Published a small, but very useful console tool to update md5sum or shasum digest files. It will read existing md5sum.txt files and add new files to it without rereading the whole directory tree.

This makes digup very useful to update and verify incremental archives like chronological data storages or music collections, which are nowadays commonly stored and backuped on hard disks. Using a full file digest scan even slowly creeping bad blocks on old hard disks can be detected. By using a crontab entry, this check can be performed unattended and routinely.

For more information, the source code and binaries for various platforms see the digup web page.

After two weeks of hard work, my first LibriVox recording is finally finished! The basic idea behind LibriVox is to read public domain texts and to put the recordings back into the public domain. More about that on librivox.org.

My personal motivation behind recording, besides a lasting inclination towards fantasy and science fictions texts, is to practice my rusty English pronunciation. By reading and rereading the texts I believe my English will get more fluent and in the end also achieve better articulation.

The first recording is "The Last Evolution" by John W. Campbell, Jr. a science fiction short story available from Project Gutenberg. I have also made a quick LaTeX typesetted version of the Gutenberg etext for more comfortable reading and with slight corrections: lastevolution_campbell_text.pdf (153 KB).

Story Summary / Teaser

A future Earth population is unexpectedly attacked by powerful extraterrestrial Outsiders. However, the highly developed civilization of humans and machines quickly builds up forces and defends itself. This desperate, life threatening struggle against the invading aliens leads to The Last Evolution.

Audio Recording - Runtime: 58:42

MP3 encoded with standard lame VBR preset (obviously better than CBR)

lastevolution_campbell_tb_vbr.mp3 (42.7 MB)

If someone drops me a line with a good reason for uploading 250 MB, then I can also provide a lossless 24-bit FLAC file. Just burning a CD is not a good enough reason.

The recording is now also available on archive.org in the LibriVox Short Science Fiction Collection 026.

Released a minor updated source code version for Flex Bison C++ Example. The example source code is released into the public domain or, at your option, under the Do What The Fuck You Want To Public License (WTFPL).

This minor bugfix release fixes up two simple compilation issues with the newest bison version 2.4.1.

For more information and the download package see the Flex Bison C++ Example web page.

While publishing screenshots for CryptoTE (nice cross-platform text editor with integrated cryptography) the idea of making a short tutorial screencast came up. A screencast is basically a video made directly from the computer screen with no camera involved. Usually speech comments are added to create a sort of impromptu screen presentation. Thus I could show off the cool features of CryptoTE, and people could see what the program is about without installing it.

So far the cool and very trendy idea, now for sorting out the technical difficulties in making such a video. In theory a screencast video should be well compressible with a lossless codec. Unresized screenshots in full-resolution are also better compressed using the lossless PNG format than with JPEG, the PNG files are much smaller and show no blurry edges. Similarly screencasts, being only a sequence of full-resolution, losslessly recorded screenshots with some little mouse-movement, should be compressed losslessly.

On the digital inspiration blog I found a detailed "Screencasting Software Guide - Review of Desktop Screen Recording Tools" for all platforms. However, because my primary operating system is Linux (and since I also wanted to show that in the screencast), the range of tools that actually work is very limited.

After almost one year of personally testing the program, I decided to publicly released the first version of CryptoTE v0.5.390. One year in the making, CryptoTE is a very useful little text-editor with integrated cryptography. The name stands for CRYPTOgraphy Text Editor and it transparently encrypts text files storing them into secure containers. The program incorporates the popular editing component Scintilla and makes heavy use of wxWidgets.

For more information, the source code and binaries for various platforms see the CryptoTE web page.

Today I gave the final completion presentation for my diploma thesis. The talk showcased a selection of results published in the thesis. Results and experiments are only sketched, as all further detailed information can be found in the thesis PDF itself.

The talk contains side-by-side comparison plots of feature enhancements made to ns-3 and verifications thereof using ns-2. Furthermore, the EDCA extensions implemented in ns-3 are tested against analytically calculated reference values. In the end, a speed test comparison is done between ns-2 and ns-3, which uses the implemented classes to run an experiment scenario identically on both simulators.

The slides are available as PDFs in following two variants:

Here the table of contents:

1. Thesis Objectives
2. Enhancements
   1. Propagation Loss Models
   2. Reception Criteria
   3. Frame Capture Effect
   4. EDCA Implementation
3. Speed Comparison
4. Conclusion
5. Appendix
   1. Enlarged Plots and Figures
      1. Propagation Loss Models
      2. Reception Criteria
      3. Frame Capture Effect
      4. EDCA Implementation

After a very exhausting last week with lots of writing and little sleep, my diploma thesis is finally complete. The thesis is on enhancements to the 802.11 model and EDCA (enhanced distributed coordination access) QoS (quality of service) extensions in the new network simulator ns-3.

The thesis is written in English and a copy of the abstract and table of contents is located below. There is also a Zusammenfassung in German.

It is available as PDF in different variants:

Beyond the thesis itself, an extra page contains additional material like the source code, plot results and a snapshot of ns-3 at that time.

Shortened Table of Contents

• 1. Introduction
     1. Motivation
     2. Contributions
• I   Related Work
  1. IEEE 802.11
     1. 802: The Big Picture
     2. Outline of 802 and 802.11 Layers
     3. PHY Layers
     4. MAC Layer
  2. The ns-2 Network Simulator
     1. Overview
     2. Problems with 802.11 and Overhaul by DSN
  3. The ns-3 Network Simulator
     1. Design Overview
     2. Architecture of 802.11 Implementation
• II   Enhancements
  1. Propagation Model Enhancements
     1. Propagation in ns-3
     2. Basic Propagation Loss Models
     3. Further Models in ns-3.4
     4. Nakagami-m Fast Fading
     5. Implementation and Verification
  2. PHY Layer Enhancements
     1. Modeling the Transceiver
     2. Implementation of Cumulative Noise
     3. SINR Reception Criterion
     4. Frame Capture Effect
     5. Implementation Issues
     6. BER/PER Reception Criterion
     7. Verification
     8. Discussion of Reception Criteria
  3. EDCA QoS Extensions
     1. Modeling DCF
     2. Extending Model with EDCA
     3. Implementation Issues
     4. Verification
  4. Speed Comparison – ns-2 vs. ns-3
     1. Highway Lanes Scenario
  5. Conclusion
     1. Summary
     2. Future Work
  6. Bibliography
  7. Background
     1. A Note on Decibel
  8. Extra Figures and Tables
     1. 802.11a Convolutional Encoder
     2. Default EDCA Parameters
  9. ns-3 Crash Course
     1. Callbacks
     2. Objects, Ptrs, Attributes and TraceSources
     3. Highway Lanes Scenario Code

For the last three months I have been working intensely on my diploma thesis. The thesis will be about 802.11 enhancements and EDCA QoS extensions in the new network simulator ns-3.

Today I gave my halftime presentation about the current status of my efforts. The talk is composed of a short introduction into ns-3, followed by a detailed discussion of WLAN packet reception criteria and finishes with a review of DCF and how EDCA extends it.

Be warned: many slides are not all self-explanatory and therefore less suitable as a casual introduction into the topics. They are slides meant for presentation.

The slides are available as PDFs in following three variants:

Here the table of contents:

1. ns-3 Basics
   1. Introduction
   2. Showcase: Design Patterns
   3. Current State
2. Wifi in ns-3
   1. State of 802.11
   2. PHY Layer
   3. Signals, Noise and Interference
   4. Short Recapitulation of DCF
   5. QoS with EDCA
3. Conclusion