Wireless LANs (cont)

Bluetooth

What Is Bluetooth?

Personal Ad-hoc Personal Ad-hoc NetworksNetworks

Cable Cable ReplacementReplacement

Landline

Data/Voice Data/Voice Access PointsAccess Points

Example...

Some Bluetooth Facts….• 2.4 GHz ISM Open band

– Globally free available frequency, 89 MHz of spectrum available

– FHSS radio (1600 hops/s and 79 frequencies)

• 10 -100 m range– 8 active devices per piconet (share datarate)

– Up to 10 piconets in bubble (full datarate)

• 1 Mbps gross rate

• Simultaneous voice/data capable– 432 Kbps (full duplex), 721/56 Kbps (asymmetric)or– 3 simultaneous full duplex voice channels per piconetor– a combination of data and voice

Network Topology – Piconet

master

slave 1

slave 2

slave 3

• Piconets created ad-hoc• Master-Slave concept

• Piconet defined by itsfrequency hopping sequence

UnconnectedStandby

ConnectingStates

ActiveStates

Low PowerModes

Piconet establishment

• Ad-hoc setup

• Connection oriented

• Power save modes

active slave

master

parked slavestandby

connectingslaves

The piconet

ID a

P

M Sor

sb

A

D

C

B

E

ID b

ID a

ID c

ID d

ID e

M

P

S

S

sb

ID a

ID c

ID d

ID a

IDa

IDa

ID e

ID b

• All devices in a piconet hop together– To form a piconet: master gives slaves its clock and device ID

• Hopping pattern determined by device ID (48-bit)

• Phase in hopping pattern determined by Clock

• Non-piconet devices are in standby• Piconet Addressing

– Active Member Address (AMA, 3-bits)

– Parked Member Address (PMA, 8-bits)

FH/TDD Channel

One slot: 625 s

t

t

master

slave

f(k) f(k+1) f(k+2)

One frame: 1250 s

access codepacket header payload

72 54 0-2745

Packet Format

Packet Types

72 bits 54bits 0-2475 bits Bluetooth Packet

• Bluetooth Protocol supports 16 packet types, 15 types defined4 Control packets common to both links

POLL,NULL,FHS and ID4 SCO packets used to carry voice with different payload lengths.

HV1,HV2,HV3 and DV, where DV carries both voice and data 7 ACL packets with different payload lengths

DM1,DM3,DM5,DH1,DH3,DH5 and AUX1 Carries data only

Access code Header Payload

Multi-slot Packets

f(k)

625 s

f(k+1) f(k+2) f(k+3) f(k+4)

f(k+3) f(k+4)f(k)

f(k)

f(k+5)

f(k+5)

f(k+5)

Error handling

• Forward-error correction (FEC)– headers are protected with 1/3 rate FEC and 8 bit CRC (HEC)– payloads may be FEC protected

• 1/3 rate: simple bit repetition (SCO packets only)• 2/3 rate: (10,15) shortened Hamming code• 3/3 rate: no FEC

• ARQ (ACL packets only)– 16-bit CRC (CRC-CCITT) & 1-bit ACK/NACK– 1-bit sequence number

access code header payload

72bits 54bits 0-2745bits

Physical Link Definition

• Synchronous Connection-Oriented (SCO) Link

– circuit switching

– symmetric, synchronous services

– slot reservation at fixed intervals

• Asynchronous Connection-Less (ACL) Link– packet switching

– (a)symmetric, asynchronous services

– polling access scheme

Mixed Link Example

MASTER

SLAVE 1

SLAVE 2

SLAVE 3

ACL ACLSCO SCO SCO SCO ACLACL

Data Rates (kb/s)

DM1

DH1

DM3

DH3

DM5

DH5

108.8

172.8

256.0

384.0

286.7

432.6

108.8

172.8

384.0

576.0

477.8

721.0

108.8

172.8

54.4

86.4

36.3

57.6

TYPE symmetric asymmetric

printer

laptop

laptop

mouse

mobile phone

headset

LANaccess point

printer

laptop

laptop

mouse

mobile phone

headset

access point

slave

master

master/slave

Multiple Piconets: A Scatternet

slave

master

master/slave

Multiple Piconets: A Scatternet

masterslave 1

slave 2

slave 3

masterslave 4 slave 5

(MANET) IP Hosts(MANET) IP Hosts

BluetoothBluetooth

Link and BasebandLink and Baseband

LayerLayer

Ad-hoc IP networking on Bluetooth

• Scatternet - A device present in more than one piconet– How to jump efficiently between piconets?– Delay sensitive applications?

– Things happening in “sleeping” piconets?

Some issues….

LANaccess point

Scatternet Forming/Reforming

• “Optimal” scatternet configuration depends on– Connectivity and Node density

– Traffic Distribution (Traffic matrix)

– Mobility&Traffic dynamics - steady state ever reached?

– Integration of connection establishment and (ad-hoc) routing?

At t... At t+t.

”Work” your Bluetooth Network

• Bluetooth handles overlaid Piconets well• Overall capacity gained by setting up new piconets

s

s

s

sm

s s

ss

m

s

sm

m

s

s

Smart Scatternet...

• Move out large slave to slave traffic• Still part of old piconet - a scatternet

s

s

s

sm

s s

ss

s

m

s

s

sms

ss

S-M 10 % of trafficS-S 90 % of traffic

P1 P1

P2S-M 55 % of trafficS-S 45 % of traffic

ss

Ad-hoc networking

master

slave 1

slave 2

slave 3

masterslave 4 slave 5

Bluetooth

IPIP

L2L2(Broadcast (Broadcast segment)segment)

Piconet scheduling

• Intra-piconet scheduling– Master controlled polling

algorithm

– Round Robin?

• Inter-piconet scheduling– One transceiver

– Different FHS

master

slave 1

slave 2

slave 3

1 2 3 1 2 3

1 2 3 1 2 3

4 4

slave 3 master

slave 4

Inter-piconet Timing

• Interpiconet communication may be “costly”

• An interpiconet unit active in only one piconet at a time

• SNIFF Mode - Periodic presence in each piconet

s

s

s

m1

ss

P1s

s

s

s

s

P2

A m2

P2

P1

INQUIRY Scan/PAGE Scan

SNIFF Mode

• SNIFF Parameters– Tsniff

– max(Nsniffattempt, Nsnifftimeout) = Wsniff

• Approximately one frame lost per “Piconet switch”

• Trade off: Delay vs. Throughput

– Delay: Tsniff

– Throughput:

TsniffP1

TsniffP2

WsniffP2

P2

P1

WsniffP2

) W(1

W

sniff

sniff

Bluetooth Experiments Gerla, M et al, Tyrrenia Conf, sept 2000

• Experiment #!: TCP throughput in a single piconet. Throughput versus the no. of TCP connections. Each TCP connection starts from a different slave on the common piconet, and goes through the access point (BT master).

• Experiment #2: TCP throughput when multiple piconets are used in parallel. Each piconet here supports a separate TCP connection.

• Experiment #3: TCP and IP Telephony in a multiple piconet configuration. IP Telephony uses ACL channel. Question: can TCP and Telephony coexist?

S

LAN

IP backbone

M1

IP router

M2 M3

LAN

IP backbone

IP router

M1 M2 M3

S 1

S 2

S 3

M3

IP backbone

M2

M1

LAN

IP router

S

(a) (b) (c)Fig. 4.

Exp # 1:TCP throughput in Bluetooth (single piconet)

Bluetooth - Single Piconet

0.687

0.688

0.689

0.69

0.691

0.692

0.693

0.694

1 2 3 4 5 6 7

No. Of TCP Connections

Tota

l TC

P T

hrou

ghpu

t (M

bps)

Bluetooth

Exp #2:TCP Throughput in WaveLAN vs BT (multiple piconets)

Bluetooth vs WaveLan

0

1

2

3

4

5

6

7

1 2 3 4 5 6 7 8 9 10

No. of TCP connections

Tota

l TC

P T

hrou

ghpu

t (M

bps) Bluetooth

WaveLan

Exp #2 (cont): Throughput of TCP flows

Throughput of Individual TCP flows

0

0.2

0.4

0.6

0.8

1

1.2

1 2 3 4 5 6 7 8 9 10

Flow Number --->

Thro

ughp

ut (M

bps)

--->

WaveLan

Bluetooth

TCP and IP Telephony

• Voice carried on the ACL channel• Four piconets• In each piconet: 1 TCP and 6 Voice connections• TCP connections “always on” (file transfers)• Voice: ON-OFF model; 8Kbps coding rate• Voice packets: 20ms packetization -> 20 bytes• With header overhead: voice pkt = 30 bytes

Exp #3: Bluetooth; TCP + VoIP

IP Telephony Delay Distribution

0

0.02

0.04

0.06

0.08

0.1

Delay (ms)--->

Frac

tion

of P

kts-

-->

Exp #3: Bluetooth; TCP + VoIP

IP Telephony Complementary Cumulative Distribution

00.10.20.30.40.50.60.70.80.9

1

2 6 10 14 18 22 24 28 32 36 40 60

Delay (ms) --->

Fra

ctio

n o

f P

kts

--->

Exp #3: WaveLan 802.11: TCP + VoIP

IP Telephony Delay Distribution

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

Delay (ms) --->

Frac

tion

of P

kts

--->

Exp #3: WaveLan 802.11: TCP + VoIP

IP Telephony Complementary Cumulative Delay Distribution

00.10.20.30.40.5

0.60.70.80.9

1

Delay (ms) --->

Frac

tion

of P

kts

--->

With 750 ms playout buffer, 5% packets lost

Simulation: what have we learned?

• Bluetooth performance predictable, dependable• Fair sharing across TCP connections (IEEE 802.11 is

unfair, “capture”- prone)• BT aggregate throughput exceeds IEEE 802.11• BT supports voice well even in heavy TCP load (IEEE

802.11 cannot deliver voice with TCP load)• BT not overly sensitive to microwave ovens

Future work• BT load sensitive polling schedule• BT in low latency applications (sensors on walls)• BT scatternets (formation, schedules, routing etc) • BT vs UMTS comparison

Bluetooth SIG2 - PAN WG

• Personal Area Network• Ad-hoc Bluetooth work groups• QoS support (audio/video)• Possibly: “associated” members

– opens up for academia

– research oriented work

Bluetooth Program Update

• Final Specification published Monday 7/26/99– Result of work from ~200 engineers– Updated Specification 1.0 B published 12/1/99

• SIG Membership Exceeds 1,700 Companies!– Becoming the choice for wireless connectivity– Membership list at www.bluetooth.com

• Program on Track for Products in 2000– Products announced– Next step is Qualification Program

• Specification is basis for the proposed IEEE 802.15.1 standard

PAN Impact on Internet Access for Mobile Devices

• PAN allows sharing of “gateway” device– E.g., Only one cellular “modem” needed

– E.g., Only one ADSL connection needed

• PAN allows sharing of access “tariff”– All personal devices share same account

• Allows multiple combinations of wireless and wired technology for Internet access with one or two communication interfaces

PAN to Cellular Data Network

• Available today using cables or IR• 2nd generation cellular better than analog• Cost and speed are still issues• RF value add is wireless connectivity without “line

of sight” limitations• Also allows “unconscious” data reception

PAN to WWAN

PAN to Wired Infrastructure

• Wireless “last hop” to the Internet

• Public kiosks provide alternative to wireless wide-area networks

PSTN, ISDN,PSTN, ISDN,HomePNA, xDSLHomePNA, xDSL

PAN to LAN/WAN

Summary

• Bluetooth is a radio system (not a radio)– Building block for personal area networks

– More information available at:

http://www.bluetooth.com• PAN will improve the cost and convenience of

achieving mobile Internet access