Monthly Archives: February 2009

IPv6 addresses problem

IPv6 is proposed as an almost unlimited source of addresses to overcome the IPv4 address shortage some people have suggested. As IPv6 addresses are 128-bit long, 2^128 (aprox 3.4 x 10^38 ) addresses are possible. This should be large enough.

To put things into perspective consider the following problem: How many IPv6 addresses could you put into each squared centimeter of the planet? (Assume the Earth is a regular sphere of 40.000 Km of perimeter).

And a second part … compare the above number of IPv6 addresses per square centimeter to the total address space of IPv4.


Fragmentation exercise

A 4000 byte-long datagram has to be transmitted over a network whose MTU is 512 bytes. Determine the number of fragments and, for each one of them, write down the fragment offset field contents and the number of data bytes of each fragment.

Solution was presented as a spreadsheet in the class. Here you have a copy. You can export it to your favorite spreadsheet software too (to see the formulas).

Third assignment announcement

Third and forth assignments will be based on a peer-to-peer protocol invented for the occasion. The so-called “P+2” protocol has been created to be one of the simplest P2P protocols (but not any simpler). You need to read and to understand the protocol specification. Protocol was already presented in the class but if there is general call I will repeat the explanation.

This assignment covers three different servers needed to create a full implementation. Assignment’s servers can be tested to work using either telnet, netcat (nc) or sock commands. Java language is mandatory for Spanish students but the rest may use the language of your choice. A working implementation of a peer is available too (just a binary version).

You can download assignment text from here. Or you can just go to the file repository (linked on the top right corner, under the new stuff title).

There is a sample peer running too. You may not need it yet for this assignment. Anyway, it is available at

You are welcome to ask me for help. Please remember you have to write code by yourself. As assignments are marked individually, it is not something you can develop jointly with a classmate. If two or more assignments are copied from each other all the involved parties will fail the assignment. Due date is March 13th.


Second term starts

Chapter 4 slides are already available. For those of you joining us for the second term please note you should read the syllabus that contains important details about how the subject works.

Next week we’ll start with the lab again. Lab#6 is out too.

Marks are out

Not all of you have sent me your own grading of your exam. The reason I was asking you to do that is not because I can save some work this way but because I want you to have a look at your own answers. Most of your marks are quite close to what I’ve got, at least from the set of students who sent them to me.

You can check your mark on-line. There a few more students who have never attended lectures that will appear at the end of the list of names. This marks are not final as you still have a choice to check your exam. If you want to do that, please tell me so next week in the classroom (or send me an e-mail).

You can see we have a tie on the top performers. I want to congratulate both: Rasmus and Juliusz. Keep up the good work!

Solved 1st term exam Feb 2009

Feb2009 Solved

You know what you have answered. Now you know the right answers. So please check them out, use a binary logic (an answer is either right or wrong, and it scores or not) and calculate your mark and email it to me.