Technology

A bit of satellite technology

As mentioned here, I work in the satellite industry. I am pretty new to it and everyday is a learning experience. Today, I sat down with our in house satellite guru and found out how one calculates the bandwidth occupied by a carrier from the from the data rate on a satellite link. The formula is

BWAL = (Sr*1.4)

Where
BWAL = Bandwidth allocated for the satellite link in Khz.
Sr = Symbolrate of the link in Ksym/s (Kilo Symbols per second).

Sr in turn is calculated using the following formula

Sr = Dr*(1/MI)*(1/FEC)*(1/RS)

Where
Dr = Datarate in Kbps.
MI = Modulation Index (The values of MI for the different modulations are BPSK=1 | QPSK = 2 | 8PSK = 3 | 16PSK=4 | 16QAM = 4).
FEC = Forward Error Correction.
RS = Reed Solomon value. This can vary depending on what values are being used. Reed Solomon is an external codec as compared to Turbo which is a stand alone codec. If RS is not being used in the link, then a value of 1 is used.

Pretty confusing eh :). As if though this is not enough, there is another value called Information rate (Ir). And the formula for that is

Ir = Dr(1/RS)

Think that is enough satellite technology for one day :).

January 24, 2004 by Networking Technology Uncategorized 0

Link Speed – Maximum speed per session

I work at a teleport and most of our business is related to providing Internet service to ISPs in South Asia. One of the most frequent complaints that our help desk gets is “My link is slow, you guys are not providing us the complete speed”. Usually it is a case of the customer not understanding the finesse of TCP/IP. I came across this article by Adam Grow III. He uses the following formula to calculate the maximum possible speed per session on a link.

Throughput = 8*(TCPS/PropDelay)

Where
Throughput is measured in Kilobits per seconds (Kbps)
TCPS = Size of the TCP/IP stack in byte (Windows default is 8192)
PropDelay = propogation delay in seconds

Using the above formula, for a geostationary satellite (where the propogation delay is ~540ms), the throughput is ~120Kbps. So even if the client has a 1Mb link and he just has one session, he can only use a fraction of the link. Only multiple sessions can saturate the link.

January 20, 2004 by Networking Technology Uncategorized 1

IE Bug – Pretty Scary

During my daily visit to Richard Bejtlich’ blog, I came information about this flaw in IE which can be exploited to make people believe that they are viewing/visting one site (URL) when in fact they are located on another website. To quote from the “Zap The Dingbat” (who actually discovered the bug)

Vulnerability
There is a flaw in the way that Internet Explorer displays URLs in the address bar.
By opening a specially crafted URL an attacker can open a page that appears to be from a different domain from the current location.Exploit
By opening a window using the http://user@domain nomenclature an attacker can hide the real location of the page by including a non printing character (%01) before the “@”.
Internet Explorer doesn’t display the rest of the URL making the page appear to be at a different domain.

For example, if you click on this button, you will see the URL http://www.microsoft.com in the address bar if you are using IE. But the full address of the URL is http://www.microsoft.com%[email protected]/security/ex01/vun2.htm.

Pretty scary eh.. Just imagine how much this can be abused. People can be tricked into entering their credit card information, usernames/passwords etc.. by mimicking valid sites. And as if though this is not bad enough, Micro$oft hasn’t even released a patch for this yet. So for now, either you type in all addresses manually in the address bar or use trusted saved bookmarks. I would recommend scrapping IE and to start using Mozilla Firebird as your default browser. It is fast, small, adheres to standards and is FREE [as in beer].

January 18, 2004 by Networking Technology Uncategorized Web 0

Zaurus – More Pictures

More from the previous post. I collected some more pictures from the Zaurus migration. Didn’t want to post all of them to conserve bandwidth. For the interested, here are the links

http://www.kudithipudi.org/pics/1_14_2004/applications.png
http://www.kudithipudi.org/pics/1_14_2004/internet.png
http://www.kudithipudi.org/pics/1_14_2004/multimedia.png
http://www.kudithipudi.org/pics/1_14_2004/pim.png
http://www.kudithipudi.org/pics/1_14_2004/settings.png

January 14, 2004 by Fun Technology Uncategorized 0

Zaurus – English ROM

I bought a Sharp Zaurus 760 from Japan through one of my friends a couple of months back. This model is not sold in the US and I have been wanting to get my hands on it for a long time. I was well aware of the fact that the interface was all in Japanese, but since it runs Linux, I was confident of being able to hack it and change the locale settings. And there are a lot of enthusiast sites on the Internet which have information about this. Well, I got the PDA or rather Personal Mobile Tool (as Sharp likes to call it) and changed the locale settings by following the instructions in the following links
http://members.rogers.com/e46m3/zaurus/
http://downloads.conics.net/pda/zaurus-sl-c700/eng-inst/
http://www.zaurususergroup.com/index.php

Although I got most of the settings and menu options converted into English, I was still not satisfied. I wanted to modify the ROM to a complete english setting. Unfortunately, I am not such a Linux Guru (aspire to become one 🙂 ). Months passed by and as happens with such toys, it started piling dust until I came upon this site. They claimed to have a completely customized ROM with english. It was 11:00 PM in the night and the battery on the Zaurus was completely drained. Well, such goodies shouldn’t be kept waiting :). So I charged the batteries for ~ 15 minutes and got to work. Here is what I did

1) Download the ROM image from Cacko.biz.
2) Follow instructions found here.
3) Reboot the Zaurus and presto… you have an English ROM

Note: Apparently you cannot start up the Zaurus if your battery is completely dead although it is connected to an AC power source. You will have to wait at least 15-20 minutes for the batteries to charge up partially. Weird..

Here is a screenshot of the Zaurus running Netfront. It is connected to the Internet with a prism wireless card.
Zaurus :: Netfront :: BBC

That is the original screen size (640X480 pixels!!). Isn’t that impressive. I just cannot understand why Sharp doesn’t release these great PDAs in the US. They do have the Zaurus 5xxx series for sale over here.

Thanks to the Cacko Group, I now have an english version of the ROM. The same group has a X11 based distribution for the Zaurus. I will try that sometime next week. If you are having trouble getting to the main site (it is damn slow!!!), try this mirror site.

January 14, 2004 by Fun Technology Uncategorized 0

head

I was asked by one of my friends, how he could get the top 10 processes in a Unix system. I knew of the usual commands “top”and “ps” and never thought of how you could just get the top 10. Interestingly there is a command called “head“. So if you wanted the top 10 processes you would use “ps -auxw | head“. “man head” returns the following

NAME
head – output the first part of files

SYNOPSIS
head [OPTION]… [FILE]…

DESCRIPTION
Print first 10 lines of each FILE to standard output. With more than
one FILE, precede each with a header giving the file name. With no
FILE, or when FILE is -, read standard input.

January 10, 2004 by Linux Technology Uncategorized 0

The Tao Of Security

I came across this blog by Richard Bejtlich while I was researching for security related sites. Richard is a principal consultant at Foundstone and his knowledge and methodology just amazes me. I visit this site everyday if not more :). I hope to add more bits about technology as I come across interesting things.

January 5, 2004 by Technology Uncategorized Web 0

New blogging software!

In the spirit of New Year, I decided to try a new blogging software . Apparently the one I used before is not being actively developed anymore. And WordPress is the continuation of the older B2 project. The interface looks a lot cleaner and it has a lot more features in the background. Only problem was that I couldn’t figure out how to import all my old posts. I did make a backup of the old database. Will try to see if I can manually import them. Isn’t life wonderful 🙂 .

January 5, 2004 by Technology Uncategorized Web 0

Sun[set or rise]??

You might have already noticed all the buzz being generated in the tech. world due Sun’s annoucement that is might have to write off 1 Billion [yeah, you heard that right] dollars for this quarter. A lot of people are saying that this is the start of the end. It is funny how bad decisions made by management can affect a company :). I always admired Sun for being a “technology” company, but in the last few years instead of being innovative and adopting to changing market needs, Sun stagnated. I mean, how many companies would think of going with Sun when they can get comparable technology [Linux+Inte/AMD] at a far cheaper price. What is wrong with people in the upper management? I have seen several companies go down just because of bad decesions by management. Do people loose their brains once they get there?? I do hope [if not for the shareholders, at least for the employees] that Sun can get its act together.

October 4, 2003 by Rantings Technology Uncategorized 0