Download 5211 Data Comm 1 - Cincinnati State

5211 Data Comm 1
Paul Weingartner
7-2004
Presentation #2
Cabling & Coax
• Termination is a very important topic often
not covered.
• When signals are sent down a wire/cable if
they are not fully absorbed in the load at
the end, they can be reflected back.
• This reflected signal will collide with other
signals coming down the line. The result
is garbled data.
• Which has to be re-transmitted
The problem
• Is called SWR – Standing Wave Ratio
• People in RF communications know it as
VSWR (voltage SWR) and use RF devices
to match the impedance
The fix
• Many devices have the appropriate
termination (resistors) included in them.
• Other times a “terminator” must be
installed.
• Terminators are also in unused Rambus
memory slots, some mother board
expansion busses, etc.
Fiber optic cable
• Laser light emitters generate light at a very
narrow wave length
• White light has all colors (wavelengths in
it) – play with a prism
• Secure communications
• Impervious to noise (RF)
Fiber modulation techniques
• Single mode (wave length)
• Wave division multiplexing (WDM)
• Dense WDM (DWDM)
Wireless comm
• Simply put, speed is bandwidth
• To send high speed data, you need wide
channels to transmit the data.
• This effectively means VHF and above
• 800 MHz is the lower limit of what is
considered “microwave”
Point to point links
• Bell telephone has used microwave links
for many years.
• Referred to as “Terrestrial” links
Satellite comm
• There are two popular flavors that are
being used
– For home/small biz users, “Direct PC” is an
option
– For businesses, VSAT (Very Small Aperature
Terminal Sat equipment)
• Issues
Cellular phones
• Analog
• Digital
Analog cell
•Who cares!
– mod
•TDMA
types
•CDMA
•GSM
Cell – data speeds
• Analog – 14,400 b/s (good day)
• Digital – 1st gen – 14.4k
• Dig – 3rd gen – 144k
– What is the real throughput???
• Future – 1Mb/s
Wi-fi – Wireless computer access
• There are a series of standards
– 802.11a 54Mb
– 802.11b Wi-fi 11Mb
– 802.11g 54Mb
– 802.11i (find out)
– 802.16 – Wi-Max
• Range – up to 1000’ with standard
antennas (2+ miles with beams)
Bluetooth
• Short range – up to 30 ft
• 2.45 GHz
• How fast?
MODEM – Chap 4
• The only way to send data over any
distance is to use some type of modulation
technique
• Audio – Acoustic can be used with
telephones
• Signals are often converted to different
levels (voltages/currents) in order to send
them over long distances)
Devices
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Analog modems
Cable modems
CSU/DSU
FRAD
ISDN