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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.
Release: The contributor grants a free, irrevocable license to the IEEE to incorporate material contained in this contribution, and any modifications thereof, in the creation of an IEEE Standards publication; to copyright in the IEEE’s name any IEEE Standards publication even though it may include portions of this contribution; and at the IEEE’s sole discretion to permit others to reproduce in whole or in part the resulting IEEE Standards publication. The contributor also acknowledges and accepts that this contribution may be made public by IEEE 802.11.
Patent Policy and Procedures: The contributor is familiar with the IEEE 802 Patent Policy and Procedures <http:// ieee802.org/guides/bylaws/sb-bylaws.pdf>, including the statement "IEEE standards may include the known use of patent(s), including patent applications, provided the IEEE receives assurance from the patent holder or applicant with respect to patents essential for compliance with both mandatory and optional portions of the standard." Early disclosure to the Working Group of patent information that might be relevant to the standard is essential to reduce the possibility for delays in the development process and increase the likelihood that the draft publication will be approved for publication. Please notify the Chair < [email protected]> as early as possible, in written or electronic form, if patented technology (or technology under patent application) might be incorporated into a draft standard being developed within the IEEE 802.11 Working Group. If you have questions, contact the IEEE Patent Committee Administrator at <[email protected]>.
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
M. Benveniste (Avaya Labs)
Slide 2
doc.: IEEE 802.11-07/2454r1
Submission
Performance Evaluation of ‘Express Forwarding’for a Single-Channel Mesh
Mathilde Benveniste
Kaustubh SinkarAvaya Labs - Research
September 2007
M. Benveniste (Avaya Labs)
Slide 3
doc.: IEEE 802.11-07/2454r1
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
M. Benveniste (Avaya Labs)
Slide 4
doc.: IEEE 802.11-07/2454r1
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
M. Benveniste (Avaya Labs)
Slide 5
doc.: IEEE 802.11-07/2454r1
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
M. Benveniste (Avaya Labs)
Slide 6
doc.: IEEE 802.11-07/2454r1
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
M. Benveniste (Avaya Labs)
Slide 7
doc.: IEEE 802.11-07/2454r1
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
M. Benveniste (Avaya Labs)
Slide 8
doc.: IEEE 802.11-07/2454r1
Submission
Performance EvaluationPerformance EvaluationPerformance EvaluationPerformance Evaluation
September 2007
M. Benveniste (Avaya Labs)
Slide 9
doc.: IEEE 802.11-07/2454r1
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
M. Benveniste (Avaya Labs)
Slide 10
doc.: IEEE 802.11-07/2454r1
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
M. Benveniste (Avaya Labs)
Slide 11
doc.: IEEE 802.11-07/2454r1
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
M. Benveniste (Avaya Labs)
Slide 12
doc.: IEEE 802.11-07/2454r1
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
M. Benveniste (Avaya Labs)
Slide 13
doc.: IEEE 802.11-07/2454r1
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
M. Benveniste (Avaya Labs)
Slide 14
doc.: IEEE 802.11-07/2454r1
Submission
Scenario 1: 4-hop Delays (CDF)
Uplink DelayUplink DelayDownlink DelayDownlink Delay
September 2007
M. Benveniste (Avaya Labs)
Slide 15
doc.: IEEE 802.11-07/2454r1
Submission
Scenario 1: Dropped Frames*
With Express ForwardingFewer frames are dropped by
all nodes
* Frames are dropped if retransmitted 7 times unsuccessfully
September 2007
M. Benveniste (Avaya Labs)
Slide 16
doc.: IEEE 802.11-07/2454r1
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
M. Benveniste (Avaya Labs)
Slide 17
doc.: IEEE 802.11-07/2454r1
Submission
Scenario 2: 802.11b Mesh (6 hops)
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
M. Benveniste (Avaya Labs)
Slide 18
doc.: IEEE 802.11-07/2454r1
Submission
Scenario 2: 802.11b Mesh (6 hops)
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
M. Benveniste (Avaya Labs)
Slide 19
doc.: IEEE 802.11-07/2454r1
Submission
Scenario 2: Mean Delays
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
M. Benveniste (Avaya Labs)
Slide 20
doc.: IEEE 802.11-07/2454r1
Submission
Scenario 2: 6-hop Delays (CDF)
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
M. Benveniste (Avaya Labs)
Slide 21
doc.: IEEE 802.11-07/2454r1
Submission
Scenario 2: Dropped Frames
With Express ForwardingFewer frames are
dropped by all nodes
September 2007
M. Benveniste (Avaya Labs)
Slide 22
doc.: IEEE 802.11-07/2454r1
Submission
Scenario 2 – Summary of Results
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
M. Benveniste (Avaya Labs)
Slide 23
doc.: IEEE 802.11-07/2454r1
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
M. Benveniste (Avaya Labs)
Slide 24
doc.: IEEE 802.11-07/2454r1
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
M. Benveniste (Avaya Labs)
Slide 25
doc.: IEEE 802.11-07/2454r1
Submission
Scenario 3: Mean Delays
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
M. Benveniste (Avaya Labs)
Slide 26
doc.: IEEE 802.11-07/2454r1
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
M. Benveniste (Avaya Labs)
Slide 27
doc.: IEEE 802.11-07/2454r1
Submission
Scenario 3: 5-hop Delays (CDF)
P -> Node5 DelayP -> Node5 Delay Node5 -> P DelayNode5 -> P Delay
September 2007
M. Benveniste (Avaya Labs)
Slide 28
doc.: IEEE 802.11-07/2454r1
Submission
Scenario 3: 2-hop Delays (CDF)
P -> Node18 DelayP -> Node18 Delay Node18 -> P DelayNode18 -> P Delay
(sec) (sec)
September 2007
M. Benveniste (Avaya Labs)
Slide 29
doc.: IEEE 802.11-07/2454r1
Submission
(sec)
Scenario 3: Video (H) Delays (CDF)
Node11 -> Node20 DelayNode11 -> Node20 Delay Node25 -> Node6 DelayNode25 -> Node6 Delay
(sec)
September 2007
M. Benveniste (Avaya Labs)
Slide 30
doc.: IEEE 802.11-07/2454r1
Submission
Scenario 3: Dropped Frames
• There are practically no dropped frames with express forwarding
September 2007
M. Benveniste (Avaya Labs)
Slide 31
doc.: IEEE 802.11-07/2454r1
Submission
Scenario 3 – Summary of Results
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
M. Benveniste (Avaya Labs)
Slide 32
doc.: IEEE 802.11-07/2454r1
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
M. Benveniste (Avaya Labs)
Slide 33
doc.: IEEE 802.11-07/2454r1
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
Data @ 54 Mbps ACK @ 24 Mbps
X
XTOTAL LOAD: 16 Mbps
Long Flows removed
September 2007
M. Benveniste (Avaya Labs)
Slide 34
doc.: IEEE 802.11-07/2454r1
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
M. Benveniste (Avaya Labs)
Slide 35
doc.: IEEE 802.11-07/2454r1
Submission
Scenario 3.1: Mean Delays (ms)
Flows
Express Forwarding Disabled
Express Forwarding Enabled
Express Forwarding With Express Re-TX
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
M. Benveniste (Avaya Labs)
Slide 36
doc.: IEEE 802.11-07/2454r1
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
M. Benveniste (Avaya Labs)
Slide 37
doc.: IEEE 802.11-07/2454r1
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
Data @ 54 Mbps ACK @ 24 Mbps
September 2007
M. Benveniste (Avaya Labs)
Slide 38
doc.: IEEE 802.11-07/2454r1
Submission
Scenario 4: Mean Delays
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
M. Benveniste (Avaya Labs)
Slide 39
doc.: IEEE 802.11-07/2454r1
Submission
Express Forwarding Disabled
Express Forwarding Enabled
Express Forwarding With Express Re-TX
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
M. Benveniste (Avaya Labs)
Slide 40
doc.: IEEE 802.11-07/2454r1
Submission
Scenario 4: 5-hop Delays (CDF)
Downlink DelayDownlink Delay Uplink DelayUplink Delay
September 2007
M. Benveniste (Avaya Labs)
Slide 41
doc.: IEEE 802.11-07/2454r1
Submission
Scenario 4: 2-hop Delays (CDF)
Downlink DelayDownlink Delay Uplink DelayUplink Delay
September 2007
M. Benveniste (Avaya Labs)
Slide 42
doc.: IEEE 802.11-07/2454r1
Submission
Scenario 4: Dropped Frames
Fewer dropped frames with express forwarding
September 2007
M. Benveniste (Avaya Labs)
Slide 43
doc.: IEEE 802.11-07/2454r1
Submission
Scenario 4 – Summary of Results
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
M. Benveniste (Avaya Labs)
Slide 44
doc.: IEEE 802.11-07/2454r1
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
M. Benveniste (Avaya Labs)
Slide 45
doc.: IEEE 802.11-07/2454r1
Submission
Back up
September 2007
M. Benveniste (Avaya Labs)
Slide 46
doc.: IEEE 802.11-07/2454r1
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
M. Benveniste (Avaya Labs)
Slide 47
doc.: IEEE 802.11-07/2454r1
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