Is an Office Without Wires Feasible? Sharad Agarwal Jakob Eriksson, Victor Bahl, Jitu Padhye

2.JUNE All-Wireless Office No wires No switches No APs

2.JUNE All-Wireless Office Not large corporation Small offices – 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

2.JUNE All-Wireless Office Office PCs –Two 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

2.JUNE 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 band –Routing metric –User-server placement –Spatial reuse, hidden terminal

2.JUNE Don’t We Already Know? Typical evaluation –Select sender, receiver at random; 1 TCP flow, 2 mins –Repeat 100 times, calculate median

2.JUNE 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, 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

2.JUNE 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)

2.JUNE 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

2.JUNE Mesh Testbed CentralDistantExtreme User User User User ,207 User ,210 User ,214 User ,216 User ,202 User ,204 User ,225 User ,226 Domain Controllers214,215204,226201,227 Source Depots ,227 Exchange ,227 Proxies216,219201,225201,227 Config Netgear WG Netgear WAB/G ORiNOCO Proxim Transmit Power RTS / CTS Aa-56a % Ba-56a %on Ca-56g % D g-10a-56100% E g-10a-5650% F g-10a %

2.JUNE Light Load, Central Placement

2.JUNE Heavy Load, Distant Placement

2.JUNE Summary of Results Results are unusual –Captured traffic is very different than synthetic –Prior work’s throughput results not very helpful Many configurations – median delay <20ms – hardware had upto 2.5x difference – 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"Feasibility Study of Mesh Networks for All-Wireless Offices"

2.JUNE 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