multinet: connecting to multiple ieee 802.11 networks using a single radio
DESCRIPTION
MultiNet: Connecting to Multiple IEEE 802.11 Networks Using a Single Radio. Ranveer Chandra, Cornell University joint work with: Victor Bahl (MSR) and Pradeep Bahl (Windows Networking). Motivation. A Sample Scenario. Company ‘B’ guy at Company ‘A’. Company ‘A’ employee. - PowerPoint PPT PresentationTRANSCRIPT
MultiNet:Connecting to Multiple IEEE 802.11 Networks
Using a Single Radio
Ranveer Chandra, Cornell University
joint work with:
Victor Bahl (MSR) and Pradeep Bahl (Windows Networking)
MotivationA Sample Scenario
Company ‘B’ guy at Company ‘A’
Ad Hoc
Infrastructure
Company ‘A’ employee
Company ‘A’ employee
May not have more than one wireless
card!
Other applications:
• Gateway node of a wireless ad hoc network
• Extending the range of an infrastructure network
Why is it so difficult?
Why can’t we use two wireless cards?Power, form factor, and what if we want to connect to10 networks
How is it so different from Ethernet?Wireless networks require association and authentication to communicate on a network. You can only be connected to one network at a time.
OK.. Why not just connect to the network on which you want to send the packet?The association and authentication steps take time. Moreover, even if this time were reduced, a new scheme is required to maintain the state of each network, to simultaneously support connections on multiple networks.
Our Problem
Provide a mechanism for users to connect to multiple networks, such that:- The overhead is transparent to the user- The performance is acceptable on each network- The performance does not degrade with the number of switching nodes- It works with commercial wireless cards.
A set of suggestions for improving performance without breaking the 802.11 protocol
The virtual instances:• Maintain the network state, such as the IP address, and the SSID of the network• Present an always active network interface to the upper layers
Our Approach: MultiNetIdea: • Virtualize the wireless card, one instance per desired network. • Multiplex the card across all the networks
Intermediate layer between IP and MAC: • Maintains a virtual instance of the wireless card per network• Multiplexes across networks, activates one virtual instance at a time. • Buffers packets for inactive networks
Application is unaware of network switching
Implementation on Windows XPCombination of NDIS IM driver and a user level service
Drivero MultiNet Miniport Driver (MMD): Miniport instances. One per network, and IP sees each miniport instance as a different network card.o MultiNet Protocol Driver (MPD): Manages miniports, switches card and buffers packets.
Serviceo Maintains synchronization with other MultiNet nodeso Sends signals to the IM driver using IOCTLs.
MultiNet: Screen Snapshot
Switching: Is it feasible?How long does it take to switch from one network to another?
12.2 12.4 12.6 12.8 13 13.2 13.4 13.6 13.8 14 14.2 14.4 14.6 14.8 15 15.2 15.4 15.6 15.8 16 16.2
Time in Seconds
802.11 Ack
802.11 Beacon
802.11 CTS
802.11 Probe Req
802.11 Probe Resp
802.11 RTS
TCP FTP Data
Steps 1,2 ~ 70 msDelay! ~ 3.8 seconds
Reduced by 3.7 seconds3.87 sec to go from IS to AH
network
Reduced it to 170 ms by trapping media disconnects
Conclusion: Although feasible, switching still takes considerable time. MultiNet should be designed to handle large switching delays, and should perform better when this delay is reduced.
MultiNet: Switching NetworksProblem Statement: When does the card switch from one network to another?
The solution should:• allow users to specify priorities among the connected networks• give more time to networks that have seen more traffic• not starve networks with low traffic
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Time (in seconds)
Ac
tiv
ity
Pe
rio
d (
in m
s)
-130
-110
-90
-70
-50
-30
-10
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Tra
ffic
(in
pa
ck
ets
)
Ad hoc Infrastructure TrafficAH TrafficIS
One approach:See traffic over a window of‘x’ time slots, and give time proportional to the numberof packets seen on the network.Plusses:- better utilization of network time- avoids need for zero configurationMinuses:- Might not work with multihop networks
MultiNet: Buffering PacketsProblem Statement:
(i) Deliver packets sent by the MultiNet node when the network is not active(ii) Deliver packets sent to the MultiNet node when the node is not active
B
A
MultiNet Node in ad hoc mode
Proposed Architecture: • Access points store switching state and buffer packets for Multinet Nodes
(Analogous to Power Save Mode of IEEE 802.11 for IS networks)
• Nodes in ad hoc networks also store the same information for MultiNet nodes in the ad hoc network
(Works for a single hop ad hoc network)
MultiNet: Power Consumption
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Time (in Seconds)
Pa
ck
et
Siz
e (
in B
yte
s)
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Time (in Seconds)
Pa
ck
et
Siz
e (
in B
yte
s)
Traffic on the IS network(Surge trace)
Traffic on the AH network(Real trace)
TEST MACHINE
How much power is saved using MultiNet?
MultiNet: Power Consumption
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Time (In Seconds)E
nerg
y (In
Jou
les)
Two Radio PS MultiNet No PS MultiNet PS
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Time (In Seconds)
En
erg
y C
on
sum
ed (
In J
ou
les)
Two Radios MultiNet
Without Power SaveMultiNet uses much less power
than the two radio scheme
With Power SaveThe PSM optimized MultiNet uses
much less power.
Future Work• Test MultiNet with more than 2 networks • Improving performance through tighter coupling with newer drivers
and/or MAC changes • Better bandwidth sharing with legacy non-MultiNet nodes • Improve TCP Performance over MultiNet• Make code available for download
Contributions of this paper• Proposes a new virtualization architecture for wireless cards.• Relaxes a physical constraint of the number of wireless cards that
can be used by an application.• Actually builds and shows the feasibility of such a system!
Conclusions