Available Bandwidth Measurement Using Real Time Operating Systems

1
Available Bandwidth Measurement Using Real Time
Operating Systems

• Dennis S. Knoop

2
Proposal

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

3
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

4
Project Plan

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

5
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

6
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

7
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

8
RTLinux

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

9
RTLinux

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

10
ABWM Tool

• Original Tool
• Simplified Formula (Bw S/ti)
• Analysis
• Sending time gaps are not consistent
• Improvements required
• Critical -Timing of initial time gaps
• Re-Engineering/Port to RTOS chosen

11
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

12
Linux Schedulers

• SCHED_OTHER
• Default Nice level and quantum
• SCHED_FIFO
• First-In First-Out
• SCHED_RR
• Round Robin

13
Linux

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

14
Comparison of Results
ABWM
ABWM-rr




















Ran May 7, 2002
15
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

16
Conclusion

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