Older blog entries for Raphael (starting at number 31)

ADSL adventures, part 2

Once I managed to get the necessary information for configuring my Speedtouch 350 DSL modem (see part 1), the next logical thing to do was to start using it. Or at least try to.

The first problem was that Belgacom apparently never sent me the letter containing the user name and password that I was supposed to use for accessing their services. After spending a few minutes on the phone (that music sounds familiar) I got a login and password that I could use. Well, that’s what I thought. I learned later that what I got was not the login/password pair that I asked for, but just a pair of passwords (for PPPoE and for POP). No login. Doh!

My second call to the support center (ah, that music again!) was barely more successful: this time I got a user name and a (new) password, but again I discovered later that the user name that I got was incomplete (last characters missing).

The third call was more interesting. After 20 minutes of music (I really know it by now), a technician told me about the missing characters in my user name and asked me to try logging in while he was monitoring their side of the DSL line. This time, the PPP authentication was successful but then the PPP connection went down immediately after that. Strange! The modem re-tried a few seconds later, with the same results. And again, and again… After a few more minutes of debugging, he told me that he was resetting their card and asked me to power-cycle my modem. I did that and when the line came back, the connection worked and I was able to access the Internet. Oh joy! But I also noticed something else while looking at the system log of the modem: the connection speed after the reset had dropped from 3 Mbps to 1 Mbps. I mentioned that to the guy, who said that it was normal. Ah well, at least the ADSL connection was usable so I was happy (after wasting two hours on that).

According to a colleague who had a similar experience, the reason why my line went down immediately after a successful authentication was related to the 3 Mbps. By default, the DSL access is configured for 384K/3M up/down. But the offer that I had accepted had a cap at 1 Mbps (apparently, because I never got the letter with the details of the offer). Although the telco part of Belgacom handling the DSL access was happy to let me in with 3 Mbps, the ISP part of the company was not happy with that and dropped the connection immediately. That could make sense, but I am still wondering why the access line had not been configured correctly on their side in the first place and why it took so long for the problem to be identified. Ah well, at least I can use my connection now… And I am glad that I could do all the tests using the built-in web interface of the modem over Ethernet instead of USB. I’m wondering what would have happened if they had required me to use some Windows software for configuring the stuff.

Syndicated 2005-08-04 08:21:06 from Raphaël's Last Minutes

I have moved to blogs.gnome.org. I don't know yet if I will update that blog more frequently than this diary. We'll see...

Long time no write.... My last diary entry was almost one year ago!

Playing with LILO and Slashdot

This morning, I loaded the Slashdot home page and... Oops! What's there in the story at the top of the page? Three links to my LILO pages. Ouch! This is going to hurt... Welcome to the Slashdot effect! Quick look at the logs of the web server: since this morning, the server has already seen more than 20,000 visitors making more than 300,000 requests. And many people in the US are still in bed at this time. All these downloads are going to suck a significant amount of bandwidth...
Playing with LILO is fun. It is also interesting because it encourages good programming practices. Testing a modified boot screen requires a reboot of the PC, and any fatal error in the program is likely to prevent the computer from booting at all. So I take the time to re-read my code before rebooting. This reminds me of the good old time when I was programming in Z80 assembler on my ZX Spectrum.

Playing with the Linux kernel

Yesterday, I had to run some tests at work with a modified version of the Linux TCP stack. The goal was to change the initial size of the congestion window and to run some performance tests on a dedicated network (with high bandwidth*delay product). Of course, there is no /proc interface for changing that, because this would violate the standards. So I decided to add my own. I had never looked closely at the Linux kernel code before, and I never touched the TCP stack.
It took me a while to find the file that I had to change, but find, grep and emacs are very useful tools. Once I found the file (net/ipv4/tcp_input.c), it was really easy to change the way the cwnd was initialized. Half an hour later, I had created two new interfaces in /proc/sys/net/ipv4 and everything was working. I even added a new option in net/ipv4/Config.in to make these features optional. By reading or writing to the pseudo-files in /proc, I could dynamically alter the behavior of the TCP stack and make it standards-compliant or not.
This was a very interesting experience for me, because I have been working on free software for a long time, but still I did not expect that it would be so easy to add a new feature to something as complex as the TCP stack of Linux. Of course, I only had to do a very small change that was limited to a few files, but it was interesting for me to see how easy it was to understand how the /proc interfaces work and how the kernel configuration works, considering that it was the very first time that I looked at it. So I have to congratulate the kernel hackers for all this nice work.

hadess:
There is a pointer to the improvements for TCP in the Ericsson Eifel license that I mentioned. The first paragraph contains a reference to the Internet-Draft that describes the Eifel algorithm. Mind you, this is a draft and not yet an RFC.
In the References section of the draft, there is a link to a paper that gives a bit more information about why the Eifel algorithm could be useful for TCP.
Oh and by the way, I come from the french-speaking part of Belgium, not from France. ;-)

schoen:
I just saw your AskAdvogato message in which you ask how to keep ants out without killing them. Although killing them is usually the easiest solution (using boxes with small ant-sized holes containing a poison that the ants eat), the best way to keep them out is to make it hard for them to get in. If it is not possible for you to seal all openings in your house, you can try to smear grease in their path, or to use chalk or talc powder around the openings through which the ants enter your house. They hate these things because it makes it harder for them to walk, and they give up after a while... or find another opening that you had forgotten. Good luck!

More patents usable in free software...

Following the example set by Raph with his royalty free license for using his patents in free software (released under the GPL), there is now a similar license granted by Ericsson for some proposed improvements of the TCP protocol (the Eifel algorithm). More power to free software!

That license allows GPLed software to include the proposed improvements to the TCP stack, as well as any operating system that is entirely Open Source. So this covers Linux, FreeBSD, OpenBSD and NetBSD, among others.

(Disclaimer: I work for Ericsson and I contributed to the wording of that license, but I am currently only speaking for myself, not for my employer.)

David O'Toole writes:

[...] Looking at stuff like this makes me get just a tiny bit upset about how badly the linux world is dragging its political feet with respect to improving the interface. I'm not talking about making all the OK buttons respond to the Enter key (currently my biggest pet peeve about GNOME, and it's slowly being fixed---recent GIMP etc.)

I'm talking about the imaging model. I don't want to criticize X unfairly. The X Window System was brilliant for its time and in its environment. But it simply does not support what people want to do now well enough to continue. Fast vector imaging, transparency, high-resolution monitors, antialiasing. Yes, you can implement software on top but there's no standard and it's slow.

The first defense I hear all the time is network transparency. I respond: who cares.
[...]

Well... I, for one, care very much about the network transparency of X. I am currently typing this from a Solaris machine on which I have other windows displayed remotely from a Linux machine and other Solaris machines. Not only some XTerms and Emacs that could also work over telnet/rsh/ssh, but also graphical applications like Purify, Quantify, Netscape, XMMS and some other goodies. They are all on the same LAN so speed is not really an issue. Without X's ability to display anything anywhere, writing and debugging my programs would be much harder.

So maybe I am among the 1% of people who really use the remote displays and would not be satisfied with text-based remote logins. This does not mean that nothing should be done for the other 99% who would like to get a much better performance from the applications that are running on the local display.

I don't think that it is necessary to throw X away and to start again from scratch. The DGA extension (available on OpenWindows and XFree86) proves that you can get decent performance out of X, although this requires some specific code that is rather ugly and not easy to write and maintain. Most programmers do not want to write some additional code for specific X extensions, and indeed they should not be required to do so.

But it would be possible to get a better performance while keeping the X API. Imagine that someone modifies the shared X library (libX11.so) so that if the client connects to the local server, all X calls which are normally sent to the X server over a socket would be translated into some optimized drawing operations accessing the video buffer directly. The shared X library would more or less contain some bits of the server code (actually, a stub could dlopen the correct code). If the X client connects to a remote server, then the X function calls would fall back to the standard X protocol. All clients that are dynamically linked to that modified library would automatically benefit from these improvements without requiring any changes to the code. So it can be done without throwing away the benefits of X. Actually, I believe that some people are working on that for the moment...

Question: maximum information density in the print-scan process?

Does anybody know how much information can be stored and reliably retrieved from a piece of paper, using a standard printer (inkjet or laser, 300dpi) and a scanner (1200 dpi)? Since a piece of paper can be affected by bit rot (literally) and can be damaged in various ways, some error correction (e.g. Reed Solomon) and detection (e.g. CRC) is necessary. Also, I do not want to rely on high-quality paper so I have to accept some ink diffusion and "background noise" introduced by defects in the paper.

I found some references to 2D barcodes (such as DataMatrix, PDF-417 and others) but these codes are designed to be scanned efficiently by relatively cheap and fast CCD scanners. I am not worried about the scanning time (I am using a flatbed scanner) or the processing time (I can accept some heavy image processing). Also, I would like to encode raw bits and pack as much information as possible on a sheet of paper, regardless of its size. These 2D barcodes have a fixed or maximum symbol size and it is necessary to use several of them if I want to fill a sheet of paper, wasting space in the duplicated calibration areas and guard areas.

PDF-417 has a maximum density of 106 bytes per square centimeter (686 bytes per square inch, for you retrogrades), which is quite low. It is certainly possible to do better, but I would like to know if there are any standards for doing that. I am especially interested in methods that are in the public domain, because most 2D barcodes are patented (e.g. PDF-417 is covered by US patent 5,243,655 and DataMatrix is covered by 4,939,354, 5,053,609 and 5,124,536).

If you know any good references, please post them in a diary entry (I try to check the recent diaries once a day, but I may miss some of them) or send them to me by e-mail: quinet (at) gamers (dot) org. Thanks!

Hmmm... This is a bit long for a diary entry. But I don't think that such a question deserves an article in the front page. If you think that I should I have posted this as an article, then send me an e-mail and I will re-post this question and edit it out of my diary.

I posted my opinion on using GdkRgb in Ghostscript, in the LinuxToday article about Raph's open letter to the Ghostscript community. IMHO, GdkRgb is the best solution and those who see it as an attempt to force them to use "Gnome stuff" on their desktop do not understand the way GhostScript works or what GdkRgb is.

This is not new, but it looks like anything that mentions Gnome is flamed by KDE bigots, and vice-versa (yes, it does happen both ways). The interesting thing here is that the most vocal critics are not developers and/or show clearly that they do not understand what they are talking about. Sure, they want someone (who?) to fork GhostScript, presumably to create a highly productive KDE branch or something like that. What a bright idea! Sure, they could get rid of any Bonobo linking, but throwing GdkRgb away would be stupid.

Sigh! Even if you are careful about what you communicate (I think that Raph's letter was nice and explained very well that using GdkRgb would have no influence on KDE), some morons will find a way to interpret it in a different way.

22 Sep 2000 (updated 22 Sep 2000 at 16:58 UTC) »

I'm going to Bristol (UK) for the HUC2k symposium. I suppose that the probability of meeting someone reading Advogato at this conference is close to zero, but I will be there anyway. And I will stay in the Posthouse hotel from Sunday evening to Wednesday, so if you are reading this (maybe), and you met me at GUADEC or something (unlikely) and you will be in Bristol for the conference (extremely unlikely), then feel free to come and say hello.

Ghostscript

It is nice to see that Ghostscript has a new maintainer, in the person of raph. Congratulations and good luck! Ghostscript is already very good, and adding better antialiasing and other stuff from Libart will make it even better.

Hmm... There seems to be an account for L. Peter Deutsch on Advogato. Not very active, apparently...

Diaries, yet another meta-discussion...

At the end of a previous diary entry, raph mentioned that the diary format is working, but is not ideal for question-and-answer discussions. Well... Obviously the diaries were not designed for that, but it is great to see how they have evolved. There seems to be a need (among the free software community) for this kind of discussions, which are more public than direct e-mail, mailing lists or IRC, but whithout being restricted to a particular topic like the articles on the front page.

A first step would be to use automatic bi-directional links whenever possible. Whenever someone posts a diary entry containing a link to someone else's diary, the filter that parses the submission would at the same time add a backwards link at the end of the other diary (e.g. "[1 comment by so-and-so]"). It would then be easier to check if someone has replied to your diary entry.

But as the number of diaries grows, it becomes increasingly difficult to keep up with the postings. It will not take long before the daily submissions cannot fit on the front page. Already now, it is easy to miss some parts of a discussion if you go away for a couple of days. And the only way to read the missing parts is to look at the pages of all potential participants and check their previous entries. This is not very convenient, because you may forget some of them and you may not know that a new guy has posted some interesting comments. Of course, that could be solved by another hack to Advogato: allow the "recentlog" to take a range of dates, or at least a starting date. It would then display all diaries that have been posted or modified during that time, so that you could read last week's diaries in chronological order if you missed them. (Implementation note: Advogato should store a chronological index of all diaries, otherwise finding and sorting them would be inefficient.)

But where does that lead to? If it is easier to discuss things in the diaries, that part of Advogato would become similar to a web-based bulletin board or chat room. Or a web-based version of USENET. The comparison with USENET and other chat rooms is interesting: they allow threading (using a "References" header in the newsgroups, or direct links in the web fora) and they provide easy ways to separate the unrelated topics (different subject lines, newsgroups or chat rooms). The Advogato diaries put everything in one large page and it is up to the readers to separate the interesting things from the noise. But on the other hand, this can be considered as a feature that reinforces the community, because all members get the opportunity to read some articles that they might have skipped if the topics had been clearly separated. Also, another feature of the diaries is that they do not have subject lines: those who want to add them can do it (using bold and/or indentation) but nobody is forced to structure their diaries in any way. It is difficult to please everybody...

So I don't know what would be best for Advogato (anyway, who am I to judge?) but I think that there are several significant differences between the diaries and a full-featured discussion forum, and these differences may be good for Advogato. If nobody has enough spare time to add a discussion forum besides (and not as a replacement for) the diaries, then I am happy with the current situation. Hmm... Maybe it would be better with the addition of bi-directional links...

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