August 29, 2005 Mon.
46590 CSC451 01 Computer Networks MW 11:30 AM - 12:45 PM WH A118
Dr. Kowalski, Jim, Cindy, Jorje, Ricardo, Sanje, Jamal

August 31, 2005 Wed.

September 5, 2005 Mon.
Labor Day Holiday

September 7, 2005 Wed.
Nyquist's theorem: on a noiseless channel, if an arbitrary signal has been run through a low-pass filter, and if

H = bandwidth
V = discrete levels
maximum data rate = 2 H log2 V bits/sec
Shannon's theorem: on a noisy channel, if the signal-to-noise ratio is designated S / N
maximum data rate = H log2 ( 1 + S / N )

September 12, 2005 Mon.
T = 1 / f, where T = wavelength and f = frequency.
The attenuation (loss) through fiber is different for different frequencies.
Geo stationary satellites have a 270ms delay (1/2 second round trip).
ADSL = 256 4kHz channels. One channel is used for voice, one for separation, the rest for data. 4kHz filters are placed before the switch and the telephones.
No class Wed., Sept 14. Kowalski has a meeting.

September 14, 2005 Wed.
No class. Kowalski has a meeting.

September 19, 2005 Mon.
Sampling: on a 4kHz channel, 8 bits per sample, 8k times, equal 64,000 bits of data. A T1 is 1.544 m. That is just about 24 voice channels on a T1. The rest of the bits are signaling.
Data modulation: to put more data in the signal. If, instead of transmitting 8 bits to describe the sample, we transmit only that it has changed ±1v. That requires two bits so we can xmit 4 times as many channels.
The Linux operating system has 64,000 ports therefore it can be a 64k station telco switch.
Message switching. Review question 43 at the end of the chapter.

CHAPTER 3: Data Link Layer
Services provided to the network layer

• framing
• error control (requires framing)
• flow control

September 21, 2005 Wed.
No class. Kowalski has a meeting.

September 26, 2005 Mon.
Error Detection & Correction Codes
Hamming code and parity bits.
If you have parity bits i such that i = 2i, you can correct single errors.
p = parity bit, d = data bit,       p1 p2 d1 d2 p3 d3 d4
p1 is parity for bits 1, 3, 5 and 7.
p2 is parity for bits 2, 3, 6 and 7.
p3 is parity for bits 4, 5, 6 and 7.
This code will correct all single bit errors.
It takes more parity bits to enable error correction than it does to enable error detection. If their are few errors, it uses less bandwidth to request re-transmission than transmitting error correction bits.
At current speeds, noise or signal interference causes bursts of errors. Error correction is still less efficient.
Error detection for large blocks of data uses integer division. If A % B = C, we transmit C. If the receiving end has A % B != C, retransmission is requested.

September 28, 2005 Wed.
Error - Detecting Codes

calculation of the polynomial code checksum
Elementary Data Link Protocols
protocol: set of rules governing behavior between 2 entities.
Flow Control
* an unrestricted simplex protocol
* a simplex stop-and-wait protocol
* a simplex protocol for a noisy channel
Sliding Window Protocol
* one-bit sliding window
* go back N
receiver has 1 memory buffer.
* selective repeat
receiver has multiple memory buffers.

October 3, 2005 Mon.
possible test questions, 1.1 .9 .20 .27, 2.2 -.7 .9 .30, .43, 3.5 .8 .9 .12 .14 .32
CHAPTER 4: The Medium Access Control Sublayer

medium as in media
Static Channel Allocation, LAN's and MAN's
Dynamic Channel Allocation, LAN's and MAN's
Broadcast Type and Collision

October 5, 2005 Wed.