Multirate Anypath Routing in Wireless Mesh Networks

Rafael Laufer†, Henri Dubois-Ferrière‡, Leonard Kleinrock†

Acknowledgments to Martin Vetterli and Deborah Estrin

†Computer Science Department

University of California at Los Angeles

‡Riverbed Technology, Inc.

Lausanne, Switzerland

Loss and Instability

M. Lukac, Measuring Wireless Link Quality, 2007

Wireless Networks

Different properties for the wireless medium Lossy and unstable links Limited transmission range Collisions and hidden terminals Intra- and inter-flow interference Broadcast nature

Same routing paradigm for wireless networks? Can the broadcast medium work in our favor?

Anycast Forwarding

Packet sent to multiple nodes simultaneously High chance of at least one node receiving it Node with the shortest distance forwards it on Coordination with overhearing and suppression

Anypath Routing

Every node forwards the packet to a set of nodes A set of paths from the source to the destination This set of paths is called an anypath

Our Contributions

Potential issues with single-rate anypath routing New routing paradigm for wireless networks

Anypath routing with multiple bit rates

Rate diversity imposes new challenges Introduction of a routing metric for multirate Routing algorithm for a single and multiple rates

Not exponential Same complexity as Dijkstra’s and optimal

Indoor 18-node 802.11b testbed measurements

Single-Rate Anypath Routing

Under-utilization of available bandwidth resources Some hyperlinks perform well at higher rates Others may only work at low rates

Transmission Rate

De

live

ry p

rob

abi

lity

Optimal operation point

Single-Rate Anypath Routing

Network disconnection at high rates Higher rates have a shorter transmission range Significant decrease in network density Lossier links and eventually disconnection Connectivity guaranteed only at low rates!

Multirate Anypath Routing

Every node forwards the packet to a set of nodes A transmission rate for each forwarding set A set of paths with potentially different rates We call this a multirate anypath

Challenges

Loss ratios usually increase with rate Higher rate is not always beneficial

Shorter radio range for higher rates Different connectivity and density for each rate Higher rates

Less spatial diversity and more hops between nodes Lower rates

More spatial diversity and less hops between nodes How to choose both the forwarding set and rate?

Shortest multirate anypath problem

Multirate Anypath Cost

What is the cost of a multirate anypath? Composed of two different components

Hyperlink cost Remaining cost

diJ DJ

diJ

DJ

i

J

(r)

(r)

(r) (r)

Expected transmission time (ETT) Average time used to transmit a packet Assuming a link with delivery probability Transmission rate and packet size

Expected anypath transmission time (EATT) Tradeoff between bit rate and delivery probability

Routing Metric

Remaining Cost

Weighted average of the distances of nodes in J

If D1 ... Dn, node j is the relay with probability

Weight wj(r) defined as

with

The Single-Rate Case

Link-state routing protocol Shortest Anypath First algorithm Running time of O(V log V + E)

0

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The Single-Rate Case

Link-state routing protocol Shortest Anypath First algorithm Running time of O(V log V + E)

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The Multirate Case

Shortest Multirate Anypath First algorithm A distance estimate for each rate Running time of O(V log V + ER)

(.4,.2) (.6,.1)

(.4,.1)

(.6,.5)

(.3,.2)

(.3,.1)

(.5,.2

)

(.8,.4)

(.2,.1)

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) (.9,.4)(.7,.2)

(.6,.3)

(.9,.6)

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(.3,.3)

(.2,.1)

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)

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Shortest Multirate Anypath First

Why does it work? Three properties assuming D1 D2 ... Dn

Property 1 Shortest forwarding set is of the form J = {1, 2,..., j}

D1

D2

D3

Shortest Anypath First

Why does it work? Still assuming D1 D2 ... Dn

Property 2 Nodes are settled in order {1, 2,...,n} Forwarding sets tested in order {1}, {1, 2},..., {1, 2,..., j}

{1}{1,2}{1,2,3}

D1

D2

D3

DiDi’Di’’

Shortest Multirate Anypath First

Why does it work? Still assuming D1 D2 ... Dn

Property 3 Distance using {1} higher than distance using {1,2},

which is higher than using {1,2,3}, until {1, 2,..., j}

Di Di’ Di’’

{1}{1,2}{1,2,3}

D1

D2

D3

Shortest Multirate Anypath First

Putting it all together Three properties assuming D1 D2 ... Dn

Shortest forwarding set is of the form J = {1, 2,..., j} Forwarding sets tested in order {1}, {1, 2},..., {1, 2,..., j} Distance using {1} higher than distance using {1,2},

which is higher than using {1,2,3}, until {1, 2,..., j}

All properties and optimality proven in the paper

802.11b Indoor Testbed

802.11b Indoor Testbed

Stargate microserver Intel 400-MHz Xscale PXA255 processor 64 MB of SDRAM Linux OS

SMC EliteConnect SMC2532W-B PCMCIA IEEE 802.11b Prism2 chipset and HostAP driver Maximum transmission power of 200 mW Proprietary power control algorithm

802.11b Indoor Testbed

Wireless mesh network 3-dB omni-directional rubber duck antenna 30-dB SA3-XX attenuator Weaker signal during both transmission and reception Larger distance emulated

Network diameter At 11 Mbps, up to 8 hops with 3.1 hops on average At 1 Mbps, up to 3 hops with 1.5 hops on average

802.11b Indoor Testbed

Software Click modular router MORE software package Modified HostAP driver Raw 802.11 frames

Measure the delivery probability of each link 1500-byte frames Transmitted at 1, 2, 5.5 and 11 Mbps

Distribution of Delivery Probabilities

Evaluation Metric

Multirate anypath routing Always lower cost than single-rate anypath

Gain of multirate over single-rate anypath Ratio between single-rate and multirate distances How many times is multirate anypath better?

GDi

Di’=

Gain of Multirate Anypath Routing

Transmission Rate Distribution

Conclusions

Opportunistic routing paradigm for multiple rates Range and delivery probability change with rate Shortest multirate anypath problem Introduction of the EATT routing metric Shortest Multirate Anypath First algorithm Measurements from an indoor 802.11b testbed

Single rate may lead to network disconnection Multirate outperforms 11-Mbps anypath routing by 80%

on average and up to 6.4x with full connectivity Distribution of bit rates not concentrated at any rate

Multirate Anypath Routing in Wireless Mesh Networks

Rafael Laufer†, Henri Dubois-Ferrière‡, Leonard Kleinrock†

Acknowledgments to Martin Vetterli and Deborah Estrin

†Computer Science Department

University of California at Los Angeles

‡Riverbed Technology, Inc.

Lausanne, Switzerland