Is an Office Without Wires Feasible

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Is an Office Without Wires Feasible?

• Sharad Agarwal
• Jakob Eriksson, Victor Bahl, Jitu Padhye

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All-Wireless Office

• No wires
• No switches
• No APs

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All-Wireless Office

• Not large corporation
• Small offices
• 10-100 PCs
• Rapid deployment
• Short-term office
• Low-cost solution
• Not replacement for wire

• Looking for good performance
• how long a user waits for a transaction
• small additional delay

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All-Wireless Office

• Office PCs
• Two 802.11 interfaces
• simultaneous xmit rcv on non-interfering
  channels
• frequency diversity range-rate tradeoff
• Office servers
• mail, domain controllers, code repositories
• proxies with wires
• Mesh routing
• A lot of prior work
• Routing protocols
• Link quality metrics

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Questions

• What additional delay penalty will a mesh network
  impose
• In typical office configurations
• With typical office traffic
• How should an administrator pick
• Wireless hardware
• IEEE 802.11 band
• Routing metric
• User-server placement
• Spatial reuse, hidden terminal

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Dont We Already Know?

• Typical evaluation
• Select sender, receiver at random 1 TCP flow, 2
  mins
• Repeat 100 times, calculate median

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Methodology

• Capture traffic from 11 office users
• Packet level capture insufficient
• TCP effects in wireless, multihop very different
• Socket level is best open, send, receive, close
• Replay on mesh testbed among office users
• MCL by Draves, Padhye, Zill _at_ MSR (2004)
• DSR-like routing with virtual link layer
  optimizations
• Link metrics hop, RTT, PKTPAIR, ETX, WCETT
• Assign users, application servers to testbed
• Examine several design choices
• Not disrupt actual users

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Captured Traffic

• Very diverse traffic types, sizes, concurrency
• Map each type to 1-2 mesh machines for replay
• Non-winsock traffic not captured
• Get user RPC miss SMB, NBT (almost all IDS for
  us)

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Replay Model

• Concurrent sessions
• Session
• connect to disconnect
• multiple transactions not concurrent
• Transaction
• 1 send, 0 receives
• Response time
• start of send
• end of last receive of the transaction

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Mesh Testbed
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Light Load, Central Placement
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Heavy Load, Distant Placement
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Summary of Results

• Results are unusual
• Captured traffic is very different than synthetic
• Prior works throughput results not very helpful
• Many configurations median delay lt20ms
• 802.11 hardware had upto 2.5x difference
• 802.11 band had upto 2x difference
• Server placement had upto 3x difference
• No benefit of spatial reuse, hidden node
  avoidance
• 2 routing metrics bad, 3 good very similar
• "Feasibility Study of Mesh Networks for
  All-Wireless Offices", in ACM Mobisys, June 2006

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Open Issues / Limitations

• 1 testbed, 1 set of user traces
• but many configurations, different time periods
• Performance can be improved further
• cross interference detection adaptation
• gateway balancing
• Skipped some real world issues
• fairness
• security / DoS
• Jamming, routing disruption, resource consumption

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