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Proposed Change to 802.11 Intra-Mesh Congestion Notification Frame

This presentation proposes a small extension to the Congestion Notification element for better intra-mesh congestion management. It addresses existing congestion scenarios and proposes a solution for improved control.

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Proposed Change to 802.11 Intra-Mesh Congestion Notification Frame

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  1. Proposed Change to 802.11 Intra-Mesh Congestion Notification Frame Authors: Date: 2010-12-08 Barbara Staehle, Uni Würzburg

  2. Abstract This presentation provides a motivation for a small, simple extension of the Congestion Notification element. This extension allows a more flexible use of the Congestion Notification element for different intra-mesh congestion control mechanisms. The presentation and the corresponding submission 11-10/1428r0 address CIDs 28, 85, 204, 205. Barbara Staehle, Uni Würzburg

  3. Congestion Situation A: Solvable The Congestion Notification element described in 7.3.2.99 supports a node selective congestion control. Which is helpful in the situation depicted below: C is not able to forward packets from mesh STA B fast enough over link (C,D) and consequently sends a Congestion Notification element to mesh STA B. This causes B to apply local rate control as specified in 11C.11 in order to avoid a waste of mesh resources. In turn, B can not forward the packets from A fast enough and will send a Congestion Notification element to mesh STA A. Despite the congestion detected at mesh STA B, E is however still allowed to send packets to mesh STA B, as there is no congestion for link (B,A). Barbara Staehle, Uni Würzburg

  4. Congestion Situation B: Currently Unsolvable The Congestion Notification element described in 7.3.2.99 does, however, NOT support a flow selective congestion control which would be necessary to avoid the waste of mesh resources in the situation depicted below. Due to the same reasons as before, B has to use the Congestion Notification element to cause A to apply local rate control as specified in 11C.11 in order to avoid a waste of mesh resources. However, B could still forward packets from mesh STA A to mesh STA E. But as the format indicated in the standard does not provide the possibility to indicate that A should apply rate control only to packets destined for D and not for packets with mesh destination E, the congestion control causes an unnecessary throughput reduction. Barbara Staehle, Uni Würzburg

  5. Proposed Solution • Extend the format of the Congestion Notification element with the mesh destination in order to indicating which path causes the congestion. • “The Destination Mesh STA Address field is represented as a 48-bit MAC address and is set to the address of the mesh destination for which the intra-mesh congestion control shall be applied. It is set to the broadcast address if the intra-mesh congestion control shall be applied to all destinations.” (i.e. broadcast address = current functionality) • multiple Congestion Notification elements in a single Congestion Control Notification frame • full proposed normative text in 11-10/1428r0 (only a few lines) Barbara Staehle, Uni Würzburg

  6. References • 11-10/1428r0 M. Bahr, B. Staehle, D. Staehle: „Destination Address in Congestion Notification“ • IEEE 802.11s Draft Standard D7.03 Barbara Staehle, Uni Würzburg

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