無線網狀網路中公平的連結競爭及節點競爭

Abstract

隨著IEEE 802.11s草案(draft)的提出，使得無線網狀網路技術更適用於骨幹網路的架設；然而在目前的草案中，並沒有針對”公平性問題”提出任何相關的解決方式，導致靠近骨幹出口的少數近端節點將獨佔頻寬、造成末端節點餓死，無法提供任何頻寬給該節點所服務之工作站使用。本論文分析802.11無線網路中公平性問題的成因，有節點競爭問題以及連接競爭問題，提出Fair Link and Node Contention(FLNC)演算法，動態地使用三種機制，包括雙重佇列輪詢機制(DRR)分隔近端節點與遠端節點流量解決節點競爭問題，以及RTS/CTS機制並搭配調整競爭視窗解決連結競爭問題。透過模擬的結果顯示，在四個節點的串列網路拓樸與五個節點的樹狀網路拓樸飽和流量環境下，可以消除不公平問題帶來的9 Mbps傳輸速度的差異。

The proposed IEEE 802.11s draft makes the wireless technique more suitable for backhaul network. However, there is no any solution addressing on the fairness problem in the latest version of 802.11s daft, which causes near-portal nodes occupying most channel resource and the further nodes starved. This thesis points out that the fairness problem results from the node contention and the link contention, and proposes the Fair Link and Node Contention (FLNC) algorithm that uses the round-robin mechanism among dual queues to solve the node contention, and adopts RTS/CTS mechanism and adjusts the size of contention window to relieve the link contention. By simulation result, we show that on a 4-node chain topology and a 5-node tree topology with saturated offered load, using FLNC can decrease the 9-Mbps throughput difference coming from fairness problem.