Some Simulation Results for ‘Express Forwarding’ Date: 2007-07-16 Authors: Name Address Company Phone Email Mathilde Benveniste 233 Mt Airy Road Basking Ridge, NJ 07920, US Avaya Labs-Research 908-696-5206 benveniste@ieee.org Kaustubh Sinkar 908-696-5284 ksinkar@avaya.com 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 <stuart.kerry@philips.com> 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 <patcom@ieee.org>. M. Benveniste (Avaya Labs)

Some Simulation Results for ‘Express Forwarding’ Mathilde Benveniste Kaustubh Sinkar Avaya Labs - Research M. Benveniste (Avaya Labs)

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 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 The mesh latency/jitter allowance for traffic streams traversing the wired network is less than for traffic staying on the mesh A target of 10 ms for maximum latency/jitter was set for top priority AC in 802.11 TGe Reducing the worst-case delay causes all frames of a QoS traffic stream to experience lower delay A shorter jitter buffer is needed M. Benveniste (Avaya Labs)

Express Forwarding – Review Ref Doc 11-07/415, 639 ‘Express forwarding’ reduces the end-to-end delay of selected frames by granting forwarding nodes immediate access to the channel Frames qualifying for express forwarding 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 M. Benveniste (Avaya Labs)

Express Forwarding Illustration Ref Doc 11-07/415, 639 DT0 NAV setting at receiving node DTI NAV setting at all other neighbor nodes Value in Duration field Channel 1-2 Frame ACK 2-3 3-4 time 5 3-hop path 1-4 1 2 3 4 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 The forwarding nodes, 2 and 3, adjust the Duration value on the received frame by subtracting an increment when setting their NAV The non-forwarding neighbor nodes – e.g. 5 – sets NAV by Duration field M. Benveniste (Avaya Labs)

Simulation Study VIDEO VOIP 11b channel Traffic Flow description 6 flows: 3 Video and 3 VoIP flows One flow is express forwarded: 6-hop VoIP flow from/to Portal Five flows are not express forwarded: Single-hop peer-to-peer flows Next-hop neighbors don’t hear one another Flow description - VIDEO flows: Uni-directional, Frame 1464 Bytes, 8 ms inter-arrival time (exp) - VOIP flows: Bi-directional, Frame 200 Bytes, 20 ms inter-arrival time (fixed) M. Benveniste (Avaya Labs)

End-to-end delay for flow node_16 -> Portal Uplink Delay End-to-end delay for flow node_16 -> Portal M. Benveniste (Avaya Labs)

End-to-end delay for flow Portal -> Node_16 Downlink Delay End-to-end delay for flow Portal -> Node_16 M. Benveniste (Avaya Labs)

Delay Overview Flow Traffic Type E-to-E Delay (ms) Express Forwarding   Flow Traffic Type E-to-E Delay (ms) Express Forwarding Enabled P-N_16 Disabled P-N_16 node_2 -> node_1 Video 4 3 node_5 -> node_3 VoIP 6 node_6 -> node_4 5 node_7 -> node_8 20 node_9 <-> node_10 2 Portal <-> node_16 44 / 35 93 / 99 M. Benveniste (Avaya Labs)

Conclusions Express forwarding reduced end-to-end delay of the multi-hop transmission to less than half Neighboring transmissions did not suffer significant delay increase The benefit of express forwarding is substantial M. Benveniste (Avaya Labs)