Weekend homework

There are a few exercises to do at home.

Please note next lecture previous reading is quite extensive:

• Kurose2010 section 3.5.6 (skip TCP state machine)
• RFC 879: The TCP Maximum Segment Size and Related Topics, section. 3
• RFC 793: TRANSMISSION CONTROL PROTOCOL,section.3.1 (Header format)
• RFC 2018: TCP Selective Acknowledgment Options
• RFC 1323: TCP Extensions for High Performance, section.2 & 3

Lab#6: UDP sockets

Oops, wrong image :-D

This week's lab is about how to use UDP in Java. UDP is a connectionless transport protocol that provides no guarantee but to be fast and simple. Unfortunately, UDP handling in Java is all but simple. To start with, you need two different clasess, DatagramSocket and DatagramPacket to send and receive data. And these do not even address how to perform a DNS query. For that, you'll need another class: InetAddress. But this is not where the trouble end. You need to switch back and forth from byte arrays to strings for some applications, and this job is not very cleanly done either. So welcome to some heavy coding session.

Lecture#10 Reading

It is Kurose's section 3.5 about TCP.

This time I won't believe you don't have any questions so please, post your doubts and questions as a comment so I can address them properly in my lecture.

Port Mirroring

To monitor network traffic on a switched Ethernet network some help from the switch hardware is needed.  Cisco calls this port mirroring and it allows all the traffic of certain ports to appear on a given port (where a sniffer like Wireshark can record it).

As I mentioned in the class, sniffers can be detected when connected to a wired network using some clever tricks, though there are certain countermeasures too.

Some of you (Jordi I reckon) mentioned problems about sniffing on WPA networks, I guess this thread summarizes all about it.

Lab#5: Threads

Sometimes we need applications to perform two or more tasks at a time. Blocking calls may stop all program activity. If you are not happy with that, threads can help you have just only one of them blocked while your program continues doing other tasks.

You can get the lab text here.

By the way, no previous reading for next lecture.

Lab#4: More sockets

Now available at the usual place. In this lab we will explore how to create an iterative server.

Reminder

Tomorrow Nov, 4th, 2011, there is no Redes class (it is supposed to be a Tuesday schedule instead).  So don't forget it.