wireless lans (cont) bluetooth. what is bluetooth? personal ad-hoc networks cable replacement...
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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