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# TCP/IP

!!! **** MODIFICATION regarding: office hours, see midterms and get hws 3&4 back
!!! **** MODIFICATION **** !!!

At this time slot (28.02.2007, 15:00 - 16:30) we do _only_ "TAs answer questions on theory slides and in-class exercises".

A separete session to see your midterms and get hw 3&4 back is Thursday, 15:00-16:00, BC329.

TAs
Posted by Slavisa Sarafijanovic at 18:04
Wed 28th, 15-16:30, BC 329: office hours + see midterms + get homeworks 3&4 back
Room: BC 329
Time: 28.02.2007, 15:00 - 16:30

What:
- TAs answer quesitons on slides or exercises
- you get back your hw3&4 (with small probability it can happen hw4 is not graded by that time)

TAs
Posted by Slavisa Sarafijanovic at 15:03
will be answered on Monday (26th)

Also, from Monday on, new questions will be answered with small delay.
Posted by Slavisa Sarafijanovic at 20:01
Algebra...
===== 1.archi.pdf =====

----- slide 34, example:

first problem/question:

"S/N=signal noise ratio (not expressed in dB)" what is the meaning? We shouldn't use dBs?

second problem/question:

C_max = B*log_2(1+S/N) = 3000*log(1+30) = (~) 3000*log(2^5) = 3000*5 = 15kb/s
Am I wrong?

---- slide 39, stop&go solution:

left-top:
packet P1 sent
T=L/b

Thanks.
Posted by Raphaël Tagliani at 17:50
typos
I'm not really sure that all of them are typos, but as they look strange to me, I put them here anyway...
The part between "" is taken from the slides and below, is the correction I propose.

bridging.ppt

p.20
"How: Define pk(i) as the cost of the best path from i to anywhere in at most k hops."
pk(i) is the attribute of a path, not its cost.

p.47/50
The top right link is labeled L14, but it should be L13.

p.51
"all bridges send a BPDU to neighbours every helloTimer ( = 2*2s = 4s)"
either a BPDU is send every helloTimer ( = 2s) or every 2 helloTimer( = 2*2s = 4s)

ls.ppt

p.26
"cannot pass to X5 a packet to A1 and to X3 a packet to A2"
should be from A1 and from A2 instead of to A1 and to A2

p.33
The figure lists routers A, C, F, F. It should be A, C, B, D

p.87
in area 1 topology database, the cost to n2 through the upper router is 34, not 22.

security.ppt

p.5
"Q2: describe the content of a packet from A to B visible at point 1."
There's no host B, but a server S.

p.16
"A2: contains an encrypted block of data inside a TCP packet with srce port=22, dest port=3456, IP srce=A, IP dest=S"
The port numbers are inverted., the src port on A is 3456 and the dest port is 22

mixed.ppt

p.32
"A: at 1 SA=132.146.243.30 DA=120.130.26.10
at 2 SA=PREFIX:: 132.146.243.30 DA=FEDC:BA98::7654:3210:"
1 and 2 are inverted. 1 is on IPv6 so it should have IPv6 src and dest. 2 is on IPv4 so it should have IPv4 src and dest.
Posted by René Giller at 19:12
Hi!

I just wanted to know if it would be possible that you post all the tests and lab notes on the site with our sciper or if not tell us when they'll be available in front of your office.

Thanks alot,

Christophe.
Posted by Christophe Gudin at 19:08
Last set of questions
Hi, some last questions (I hope):

bridging.ppt

p.47
Why is link L8 on B3 listed as "designated" ? Links L7 and L8 are on the same LAN, so, only one link can be designated, the other one should be backup, shouldn't it ?

ls.ppt

p.66/67
I don't understand what the forwarding address field in an AS-external-LSA represents and what is it used for.
- Is it the address of an AS boundary router in another AS ? But this information is useful only to the AS boundary router which originated the LSA, so why inform every one of it ?
- Is it the address of the router, in this AS, toward which traffic had to be send to reach the network described in link state id (in LSA header) ? But in this case, the forwarding address will always be the same as the advertising router (unless AS boundary router advertise routes to a linked AS through another AS boundary router).
In the example on p.73, the forwarding address is set to 0.0.0.0, what does this value means ?
- Is it to describe a default route ?
- Is a special value which means "advertising router" ?

p.76/77
Router 10.1.1.1 announce an infinite distance to AS boundary router 10.1.1.1 which is the same router. So 10.1.1.1 announce an infinite distance to itself ! Is it correct ?
Posted by René Giller at 18:38
Office hours
Hi all,
this is just to announce what follows:
before the exam, you will have office hours for checking your midterms and TPs,
and for any question. We will communicate you soon (through this blog) date and time.
Enjoy
Posted by Gianluca Rizzo at 17:59
Office hours
Hi all,
this is just to announce what follows:
before the exam, you will have office hours for checking your midterms and TPs,
and for any question. We will communicate you soon (through this blog) date and time.
Enjoy
Posted by Gianluca Rizzo at 17:59
Office hour for questions on the midterm
Hi,

is it possible to get a possibility to ask some questions on the midterms?
In my case, i got a question on the first part of question 2 in midterm 2.
I was allready present during the office hours, but i was told that you(the assistants) would announce a kind of "question hour" where alle of the assistants would be there to answer on questions.

Thx

J.T.
Posted by Johann Töws at 12:08
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