Documentation to "simulation of a packet processing system" PPS

Disclaimer:

This software is (c) 2000 by the LKN - Lehrstuhl fuer Kommunikationsnetze at TU Muenchen (www.lkn.e-technik.tu-muenchen.de).
Software coding and documentation by Daniel Roegelein (daro@roegelein.net).
Idea to the project by Dipl.-Ing. Anton Riedl of LKN (anton.riedl@ei.tum.de).
Any suggestions are appreciated.

System requirements of this version

PPS runs on i386-systems with a VGA compatible graphics adapter under DOS 5.0 up to Windows 2000/XP.
(Please mind the Windows NT/2000 performance note!)
This documentation is written according to version 0.8.

Download

You may download the software for Windows here.

Overview on the software

PPS is a simulation software of a packet processing system. In brief, it consists of a source generating traffic (packets), a variable buffering instance and a processor with adjustable speed.
The system is qualified as M/D/s - System, which implies a Markoff reception process with negative exponential distribution of inter-packet-times (infinite number of sources), a discrete but variable speed of the packet processor, and a variable buffer size s.
All important parameters can be supplied by the user.
Several graphs show the distribution of inter-packet-time in milliseconds (msecs), the packet length's distribution in bytes and the average buffer usage in percent of the maximum size.
Aditionally, red bars represent calculated or measured average values.
Some numeric values are shown in a seperate window, one of which is SimS/sec.
The software simulates one second of system behaviour in 1000 simulation steps (SimS). If e.g. 20000 SimS/sec are achieved, 20 seconds of system behaviour can be simulated in one second real time. All references to time, e.g. bytes/sec, mean simulated, not real time.

The graphical user interface

PPS runs in full-screen vga mode (640x480). Within the GUI the user can interact with the software simply by using the mouse (or the keyboard for some basic functions).
All important elements are described below.




Globals
	EXIT (or hitting ESC) quits the program.
	With these three buttons referred to as play, pause and stop the simulation process can be initiated, paused, stopped and reset. The current status is represented by an highlighted (blue) button. From status stop the user can initiate the simulation by pressing play or hitting the space bar on the keyboard, reset the simulation by pressing stop again. From status play the user can pause the process by pressing pause or hitting the space bar, stop the process by pressing stop. From status paused the user can resume the process by pressing play or hitting the space bar, stop the process by pressing stop.
	The distribution bars can be clicked for a larger view.

Description of instances

Source
	"Source" simulates an infinite number of statistically independent sources. The probability of packet generation after a certain time converges towards a negative exponential distribution in this case, which is simulated here. Hence, the time between packet generations will be distributed according to: To is the estimated value in msecs an must be supplied by the user. Once a packet is to be generated, its length must be calculated. This length is composed by a constant offset "Dat. offs." and a part that can be Negative Exponential- or Uniform- distributed. The chosen distribution is highlighted in blue/yellow. It is also possible to disable the distributed part. If Negative Exponential Distribution (EXD) is chosen, packet lengths will be distributed according to: Lo is the estimated value in bytes and must be supplied by the user. If Uniform Distribution (UFD) is chosen, packet lengths between 1 and Max. will be generated with equal probability.
Buffer
	The "buffer" is the instance between source and processor. Its current fillstate is indicated by a bar graph. All generated packets, i.e. a certain number of bytes, will be stored here by the source, enough space provided. If a packet cannot be completely stored in the buffer (because the remaining size is smaller than the packet length), it will be rejected and an overrun condition is signalled by a red top field of the bar graph. The frequency of this event is also referred to as packet loss probability B. The processor then takes out bytes at processing speed. Shouldn't there be enough bytes left for a simulation step, those remaining will be withdrawn and an underrun condition is indicated (red lower field). Note: These (non-linear) effects cause temporary reductions of either generation or processing rate and may direct into stable systems showing unstable behaviour (bouncing buffer distribution graph). The buffer size s has to be supplied by the user.
Processor
	The processor takes bytes out of the buffer at processing speed (eps).

Windows NT/2000 performance note

The forementioned OS's reduce CPU time of applications considered idling, i.e. no basic I/O (keyboard, mouse...) is being detected.
This may result into unsatisfactory SimS/sec values (~1000). As remedy the shift key might be pressed :-) or Windows 98 should be used.

Enjoy!