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Allows clocks in sending and receiving nodes to synchronize to each other
no need for a centralized, global clock among nodes!
Hey, this is physical-layer stuff!
MAC Addresses Each adapter on LAN has unique MAC address Broadcast address = FF-FF-FF-FF-FF-FF = adapter 1A-2F-BB-76-09-AD 58-23-D7-FA-20-B0 0C-C4-11-6F-E3-98 71-65-F7-2B-08-53 LAN (wired or wireless)
Ethernet and other 802 protocol offer a best-efforts datagram service. LLC can be added to provides 3 service options: unreliable datagram service, acked datagram service, reliable connection-oriented service
Range is 10 to 20 meters and cannot penetrate walls.
Does not work outdoors.
802.11 FHSS ( Frequence Hopping Spread Spectrum )
Offers good resistance to multipath fading.
79 non-overlapping channels, each 1 Mhz wide at low end of 2.4 GHz ISM band.
Same pseudo-random number generator used by all stations.
Dwell time: min. time on channel before hopping (400msec).
Multipath Fading The deflection of a radio signal off obstacles which can cause interference during signal reception. Multipath occurs when a radio signal is received directly by an antenna and later the same signal is received again, reflected from a building or mountain. "Ghosting" of a TV signal is a form of muiltipath. Under certain conditions, two or more of the signals can interfere with each other and create "fading" (a loss of signal) in the communications link.