1. Design and implementation of
Department of Communication System Engineering
Ben-Gurion University of the Negev
Design and implementation of
LOad based Contention resOlution Media Access Control
(LOCO-MAC) Protocol
By:
Itay Dagan
Shimrit Malichi
Instructors :
Dr. Yehuda Ben-Shimol
Mr. Yoav Ben-Yechezkel
June, 2007

2. Outline Summary Background Ad hoc network Channel access control
Project overview
Goals
Work flow
Implementation
Summary

3. Statement of the Problem
What is wireless ad hoc network?
מה זה רשת אד הוק - אוסף של תחנות עצמאיות המתקשרות דרך אותו ערוץ, ללא צורך ברכיב תקשורת כלשהו שינהל ויפקח על העברת נתונים תקינה בין התחנות השונות. רשת מסוג זה יכולה להתקיים ללא התבססות על תשתית קיימת וללא הצורך בעבודה מול תחנה מרכזית.
למה זה טוב? ציוותי הצלה / צבא
***מול 80211***
Usages
Military
Rescue teams

4. Channel Access Challenges
When stations share the same medium, many requirements should be considered:
Low access time to free channel
Low collision probability
Fast resolution of colliding nodes
Hidden terminal effects
Fairness - resource sharing among stations
Topology independent
On ad hoc networks, the stations themselves must handle all the constraints mentioned above because there is no central component that coordinates between them.
high throughput

5. Hidden node problem
C is out of the range of the transmitter A C is in the range of the receiver B. C and A are hidden from each other and transmissions to B will collide at station B.
B transmits to A. Nothing physically prevents C from transmitting to D (it will not disturb A to receive transmission from B).

6. Project Overview
Enhancing an existing MAC protocol for wireless ad hoc networks that provides:
High overall network throughput
Reasonable packet delay time
Protocol Design
Layering
FSM description
Design up to the function level
Implementation with the OMNeT++ network simulator
Calculate protocol's throughput and efficiency
Various topologies and users behaviours.
A network simulator (OMNeT++) is used to verify the effectiveness of the protocol under different communication scenarios.

7. The LOCO MAC Solution
LOCO MAC provides load adaptive mechanisms that allow fair bandwidth share among several competing stations.
System model
master stations (MSs)
slave stations (SSs)
Current master holds a master token for a “MSsession” time
Time to transmit a control message from the MS to one-hop away SS (TMaCtl ).
2. Messages propagation time (τ ).
3. Contention Period (CP) for SS hearing the control message to respond (TCP ).
Master session division
MSsessioni
MSsessioni+1
MSsessioni+2
CR1
CR2
CR3
CRN Tx
time t
TCP
CR1 allows a MS to estimate the load of its connected SSs and differentiate the most loaded ones.

8. Load Calculation Model
The station with the highest load is granted with channel access.
Station’s load is measured in terms of
queue length
maximum end-to-end packet delay time
Load function:
i - station index ; Qi - queue length ; α - a weighting parameter
Dmax - packet’s maximum accumulated delay max {Qi} - max packet delay in the cluster
max {Dmax} - max queue length in the cluster
Station sends its RTS signal on ATi=max{0,1-Li}Tcp

9. Control Messages SS transmits a pulse to the MS
HLIR - Highest Load Indication Request: MS initiates a competition
RTS - Ready-To-Send:
SS transmits a pulse to the MS
CTS - Clear-To-Send:
MS broadcasts the estimated time of the “winning” SS
COL - Collision:
MS broadcasts in case several SSs collide
ESG - End of Slave Grant:
SS sends ESG to the MS
MG - Master Grant:
MS passes the master-token to another master

10. Transmission
2nd CR - CTS MSG
1st CR - HLIR MSG

11. Transmission
3rd CR - CTS MSG
1st CR - HLIR MSG
2nd CR - COL MSG

12. Design - Block Diagram Queue management Load function calculations
Interface to upper layer
State machine management
Interface to lower layer

13. Master State-Machine

14. Slave State-Machine

15. Simulation Implementation
OMNeT++
An object-oriented modular discrete event network simulator.
Modular. Components are programmed in C++, and then assembled into
larger components and models using a high-level language (NED).
Extensive GUI support.
OMNeT++ is used to verify the effectiveness of the protocol under different communication scenarios.

16. Summary: what have we learned
How to design a MAC protocol for wireless ad hoc networks
Modeling techniques
FSM
Layers
Implementation with OMNeT++ network simulator
Workspace setup - Inet Framework
Practicing C++
Team Work
A network simulator (OMNeT++) is used to verify the effectiveness of the protocol under different communication scenarios.

17. The End
Questions?