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

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

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

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

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).

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.

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.

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

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

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

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

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

Master State-Machine

Slave State-Machine

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.

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.

The End Questions?