is an office without wires feasible? sharad agarwal jakob eriksson, victor bahl, jitu padhye
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2.JUNE.2006 33
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
2.JUNE.2006 4
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
2.JUNE.2006 55
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
2.JUNE.2006 66
Don’t We Already Know?• Typical evaluation
– Select sender, receiver at random; 1 TCP flow, 2 mins– Repeat 100 times, calculate median
0
500
1000
1500
2000
2500
3000
3500
WCETT ETX Shortest Path
Th
rou
gh
pu
t (K
bp
s)
Single Radio Two Radios
2.JUNE.2006 77
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 @ 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.2006 8
0100020003000400050006000700080009000
Email + PFS DomainController
Proxies Source Depot Other Internal OtherExternal
MB
Tra
ns
ferr
ed
Received
Sent
8
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.2006 99
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.2006 1010
Mesh Testbed
DN
UP
EL 32
~ 32 m
~ 76 m
226
227
225
219
215
220217
218
216
210
214211
209
208
207205
206
203
201202
204
Central Distant Extreme
User 01 203 203 203
User 02 205 205 205
User 03 207 206 206
User 04 208 208 208,207
User 05 209 209 209,210
User 06 211 211 211,214
User 07 226 215 215,216
User 08 225 217 217,202
User 09 218 218 218,204
User 10 227 219 219,225
User 11 204 220 220,226
Domain Controllers 214,215 204,226 201,227
Source Depots 217 227 201,227
Exchange 220 202 201,227
Proxies 216,219 201,225 201,227
ConfigNetgear
WGNetgear WAB/G
ORiNOCO Proxim
Transmit Power
RTS / CTS
A a-56 a-36 100%
B a-56 a-36 100% on
C a-56 g-10 100%
D g-10 a-56 100%
E g-10 a-56 50%
F g-10 a-56 12.50%
DN
UP
EL 32
~ 32 m
~ 76 m
226
227
225
219
215
220217
218
216
210
214211
209
208
207205
206
203
201202
204
DN
UP
EL 32
~ 32 m
~ 76 m
226
227
225
219
215
220217
218
216
210
214211
209
208
207205
206
203
201202
204
DN
UP
EL 32
~ 32 m
~ 76 m
226
227
225
219
215
220217
218
216
210
214211
209
208
207205
206
203
201202
204
2.JUNE.2006 1313
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– 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
2.JUNE.2006 1414
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