CPSC 3600 - DAY 17
APRIL 3, 2017

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Various technologies exist, no clear dominant technology.

Personal Area Networks (PANs)

+---------------------+-------------------------------------------------------+
| Type		      |	 Purpose					      |
+---------------------+-------------------------------------------------------+
| Bluetooth	      | Communication over a short distance between a small   |
|		      | Peripheral device such as a headset or mouse and a    |
|		      | system such as a cell phone or a computer	      |
+---------------------+-------------------------------------------------------+
| InfraRed	      | Line of sight communication between devices, often a  |
|		      | hand-held controller, and a nearby system such as a   |
|		      | computer or entertainment center		      |
+---------------------+-------------------------------------------------------+
| ISM Wireless	      | Communication using frequencies set aside for 	      |
|		      | industrial and medical devices			      |
+---------------------+-------------------------------------------------------+

WiMax - Fixed vs Mobile

Backhaul - the connection between a service provider's central network facility
and remote locaitons, such as cell towers.

Multiple WiFi standards based on frequency bands and data rates

Spread Spectrum Techniques

	Direct Sequence Spread Spread Spectrum - where a sender multiplies the
	outgoing data by a sequence to form multiple frequencies and the 
	receiver multiplies by the same sequence to decode.

	Frequency Hopping Spread Spectrum - A sender uses a sequence of freq.
	to transmit data, and a receiver uses the same sequence of frequencies
	to extract data

	Orthogonal Frequency Division Multiplexing - A frequency division 
	multiplexing scheme where the transmission band is divided into many
	carriers in such a way that the carriers do not interfere.

Two Types of LANs:

	Ad hod - wireless hosts communicate among themselves without a base 
	station

	Infrastructure - wireless host only communicates with an access point,
	and the access point relays all of the packets.

If access points are too far apart, then a dead zone will exist between them.

Complex - Access points coordinate handoff of a node from one access point to
another

Managed over wireless connection between access points

Prioritizes a node's connection based on signal strength

Simple coordination lead by access point venders
	Allows for cheaper, less complex access points

Point Coordination Function (PCF) - An access point configures station to
avoid transmission interference

Distributed Coordinated Function (DCF) - Uses a random access protocol to
communicate between multiple devices. Utilizes CSMA/CA to avoid hidden station
problem.

DCF:
	Uses Ready to send (RTS) and Clear to Send (CTS) messages
	Typical wifi signals don't use collision detection.  The receivers 
	instead send an acknowledgement (ACK) message to determine if the
	packet was received.

	Includes 3 Timing Parameters
		Short Inter-Frame Space (SIFS up to 10 microseconds)
		Slot Time - 20 microseconds
		Distributed Inter-Frame Space (DIFS)