet type (4)• Flow control (1)• 1-bit ARQ (1)• Sequencing (1)• HEC (8)

Access code

Header Payload

54 bits

Purpose

Broadcast packets are not ACKed

For filtering retransmitted packets

18 bitstotal

ss

m

s

16 packet types (some unused)

Max 7 active slaves

Verify header integrity


Multiple Piconets

• Piconets may overlap in space and time.• They can work independently.

– Each with its own hopping sequence.

– Packets with different access codes.

• Or they can overlap, i.e., nodes can participate in more than 1 piconet.– “Time sharing”.


Scatternets

• Interconnection of multiple piconets.

Master

Slave


Scatternets (cont’d…)

• Interconnection by bridge nodes.– Bridge nodes are members of piconets they

interconnect.– Bridge node “stay” in a piconet for some time,

then switch to another piconet by changing hop sequence.

– Do this for all member piconets.– Send and receive in each piconet.– Forward from one piconet to another.


Link Controller and Link Manager

RF

Baseband

Link Manager

L2CAP

RFCOMM/SDP

Applications

Link Controller


Carries out inquiry and paging operations; manages multiple links and different piconets.

Attaching/detaching slaves frompiconet; power management; security.


Power Management

• Low-power modes: prolong battery life.– Devices can be turned-off when idle.

– Devices wake up periodically to send/receive data.


Low-Power Operation• 3 modes:

– Hold: node sleeps for specified interval.• Master can put slaves in hold while searching for new

members, attending another piconet, etc.• No ACL packets.

– Sniff: slave low-duty cycle mode.• Slave wakes up periodically to talk to master.• Fixed “sniff” intervals.

– Park: • Very low power state.• Used to admit more than 7 slaves in piconet.

– Slave gives up its active member address.– Receives “parked” member address.

• Wakes up periodically listening for broadcasts which can be used to “unpark” node.


Security

• Authentication and encryption.• LMP provides mechanisms for negotiation of

encryption modes, keys, etc.



RF

Baseband

Link Manager

L2CAP

RFCOMM/SDP

Applications

Link Controller


Optional interface layerbetween higher and lower layers of the BT stack.

E.g., when lower- and higherBT layers run on different Devices: PCMCIA card and PC’s processor.


L2CAP

Logical Link Control andAdaptation Protocol=

Session Layer.

L2CAP provides• Protocol multiplexing• Quality of service negotiationRF

Baseband

Link Manager

L2CAP

RFCOMM/SDP

Applications

Link Controller



RFCOMM/SDP

RF

Baseband

Link Manager

L2CAP

RFCOMM/SDP

Applications

Link Controller

Host Controller InterfaceService discovery, serial port interface.


References:

• Bluetooth papers in reading list.• Johansson and Gerla’s Bluetooth Tutorial at

Mobicom 2001.• Bluetooth 1.1: Connect Without Cables, Bray

and Sturman.


Features Cost20 dBm (~100 m)

Point-to-multipoint

No Scatternet

ApplicationsFile Transfer,

Dial-Up Networking

LAN access, Fax, …

169 $

---

200 $

0 dBm (~10 m)

Point-to-multipoint

No Scatternet

File Transfer,

Dial-Up Networking

LAN access, Fax, …169 $

---

CompanyToshiba,

Motorola,

Digianswer

IBM, TDK

3COM

10 m user-user;

100 m user-Base Station

Point-to-multipoint

SW- & FW-upgradeable

File Transfer,

Dial-Up Networking

LAN access, Fax, E-mail

Unconscious connection

149 $

Nokia

10 m user-user;

Point-to-point

Connectivity Battery

for the cell phone

File Transfer,

Dial-Up Networking

LAN access, Fax, E-mail

Unconscious connection

149 $

Ericsson,

Sigma

10 m user-user;

Point-to-point;

ARM processor;

USB; RFCOMM ports

Basic BT Radio stack

Embedded or Host stack

Programmable

500 $

1500$

Bluetooth on the market:Bluetooth on the market:PC cards, Cell phones, Head sets, Chip sets,…

cmpe 257 - wireless and mobile networking 1 cmpe 257 spring 2006 bluetooth wireless and mobile...

Documents

bluetooth wireless

mobile networking

bluetooth slide

wireless lans

mobile networks

mobile phones

bluetooth stack

bluetooth standard