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Routing Metrics and Protocols for Wireless Mesh Networks

Routing Metrics and Protocols for Wireless Mesh Networks. Speaker : 吳靖緯 MA0G0101. 2011.12.22. Outline. Abstract Wireless Mesh Routing Routing Metrics Routing Protocols Conclusion. Abstract.

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Routing Metrics and Protocols for Wireless Mesh Networks

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  1. Routing Metrics and Protocols for Wireless Mesh Networks Speaker : 吳靖緯 MA0G0101 2011.12.22

  2. Outline • Abstract • Wireless Mesh Routing • Routing Metrics • Routing Protocols • Conclusion

  3. Abstract • WMNs are low-cost access networks built on cooperative routing over a backbone composed of stationary wireless routers. • WMNs must deal with the highly unstable wireless medium. • Therefore, the design of algorithms that consider link quality to choose the best routes are enabling routing metrics and protocols to evolve.

  4. Abstract • In this work, we analyze the state of the art in WMN metrics and propose a taxonomy for WMN routing protocols. • Performance measurements for a WMN, deployed using various routing metrics, are presented and corroborate our analysis.

  5. Wireless Mesh Routing • WMN backbone routers use multihop communication similarly to ad hoc networks.

  6. Wireless Mesh Routing • The backbone routers typically are stationary, which permits routing metrics to model link quality instead of simply using the number of hops. • Assuming that the common-case application in WMNs is Internet access, traffic is concentrated on links close to the gateways.

  7. Routing Metrics • Ad hoc networks usually use the hop count as a routing metric. • This metric is appropriate for ad hoc networks because new paths must be found rapidly, whereas high-quality routes may not be found in due time. • In WMNs, the stationary topology benefits quality-aware routing metrics.

  8. Routing Metrics • Wireless ad hoc network • 不需要依賴一個既存的網路架構，像是有線系統的路由器，或是無線系統的無線網路基地台。 • 每一個節點，都有能力轉送網路封包給其他節點，所以網路是由節點與節點間動態連結所形成的。 • 由於網路中的節點沒有當前網路拓撲結構的先驗知識，通常在需要通信時才能知道連線品質。

  9. Routing Metrics • Expected Transmission Count(ETX) • ETX衡量節點間週期性的傳送一個訊息，也週期地以傳送回應給鄰居訊息遺失情形，節點根據這些數據產生新的ETX。 • 節點依據此新的ETX產生新的衡量，若訊息或回應訊息遺失了，節點會將增加衡量，作為反應此遺失的補償。 • 兩變數相乘之後的倒數即是衡量ETX的數值 ：週期時間內成功收到訊息封包的比率 ：週期時間內成功的回應訊息封包比率

  10. Routing Metrics • ETX範例應用 • 考慮兩個節點，節點A與B。A與B每一秒鐘廣播一個訊息。 • 在十秒鐘的週期內，A節點接收到B節點7個訊息，而B節點在十秒鐘的週期內接收到A節點8個訊息。 • B節點將此資訊以單點廣播的方式回覆給節點A，則節點A認知到由A傳送到B節點成功的機率為：(1－0.2) x (1－0.3) ＝0.56，則重新計算產生的衡量ETX值為1／0.56＝1.78。 • Expected TransmissionTime(ETT) • ETT是預計傳輸時間，使用公式如下 ：表示封包大小 ：代表鏈結頻寬

  11. Routing Metrics • Table 1 summarizes the main characteristics of the routing metrics discussed.

  12. Routing Protocols Ad hoc routing • Ad hoc routing protocols are usually proactive, reactive, orhybrid. • The proactive strategy operates like classic routing onwired networks. Routers keep at least one route to any destinationin the network. • Reactive protocols, request a route to a destination only when a node has a datapacket to send. If a node does not have data packets to send toa particular destination, the node will never request a route to it.

  13. Routing Protocols Controlled-flooding • Controlled-flooding protocols use algorithms designed toreduce control overhead. • The basic assumption is that flooding the network is not efficient because most communication in wireless networks is between nearby nodes. • Therefore, there is no need to send control packets to the distant nodes as frequently as to nearby ones.

  14. Routing Protocols • Another way to reduce overhead is to limit the number of nodes responsible for flooding the network. • A common approach is to use algorithms that find the minimum set of nodes required to forward routing information to all destinations in the network.

  15. Routing Protocols Opportunistic • Opportunistic protocols improve classical routing based on cooperative diversity schemes. • These protocols guarantee that the data is always forwarded whenever there is at least one next hop. • In addition, the chosen route likely uses the best quality links, considering short-term variations.

  16. Routing Protocols • WMN protocols and their respective routing metrics.

  17. Conclusion • Routing protocols were classified in four categories: ad hoc-based, traffic-aware, controlled-flooding, and opportunistic. • Our results confirm that the hop metric performs poorly because it is not aware of link-quality variations. • ML, ETX, and ETT, showed better results, considering the different performance measures in accordance with the design of each metric.

  18. Conclusion • The design of WMNs presents a number of open issues, ranging from routing metrics to security. • This is accomplished by better reflecting PHY-layer variations onto routing metrics or by better using the available radio spectrum to directly improve the network throughput.

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