Reversing the Collision Avoidance Handshake in Wireless Networks
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Transcript of Reversing the Collision Avoidance Handshake in Wireless Networks
Reversing the Collision Avoidance Handshakein Wireless Networks
J.J. Garcia-Luna-Aceves and Makis Tzamaloukas (jj,[email protected])
Computer and Communications Research Group (CCRG)http://www.cse.ucsc.edu/research/ccrg
Computer Engineering DepartmentJack Baskin School of Engineering
University of CaliforniaSanta Cruz, CA 95064
MobiCom '99, 15-20 August
JJ. Garcia-Luna-Aceves and A. Tzamaloukas
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Presentation Outline
Sender-Initiated Collision Avoidance Protocols Motivation Polling Issues Correct Collision Avoidance RIMA protocols Throughput and Delay Analysis Conclusions
MobiCom '99, 15-20 August
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Sender-Initiated Protocols
SRMA (Kleinrock and Tobagi, August ‘76) MACA (Karn, April ‘90) MACAW (Bharghavan, Demers, Shenker
and Zhang, August ‘94) FAMA (Garcia-Luna-Aceves and Fullmer,
September ‘97) IEEE 802.11 (July ‘97)
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Motivation
The recipient of data packet is the point of interest Recast the collision avoidance dialogues so that the receiver,
sender or both can have control of the dialogue Provide equal or better throughput than any sender-initiated
IEEE 802.11-like MAC protocol Be applicable to multi-channel frequency-hopping or direct-
sequence spread-spectrum radios To date no receiver-initiated MAC protocol ensures correct
collision avoidance The receivers poll the senders
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Ensuring Correct Collision Avoidance
First receiver-initiated MAC protocol was MACA-BI (Talucci and Gerla):– a node sends a DATA packet if it has
previously received an RTR– a polled node can send a DATA packet either to
the polling node or to any other neighbor– does not guarantee correct floor acquisition
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Ensuring Correct Collision Avoidance
At time t0, nodes a and d send RTRs to b and e; at time t1 both b and e send DATA to c resulting in a collision
a b c
d
e
t0 RTR to b RTR to e
DATA to ct1 DATA to c
MobiCom '99, 15-20 August
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Ensuring Correct Collision Avoidance
At time t0, node a sends an RTR to b; at time t1, b sends DATA to a; at time t2 < t1 + , c sends an RTR to d; at time t3, d sends DATA to c; if data packets last longer than + 3 the DATA from b and d collide at c
a b c d
t0 RTR
RTR
DATAt1
DATA
t2
t3
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Ensuring Correct Collision Avoidance
With RIMA-SP correct floor acquisition is guaranteed:– the polled node transmits a DATA packet only to the polling node– a collision avoidance period of seconds is required at a polled node prior to answering an RTR; we have shown that =
– an additional control signal is introduced; we call this signal No-Transmission-Request (NTR)
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RIMA-SP illustrated
RTR
RTR
RTR
RTR ZX
RTR
X Zdata
RTR
RTR
RTRRTR
ZX
RTR
X Z
BACKOFF
RTR
RTR
RTR
RTR ZX
RTR
NTR
NTR
NTR
NTR ZX
NTR
RTR
data
Successful handshake
Colliding RTRs
Hidden node interference
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RIMA-SP timing diagrams
RTRWaiting period
DATAX
Z
RTR NTR BACKOFFX
Z interference
RTR
RTR
collision
X
Z
channel BACKOFF
Node X sends an RTR and after seconds receives a DATA packet
Nodes X and Z send RTRs within seconds and therefore a collision occurs
Due to interference from node Z, nodeX sends an NTR to stop the handshake
Noise detected at Z
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Polling Issues
When to poll: whether or not the polling rate is independent of the data rate at polling nodes– independent polling– data driven polling
To whom: whether the poll is sent to a particular neighbor or to all neighbors; for dense networks a schedule must be provided to the poll recipients
How: whether the polling packet asks for permission to transmit as well
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RIMA Protocols
Polling done with RTR (Request-To-Receive) packet Three Receiver Initiated Medium Access (RIMA) protocols
defined based on the type of polling:– RIMA-SP: A simple poll receiver initiated protocol
(only the receiver sends data in a successful busy period)– RIMA-DP: A dual poll receiver initiated protocol (2
data packets are sent in the same successful busy period)– RIMA-BP: A broadcast poll receiver initiated protocol
(the RTR is sent to everybody)
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RIMA-DP illustrated
RTR
RTR
RTR
RTRZX
RTR
X ZCTS
data
data
data
dataZX
data
RTR
RTR
RTR
RTR ZX
RTR
X Zdata
data
data
data
data ZX
data
RTR
RTR
RTR
RTRZX
RTR
X Z
BACKOFF
RTR
RTR
RTR
RTR
RTRZX
RTR
NTR
NTR
NTR
NTR ZX
NTRdata
Success 1
Success 2
Failure 1 Failure 2
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RIMA-DP timing diagrams
RTR NTR
Noise detected at Z
BACKOFFX
Z interference
RTRWaiting period
DATA
CTS
X
Z
RTRWaiting period
DATAX
Z
RTR
RTR
collision
X
Z
channel BACKOFF
Node X sends an RTR and after seconds receives a DATA packet and then sends its DATA
Node X sends an RTR and node Z replies with a CTS; node X sends its DATA
Nodes X and Z send RTRs within seconds and therefore a collision occurs
Due to interference from node Z, node X sends an NTR to stop the handshake
DATA
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RIMA-BP illustrated
RTR
RTR
RTR
X
RTR
ZRTR
RTRZX
BACKOFF
RTR
RTR
RTR
RTRZX
RTR
X ZRTS data
ZX
RTR
RTR
RTR
RTR ZX
RTR
Y
X ZRTS
NTR
NTR
NTR
NTR Z
Y
X
NTR
RTSRTS
Success 1
Failure 1
Failure 2
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RIMA-BP timing diagrams
RTR
RTR
collision
X
Z
channel BACKOFF
RTRWaiting period
DATARTS
X
Z
RTR
RTS
X
Z
RTSY
collision NTR
Node X sends an RTR; node Z responds with a RTS and after seconds sends its DATA
Node X sends an RTR; nodes Z and Y send an RTS within seconds; node X sends an NTR to stop the handshake
Nodes X and Z send RTRs within seconds and therefore a collision occurs
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Throughput Analysis Model
fully-connected network of N nodes single, unslotted channel, error-free the size for an RTR, RTS and CTS is seconds; the size for a
data packet is seconds the turn-around time is considered to be part of the duration of
control and data packet the propagation delay of the channel is seconds a polled node receiving an RTR always has a data packet to
send the probability that the packet is addressed to the polling node
is 1/N
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Throughput Analysis
500 Byte data packets; 1Mbps network speed; maximum distance between nodes is 1 mile; on the left a 10 node network; on the right a 50 node network
10-3
10-2
10-1
100
101
102
103
104
105
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1a = 0.00025; b = 0.04; c = 0.005
Offered Load: G
S (T
hrou
ghpu
t)
MACA oooFAMA-NCS ---MACA-BI -.-RIMA-SP +++RIMA-DP ___
RIMA-BP xxx
10-3
10-2
10-1
100
101
102
103
104
105
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1a = 0.00025; b = 0.04; c = 0.005
Offered Load: G
S (T
hrou
ghpu
t)
MACA oooFAMA-NCS ---MACA-BI -.-RIMA-SP +++RIMA-DP ___
RIMA-BP xxx
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Delay Analysis
500 Byte data packets; 1Mbps network speed; maximum distance between nodes is 1 mile
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 110
0
101
102
103
a = 0.0001; b = 0.02; c = 0.002
Dela
y
S (throughput)
FAMA RIMA-DP
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Heavy Traffic Approximation
MACA-BI analysis assumes that there is always a DATA packet after a successful poll
To present a fair comparison between MACA-BI and RIMA protocols we analyze a heavy load approximation where there is always a DATA packet to be sent after receiving an RTR
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JJ. Garcia-Luna-Aceves and A. Tzamaloukas
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Throughput Analysis
500 Byte data packets; 1Mbps network speed; maximum distance between nodes is 1 mile; network of 50 nodes; heavy load approximation throughput: any polled node always has data to send to any polling node
10-3
10-2
10-1
100
101
102
103
104
105
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1a = 0.00025; b = 0.04; c = 0.005
Offered Load: G
S (T
hrou
ghpu
t)MACA oooFAMA-NCS ---MACA-BI -.-RIMA-SP +++RIMA-DP ___
RIMA-BP xxx
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Conclusions
RIMA protocols provide correct collision avoidance in the presence of hidden terminals
The throughput achieved with RIMA-DP is higher than any other sender initiated MAC protocol for fully connected networks
RIMA-DP achieves higher throughput than all other collision avoidance protocols in fully-connected networks under heavy load approximation
Relative differences in performance remain the same in networks with hidden terminals
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Simulation Results
BaseN1
N2
B1 B2
N1
N1
N1N1
(a) (b)
(c)
Base
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Simulation Results
Network RIMA FAMA MACAW
(a) .83 .76 .63
(b) .58 .58 .49
(c) (B1) .76 .74 .45
(d) (B2) .76 .74 .39