Gateway Selection in Rural Wireless Mesh Networks

Team: Lara Deek, Arvin Faruque, David Johnson

http://www.octavetech.com/blog/wp-content/uploads/2008/03/long-range-wireless.jpg

Introduction: Rural Wireless Mesh Networks (WMNs) A mesh network comprised of multiple, commodity devices that

provides Internet access to rural areas Topology differs from hub-and-spoke wireless networks

Applications: Education, health care Benefits: cost, robustness, infrastructure requirement

Introduction: Rural WMN Examples Digital Gangetic Plains (India)

OLPC Project:

Each XO-1 will operate as a WMN node

Image from http://www.cse.iitk.ac.in/users/braman/dgp.html

Image from http://laptop.org/en/laptop/hardware/specs.shtml

Introduction: Mesh Network Gateway Selection Mesh networks connect to the rest of the Internet via gateways Rural and municipal WMNs have different bandwidth constraints

• Municipal: bottleneck is wireless links

• Rural: bottleneck is at gateways

Problem: Inefficiently utilized gateways WMN can have severe consequences in rural areas

Our goal: modify an existing mesh routing protocol attempt to optimally select gateways

B.A.T.M.A.N.(1)

B F

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A wants to reach X

B.A.T.M.A.N. (2)

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A:10

A:9

Nodes broadcast originator messages (OGM's) every second OGM's are rebroadcast Other nodes measure how many OGM's are received in a fixed

time window

B.A.T.M.A.N. (3)

B F

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D BATMAN routing table

TO VIA QA B 8A C 7

D Final routing table

TO VIA A B

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B.A.T.M.A.N. (4)

B F

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A:6

G BATMAN routing table

TO VIA QA D 6

A E 7

G Final routing table

TO VIA A E

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A:4A:7

B.A.T.M.A.N. (5)

B F

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X BATMAN routing table

TO VIA QA G 5

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X Final routing table

TO VIA A E

B.A.T.M.A.N. (6)

B F

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X BATMAN routing table

TO VIA QA G 5

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TO VIA QA C 7

A D 4

C BATMAN routing table

TO VIA QA A 9

Current GW selection techniques

Minimum hop count to gateways

Used by routing protocols like AODV

Creates single over congested gateways

B F

C

A

E

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XG

GW1

GW2

Current GW selection techniques

Best link quality to GW Used by

source routing protocols like MIT Srcr

Link state protocols like OLSR

Prevents congested links to GW

Not global optimum of GW BW usage

B F

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XG

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GW2

2.2

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Current GW selection techniques

BATMAN has advanced a little further

GW can advertise downlink speed

User can choose GW selection based on GW with best BW Stable GW (need

history) GWBW x LQ

Can't trust advertised GW BW

Doesn't achieve fairness

B F

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XG

GW1

GW2

10

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256 kbps

512 kbps

8 7

Proposed Solution: Introducing intelligence to the core of the WMN Introduce information about gateway performance into the network

Nodes at “intelligence boundary” have gateway performance information, need to transfer this information to the other nodes

Transfer this information via: “Batsignal” packets that are flooded through the network

Proposed Solution: What does the boundary node measure? When nodes will select gateways, they will need to estimate the amount of bandwidth

they will get:

Example:

Hence, boundary nodes must transmit current total gateway bandwidth and current # of VPNs

Total gateway capacity is the sum of

• Measured extra bandwidth (measured through active probes)

• The sum of the current bandwidths of the VPNs

Prospective _VPN _Capacity Total _Capacity

#VPNs1

Prospective_VPN _BW 1

3Total _BW

Prospective_VPN _BW 1

2Total _BW

Proposed Solution: Batsignals1. A node at the intelligence boundary periodically

Record gateway measurement If the measurement is not drastically different than a previous value, then transmit a

Batsignal packet only if we have not recently transmitted a batsignal packet If the measurement is drastically different from a previous value, immediately transmit a

Batsignal packet

2. All other nodes Forward a received bat-signal to its neighbors (if it has not expired) Update their own gateway preference tables

Packet time to liveTTL

Number of VPNs on gatewayVPNs

Total download bandwidthDB

Time stampTS

Gateway ID (0-255)GWID

DescriptionField

Batsignal Packet Node Gateway Preference TableGWID Metric Total

down BW

# VPNs Time-stamp

1

Etc…

Proposed Solution: Using Batsignal data to pick a gateway

To choose a gateway, the following metric based on table data and link quality (computed only when current_time - timestamp is below a threshold) is used

Gateway flapping: When a gateway comes up and goes down frequently, a large number of conflicting Batsignal's will be broadcasted to the WMN nodes.

The VPN will not switch to another gateway until all the flows within it have terminated (Srcr)

Gateway Preference TableGWID Metric Total down

BW# VPNs Timestam

p

1

Etc…

Metric GW _Capacity

#VPNs1Link _Quality

Evaluation: UCSB Meshnet status

Evaluation: The massive mesh in South Africa

7x7 grid of 49 wireless nodes using 802.11 a/b/g radios

Each node network boots off a central server

Makes use of 30dB attenuators on radios to achieve multiple hops in small space

Has been used for extensive mesh network protocol benchmarking

Complete remote control of experiments possible

Evaluation Environment I

Parameters at the Gateway and Mesh Nodes Technologies Used

Load: traffic/congestion. Loss: signal weakness,

obstacles. Delay: . Bandwidth: of the available

communication channels between mesh nodes or between mesh nodes and gateways.

Throughput: between mesh nodes and a test server outside the mesh network.

tc: linux traffic control. iperf: TCP/UDP bandwidth

measurement tool. iptables: defines packet

processing schemes.

Evaluation Environment II

Metrics Measurement Methodology

Gateway efficiency: measures how effectively we match the throughput generated by the VPNs to the capacities of the gateways.

Gateway fairness: measures how fairly the aggregate gateway throughput is distributed among VPN flows.

Gateway Flapping: measures the frequency a mesh node switches between utilization of multiple gateways.

Measure VPN flows at each GW Have capacity of all GW’s.

Measure VPN flows. What is the time window? Average over time.

Parse BatSignals for each node and record the timestamp for each GW usage. How much hysteresis?

How are we using technologies to determine fundamental parameters?

Active Probing to determine GW throughput using a decentralized, distributed approach via trusted internet mesh nodes that form the intelligence boundary {B1, B2}.

Current Progress (from Proposal) We are in Week 4.

1. Formulate a set of preliminary evaluation metrics for the protocol. (Week 1 - Week 3). Done

2. Formulate a measurement procedure to test the efficacy of the protocol. (Week 1 - Week 2) Done

3. Emulate a gateway on a UCSB MeshNet node using Linux tools such as tc and iptables. (Week 2 - Week 3) Have developed scripts to control TC and iptables. Need to develop remote control for this script.

4. Run and evaluate the latest developers release of B.A.T.M.A.N. on the UCSB MeshNet. (Week 1 - Week 4) Have evaluated BATMAN on 3 mesh UCSB MeshNet nodes. Need to transition massive mesh (has been done before).

5. Implement solutions to Goals 1, 2, 3, and 4 and measure performance using the measurement process described in (2) and evaluation metrics described in (1) (Week 3 – Week 6) In progress, analyzing code.

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