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 log
2(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.
Slide 19
4B 5B from the patent.
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.
Wi-Fi
- IEEE 802.11 protocols
- Hotel Wi-Fi
- Hotel Wi-Fi blocking
- IEEE 802.1X
- supplicant – client device (or sometimes the software in the device)
- authenticator – network device (access point of Ethernet switch)
- authentication server – RADIUS or EAP
- SSID – service set identifier or wireless network name
- WPA2 and IEEE 802.11i & IEEE standard
- EAP – Extensible Authentication Protocol
- EAP-PSK (Pre-Shared Key)
- EAP-TLS (Transport Layer Security)
- Radius
- Basics of Digital Certificates and Certificate Authority
- best Wi-Fi router?
- WPS (Wi-Fi Protected Setup) brute force vulnerability
- Wi-Fi on planes opens door to in-flight hacking, warns US watchdog
- GAO report on air traffic control