CSCI 373 Computer Networking — Chapter 2 comments

The PowerPoint

Slide 7

Claude Shannon made many contributions to the field of computer science including the Master’s thesis that related Boolean algebra to circuit design, a Ph.D. thesis that founded information theory and the Ultimate Machine.

B log2(1 + SNR) where B is bandwidth and SNR is the signal to noise ratio, the ratio of the power of the signal to the power of the noise.

Slide 18

Also, see the Wikipedia article on Differential Manchester.
Differential Manchester

Slide 19

4B 5B from the patent.
4B 5B encoding

Slide 21

Framing is used in many point-to-point protocols.

Slide 22

The Wikipedia page lists the bits.

Slide 26

PPP is specified in RFC 1661.

In the dark ages, PPP connections would be run over modems to connect to the Internet.

Slide 30

HDLC is based on IBM’s SDLC. Once it was widely use to connect mainframes. It is part of the System Network Architecture (SNA) protocol family which was largely developed in Research Triangle Park.

Slide 32

Bit stuffing is used in many serial link protocols. It is easy to implement, but is does make the transmission speed a little unpredictable.

Slide 37

I hope we did parity in CSCI 255.

Slide 43

The IP checksum is computed so frequently that it may be written in assembly language.

Slide 44

The Cyclic Redundancy Check (CRC) is based on polynomial rings with coefficients over the Galois Field of order 2. The error-correcting properties of particular CRC polynomials can be proven using techniques from abstract algebra.

Slide 49

Slide 51

CRC-8 is x8 + x2 + x + 1.

x8 + x2 + x + 1 = (x + 1) (x7 + x6 + x5 + x4 + x2 + 1)

Slide 52

Polynomials like these are also used to encrypt cell phone conversations.

Slide 54

TCP déjà vu. Go to slide 78.

Slide 78

20 years since the mid-1970s? Go to slide 88.

Slide 88

It’s still pretty much the same address and frame format.

Slide 94

This was in the old days of the shared cable. Matt’s Tech Projects has a page building a 10base5 “thick Ethernet” network with a lot of pictures.

Now go to slide 106.

Slide 106

Since wireless links “share” a common media, they must be strictly controlled.

Slide 109

The actress Hedy Lamarr and composer George Antheil patented spread spectrum frequency hoping in 1941. They proposed using a piano rolls to synchronize transmission over 88 frequencies. The Navy wasn’t interested for a couple of decades.

Slide 110

CDMA uses a chipping code.

Slide 115

Someone must have taken my notebook’s antennae.

Slide 118

802.11 is a large set of standards. The Wi-Fi Alliance certifies Wi-Fi® implementations.

Slide 120

Oops... Someone got the wrong figure in the slide. It should be Figure 2.31, where B can reach A and C, and C can reach B and D, but A cannot reach D.

Slide 121

The picture is on slide 122 and slide 120.