1. Mobility in 802.11-based Multihop networks
Rami Neiman, Yaron Perry Supervisor: Dr. Omer Gurewitz
Ben Gurion University Department of Communication Systems Engineering 2009

2. Wireless Mesh Network
A hybrid network, built on a mix of fixed and mobile nodes interconnected via wireless links
A fully wireless network that employs multihop communications to forward traffic en route to/from wired Internet entry points.
A commercial extension of mobile ad hoc networks
Envisioned as the economically viable networking paradigm to build up broadband and largescale wireless commodity networks.

3. The problem Long outage periods
No standard handoff scheme is specified for
Client maintains current AP association until it fails and then initiates a new association to a new AP.
No network-managed handoff.
Long outage periods

4. Project goal
Experimentally evaluate and compare various handoff policies over based Multihop networks using NS2 network simulator.
Determine which policy would be optimal for WMN architecture to support user mobility.

5. Baseline handoff policies
Maintain Until Broken
Client maintains it’s current association until it fails and only then initiates a handoff procedure
Always Strongest Signal
Client always initiates a handoff procedure when an AP with a stronger signal comes in range
Averaged With Hysteresis
Similar to Always Strongest Signal, however handoff is initiated only when signal strength difference exceeds certain threshold value.

6. Methods:
Ns2
Discrete event simulator targeted at networking research .
Provides substantial support for simulation of TCP, routing, and multicast protocols over wired and wireless (local and satellite) networks.

7. NS problems: Does not support WMN implementation out of the box.
When running on WMN NS2 overloads handoff process by routing, thus making it difficult to evaluate handoff properties.
Does not have an implementation of a full wireless Access Point.

8. Overcoming NS2 problems
To prevent NS from suppressing handoff procedure by routing we’ve constructed a multi-interface Access Point node that have the following structure:
Zero-Delay Link
Inter-Interface
Bridge
Zero-Delay
Link
Interface to
Backhaul tier
Access interface for mobile users

9. The simulation One wired gateway. 25 Access point nodes.
One mobile node.
CBR udp traffic.

10. Simulation
Here’s a small taste of our work

11. Simulation Results As was inspected the outage periods do
exist in Mobile host’s traffic throughput.
This due to the poor handoff implementation
of IEEE standard.

12. Work Done (so far) Implementing WMN in Ns2.
Separating AP’s interfaces to distinguish between network tiers.
Realistic handoff implementation which is not being overridden by routing.

13. Future work
Modifying the mac layer class in NS to enable various handoff policies.
Collecting statistical information from simulations.
Deciding which handoff policy performs the best in WMN architecture.

14. Any questions?