Nice video

Just in case you wondered how fiber optics really work ...

Marks have been published

You can find them here. The last column is where the final mark is. Please remember that each term mark is obtained from attendance(10%), assignments(20%) and exam(90%-70% depending on the correct assignments turned in, 90% if none, 70% if two).

Final mark average is 55%. Nine people failed and twenty one passed the subject.

Marked exams will be published shortly for you to double check the grading process.

Update:

• First term exam is no longer online.
• Second term exam is no longer online. And solved exam is here.

Error Fix (Jun 18): There was an error in the assignments marks, it should be fixed now.

Network security videos

If you want to review some of the basic concepts on network security while practicing your Spanish skills, you want to have a look to these videos.

Fourth assignment solution

Google Code Jam 2011

In just a few hours it will start the Qualification Round for CodeJam. CodeJam is an open contest for programmers to show how good they are. Winner can get up to $10.000 in cash.

How to tell if it is blocked in China?

As you may know, some countries do block certain websites "for the own good of their population". It is an activity other countries will call censorship. But ... how do you know if your site is blocked in a given country?

The obvious answer is to ask a local to try your site, but this system, though it works nicely if you know someone there, it may not be practical for some destinations.

Alternatively, you can use services like this one to perform a check on a website from different locations. Of course they have just a few available (some of them in China).

Next week I am going to China and while I was expecting them to be able to see our blog I realized that was not the case because all blogger.com blogs are blocked by the Great Firewall of China. Fortunately, I was able to easily move all the content to a wordpress.com blog that works nicely there.

Fourth (and last) assignment is out

I have prepared a fourth assignment that I expect you all to find it easy (as the last one was challenging for many of you). Again, we are dealing with UDP communication and in this case your job is to create a chat server.

As we did for third assignment, the client program is going to be netcat command (nc).

This last assignment is due by noon on the May 5th, 2011. No late submissions will be accepted. Please remember to do the assignment just by yourself.

By now, you should already know assignment can be downloaded by clicking on the title of this entry, shouldn't you?

Third assignment solution

It seems many of you have found the third assignment frightening or maybe you were too busy with other subjects (or partying?). The success ratio of entries turned-in has been 100% but I know of some students who dropped it after a while.

Please remember the solution provided here (click on this entry title) is just one reference solution for you to study. In fact some of the solutions followed a completely different approach (one thread per pending wake-up).

Of course, "regular expression" parsing is beyond the scope of our subject and it won't be in the exams either.

Marks appear in the "Assignments" tab of the attendance record page.

Scary news

Apparently an attacker obtained valid certificates to the names of several companies including Yahoo and Google. These could later be used to help them distribute fake information and software that would look legit.

Third assignment: Wake on LAN server

The third assignment is a server to wake up computers through the network. The server allows clients to schedule a wake-up operation into the future. This third assignment only uses UDP protocol.

For managing the list of pending wake-up requests a hash table (or similar) can make your job easier.

Update: I have added a sample server on the campus network. You can reach it with command nc -u msanchez.upv.es 2323 and it works as the exercise requests. Please note you can only interact with it from inside the campus network, otherwise you'll be blocked by the campus firewall. If you want to use it from your home, please create a VPN connection to the campus network.

You can receive the response by specifying your own IP address and running this other command: nc -ulp 7 on your computer (for this command you'll need administrative rights). Please remember the message is scheduled to be transmitted once the time has passed. If this command is not running before datagram is transmitted then datagram will be lost (it is not queued anywhere).

Update: One small detail is that nc command will add an end-of-line marker (char 0x0a in OSX and Linux) to the text you just typed at the terminal when you press enter key.

Update II (March 9th): An unscheduled power outage left the sample server out of service for a few days. Now it is back online.

World IPv6 Day Test

Next June 8th, several companies have decided to have their websites available for IPv6 traffic too. Click on this entry title to get more information.

Redes rules

For those of you joining us lately, here you have the course syllabus-
Re Des 2010

1st term marks

All your exams have been marked and you can see the results on the "Exams" tab of the attendance worksheet.

For a limited time, your written exam is available for you to double-check the grading process. If you detect any error, please let me know. If you have any question about marking process or the answers of the solved exam feel free to contact me. Please note that the document below contains all the exams in no specific order, so you may need to scroll down a bit if yours is the last one.

For your own protection, saving or printing this document is not permitted. Nor this document is available to a regular visitor on the hosting service.

Solved 1st term exam

You will find below the solved exam. Please have a careful look at the answered provided there and considering your own answers to the written exam, mark your own answers and email me the mark you think you have obtained. Consider only good or bad answers (that will be worth 2% or 0%). Do this as soon as possible (as your memory about your own answers will fade away).

You can get a full-page document view by clicking on this entry title. Do not hesitate contacting me if you find an error on any of the provided answers.
Solved 1st Term2011