Doc.: IEEE 802.11-07/2454r1 Submission September 2007 M. Benveniste (Avaya Labs)Slide 1 Performance...

September 2007

M. Benveniste (Avaya Labs)

Slide 1

doc.: IEEE 802.11-07/2454r1

Submission

Performance Evaluation of ‘Express Forwarding’for a Single-Channel Mesh

Notice: This document has been prepared to assist IEEE 802.11. It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein.

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Date: 2007-09-16

Authors:Name Address Company Phone EmailMathilde Benveniste

233 Mt Airy RoadBasking Ridge, NJ 07920, US

Avaya Labs-Research

973-761-6105 [email protected]

Kaustubh Sinkar 233 Mt Airy RoadBasking Ridge, NJ 07920, US

Avaya Labs-Research

908-696-5284 [email protected]

September 2007


Slide 2

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Submission

Performance Evaluation of ‘Express Forwarding’for a Single-Channel Mesh

Mathilde Benveniste

Kaustubh SinkarAvaya Labs - Research

September 2007


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Submission

IntroductionIntroduction

• VoIP cannot meet QoS requirements on a wireless mesh unless there is a way to reduce delay/jitter– End-to-end delay and jitter can be too high in a single-channel

mesh because of multi-hop transmissions• Delay/jitter determines the delay experienced by the end-user

receiving QoS traffic– Frames are kept in a jitter buffer on receiving device for smooth

delivery• Reducing the worst-case delay causes all frames of a QoS traffic

stream to experience lower delay– A shorter jitter buffer is needed

• This presentation shows the performance of ‘Express Forwarding’ and ‘Express Retransmission’ – These optional features help multi-hop QoS traffic get through the

mesh fast with minimum impact on other traffic

September 2007


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Submission

Delay BudgetDelay Budget

• Recommended one-way total delay (ITU G.114) – 150 ms• Delay introduced in IP network and end system – 110 ms

– IP network delay – sum of transmission and queuing delays traveling thru IP network (~50 ms)

– End-system delay – sum of the encoding (20 ms), decoding (small), jitter buffer (~40 ms), and other data handling delays

• The target for maximum latency in wireless media should be 40 ms*

* In 802.11 TGe, a target of 10 ms was used for WLAN delay in top-priority ACs

September 2007


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Submission

Express Forwarding – ReviewRef Doc 11-07/2452, 2453

• ‘Express forwarding’ reduces the end-to-end delay of selected frames by granting forwarding nodes immediate access to the channel

• Criteria for express forwarding frames are:– Time sensitive QoS [TSQ] frames – e.g. VO/VI– Frames on paths traversing more than a specified number of hops– Other

• Single-hop frames are not express-forwarded • ‘Time critical’ frames are single-hop frames that do not yield

priority to express forwarded frames; such frames are– Top-priority management frames– Top-priority frames experiencing longer delay than a specified

limit

September 2007


Slide 6

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Submission

Express Forwarding IllustrationExpress Forwarding IllustrationRef Doc 11-07/2452, 2453

• The Duration field is set at a value longer than usual when a TSQ frame is transmitted to a forwarding node of a multi-hop path; DT0 added

• The forwarding nodes, 2 and 3, adjust the Duration value on the received frame by subtracting an increment DTI when setting their NAV

• Nodes with a ‘time critical’ frame subtract the increment DT0 from Duration field• The non-forwarding neighbor nodes (e.g. 5) sets NAV by Duration field

NAV setting at all other neighbor nodes

NAV setting at receiving node

Channel time

ACK

Value in Duration field

1 2

1-2

Frame

3 4

2-3

DT0

3-hop path 1-4

3-4

5

DTI

ANIMATED

September 2007


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Submission

Express RetransmissionExpress RetransmissionRef Doc 11-07/2452, 2453• Conventional retransmission typically involves backoff and use of a wider

contention window • With ‘express retransmission’, backoff is dispensed and frame is

retransmitted within DT0 following ACKtimeout • Because of its prioritization, an express retransmitted frame is less likely

to collide with one that is not• Only the first retransmission attempt receives priority treatment

• Prevents two express retransmitted frames from colliding repeatedly

Channel time

ACKtimeout

TSQ

Frame

DT0

DTI

TSQ

Retransmission

NAV setting at all other neighbor nodes

NAV setting at receiving node

Value in Duration field of TSQ frame

September 2007


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Submission

Performance EvaluationPerformance EvaluationPerformance EvaluationPerformance Evaluation

September 2007


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Submission

Scenarios

1. 802.11b Mesh (4 hops)– Light load

2. 802.11b Mesh (6 hops)– Heavy load, concentration near portal

3. 802.11g Mesh (5 and 2 hops)– Long data range– Multiple flows thru portal

4. 802.11a Mesh (5 and 2 hops)– Short data range– Heavy load, multiple flows thru portal

All scenarios consider only high-priority traffic (VOIP and Video) – worst-case scenarios

OPNET Modeler used for simulations

September 2007


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Submission

ParametersNetwork 802.11a 802.11g 802.11b

Slot Time 9 usec 9 usec 20 usec

Sifs Time 16 usec 10 usec 10 usec

Phy_CWmin 15 15 15

Phy_CWmax 1023 1023 1023

PLCP overhead control 20 usec 20 usec 96 usec

PLCP overhead data 20 usec 20 usec 96 usec

Control Data Rate 24 Mbps 24 Mbps 5.5 Mbps

Difs Time sifs + 2*slot_time = 34 usec sifs + 2*slot_time = 28 usec sifs + 2*slot_time = 50 usec

Eifs_time difs + sifs + ACK @ 24 Mbps difs + sifs + ACK @ 24 Mbps difs + sifs + ACK @ 5.5 Mbps

aifsn 2 2 2

Aifs [ac]aifsn[ac] * slot_time + sifs_time = 28 usec

aifsn[ac] * slot_time + sifs_time = 28 usec

aifsn[ac] * slot_time + sifs_time = 50 usec

ACK tx rate 24 Mbps 24 Mbps 5.5 Mbps

DATA tx rate 54 Mbps 54 Mbps 11 Mbps

Cwmax 1023 1023 1023

Cwmin 15 15 15

September 2007


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Submission

Scenario 1: 802.11b Mesh (4 hops)

Examines the effectiveness of Express Forwarding in an lightly loaded 11b single channel network

• Multi-hop path of 4 hops• Peer-to-peer mesh or independent WLAN flows on same channel

surround multi-hop path• Low total traffic load (3.9 Mbps), symmetrically distributed along the

multi-hop path

September 2007


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Submission

Scenario 1: 802.11b Mesh (4 hops) Traffic description

VIDEO (L): Low Resolution, 1.4 Mbps

payload size: 1464 bytes, inter-arrival 8 ms

VOIP : G711, 0.16 Mbpspayload size: 200 bytes, inter-arrival 20 ms

P

9 10

7 8 1 23 5

12 13 11 16

VOIP

VOIP

VOIP

VIDEO (L) VIDEO (L)

Network configuration Data range: 25 m, Ack range: 31 m 4-hop path, next-hop neighbors

don’t hear each other Physical layer rates

Data @ 11 Mbps ACK @ 5.5 Mbps

TOTAL LOAD: 3.9 Mbps

September 2007


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Submission

Scenario 1: Mean Delays

Express Fwd Disabled

Express Fwd Enabled

Express Fwd With Express Rtx

Node2 > Node1 2.70 2.62 2.67

Node3 > Node5 4.46 5.30 4.23

Node5 > Node3 1.71 1.60 1.63

Node7 > Node8 4.99 4.76 4.33

Node9 > Node10 1.51 1.42 1.50

Node10 > Node9 4.40 5.30 4.97

Node16 > Portal 75.87 50.76 33.00

Portal > Node_16 72.85 49.70 32.52

With Express Forwarding4-hop VOIP ETE delay 50 ms + Express Retransmission 4-hop VOIP mean delay 33 ms

Lower delays for all other flows

Without Express Forwarding4-hop VOIP mean delay 75 ms

September 2007


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Submission

Scenario 1: 4-hop Delays (CDF)

Uplink DelayUplink DelayDownlink DelayDownlink Delay

September 2007


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Submission

Scenario 1: Dropped Frames*

With Express ForwardingFewer frames are dropped by

all nodes

* Frames are dropped if retransmitted 7 times unsuccessfully

September 2007


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Submission

Scenario 1 – Summary of Results

Express Forwarding benefits• Reduces ETE delay for 4-hop VOIP flow by over 50% when combined

with Express Retransmission• All other flows (either on the mesh or in neighboring BSS) are

impacted minimally– Prioritization reduces contention – fewer collisions

• Fewer frames are dropped as a result of fewer retransmissions

September 2007


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Submission


Examines the effectiveness of Express Forwarding in more heavily loaded 11b single channel network, with increased hop count

• Multi-hop path of 6 hops• Peer-to-peer mesh or independent WLAN flows on same channel

surround multi-hop path• Total traffic load (5.7 Mbps), asymmetrically distributed along the

multi-hop path– more concentrated around portal P

September 2007


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Submission


P 12 13 14

15

11 16

3 51 2

7 8

9

10

6 4VIDEO (L)

VIDEO (L)

VIDEO (L)

VOIP

VOIP

VOIP

Traffic description VIDEO (L): Low Resolution, 1.4 Mbps

payload size: 1464 bytes, inter-arrival 8 ms

VOIP : G711, 0.16 Mbpspayload size: 200 bytes, inter-arrival 20 ms

Network configuration Data range: 25 m 6-hop path, reduced distance

between neighbors Physical layer rates

Data @ 11 Mbps ACK @ 5.5 Mbps

TOTAL LOAD: 5.7 Mbps

September 2007


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Submission


Express Fwd Disabled

Express Fwd Enabled

Express Fwd With Exp Rtx

Node2 > Node1 2.71 2.54 2.60

Node3 > Node5 1.12 1.08 1.11

Node5 > Node3 4.34 3.35 3.92

Node6 > Node4 4.54 4.37 4.74

Node7 > Node8 41.17 23.30 29.28

Node9 > Node10 4.59 3.18 3.66

Node10 > Node9 5.02 4.39 4.09

Node16 > Portal 151.32 44.12 23.20

Portal > Node16 164.50 57.55 39.01

With Express Forwarding6-hop VOIP mean delay 58 ms + Express Retransmission 6-hop VOIP mean delay 39 ms

Lower delays for all other flows

Without Express Forwarding6-hop VOIP mean delay 164 ms

September 2007


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Submission


0.0 0.1 0.2 0.3 0.4 0.5

0.0

0.2

0.4

0.6

0.8

1.0

Pro

b [<

=val

ue] o

f Pac

ket E

TE

Del

ay

Value

Express Fwd Disabled Express Fwd Enabled Express Fwd With Exp Rtx

Uplink DelayUplink DelayDownlink DelayDownlink Delay

(sec) (sec)

September 2007


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Submission

Scenario 2: Dropped Frames

With Express ForwardingFewer frames are

dropped by all nodes

September 2007


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Submission


Express Forwarding benefits• Express forwarding reduces ETE delay for 6-hop VOIP flow by over 75%

when combined with Express Retransmission• All other flows (either on the mesh or in neighboring BSS) also enjoy

delay reduction – Prioritization reduces contention – fewer collisions

• Fewer frames are dropped as a result of fewer retransmissionsTraffic concentration near the portal• Delays of other flows near the portal are longer

– Express forwarding causes these delays to be lower • The uplink and downlink delays of the multi-hop flow display small

asymmetry– While the same hops are traversed in both directions, the traffic

near the portal disadvantages the first downlink hop more as compared to the traffic near the first uplink hop

– Note: Access on the first hop of a multi-hop flow is not prioritized

September 2007


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Submission

Scenario 3: 802.11g Mesh (5 hops)

Examines the effectiveness of Express Forwarding in an 11g single channel network with long transmit range (391 meters)

• Multi-hop paths of 5 and 2 hops • Peer-to-peer mesh or independent WLAN flows on same channel

surround multi-hop paths• Total traffic load (17 Mbps), asymmetrically distributed along the

multi-hop path• Multiple VOIP flows and Video go thru portal P

September 2007


Slide 24

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Submission

P

1

2

3

4 5

VIDEO (L)

VIDEO (H)

VIDEO (H)

VIDEO (L)

VIDEO (L)VIDEO (L)

VIDEO (L) VOIP

VOIP

VOIP

VOIP

VOIP

17

18

21 13 25

24

11 206

7 8

2216

10

12

1914

9

Scenario 3: 802.11g Mesh (5 hops) Traffic description

VIDEO (L): Low Resolution, 1.4 Mbps

payload size: 1464 bytes, inter-arrival 8 ms VIDEO (H): High Resolution, 4.2 Mbps

payload size: 1464 bytes, inter-arrival 2.83 ms VOIP : G711, 0.16 Mbpspayload size: 200 bytes, inter-arrival 20 ms

Network configuration TX RANGE: 391 m 5-hop path, next-hop neighbors don’t hear

each other Physical layer rates

Data @ 54 Mbps ACK @ 24 Mbps

TOTAL LOAD: 17 Mbps

September 2007


Slide 25

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Submission


Without Express Forwarding5-hop VOIP delay 91 ms2-hop VOIP delay 43 msFlow 25-6 is unstableFlow 11-20 delay 100 ms

With Express Forwarding5-hop VOIP delay 4 ms2-hop VOIP delay 3 msFlow 25-6 delay 4 msFlow 11-20 delay 3 ms + Express Retransmission 5-hop VOIP delay 3 ms2-hop VOIP delay <3 msFlow 25-6 delay 3 msFlow 11-20 delay <3 ms

Substantially lower delays for all other flows

September 2007


Slide 26

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Submission

Scenario 3: Mean Delays (ms)

Flows

Express Forwarding Disabled

Express Forwarding Enabled

Express Forwarding With Express Re-TX

Without Multi-hop Flows

Portal->Node_5 90.76 4.20 3.39 NA

Portal->Node_16 36.68 2.90 2.64 1.18

Portal->Node_17 40.97 3.39 2.77 1.14

Portal->Node_18 43.18 3.32 2.64 NA

Portal->Node_22 36.16 5.21 4.50 1.45

Node_5->Portal 68.67 4.04 2.18 NA

Node_7->Node_8 4.89 1.49 1.08 0.63

Node_8->Node_7 5.53 1.47 1.36 0.65

Node_11->Node_20 137.82 3.37 2.72 1.21

Node_12->Node_10 9.05 2.18 1.90 1.23

Node_13->Node_21 14.03 1.83 1.67 1.09

Node_16->Portal 8.87 2.69 2.56 1.38

Node_17->Portal 11.80 1.89 1.55 1.07

Node_18->Portal 23.38 2.84 2.11 NA

Node_19->Node_14 11.71 1.79 1.53 0.76

Node_24->Node_9 10.79 1.96 1.77 0.92

Node_25->Node_6 1119.60 3.70 2.94 1.16

September 2007


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Submission


P -> Node5 DelayP -> Node5 Delay Node5 -> P DelayNode5 -> P Delay

September 2007


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Submission


P -> Node18 DelayP -> Node18 Delay Node18 -> P DelayNode18 -> P Delay

(sec) (sec)

September 2007


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Submission

(sec)

Scenario 3: Video (H) Delays (CDF)

Node11 -> Node20 DelayNode11 -> Node20 Delay Node25 -> Node6 DelayNode25 -> Node6 Delay

(sec)

September 2007


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Submission


• There are practically no dropped frames with express forwarding

September 2007


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Submission


Express Forwarding benefits• ETE delay for 5-hop and 2-hop VOIP flows is reduced by 95% • All other flows (either on the mesh or in neighboring BSS) also enjoy

substantial delay reduction – The long delays experienced by the Video (H) flows disappear when multi-

hop flows are express forwarded Long Ack range• Synergy with longer Ack range (47 % longer than Data range)

magnifies the benefit of express forwarding, with result few retransmissions

– Low retransmissions lead to few dropped frames• With few retransmissions, Express Retransmission provides little

further delay reduction Multi-hop flows• Express forwarding removes the deleterious effect of multi-hop flows

on other traffic

September 2007


Slide 32

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Submission

P

1

2

3

4 5

VIDEO (L)

VIDEO (H)

VIDEO (H)

VIDEO (L)

VIDEO (L)VIDEO (L)

VIDEO (L) VOIP

VOIP

VOIP

VOIP

VOIP

17

18

21 13 25

24

11 206

7 8

2216

10

12

1914

9

Multi-hop effect in single-channel meshMulti-hop effect in single-channel mesh If the ACK from 2 (or 3) causes collision at

Node6, retransmission of frame from 25 will wait till multi-hop TX P->5 completes

The sooner the latter completes, the sooner the transmission 25->6 will complete

Express forwarding reduces time of transmission P->5, thus shortens delay for flow 25->6

With Express Forwarding, the ACK from 2 prevents collision by 25 with subsequent transmission from 2

Multi-hop flow P -> 5 impacts flow 25 -> 6Multi-hop flow P -> 5 impacts flow 25 -> 6

ANIMATED

A collision with the ACK leads to longer backoff for

Node25

Nodes 2, 3, 4 & 5 likely to draw

shorter backoff than Node25

Data Range

Ack Range

September 2007


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Submission

Scenario 3.1: Multi-hop flows removed

P

1

2

3

4 5

VIDEO (L)

VIDEO (H)

VIDEO (H)

VIDEO (L)

VIDEO (L)VIDEO (L)

VIDEO (L) VOIP

VOIP

VOIP

VOIP

VOIP

17

18

21 13 25

24

11 206

7 8

2216

10

12

1914

9

Traffic description The same as Scenario 3, without the “long” flows – i.e. multi-hop flows (P->Node5 and P->Node18)

Network configuration TX RANGE: 391 m 5-hop path, next-hop neighbors don’t hear

each other Physical layer rates


X

XTOTAL LOAD: 16 Mbps

Long Flows removed

September 2007


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Submission

Scenario 3.1: Mean Delays

Delays are substantially shorter without the multi-hop flows

Express Forwarding reduces the negative effect of multi-hop flows on other traffic

September 2007


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Submission

Scenario 3.1: Mean Delays (ms)

Flows




Without Long Flows

Portal->Node_5 90.76 4.20 3.39 NA

Portal->Node_16 36.68 2.90 2.64 1.18

Portal->Node_17 40.97 3.39 2.77 1.14

Portal->Node_18 43.18 3.32 2.64 NA

Portal->Node_22 36.16 5.21 4.50 1.45

Node_5->Portal 68.67 4.04 2.18 NA

Node_7->Node_8 4.89 1.49 1.08 0.63

Node_8->Node_7 5.53 1.47 1.36 0.65

Node_11->Node_20 137.82 3.37 2.72 1.21

Node_12->Node_10 9.05 2.18 1.90 1.23

Node_13->Node_21 14.03 1.83 1.67 1.09

Node_16->Portal 8.87 2.69 2.56 1.38

Node_17->Portal 11.80 1.89 1.55 1.07

Node_18->Portal 23.38 2.84 2.11 NA

Node_19->Node_14 11.71 1.79 1.53 0.76

Node_24->Node_9 10.79 1.96 1.77 0.92

Node_25->Node_6 1119.60 3.70 2.94 1.16

September 2007


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Submission

Scenario 4: 802.11a Mesh (5 hops)

Examines the effectiveness of Express Forwarding in an 11a single channel network with short transmit range (25 meters)

• Multi-hop paths of 5 and 2 hops • Peer-to-peer mesh or independent WLAN flows on same channel

surround multi-hop paths• Total traffic load (20 Mbps), asymmetrically distributed along the

multi-hop path, is more concentrated around portal P• Multiple VOIP flows and Video go thru portal P

September 2007


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Submission

Scenario 4: 802.11a Mesh (5 hops)

P

16

22

17

18

1215

10

21

26

13

2 4 5

3

623

7

18

14 1911 20

24

12VOIP

VOIP

VOIP

VOIP

VIDEO (L) VIDEO (L)VIDEO (L)

VIDEO (L)

VIDEO (H)

VIDEO (L)

VIDEO (L)

VIDEO (L)VIDEO (L)

VIDEO (L)VIDEO (L)

VOIP

TOTAL LOAD: 20 Mbps

25

Traffic description VIDEO (L): Low Resolution, 1.4 Mbps

payload size: 1464 bytes, inter-arrival 8 ms VIDEO (H): High Resolution, 4.2 Mbps

payload size: 1464 bytes, inter-arrival 2.83 ms VOIP : G711, 0.16 Mbpspayload size: 200 bytes, inter-arrival 20 ms

Network configuration TX RANGE: 25 m 2 multi-hop paths, next-hop neighbors

don’t hear each other Physical layer rates


September 2007


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Submission


Without Express Forwarding5-hop VOIP delay 179 ms2-hop VOIP delay 79 msP->16 VOIP delay 76 msP->22 Video delay 45 ms

With Express Forwarding5-hop VOIP delay 19 ms2-hop VOIP delay 6 msP->16 VOIP delay 7 msP->22 Video delay 6 ms

+ Express Retransmission 5-hop VOIP delay 10 ms2-hop VOIP delay 4 msP->16 VOIP delay 5 msP->22 Video delay 4 ms

Substantially lower delays for all flows

September 2007


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Submission




Portal > Node5 179.12 19.31 9.51

Portal > Node16 75.90 7.24 5.44

Portal > Node17 71.90 6.30 4.34

Portal > Node18 78.92 6.39 4.08

Portal > Node22 45.23 6.38 3.95

Node5 > Portal 124.04 23.17 11.88

Node7 > Node8 2.68 1.38 1.24

Node8 > Node7 3.50 1.51 1.34

Node11 > Node20 7.87 2.74 2.26

Node12 > Node10 7.76 2.76 1.93

Node13 > Node21 5.10 2.00 1.77

Node14 > Node19 3.19 1.63 1.57

Node15 > Node23 3.64 1.59 1.47

Node16 > Portal 41.19 13.90 10.52

Node17 > Portal 6.04 1.16 1.13

Node18 > Portal 9.56 1.77 1.71

Node19 > Node24 4.86 2.51 1.72

Node21 > Node14 11.92 3.78 3.38

Node21 > Node26 11.60 3.50 2.92

Node24 > Node9 4.60 1.95 1.91

Node25 > Node6 29.15 4.98 3.77

Node25 > Node13 28.90 4.92 3.75

September 2007


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Submission


Downlink DelayDownlink Delay Uplink DelayUplink Delay

September 2007


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Submission


Downlink DelayDownlink Delay Uplink DelayUplink Delay

September 2007


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doc.: IEEE 802.11-07/2454r1

Submission


Fewer dropped frames with express forwarding

September 2007


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Submission


Express Forwarding benefits• ETE delay for 5-hop and 2-hop VOIP flows is reduced by 94% • All other flows (either on the mesh or in neighboring BSS) also enjoy

substantial delay reduction

Traffic concentration at Portal• The flows going thru the portal experience very long delays• Express forwarding on the multi-hop flows reduces delays substantially

on all flows thru the portal, both multi-hop and single-hop flows

September 2007


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Submission

Conclusion

• Express Forwarding reduces end-to-end delay and jitter of the multi-hop flows substantially

• Express Forwarding causes fewer frames to be dropped• Express Retransmission reduces retransmissions and

end-to-end delay further• Other (not express forwarded) traffic also benefits

substantially from Express Forwarding• Express Forwarding and Express Retransmission enable

multi-hop QoS traffic to get through a single-channel mesh fast with minimum impact on other traffic

September 2007


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Submission

Back up

September 2007


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Submission

Excessive latency in meshesExcessive latency in meshes

Hidden terminal collisions between two transmissions are likely to repeat

Single channel mesh•A and D cannot hear each other•C cannot receive when A transmits•B cannot receive when D transmits

•Retransmission attempts likely to fail•Increased delay for successful transmission A B

Tx X

C D

((((

((((

XTx

InterferenceInterference

September 2007


Slide 47

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Submission

Express retransmission illustrationExpress retransmission illustration

• Express retransmission (X-RTX) enables a multi-hop transmission to complete faster

Express forwarding and X-RTX on single-channel mesh•The transmissions from A->B and F->E lead to hidden terminal collisions•Express retransmission enables the TSQ frame (A->B) to succeed upon retransmission•The ACKs sent by B and C protect the frame as it is forwarded on

A B

E F

((((

Tx

Interference

X

X

TSQ

((((

Interference

DC

X-RTX TSQ TSQ ANIMATED

Doc.: IEEE 802.11-07/2454r1 Submission September 2007 M. Benveniste (Avaya Labs)Slide 1 Performance...

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Transcript of Doc.: IEEE 802.11-07/2454r1 Submission September 2007 M. Benveniste (Avaya Labs)Slide 1 Performance...