## READ BEFORE THE FINAL: Ghostbusters and problem solving should be read before the final exam period, which is 1-3 p.m. on Wednesday of finals week. Please also look at the Waggle Dancing Bees. More details about the final exam coming here over the weekend on Saturday or Sunday. Here is the LAST ASSIGNMENT/Take Home Quiz, which was handed out and started in the hands-on class on Tuesday, April 25th. It corresponds to the first section of the last chapter in the textbook, which should be read carefully while you do the assignment. You have these capture files with your textbook on the ethereal CD-ROM. They are referred to in the LAST ASSIGNMENT/Take Home Quiz handout. Here is an animation of some Ghostbuster's movie scenes. What is PUBLIC KEY CRYTOGRPAPHY? What is DIGITAL SIGNATURE? ```Page 73-74 Questions 1-5 (ftp) Due on 4/20/Thursday Page 99 Questions 1, 3 and 7 (TCP) Due on 4/20/Thursday ```

Comparing different length Vignere ciphers: The ghost.txt file with Vignere cipher length = 2, 3, 6, 12 and 24. Notice how the statistical pattern of some letters being the most frequent and some being the least frequent are obscured more as the Vignere cipher goes from two characters up to 24 characters!

Showing only the 4 or 5 most frequent letters and the 3 or 4 least frequent for 2, 3, 6, 12 and 24.

MEMORY and TIC: Memory from DRAM to SRAM to cache and the gap between DRAM speed and CPU speed, which keeps getting worse (Moore's Law).

CSMA/CD and repeaters and segments. QUIZ THREE on 02/23/Thursday.

Hamming Codeword concepts and practice, for error correction and error detection issues. The CRC method of detecting errors will NOT be on the Thursday, February 23rd quiz.

There are 5 issues to consider when connecting two nodes or computers with some media like cable. They are EFERA.
Encoding, Framing, Errors, Reliability and Access are E, F, E, R, A.
Encoding
Encoding the digital data on the signals that the analog media can transmit, and decoding it back to the digital binary pattern when received.
Framing
Sentinel approach and byte count approach to know the end of a frame. Detecting the exact start of a frame is the other issue. "Not me" and "Mine" example.
Error detection
Even and odd parity. Hamming codewords. CRC (Cyclic Redundancy Check)
Reliable delivery
Sliding windows. Timers and ACKs. Automatic resend after timer goes off if no ACK from destination host.
Access control
CSMA/CD we have already studied. The CSMA/CA and token passing we have yet to study, but will look at them later on.

# QUIZ TWO outline for Thursday Feb 9th quiz.

The Spring 1999 web page, the Spring 2000 page, Spring 2001 810:023 page, Spring 2002 810:023 page, Spring 2003 810:023 web page, Spring 2004 810:023 web page, and the Spring 2005 810:023 web page all are useful to see what kinds of topics are covered in this class. Keep in mind, the rate of change for networks, PCs and operating systems means the class will change quite a bit in response.

## Review of one question from CLASS FIVE, Tuesday, January 24th. Another useful clarification for your IP protocol and subnet masking knowledge: SUBNET MASKS -- Understanding of TCP/IP protocol at the Network Layer IP addressing level, and applying that to subnetworking your network. (Email note from February 6th, 2002 for 810:023 class). Solution to the Hobbits (Frodo.middleearth.com, etc.) subnets grouping problem #4, and the other, shorter problems. subnetsPractice and IP numbers group exercise SOLVED IN DETAIL, and perhaps very helpful. You may need to take notes on it. If you do not understand it, WRITE IT OUT. Consume some ink, to more effectively think. If the ink don't flow, the understanding don't grow (as fast or as tall or as deep). Just the solution to #4 GROUPING the middleearth.com devices and hosts on which subnet problem.

Here is email note #1, for your convenience and in case you did not receive it. What to read or preview, if you get the chance.