Cette page appartient aux archives web de l'EPFL et n'est plus tenue à jour.
This page belongs to EPFL's web archive and is no longer updated.

# TCP/IP

slot for looking at your midterms 1 and 2
You have possibility to come and see your work for midterms 1 and 2 on Tuesday the January 30th, from 10-11, in BC260.
During the slot, all the 3 assistants will be present. As different quesitons of the midterms are graded by different assistants, this is a good ocasion for you to get all your questions answered.

TAs
Posted by Slavisa Sarafijanovic at 14:46
tp4: additional hint for question on cwnd
For the Question (page 10):

Explain what limits the value of cwnd in this experiment? Refer to appropriate lines of code and observed
parameter values that matter for the explanation. Show the computation that confirms your answer, and
explain your conclusion. (Hint: think about sending window, cwnd, offered window, scale option(mentioned
in the introduction), and in_flight variable (also mentioned in the introduction). )

Additional hint: to find the answer and proper explanation, you have to take into account _ALL_ things we (already) suggested: sending window, cwnd, offered window, scale option(mentioned in the introduction), and in_flight variable (also mentioned in the introduction).
Posted by Slavisa Sarafijanovic at 14:01
we will print copies of tp4 and bring them into the lab
we will print copies of tp4 and bring them into the lab
Posted by Slavisa Sarafijanovic at 11:21
No prereq for TP4
As announced during the last lecture, there will be no prereq for TP4.
So for TP4 the whole grade will be based on the lab only.
Posted by Manuel Flury at 15:02
twnd multiplicative decrease
cc.pdf, bottom of the page 28:

1. multiplicative decrease for twnd

twnd = 0.5 * min (current window size)

should be

twnd = 0.5 * current window size = 0.5 min (cwnd, offered window)

which on the figure 2.2 gives decrease of twnd to cwnd/2, or to 2*segments size when cwnd/2 is smaller then 2*segment size.
Posted by Slavisa Sarafijanovic at 8:21
Hi, two little questions:

1) What happens to twnd during fast recovery? From what I understood it stays at 1/2 of its original size and when fast retransmit is over cwnd is set again to twnd (thus decreases). Is this correct?

2) What happens when we reduce a window and for example all the packets in the window have already be sent (thus sent packets will be out of the window...)

Thanks for the help,

Christophe Gudin.
Posted by Christophe Gudin at 11:53
1.4
I think that there is an errata when you say on page 18 at the beggining:

Y-D1 is twice....
Posted by Javier Sanchez Tamargo at 0:56
pag 8 in point 1.2
I don't understand the example in the notes that sais:

For example: with I=2, n0=n1=1...

well, my question is that I don't understand the meaning of: x0=0.1c, x1=0.5c, x2=0.1c, and x0=0.1c,x1=0.9c,x2=0.1c

what's the meaning of that? How to use it?Why is the reason of these numbers?
Posted by Javier Sanchez Tamargo at 18:48