22C:178/055:134 Topically Frequently Asked Questions

These are questions related to specific lectures and homeworks that I have answered in email and share with you.

Isn't it true that the routing table needs to list every host that is on the subnet LAN including the gateway? It is possible to simplify the list by putting in the whole subnet with the proper destination and genmask. If this were done, but some of the addresses did not have hosts connected to them, wouldn't the message to that address then just be discarded?

No - the routing table does not need to list every host on the LAN, that was the point of my lecture. Using the genmask and network address, many hosts will be correctly routed without having to explicitly list them. Of course, then IP numbers without corresponding hosts will also be routed, but those datagrams will simply be lost because ARP will be unable to translate the IP numbers when it broadcasts on the Ethernet. Fortunately, IP makes no guarantee about datagram delivery, so losing datagrams is acceptable.

But how can a missing host be differentiated from a host that simply happens to be turned off (no electricity) at a particular time? This is something for you to think about.

I checked last night for the slides for todays lecture and noticed that they were not available yet. That was also the same for last Wednesday's lecture. Since I work in the morning before class, it is more difficult for me to take time out to look for them the day of the lecture. That also doesn't leave me time to review the lecture notes before the lecture. Is it possible that you could get the slides available at least a day before the lecture?

I have mixed feelings about the timing of posting the lecture notes. Students have come to have the expectation that university courses should be just like the sales presentations given by large companies, or those special one-week courses where in advance of the course, you get a packet with all the slides printed. That way, there is no need to "take notes" the way it was in the old days. Perhaps this will eventually become a "student right" --- which dictates that professors will need to plan a semester's slides in advance and stick to them, with no accomodation to the rate at which students are picking up material.

In fact, I do have a semester's worth of slides prepared! But they are overhead slides and I have tested them on the televideo equipment: they aren't readable. Sadly, I must re-do all the slides, and the newer versions necessarily contain less information than I really would like to present. Also, this gives me an opportunity to incorporate some new developments in the networking field and "tune" the material to my audience.

Probably you are a busy person. It's likely that this course will have over seventy students, some computer science students, some engineers, some undergrads, some graduate students. The course will be better if there are useful homeworks and programming projects, which also take planning. And it is not the only course that I am currently teaching (not to mention research tasks with deadlines). So it comes down to time management. Do I prepare slides several weeks in advance, or should I also take time out to design homeworks, web pages, set up the lab experiments, meet with my TA, figure out what to do about experiments for off-campus students, and so on.

Please bear with me on the issue of having slides well in advance posted to the web page.