1. Deployment & study of Multi-hop wireless testbed
מציגים:
פיליפ יעקובובסקי אוהד בניטה
מנחה:
ד"ר עומר גורביץ'

2. Presentation of the deployed topology’s characteristics
Objectives
Presentation of the deployed topology’s characteristics 2
Suggested solutions for WMN 4
Current issues/problems in WMN 3
Review of Wireless Mesh Networks (WMN) 1

3. Wireless Mesh Networks
The network is built out of two logical parts:
Access Tier
Backhaul Tier

4. WMN - Access Tier
Composed of Subscriber Stations (SS) i.e. end stations (mobile and stationary clients) using the network services

5. WMN - Backhaul Tier
Base Stations (BS) are interconnected between them in a chain topology, constructing the Backhaul Tier.
One or more Base stations constitutes the gateway (GW) to the Internet
The traffic from the SSs is transmitted to/from the Backhaul Tier.
The antennas used are Omni-directional

6. Wireless Mesh Network

7. Hardware Specifications
Motherboard
Intel Desktop Board D945GCLF
with integrated Intel Atom Processor
Card
TP-Link TL-WN551G
(Atheros AR2413 Chipset)
Hard Drive
8GB USB Drive
Power Supply
Standard mini-ATX power supply

8. Operating System: Ubuntu Linux 8.10
Network Topology
4.95Mbs Mbs Mbs
Node1
Node2
Node3
Node4
5Mbs Mbs Mbs
Operating System: Ubuntu Linux 8.10

9. Starvation in WMN Starvation occurs for the following reasons:
Not all the stations are in radio range (Node1 is hidden from Node3 and Node4, Node2 is hidden from Node4)
RTS/CTS mechanism makes things worse by adding unnecessary overhead.
Interference from outside network BSs, transmitting over the same channel
No proper rate limiting in nodes that are closer to the gateway

10. Baseline Throughput
Node1
Node2
Node3
Node4

11. One vs. Two TCP streams
Node1
Node2
Node3
Node4

12. One vs. Multiple TCP streams – ctd.
Node1
Node2
Node3
Node4

13. One vs. Two TCP streams throughput (after changing the GW)
Node1
Node2
Node3
Node4

14. Three TCP Streams Throughput
Node1
Node2
Node3
Node4

15. Suggested Solutions Solutions for starvation and unfairness:
Increase contention window for nodes closer to the GW, avoiding long-term starvation for multi-hop nodes
Use of multi-channel transmission
Rate decrease, fair throughput division mechanism

16. Switched Channels for better performance
Multiple Channels
Switched Channels for better performance
Channels 3 and 8 were used
Node1
Node2
Node3
Node4

17. Thank You !