Class test marks

Class test has been marked. Most of you did well, congrutaltions. Those who did not, now know you need to re-read the book and class notes.

Remember you can always schedule an appointment for me to explain you what you did not get right during lectures.

From marking the tests it became clear to me that my explanation of propagation delay was not good (as many of you got your answer wrong). First, let me explain what propagation delay is not:

• Propagation delay is not the response time.
• Propagation delay is not the sum of different delay sources.
• Propagation delay is not the time it takes for a packet to be received since it was sent.

Propagation delay is the time it takes for a signal to travel the distance from transmitter to receiver. Please do not confuse transmitter with sender nor receiver with destination. First, let me explain this difference: each time a packet is retransmitted, there is a transmitter, a receiver and a link connecting the two together. In a packet switching network. Packets will flow from sender to destination as a sequence of retransmissions through different links.

While propagation delay D is measured in seconds, it is interesting to note that for a given bit rate R, propagation delay can be computed in terms of meters/bit (as if bits had some physical dimension). As 1/R is the time it takes for a bit to be transmitted and at a propagation speed S this time is equivalent to a distance = S / (1/R). Therefore, the product S x R has the dimension meters/bit and it represents what fraction of space a bit uses when propagating along the link. 

As the link distance X is known too. A second conclusion we can get is the number of bits the link can hold "while propagating" as the expression X / ( S x R ). Does your brain hurt? If so, relax for a while before heading to this week's homework.

Four links and a homework.

Wireshark program was mentioned in today's lecture. You can get it for free. Wireshark is a network sniffer and protocol analyzer software. A tool to perform to give you x-ray vision for your network traffic.

You can get canned network traffic captures. If you want to learn a bit about capture filters to perform you own capture.

Wikipedia take on ISO/OSI reference model.

And finally, there is a set of solved exercises about chapter one that you should do at home. I started translating them but I kind of got tired in the second page, so I am posting the Spanish version.

Just as a reminder, next lecture previous reading is section 2.1 of the book.

Smoking hot!

This week another speed record. Please note that for us, not only raw speed counts but also the distance  achieved here.

By the way, this week's reading is section 1.3 & 1.5.

I mistakenly mentioned section 2.1 in the classroom, that will be the reading for next week.

English fun

I mentioned the word "router" today in the classroom. I did mention that Bristish and American accent is quite different for this word. Do you want to hear 18 different pronunciations of the word?

You can read a bit about the Spanish research network and European one.

By the way, I forgot to mention next class reading are sections 1.2 & 1.3 of Kurose's book.

And just in case, here you have Chapter 1 slides from the 6th Ed of the book (similar to 5th version but finally without the annoying Comic Sans font).

First chapter of the textbook available in PDF

Linus Torvalds claimed that many things in life are better when they are free (you may want to research this quote for some fun). The first chapter of the textbook we use for this subject is made available for free download by the publisher.

You may want to grab it while it lasts. The only drawback is that this file belongs to the Spanish version of the book. Or is it an advantage? Please let me know you opinion on this with a comment (it won't bite you).

Please note there is a newer version of the book (6th edition) just published in English. You can borrow the  5th edition from the school library.

Reading section 1.1 before the first lecture will help you follow it better. If you have any questions before the class it is a good thing you sent me an email so I can properly address it in my lecture. We will follow this method along the course so we can make the classroom more efficient (any doubts from your readings or exercises you can email it to me before the lecture).

Just in case you doubt it: Tomorrow September 11 (oops, what a date) we won't start the Lab sessions as erroneously states the school time-table web app. 

A short history of the Internet

A nice introduction to the origins of the Internet. 

Here you have this course's syllabus.

Welcome to new students course 2012-13

Feel free to look back in previous posts. From now on, all the posts will pertain to this new course and I hope you will enjoy the course, but mostly I do expect you to learn all the basics about Computer Networks along this year. This what this course is all about, the basic concepts of TCP/IP networks.

I have been using a blog instead of other vehicles for distributing the course information. We will discuss this on the very first day to establish whether we keep this system or you prefer me to switch to other type of platform.

Please note that this blog is open to people outside of the course, make sure you feel comfortable about it. Attendance record and marks are made public in a transparent way from day one.

Blog format allows me to be posting news, labs or any other relevant information about the course, while you have on the right-hand side the course spreadsheet covering attendance and mark information and a file repository all relevant files can be downloaded from. Did I mention no username/password is ever required?