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SampleHW1

HW06

1. A netmask in binary is some ones (the network bits) followed by some zeroes (the host bits), until you fill in all 32 bits. When the netmask is written in dotted decimal form, not all numeric values from 0 to 255 are possible. What are the possible values for each octet in a dotted decimal netmask?
   • HINT: start with 1111 1111 (255) then 1111 1110 (254) and work your way down to 0000 0000 (0). (Or the other way around if you prefer.) What are those binary numbers in base ten?
   • Fill in the netmask table at the bottom of this page.
   • Look at the diagonal pattern of 1s and 0s: this is often called the marching ants.
2. Look at the problem discussed in Troubleshooting Network Access, section 13.4.2.1 (previously Troubleshooting Network Access, section 11.4.2.1).
   • What was the root cause of the problem?
   • What would the effect be if, instead of that problem happening to the user's machine limulus (or cashew), it happened to the name server? (Ten years ago, this used to happen all the time on campus. It happened twice to one of my NMS servers last year.)
3. Skim the History of Telecommunications.
   • Who was Elisha Gray? (The quote just after his mention is fabulous!)
   • What are party lines, and how many phones used party lines in 1950? Keep this in mind when reading Odlyzko.
   • For reference: The first ARPANET packet transmission was on October 29, 1969.
4. Skim The Underwater Web.
   • What does capacitance do to an electrical signal? (It's a simple answer, early in this reading. Don't make this a hard question! It explains why PDH came before SDH.)
   • What does resistance do to an electrical signal? (This explains distance limitations.)
5. You remember the "hubs vs switches" argument. Hubs are Layer 1 and divide bandwidth among all users, while switches are Layer 2 and theoretically multiply bandwidth. So for five or more users, switches offer better performance. The next argument is "switches vs routers." Routers are Layer 3 devices.
   • What impact do routers usually have on network performance? This makes traceroute useful.
   • Would you rather route or switch, given a choice? Consider this paper, Route Once, Switch Many, by Passmore and Bransky. Sorry, dead link ... try this and that as an overview. I'll see if I have a copy somewhere ...