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Doc.: IEEE 802.11-07/2454r0 Submission September 2007 M. Benveniste (Avaya Labs)Slide 1 Performance Evaluation of Express Forwarding for a Single-Channel.

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Presentation on theme: "Doc.: IEEE 802.11-07/2454r0 Submission September 2007 M. Benveniste (Avaya Labs)Slide 1 Performance Evaluation of Express Forwarding for a Single-Channel."— Presentation transcript:

1 doc.: IEEE 802.11-07/2454r0 Submission September 2007 M. Benveniste (Avaya Labs)Slide 1 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 IEEEs name any IEEE Standards publication even though it may include portions of this contribution; and at the IEEEs 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, 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 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.http:// ieee802.org/guides/bylaws/sb-bylaws.pdfstuart.kerry@philips.compatcom@ieee.org Date: 2007-09-16 Authors: NameAddressCompanyPhoneEmail Mathilde Benveniste 233 Mt Airy Road Basking Ridge, NJ 07920, US Avaya Labs- Research 973-761-6105benveniste@ieee. org Kaustubh Sinkar 233 Mt Airy Road Basking Ridge, NJ 07920, US Avaya Labs- Research 908-696-5284ksinkar@avaya.co m

2 doc.: IEEE 802.11-07/2454r0 Submission September 2007 M. Benveniste (Avaya Labs)Slide 2 Performance Evaluation of Express Forwarding for a Single-Channel Mesh Mathilde Benveniste Kaustubh Sinkar Avaya Labs - Research

3 doc.: IEEE 802.11-07/2454r0 Submission September 2007 M. Benveniste (Avaya Labs)Slide 3 Introduction 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

4 doc.: IEEE 802.11-07/2454r0 Submission September 2007 M. Benveniste (Avaya Labs)Slide 4 Delay 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 a wireless mesh should be 40 ms* * In 802.11 TGe, a target of 10 ms was used for WLAN delay in top-priority ACs

5 doc.: IEEE 802.11-07/2454r0 Submission September 2007 M. Benveniste (Avaya Labs)Slide 5 Express Forwarding – Review Ref 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 frames to qualify for express forwarding are: –Time sensitive QoS [TSQ] frames – e.g. VO/VI –Frames on paths traversing more than a specified number of hops –Other Time critical frames – 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

6 doc.: IEEE 802.11-07/2454r0 Submission September 2007 M. Benveniste (Avaya Labs)Slide 6 Express Forwarding Illustration Express Forwarding Illustration Ref 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 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 12 1-2 Frame 3 4 2-3 DT0 3-hop path 1-4 3-4 5 DTI ANIMATED

7 doc.: IEEE 802.11-07/2454r0 Submission September 2007 M. Benveniste (Avaya Labs)Slide 7 Express Retransmission Express Retransmission Ref Doc 11-07/2452, 2453 Retransmission typically involves backoff using a wider contention window With express retransmission, a frame is retransmitted by dispensing with backoff and transmitting within DT0 following ACKtimeout An express forwarded frame is less likely to collide on retransmission because of its prioritization Only the first retransmission attempt receives priority treatment Prevents two express forwarded 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

8 doc.: IEEE 802.11-07/2454r0 Submission September 2007 M. Benveniste (Avaya Labs)Slide 8 Performance Evaluation

9 doc.: IEEE 802.11-07/2454r0 Submission September 2007 M. Benveniste (Avaya Labs)Slide 9 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)

10 doc.: IEEE 802.11-07/2454r0 Submission September 2007 M. Benveniste (Avaya Labs)Slide 10 Parameters Network802.11a802.11g802.11b Slot Time9 usec 20 usec Sifs Time16 usec10 usec Phy_CWmin15 Phy_CWmax1023 PLCP overhead control20 usec 96 usec PLCP overhead data20 usec 96 usec Control Data Rate24 Mbps 5.5 Mbps Difs Timesifs + 2*slot_time = 28 usec sifs + 2*slot_time = 50 usec Eifs_timedifs + sifs + ACK @ 24 Mbps difs + sifs + ACK @ 5.5 Mbps aifsn222 Aifs [ac] aifsn[ac] * slot_time + sifs_time = 28 usec aifsn[ac] * slot_time + sifs_time = 50 usec ACK tx rate24 Mbps 5.5 Mbps DATA tx rate54 Mbps 11 Mbps Cwmax1023 Cwmin15

11 doc.: IEEE 802.11-07/2454r0 Submission September 2007 M. Benveniste (Avaya Labs)Slide 11 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 Surrounded by peer-to-peer mesh or independent WLAN flows on same channel Low total traffic load (3.9 Mbps), symmetrically distributed along the multi-hop path

12 doc.: IEEE 802.11-07/2454r0 Submission September 2007 M. Benveniste (Avaya Labs)Slide 12 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 Mbps payload size: 200 bytes, inter-arrival 20 ms P 910 7812 35 12131116 VOIP VIDEO (L) Network configuration Data range: 25 m, Ack range: 31 m 4-hop path, next-hop neighbors dont hear each other Physical layer rates Data @ 11 Mbps ACK @ 5.5 Mbps TOTAL LOAD: 3.9 Mbps

13 doc.: IEEE 802.11-07/2454r0 Submission September 2007 M. Benveniste (Avaya Labs)Slide 13 Scenario 1: Mean Delays Express Fwd Disabled Express Fwd Enabled Express Fwd With Express Rtx Node2 > Node12.702.622.67 Node3 > Node54.465.304.23 Node5 > Node31.711.601.63 Node7 > Node84.994.764.33 Node9 > Node101.511.421.50 Node10 > Node94.405.304.97 Node16 > Portal75.8750.7633.00 Portal > Node_1672.8549.7032.52 With Express Forwarding 4-hop VOIP ETE delay 50 ms + Express Retransmission 4-hop VOIP mean delay 33 ms Lower delays for all other flows Without Express Forwarding 4-hop VOIP mean delay 75 ms

14 doc.: IEEE 802.11-07/2454r0 Submission September 2007 M. Benveniste (Avaya Labs)Slide 14 Scenario 1: 4-hop Delays (CDF) Uplink Delay Downlink Delay

15 doc.: IEEE 802.11-07/2454r0 Submission September 2007 M. Benveniste (Avaya Labs)Slide 15 Scenario 1: Dropped Frames* With Express Forwarding Fewer frames are dropped by all nodes * Frames are dropped if retransmitted 7 times unsuccessfully

16 doc.: IEEE 802.11-07/2454r0 Submission September 2007 M. Benveniste (Avaya Labs)Slide 16 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) also enjoy delay reduction –Prioritization reduces contention – fewer collisions Fewer frames are dropped as a result of fewer retransmissions

17 doc.: IEEE 802.11-07/2454r0 Submission September 2007 M. Benveniste (Avaya Labs)Slide 17 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 Surrounded by peer-to-peer mesh or independent WLAN flows on same channel Total traffic load (5.7 Mbps), asymmetrically distributed along the multi-hop path, is more concentrated around portal P

18 doc.: IEEE 802.11-07/2454r0 Submission September 2007 M. Benveniste (Avaya Labs)Slide 18 Scenario 2: 802.11b Mesh (6 hops) P121314 15 1116 3 5 12 7 8 9 10 64 VIDEO (L) VOIP Traffic description VIDEO (L): Low Resolution, 1.4 Mbps payload size: 1464 bytes, inter-arrival 8 ms VOIP : G711, 0.16 Mbps payload 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

19 doc.: IEEE 802.11-07/2454r0 Submission September 2007 M. Benveniste (Avaya Labs)Slide 19 Scenario 2: Mean Delays Express Fwd Disabled Express Fwd Enabled Express Fwd With Exp Rtx Node2 > Node12.712.542.60 Node3 > Node51.121.081.11 Node5 > Node34.343.353.92 Node6 > Node44.544.374.74 Node7 > Node841.1723.3029.28 Node9 > Node104.593.183.66 Node10 > Node95.024.394.09 Node16 > Portal151.3244.1223.20 Portal > Node16164.5057.5539.01 With Express Forwarding 6-hop VOIP mean delay 58 ms + Express Retransmission 6-hop VOIP mean delay 39 ms Lower delays for all other flows Without Express Forwarding 6-hop VOIP mean delay 164 ms

20 doc.: IEEE 802.11-07/2454r0 Submission September 2007 M. Benveniste (Avaya Labs)Slide 20 Scenario 2: 6-hop Delays (CDF) Uplink Delay Downlink Delay (sec)

21 doc.: IEEE 802.11-07/2454r0 Submission September 2007 M. Benveniste (Avaya Labs)Slide 21 Scenario 2: Dropped Frames With Express Forwarding Fewer frames are dropped by all nodes

22 doc.: IEEE 802.11-07/2454r0 Submission September 2007 M. Benveniste (Avaya Labs)Slide 22 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 retransmissions Traffic 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

23 doc.: IEEE 802.11-07/2454r0 Submission September 2007 M. Benveniste (Avaya Labs)Slide 23 Scenario 3: 802.11g Mesh (5 hops) Examines the effectiveness of Express Forwarding in a long transmit range (391 meters) 11g single channel network Multi-hop paths of 5 and 2 hops Surrounded by peer-to-peer mesh or independent WLAN flows on same channel Total traffic load (17 Mbps), asymmetrically distributed along the multi-hop path, is more concentrated around portal P Multiple VOIP flows and Video go thru portal P

24 doc.: IEEE 802.11-07/2454r0 Submission September 2007 M. Benveniste (Avaya Labs)Slide 24 P 1 2 3 45 VIDEO (L) VIDEO (H) VIDEO (L) VOIP 17 18 211325 24 1120 6 78 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 Mbps payload size: 200 bytes, inter-arrival 20 ms Network configuration TX RANGE: 391 m 5-hop path, next-hop neighbors dont hear each other Physical layer rates Data @ 54 Mbps ACK @ 24 Mbps TOTAL LOAD: 17 Mbps

25 doc.: IEEE 802.11-07/2454r0 Submission September 2007 M. Benveniste (Avaya Labs)Slide 25 Scenario 3: Mean Delays Without Express Forwarding 5-hop VOIP delay 91 ms 2-hop VOIP delay 43 ms Flow 25-6 is unstable Flow 11-20 delay 100 ms With Express Forwarding 5-hop VOIP delay 4 ms 2-hop VOIP delay 3 ms Flow 25-6 delay 4 ms Flow 11-20 delay 3 ms + Express Retransmission 5-hop VOIP delay 3 ms 2-hop VOIP delay <3 ms Flow 25-6 delay 3 ms Flow 11-20 delay <3 ms Substantially lower delays for all other flows

26 doc.: IEEE 802.11-07/2454r0 Submission September 2007 M. Benveniste (Avaya Labs)Slide 26 Scenario 3: Mean Delays (ms) Flows Express Forwarding Disabled Express Forwarding Enabled Express Forwarding With Express Re-TX Without Multi-hop Flows Portal->Node_590.764.203.39NA Portal->Node_1636.682.902.641.18 Portal->Node_1740.973.392.771.14 Portal->Node_1843.183.322.64NA Portal->Node_2236.165.214.501.45 Node_5->Portal68.674.042.18NA Node_7->Node_84.891.491.080.63 Node_8->Node_75.531.471.360.65 Node_11->Node_20137.823.372.721.21 Node_12->Node_109.052.181.901.23 Node_13->Node_2114.031.831.671.09 Node_16->Portal8.872.692.561.38 Node_17->Portal11.801.891.551.07 Node_18->Portal23.382.842.11NA Node_19->Node_1411.711.791.530.76 Node_24->Node_910.791.961.770.92 Node_25->Node_61119.603.702.941.16

27 doc.: IEEE 802.11-07/2454r0 Submission September 2007 M. Benveniste (Avaya Labs)Slide 27 Scenario 3: 5-hop Delays (CDF) P -> Node5 Delay Node5 -> P Delay

28 doc.: IEEE 802.11-07/2454r0 Submission September 2007 M. Benveniste (Avaya Labs)Slide 28 Scenario 3: 2-hop Delays (CDF) P -> Node18 Delay Node18 -> P Delay (sec)

29 doc.: IEEE 802.11-07/2454r0 Submission September 2007 M. Benveniste (Avaya Labs)Slide 29 (sec) Scenario 3: Video (H) Delays (CDF) Node11 -> Node6 Delay Node25 -> Node6 Delay (sec)

30 doc.: IEEE 802.11-07/2454r0 Submission September 2007 M. Benveniste (Avaya Labs)Slide 30 Scenario 3: Dropped Frames There are practically no dropped frames with express forwarding

31 doc.: IEEE 802.11-07/2454r0 Submission September 2007 M. Benveniste (Avaya Labs)Slide 31 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

32 doc.: IEEE 802.11-07/2454r0 Submission September 2007 M. Benveniste (Avaya Labs)Slide 32 P 1 2 3 45 VIDEO (L) VIDEO (H) VIDEO (L) VOIP 17 18 211325 24 1120 6 78 2216 10 12 1914 9 Multi-hop effect in single-channel mesh If the ACK from 2 (or 3) causes collision at Node6, retransmission of frame from Node25 will wait till multi-hop TX P->Node5 completes The sooner the latter completes, the sooner the transmission Node25->Node6 will complete Express forwarding reduces time of transmission P->Node5, thus shortens delay for flow Node25- >Node6 With Express Forwarding, the ACK from 2 prevents collision by Node25 for the remainder of multi-hop transmission P->Node5 Multi-hop flow from P to Node5 ANIMATED

33 doc.: IEEE 802.11-07/2454r0 Submission September 2007 M. Benveniste (Avaya Labs)Slide 33 Scenario 3.1: Multi-hop flows removed P 1 2 3 45 VIDEO (L) VIDEO (H) VIDEO (L) VOIP 17 18 211325 24 1120 6 78 2216 10 12 1914 9 Traffic description The same as Scenario 3, with multi-hop flows (P->Node5 and P->Node18) removed Network configuration TX RANGE: 391 m 5-hop path, next-hop neighbors dont hear each other Physical layer rates Data @ 54 Mbps ACK @ 24 Mbps X X TOTAL LOAD: 16 Mbps

34 doc.: IEEE 802.11-07/2454r0 Submission September 2007 M. Benveniste (Avaya Labs)Slide 34 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

35 doc.: IEEE 802.11-07/2454r0 Submission September 2007 M. Benveniste (Avaya Labs)Slide 35 Scenario 3.1: Mean Delays (ms) Flows Express Forwarding Disabled Express Forwarding Enabled Express Forwarding With Express Re-TX Without Multi-hop Flows Portal->Node_590.764.203.39NA Portal->Node_1636.682.902.641.18 Portal->Node_1740.973.392.771.14 Portal->Node_1843.183.322.64NA Portal->Node_2236.165.214.501.45 Node_5->Portal68.674.042.18NA Node_7->Node_84.891.491.080.63 Node_8->Node_75.531.471.360.65 Node_11->Node_20137.823.372.721.21 Node_12->Node_109.052.181.901.23 Node_13->Node_2114.031.831.671.09 Node_16->Portal8.872.692.561.38 Node_17->Portal11.801.891.551.07 Node_18->Portal23.382.842.11NA Node_19->Node_1411.711.791.530.76 Node_24->Node_910.791.961.770.92 Node_25->Node_61119.603.702.941.16

36 doc.: IEEE 802.11-07/2454r0 Submission September 2007 M. Benveniste (Avaya Labs)Slide 36 Scenario 4: 802.11a Mesh (5 hops) Examines the effectiveness of Express Forwarding in a short transmit range (25 meters) 11a single channel network Multi-hop paths of 5 and 2 hops Surrounded by peer-to-peer mesh or independent WLAN flows on same channel 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

37 doc.: IEEE 802.11-07/2454r0 Submission September 2007 M. Benveniste (Avaya Labs)Slide 37 Scenario 4: 802.11a Mesh (5 hops) P 16 22 17 18 12 15 10 21 26 13 2 45 3 6 23 7 1 8 1419 1120 24 12 VOIP VIDEO (L) VIDEO (H) 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 Mbps payload size: 200 bytes, inter-arrival 20 ms Network configuration TX RANGE: 25 m 2 multi-hop paths, next-hop neighbors dont hear each other Physical layer rates Data @ 54 Mbps ACK @ 24 Mbps

38 doc.: IEEE 802.11-07/2454r0 Submission September 2007 M. Benveniste (Avaya Labs)Slide 38 Scenario 4: Mean Delays Without Express Forwarding 5-hop VOIP delay 179 ms 2-hop VOIP delay 79 ms P->16 VOIP delay 76 ms P->22 Video delay 45 ms With Express Forwarding 5-hop VOIP delay 19 ms 2-hop VOIP delay 6 ms P->16 VOIP delay 7 ms P->22 Video delay 6 ms + Express Retransmission 5-hop VOIP delay 10 ms 2-hop VOIP delay 4 ms P->16 VOIP delay 5 ms P->22 Video delay 4 ms Substantially lower delays for all flows

39 doc.: IEEE 802.11-07/2454r0 Submission September 2007 M. Benveniste (Avaya Labs)Slide 39 Express Forwarding Disabled Express Forwarding Enabled Express Forwarding With Express Re-TX Portal > Node5179.1219.319.51 Portal > Node1675.907.245.44 Portal > Node1771.906.304.34 Portal > Node1878.926.394.08 Portal > Node2245.236.383.95 Node5 > Portal124.0423.1711.88 Node7 > Node82.681.381.24 Node8 > Node73.501.511.34 Node11 > Node207.872.742.26 Node12 > Node107.762.761.93 Node13 > Node215.102.001.77 Node14 > Node193.191.631.57 Node15 > Node233.641.591.47 Node16 > Portal41.1913.9010.52 Node17 > Portal6.041.161.13 Node18 > Portal9.561.771.71 Node19 > Node244.862.511.72 Node21 > Node1411.923.783.38 Node21 > Node2611.603.502.92 Node24 > Node94.601.951.91 Node25 > Node629.154.983.77 Node25 > Node1328.904.923.75

40 doc.: IEEE 802.11-07/2454r0 Submission September 2007 M. Benveniste (Avaya Labs)Slide 40 Scenario 4: 5-hop Delays (CDF) Downlink Delay Uplink Delay

41 doc.: IEEE 802.11-07/2454r0 Submission September 2007 M. Benveniste (Avaya Labs)Slide 41 Scenario 4: 2-hop Delays (CDF) Downlink Delay Uplink Delay

42 doc.: IEEE 802.11-07/2454r0 Submission September 2007 M. Benveniste (Avaya Labs)Slide 42 Scenario 4: Dropped Frames Fewer dropped frames with express forwarding

43 doc.: IEEE 802.11-07/2454r0 Submission September 2007 M. Benveniste (Avaya Labs)Slide 43 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 –The long delays experienced by the Video (H) flows disappear when multi- hop flows are express forwarded 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

44 doc.: IEEE 802.11-07/2454r0 Submission September 2007 M. Benveniste (Avaya Labs)Slide 44 Conclusion Express Forwarding reduces end-to-end delay 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

45 doc.: IEEE 802.11-07/2454r0 Submission September 2007 M. Benveniste (Avaya Labs)Slide 45 Back up

46 doc.: IEEE 802.11-07/2454r0 Submission September 2007 M. Benveniste (Avaya Labs)Slide 46 Excessive 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 (((((((( (((((((( X Interference

47 doc.: IEEE 802.11-07/2454r0 Submission September 2007 M. Benveniste (Avaya Labs)Slide 47 Express 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 ANIMATED


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