enhancing tcp fairness in ad hoc wireless networks using neighborhood red
DESCRIPTION
Enhancing TCP Fairness in Ad Hoc Wireless Networks Using Neighborhood RED Kaixin Xu, Mario Gerla University of California, Los Angeles {xkx, gerla}@cs.ucla.edu Lantao Qi, Yantai Shu Tianjin University, Tianjin, China {ltqi, ytshu}@tju.edu.cn. Motivation. - PowerPoint PPT PresentationTRANSCRIPT
Enhancing TCP Fairness in Ad Hoc
Wireless Networks Using Neighborhood
RED
Kaixin Xu, Mario Gerla
University of California, Los Angeles
{xkx, gerla}@cs.ucla.edu
Lantao Qi, Yantai Shu
Tianjin University, Tianjin, China
{ltqi, ytshu}@tju.edu.cn
Motivation
TCP is important in ad hoc network apps Reliable transfer of data/image files
and multimedia streaming Congestion protection Efficient utilization and fair share of
the resources However, TCP has shown unfair
behavior in ad hoc nets
TCP Unfairness in Ad Hoc Networks 3 TCP flows contending with each other Flow 2 is nearly starved Original RED fails to improve the fairness
F T P 1
F T P 2
F T P 3
(1 0 0 , 1 0 0 ) (6 0 0 , 1 0 0 )
(3 5 0 , 3 5 0 )
(3 5 0 , 7 0 0 )(0 , 7 0 0 )
(3 5 0 , 1 0 5 0 )
(1 0 0 , 1 3 0 0 ) (6 0 0 , 1 3 0 0 )
(7 0 0 , 7 0 0 )
Why RED Does Not Work?
Why RED does not work in ad hoc networks? Congestion simultaneously affects multiple
queues Queue at a single node cannot completely
reflect the state Extend RED to the entire congested area –
Neighborhood of the node
Random Early Detection (RED) to improve fairness Active queue management scheme qwavgwavg qq 1 Average queue size:
Drop probability: , proportional to buffer occupancy
thth
thp avg
bp minmax
)min(max
Neighborhood and Its Distributed Queue A node’s
neighborhood consists of the node itself and the nodes which can interfere with this node’s signal 1-hop neighbors
directly interfere 2-hop neighbors
may interfere
Queue size of the neighborhood reflects the degree of local network congestion
A
1
5
3
4
2
6
7
9
1 0
1 2
1 1
8
Simplified Neighborhood Queue Model 2-hop neighborhood queue
model is not easy to operate Too much overhead to
propagate queue values 2 hops away
Simplified model Only include 1-hop
neighbors Two Qs at each
neighbor: Outgoing queue “Incoming queue”=
# CTS packets OH by A Distributed neighborhood
queue – the aggregate of these local queues
A
1
5
3
4
2
6
O u tg o in g Q u eu e
In co m in g Q u eu e
Neighborhood Random Early Detection (NRED) Extending RED to the distributed
neighborhood queue (Virtual) Key Problems
Counting the size of the distributed neighborhood queue
Calculating proper packet drop probability at each node
Components of Neighborhood RED Neighborhood Congestion Detection (NCD) Neighborhood Congestion Notification (NCN) Distributed Neighborhood Packet Drop
(DNPD)
Direct way: Announce queue size upon changes Too much overhead, queue location
problem? Our method: Indirectly estimate an index of
instant queue size by monitoring wireless channel
Neighborhood Congestion Detection
Average queue size is calculated using RED’s alg.
Congestion: queue size exceeds the minimal threshold
ervalsampling
timebusychannelUbusy int
Channel utilization ratio
Queue size index K is a constant
busyUKq *
A
1
5
3
4
2
6
O u tg o in g Q u eu e
In co m in g Q u eu e
Channel busy
CTS
Neighborhood Congestion Notification & Distributed Neighborhood Packet Drop Neighborhood Congestion Notification
Congested node computes drop probability following RED’s alg.
It broadcasts the drop probability to all neighbors
Distributed Neighborhood Packet Drop Neighborhood Drop Prob = Max of all
drop probabilities heard from neighbors
Performance Evaluation: Simple Scenario Both long-term and short-term
fairness is achieved Loss of aggregated throughput
Tradeoff between fairness and throughput
Channel is not fully utilized
Overall Throughput Instantaneous Throughput
F T P 1
F T P 2
F T P 3
(1 0 0 , 1 0 0 ) (6 0 0 , 1 0 0 )
(3 5 0 , 3 5 0 )
(3 5 0 , 7 0 0 )(0 , 7 0 0 )
(3 5 0 , 1 0 5 0 )
(1 0 0 , 1 3 0 0 ) (6 0 0 , 1 3 0 0 )
(7 0 0 , 7 0 0 )
Performance Evaluation: Multiple Congested Neighborhood Multiple congested neighborhoods FTP2 & FTP 5 have more competing flows,
are more likely to be starved
Overall Throughput
F T P 1 F T P 2 F T P 3
F T P 4
F T P 5
F T P 6
Lessons learned TCP unfairness has been found in ad hoc
networks Notion of “wireless neighborhood” key to solve
the “capture” problem -- > NRED for enhancing TCP fairness in ad hoc nets
Good example of “cross layer” interaction (network drops packets to let TCP know..)
Network layer solution ??? Easy to implement ???
Work in progress: Implementation of proposed schemes in the
Linux testbed Measuring channel utilization rate is an over-
layer solution and hardly to implement in practice
Performance measurement
MAC Delay Based NRED Scheme
Node with the maximum MAC delay (Q size) is not the congestion center node, but the previous hop of the congestion center
2
5
1 3
4 6
7
8
9
TCP1
TCP2
TCP3
Node with the Maximum
MAC Delay
Congestion CenterCongestion
Notification
Fig. 6. Congestion detection and notification
Packet drop probability for MAC delay based NRED
minth
1
MAC Delay
Drop Probability
maxth
maxp
pb
Simulation resultsM inth=0.07, M axth=0.12, M axP=?
0
100
200
300
400
500
600
MaxP=0.1 MaxP=0.3 MaxP=0.5 MaxP=0.7 MaxP=0.9
Ove
rall
Thro
ughp
ut (k
bps)
0.0
0.2
0.4
0.6
0.8
1.0
Fairn
ess I
ndex
TCP 1
TCP 2
TCP 3
Fairness
Total
Minth=?, Maxth=0.12, MaxP=0.5
0
100
200
300
400
500
600
Minth=0.03 Minth=0.05 Minth=0.07 Minth=0.09 Minth=0.11
Ove
rall
Thro
ughp
ut (k
bps)
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
Fairn
ess I
ndex
T CP 1
T CP 2
T CP 3
Fairness
T otal
Minth=0.07, Maxth=?, MaxP=0.5
0
100
200
300
400
500
600
Maxth=0.07 Maxth=0.09 Maxth=0.12 Maxth=0.15 Maxth=0.18
Ove
rall
Thro
ughp
ut(k
bps)
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
Fairn
ess I
ndex
T CP 1
T CP 2
T CP 3
Fairness
T otal
Fig. 8. Performances at different parameters
optimal parameters:
maxp = 0.5 maxth = 0.12 minth = 0.07
Adaptive Pause scheme
Queue length based NRED and MAC Delay Based NRED schemes can not directly find congestion
center congestion notification - hard RED: optimal parameters setting ?
被动:等待受压制节点发出通知才开始控制发包,对网络中的不公平现象反应慢,而且发送消息造成额外的带宽开销。
主动:获得竞争无线信道优势的节点要自律 Adaptive Pause
Adaptive Pause scheme
Each node monitors its bandwidth occupation and the number of its active neighbor nodes
Instead of detecting congestion, the nodes which occupy too much bandwidth, will reduce their sending rate by themselves
If the bandwidth exceeds the threshold, the node will pause an interval to stop sending
0, 0 0, 1 0, W0-2 0, W0-1
1, 0 1, W1-1
m’ , 0
m-1, 0
m’ , 1
1, 1
m-1,Wm-1-1
m, 0 m,Wm-1
,Wm’ -1m’
m,Wm-2
1111
1/W01/W0
p/W1p/W1
p/W2
p/W1
p/Wm’p/Wm’
p/Wm-1
p/Wmp/Wm
...
...
111...
111... ...
...
11... ...
11... ...
1
...
1
1- p
1- p
1- p
1- p
rPause
1 - r
...
r
Markov model for Adaptive_Pause scheme
Simulation result
Throughput of Adaptive_Pause and D_NRED
(Adaptive_Pause parameters: Tp= 1.5 s ,R= 0.5)
0
50
100
150
200
D_NRED Adaptive_Pause
kbps
吞吐
率(
) TCP1
TCP2
TCP3
Simulation result (Adaptive_Pause)
Flow 2 throughput ~ parameters: Tp , R
Simulation result (Adaptive_Pause)
Flow 2 throughput ~ parameters: Tp , R
Experiment result on TJU testbed
f
Overal l throughput of 3 TCP fl ows
0
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1000
15002000
2500
3000
3500
Drop Tai l RED NRED Pause
Thro
ughp
ut(k
bps)
0
0. 2
0. 4
0. 6
0. 8
1
Fair
ness
Ind
ex
fl ow1 fl ow2 fl ow3 total fai rness