Transcript Mesh Summit Multiradio

Routing in Multi-Radio, Multi-Hop
Wireless Mesh Networks
Richard Draves, Jitu Padhye,
Brian Zill
Microsoft Research
Self-Organizing Neighborhood Networks
• Key Properties
– No network engineer
– Very little mobility
– Energy not a concern
Internet
101
Bus Stop
206
Gas Station
(Internet TAP)
Mesh Router 7
EXIT
Mesh Router 5
Mesh Router 2
Mesh Router 3
Mesh Zone
Mesh Router 1
Mesh End Device
End Device
(Guest to Router 1)
90
• One challenge:
network capacity
• Our approach:
multiple radios
Results
• Ad-hoc routing at layer 2.5 works well
• Link quality is important, but not all metrics
are created equal
• Multiple radios provide significant capacity
improvement if the routing utilizes
channel-diversity, data rate, loss rate
(Please see our SIGCOMM & Mobicom papers for more details.)
Layer 2 vs Layer 3
• Layer 2 (link layer): like ethernet switches
− Limited to single link technology
+ Supports multiple protocols (IPv4, IPv6, IPX)
+ Preserves link abstraction
• Layer 3 (network layer)
+ Supports multiple link technologies
− Limited to single network protocol
− Link-local mechanisms don’t work
• DHCP, RA/RS
Our Approach: Routing at Layer 2.5
• A virtual link-layer
+ Supports multiple link technologies
+ Supports IPv4, IPv6 etc unmodified
+ Preserves the link abstraction
+ Agnostic to choice of ad-hoc routing algorithm
IPv4
IPv6
IPX
Mesh Connectivity Layer (with LQSR)
Ethernet
802.11
802.16
Mesh Connectivity Layer (MCL)
• Virtual ethernet adapter
– Virtual ethernet addresses
– Multiplexes heterogeneous
physical links
– Physical links need not be
ethernet
Packet Format
Ethernet
MCL
Payload:
TCP/IP,
ARP,
IPv6…
Link-Quality Source Routing (LQSR)
• Source-routed link-state routing protocol
– Derived from DSR
– Part of Mesh Connectivity Layer (layer 2.5)
– Supports link-quality modules
• Both on-demand/proactive mechanisms
– Route Discovery
– Route Maintenance
– Metric Maintenance
LQSR Metric Support
• HOP: shortest-path routing
– closest to DSR
•
•
•
•
RTT: round-trip time latency
PktPair: packet-pair latency
ETX: expected transmission count
WCETT: designed for multiple radios
Multi-Radio Routing
• Previous metrics (HOP, ETX) not suitable for multiple
radios per node
– Do not leverage channel, range, data rate diversity
• Weighted Cumulative Expected Transmission Time
– Weight links according Expected Transmission Time (ETT)
• Takes link bandwidth and loss rate into account
– Combine link ETTs into Weighted Cumulative ETTs (WCETT)
• Takes channel diversity into account
– Incorporated into source routing
WCETT: Combining link ETTs
All hops on a path on the same
channel interfere
– Add ETTs of hops that are
on the same channel
– Path throughput is
dominated by the
maximum of these sums
Given a n hop path, where each
hop can be on any one of k
channels, and tuning parameter β:
n
WCETT  (1   ) ETTi   max 1 j k X j
i 1
where
Need to avoid unnecessarily
long paths
- bad for TCP performance
- bad for global resources
Xj 
 ETT
i
hop i is on channel j
Select the path with min WCETT
Testbed
• 23 nodes in building 113
• Cheap desktop
machines
201
220
205
203
227
221
207
Approx. 61 m
– NetGear WAG or WAB
– Proxim OriNOCO
– Cards can operate
in a, b or g mode.
226
204
– HP d530 SF
• Two radios in each node
210
206
208
225
211
224
223
209
214
215
217
219
218
216
Approx. 32 m
TCP Throughput Test
• Select 100 sender-receiver pairs at random (out of
23x22 = 506)
– 2-minute TCP transfer
• Two scenarios:
– Baseline (Single radio):
• NetGear cards in 802.11a mode
• Proxim OFF
– Two radios
• NetGear cards in 802.11a mode
• Proxim cards in 802.11g mode
• Repeat for shortest-path, ETX, WCETT
Results
Median Throughput of 100 transfers
3500
2990
Single Radio
Throughput (Kbps)
3000
Two Radios
2500
2000
1601
1379
1500
1508
1155
844
1000
500
0
WCETT
ETX
Shortest Path
WCETT uses 2nd radio better than ETX or shortest path.
Two-Radio Throughput CDF
Fraction of Connections with Lower
Throughput
1
HOP
ETX
WCETT
0.8
0.6
0.4
Better
0.2
0
0
2
4
6
8
10
Throughput (Mbps)
12
14
16
Two-Radio Path Length vs Throughput
ETX
18
18
16
16
14
14
Throughput (Mbps)
Throughput (Mbps)
WCETT
12
10
8
6
4
2
12
10
8
6
4
2
0
0
0
1
2
3
4
5
Average Path Length (Hops)
6
7
0
1
2
3
4
Average Path Length (Hops)
5
6
7
WCETT Improvement by Path Length
Percentage Improvement in Median
Throughput
140
120
100
80
60
40
20
0
1
2
3
4
Path Length (with 2 radios)
>=5
Conclusions
• Ad-hoc routing at layer 2.5 works well
• Link quality is important for performance
• Previous routing metrics do not work well
in heterogeneous multi-radio scenarios
• WCETT improves performance by making
judicious use of additional capacity and
channel diversity provided by the 2nd radio