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Transmission media
Wires
twisted pair
coax
fiber
which is most noise immune? At what frequencies?
Wireless
IR, RF, satellite
Wired media
Copper cable twisted pair
shielded (STP) or not (UTP)
category levels
performance characteristics
e.g., Category 5 is 100MHz up to 100 meters
Digital Subscriber Line (DSL)
Leverages off installed twisted pair base
Many varieties
difference in downstream/upstream, distance covered, permanent
connections, shared voice
ISDN DSL (IDSL), HDSL, SDSL, ADSL, RADSL, VDSL
Some specifics (take w/ grain of salt)
ISDN 128K 128K 18k feet
HDSL 1.544M 1.544M 12k feet
SDSL 1.544M 1.544M 10k feet
ADSL 8M 1M 12k feet
RADSL 7M 1M 18k feet
VDSL 51.84M 2.3M 1k feet
Coaxial cable
What cable TV uses
For data, can transmit 10Mbps downstream and 2Mbps upstream
Fiber
Send information via light and not electrical impulse
Many advantages over copper
Rated by OC-levels (SONET)
OC-1 = 51.84 Mbps
OC-192 » 10 Gbps
Wave Division Multiplexing up to 1.28Tbps
Wireless.
General issues
Categories
Wireless LAN (near range, high b/w)
Wireless telephony (long range, low b/w)
Wide area data (long range, high b/w)
Paging (long range, very low b/w)
Satellite (long range, very low b/w)
General issues
Frequency spectrum
where the action is limited
Capacity and Frequency bandwidth
Shannon bps = delta f (1 + S/N)
Sampling rates
Nyquist
Wireless LAN
Wireless Ethernet (IEEE 802.11)
InfraRed (not regulated)
Three major RF frequency bands
900 MHz (902 - 928)
2.4 MHz (2.4000 - 2.4835)
5.8 MHz (5.7250 - 5.825)
Industrial Scientific Medical (ISM) bands
How is RF transmitted?
Spread spectrum
across a range of frequencies
Frequency hopping
signal jumps between frequency "channels"
Direct sequence
signal spread over all channels
Wireless telephony
Late 1970s - first analog systems
Cellular
AMPS is North American standard
Digital cellular
greater capacity
smaller handsets with longer battery life
Wide Area Data
Circuit-switched data
analog phone with modem (9.6 - 14.4 Kbps)
pay while connected
must initiate connection
Cellular Digital Packet Data (CDPD)
obvious advantages over circuit-switched
19.2 Kbps
How digital cellular works
2.5 techniques
Time Division Multiple Access (TDMA)
freq channels split into 6 time intervals
compatible with AMPS
data rates up to 9.6 Kbps
GSM
Global System for Mobile Comms
TDMA with 8 time slots
European standard, moving to N. America (Powertel)
incompatible with AMPS
Data rates 9.6 Kbps, but much greater possible (see Web)
CDMA
Code Division Multiple Access
An example of spread spectrum greater capacity than TDMA
Tricks for digital voice/audio
Never send silence
Compress
Send at higher rate than real time
Time compress with SOLA
Up to 300 words per minute
Specialized Mobile Radio
initial analog radio dispatch
push to talk
Motorola made digital
added for telephony, paging and packet-switched data
Nextel is example
Other packet-switched
Mobitex
Originated in Europe
In U.S. as BellSouth Mobile Data
8 Kbps
What Palm VII will use
ARDIS
Metricom
Up and coming
GPRS
128kbps compatible with current equipment
384kbps Edge
"3G’s"
Up to 2 Mbps.
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