Available Bandwidth Measurement Using Real Time Operating Systems Dennis S. Knoop

Proposal The goal of this project is to study the effectiveness of using Real-Time support to improve the accuracy of available bandwidth measurement.

Historical Background BPrope and Cprobe developed by Bob Carter and Mark Crovella Tool uses simple ICMP echo request UCCS students, under the supervision of Dr. Chow, have modified the available bandwidth tool Sending time gaps are still a problem

Project Plan Analyze current ABWM Tool Research Real-Time Operating Systems Load Real-time operating system Port current ABWM Tool to RTOS Analyze results

Real Time Operating Systems Basic Concepts  Soft Vs. Hard Soft – Task are preformed as fast as possible Hard – Task have to be preformed on time  Preemptive Vs. Non-Preemptive RTLinux – Hard/Non-Preemptive uC/OS-II – Hard/Preemptive Linux – Soft Support/Preemptive

uC/OS-II (Micro Controller Operating System Version 2) Basic Concept  Uses interrupts to control task Critical section of code  os_enter_critica()  os_exit_critical() Built for DOS applications

uC/OS-II Strengths  Handles interrupt management well (255 nested interrupts)  PC ready  Strong documentation Weaknesses  No network programming support while in critical section of code  Fully preemptive

RTLinux Basic Concept  New layer of abstraction Modules Scheduling  Fixed priority scheduler Threads  Runs normal Linux as a low priority thread

RTLinux Strengths  Own scheduling routine  Controls Linux kernel  High precision Weakneses  Not well documented  Small number of hardware devices supported  Poor memory management

ABWM Tool Original Tool  Simplified Formula (B w = S/t i ) Analysis  Sending time gaps are not consistent Improvements required  Critical -Timing of initial time gaps  Re-Engineering/Port to RTOS chosen

RTABWM Tool RTLinux -Modification Made  Used of Linux real-time support Critical Code  sendProbingMsg() function Problems Encountered  Network interface card (NIC)  RTLinux unable to support shared memory Solution  Linux real-time support

Linux Schedulers SCHED_OTHER  Default – Nice level and quantum SCHED_FIFO  First-In First-Out SCHED_RR  Round Robin

Linux Modification Made  Used Linux real-time support  Set scheduler to round robin Critical Code  fork()  receiveprobingMsg() Accuracy of results

Comparison of Results Ran: May 7, 2002 ABWMABWM-rr

Current Status Analyzed current ABW Tool Researched Real Time Operating Systems Loaded RTLinux on viva.uccs.edu server Ran sample/example programs RTLinux and uC/OS-II back shelved Chose Linux with real-time support

Conclusion Result of testing  usec accuracy Future Work  RTLinux Commercial version has shared memory support  Better network support  Integrating tool into other applications Questions?