The Physical Layer:
	- Reminder:  OSI Layers, and TCP/IP
	- Intro:  Transmitting 0 and 1
		+ With a clock
		+ Synchronization?
		+ Long run of 0 or 1
		+ Rising/Falling
		+ 1 is a transition, 0 is a not-transition (USB)
		+ T1:  No more than 15 0's in a row are allowed
		+ 4B/5B, etc.
		+ Many schemes are possible and have been tried!
	- Note:  I'll kind of assume you're experienced with home networks, etc.
		+ Ask if something doesn't make sense
		+ Let's draw a diagram too
		+ I replaced my router yesterday
		+ Router is not just physical layer
		+ Neither is a switch
		+ A hub "mostly" is
	- The chapter starts with a "math barrier"
		+ Remember signal to noise ratio, as a concept
	- The source of limitations:  Bandwidth
		+ Approximation of signals and harmonics
		+ Frequency and data transfer rate
	- "Never underestimate the bandwidth of a station wagon full of tapes"1
		+ This is a *different* meaning of bandwidth!
		+ Bad latency...
		+ Data transfer rate (often called bandwidth)
	- Twisted pair cables
		+ My speaker wire radio (annoying)
		+ 24 gauge for CAT 5e, etc
		+ Several km range in telephone applications, less for 100baseT, etc
		+ You can put ends on LAN cables at home
		+ Need CAT 6 for 10G
		+ Cat 7 is shielded
		+ Phone cords and voice modems, DSL (DSL is the next layer up)
	- Coaxial
		+ Shielded
		+ Impedance:  Related to capacitance
			* think about AC and capacitors
	- Powerline networks
		+ Normally transmits strong, low frequency signal
		+ 12 or 14 gauge
		+ not twisted
		+ Power supplies are "noisy"
		+ 100 Mbits are possible
	- Fiber Optic
		+ *very* fast theoretical max (50,000 Gbit)
		+ Limited by conversion from light to electric signal (100 Gbit)
		+ 100 km without amplification
		+ glass core, glass cladding, plastic or other jacket
			* Don't bend it too much
		+ LED vs. Laser
		+ thin
		+ Doesn't require many repeaters
		+ Fiber Summary:  Expensive in home use, saves telecom companies money
	- Electromagnetic ("radio")
		+ EM Spectrum (book chart)
		+ Signal to noise ratio
		+ directional antennas help this a lot
			- Microwaves can be directed
			- For long range, towers must be tall
			- 100 meter tower enables 80 KM without repeater 
		+ Regular wires can act as antennas (Cadillac example)
		+ Lower frequencies are less prone to problems (rain, walls, etc)
			- 4 GHz and above is affected by rain
		+ Interference means frequencies are regulated
		+ Don't microwave your wireless card
		+ Frequency auctions
		+ ISM bands (900 mhz, 2.4 ghz, 5 ghz, 57-64 ghz)
		+ There are quite a few wireless communication protocols using 2.4 or 5 ghz
	- Infared (which is also EM)
		+ Directional, blocked by most things, TV remotes
	- Visible Light
		+ Lasers can work in clear weather
		+ Book hotel examples
	- Satellites
		+ Orbits:  Show Wikipedia picture
		+ Orbits and ITU
		+ A single satallite in GEO can reach a large part of the Earth
		+ Latency:  More if the satellite is further away! 250-300 ms
		+ Voyager 2 has 34-hour ping time
		+ LEO:  Iridium (750 KM)
			- Satellite phones weren't popular
			- Satellites were sold for $25 million
			- Re-launched in 2001, used in remote locations
			- Satellites communicate with each other to make connections
			- In-orbit spares and fuel
			- Collision with Kosmos
		+ Another LEO Network:  Globalstar
			- Ground links used to travel around the Earth
		+ Indonesia has 13,677 islands
		+ Broadcast vs. point to point

Speeds of some links:  Let's see