Is Spanning Tree Protocol Right for ESS Mesh

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Is Spanning Tree Protocol Right for ESS Mesh?

• Tyan-Shu Jou, Ted Kuo, and Ming Sheu
• tsjou_at_janusysnetworks.com
• Janusys Networks, Inc.
• Date May 11, 2004

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Forwarding Topologies to Prevent Traffic Looping
on an ESS Mesh

• One global spanning tree (802.1d/802.1w)
• Shortest Path based routing algorithms
• (Spanning tree algorithms are essentially
  Distance Vector routing protocol running at Layer
  2 that computes the lowest cost paths to the
  designated Root node)

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Advantages of Using Spanning Tree on ESS Mesh

• Proven standard algorithm
• Rapid Spanning Tree (802.1w) can converge within
  a short time
• (Although on wireless networks, link up/down
  detection are timer dependent)
• Low processing overhead

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Disadvantages of using Spanning Tree on ESS Mesh

• Not optimal connections between wireless peers
• Not intended for dynamic topology the global
  tree has to be reconstructed for any link change
• Load sharing is difficulteg., in case multiple
  border nodes to wired network exist
• Difficult to reflect dynamic metrics such as
  receiving signal strength

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Examples of Shortest-path forwarding Algorithms

• OSPFv3 extension for wireless ad-hoc network
• IETF MANET 4 IP routing protocols for wireless
  ad-hoc network
• Many others (NRL Dynamic backbone, Zigbee, )

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Questions for the SG

• Should we decide which layer (or, what address)
  the forwarding algorithm should be based?
• Should we decide one forwarding algorithm?
• Can we only define the communication message
  format rather than the algorithm?
• Can we only define the MAC interface so the same
  hardware module can be shared?
• How much interoperability among vendors required?