Transcript Data Communications

Data Communications
• Network Connections
– Data Terminal Equipment (DTE)
• VDT, Clients, workstations, FEP
– Data Circuit Terminating Equipment (DCE)
• Interface between network and DTE - Analog or
Digital
Analog - Modem
• Analog - Modem
– Signaling Rate / Second - (Baud) symbols per second
– Data Rate / Second - bits per second
• Nyquist’s Limit for Signaling Rate - twice passband
(2B) - not achievable in practice
Analog - Modem
• Nyquist’s Limit for Signaling Rate
– Practical Limits (voice grade phone lines) 2400 Baud (symbols per second)
– Limits data through put if one bit per symbol
– Methods of achieving higher bits per symbol?
• Symbols that represent 2 bits per symbol
S1=00, S2=01, S3=10, S4=11
• Symbols that represent 4 bits per symbol
S1=0000, S2=0001, S3=0010, S4=0011 . . . .
S15=1100, S16=1111
Analog - Modem
• Nyquist’s Limit for Signaling Rate
– page 297 data stream vs. symbols
Analog - Modem
• Nyquist’s Limit for Signaling Rate
– Multi-level signaling
• Amplitude
• Phase
– Figure 7.2
Analog - Modem
• 16-QAM
–
–
–
–
4 Amplitudes
4 Phases
1800 Hz carrier
Figure 7.3
Analog - Modem
• Error Region - Figure 7.2a
• Practical 16-QAM
– 3 amplitudes
– 12 phases
– Figure 7.4
Analog - Modem
• Error Control
– Error Detection in Modem Protocols
• V. standards (v dot) standards - established
by CCITT for manufacturers to ensure
compatibility
• modem standards - compatible speeds,
compression, and error correction
• Comite Consultatif Internationale de
Telegraphie et Telephonie
– This is an international committee based in
Geneva, Switzerland, that recommends
Analog - Modem
• CCITT changed to ITU-T
Standard
V.22
V.22bis
V.32
V.32bis
V.32terb
o
V.34
V.34bis
Meaning
Provides 1200 bits per second at 600 baud. (state changes per second)
The first true world standard, it allows 2400 bits per second at 600 baud
Provides 4800 and 9600 bits per second at 2400 baud
Provides 14,400 bits per second or fallback to 12,000, 9600, 7200, and 4800 bits per
second
Provides 19,200 bits per second or fallback to 12,000, 9600, 7200, and 4800 bits per
second; can operate at higher data rates with compression; was not a CCITT/ITU standard
Provides 28,800 bits per second or fallback to 24,000 and 19,200 bits per second and
backwards compatility with V.32 and V.32bis
Provides up to 33,600 bits per second or fallback to 31,200 or V.34 transfer rates
The trunk interface between a network access device and a packet network at data rates
greater than 19.2 Kbps. V.35 may use the bandwidths of several telephone circuits as a
group. There are V.35 Gender Changers and Adapters.
An ITU standard for high-speed synchronous data exchange. In the U.S., V.35 is the
interface standard used by most routers and DSUs that connect to T-1 carriers.
V.35
V.42
V.90
Same transfer rate as V.32, V.32bis, and other standards but with better error correction
and therefore more reliable
Provides up to 56,000 bits per second downstream (but in practice somewhat less).
Derived from the x2 technology of 3Com (US Robotics) and Rockwell's technology.
Analog - Modem
• bis/ter Sometimes ITU standard names have
a suffix, either "bis" or "ter". These mean
"two" and "three", respectively. So V.32bis
is like saying, "V.32 -- The Sequel!" "terbo"
seems to be a play on words.
Analog - Modem
DUPLEX MODEM TRANSMISSION STANDARDS:
•
Bell 103 300bps USA standard.
•
V.21 300bps.
•
Bell 212A 1200bps USA standard. (same as V.22? *)
•
V.22 1200bps with fall back to 600bps
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V.23 1200bps with 75bps back channel, fall back to 600bps/75bps
•
Used by Brazilian Videotext service.
•
V.22bis 2400bps with fall back to V.22
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V.32 9600bps with fall back to 4800bps
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V.32bis 14400bps with fall back to 12000bps, 9600bps, 7200bps and 4800bps
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V.32terbo 19200bps, with fall back to 16800bps and V.32bis
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V.34 28800bps. Approved 6/9/94. Previously called V.FAST. Includes:
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o "line probing", to test reliability of a connection.
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o 28800bps half-duplex transmission for FAXes.
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o fallback to existing V-series modems.
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o 200bps channel for modem control data.
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o Trellis coding to correct for line noise.
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o Handshaking with telephone network equipment. *
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V.FC "V.Fast Class" 28800bps industry standard, by Rockwell and Hayes.
•
Not an ITU-T recommendation, despite the "V." prefix.
•
Incompatible with V.34, but many modem vendors may offer
•
dual-standard modems
Analog - Modem
• V.90
– 56k Standard
– V.90 also know as V.PCM (Pulse Coded
Modulation)
– V.90 assumes there is only 1 analog portion of
the downstream transmission path (the
upstream data conforms to the V.34 standard)
– Analog to Digital Converter (ADC),
Quantization Noise
Analog - Modem
• V.90
Analog - Modem
• V.92 Modem Standard
• The International Telecommunication Union (ITU-T) has announced
an improved ITU-T 56K modem standard: V.92. Though the top speed
for downloads is still 56K, V.92 has a number of enhancements:
 Startup time - the time needed to establish a connection - has been
reduced, making hopping on and off the Internet much easier. This should
make it easier to hop on and off the Internet. Reports from months ago
claimed that startup time had been reduced from around twenty seconds to
about five seconds, though more recent reports put the figure at ten
seconds. (One difference in the figures may be whether or not dialing time
is included, or if the figures only cover the time when the two modems are
screeching at each other during the connection phase.)
 V.92 has a standard method of disconnecting the modem long enough to
let you know that someone is trying to call you without losing the
connection, a feature being referred to as "Internet call waiting."
 The maximum upload speed has been increased from 33.6K to 48K,
which should improve video conferencing and general uploading.
Satellite Communications
• Common Applications - Radio Relay - data,
voice, video
Satellite Communications
• RF Bands
Band Name
HF-band
VHF-band
P-band
UHF-band
L-band
FCC's digital radio
S-band
C-band
X-band
Ku-band (Europe)
Ku-band (America)
Ka-band
Frequency Range
1.8-30 MHz
50-146 MHz
0.230-1.000 GHz
0.430-1.300 GHz
1.530-2.700 GHz
2.310-2.360 GHz
2.700-3.500 GHz
Downlink: 3.700-4.200 GHz
Uplink: 5.925-6.425 GHz
Downlink: 7.250-7.745 GHz
Uplink: 7.900-8.395 GHz
Downlink: FSS: 10.700-11.700 GHz
DBS: 11.700-12.50 0 GHz
Telecom: 12.500-12.750 GHz
Uplink: FSS and Telecom: 14.000-14.800 GHz;
DBS: 17.300-18.100 GHz
Downlink: FSS: 11.700-12.200 GHz
DBS: 12.200-12.700 GHz
Uplink: FSS: 14.000-14.500 GHz
DBS: 17.300-17.800 GHz
Roughly 18-31 GHz
Satellite Communications
• Orbits - GEO -
– 35,786 kilometers
22,241 statute miles
– 6,900 mph
– 7,000 circular footprint
– Spacing >= 2o degrees,
or >= 9o (broadcast)
– 1 revolution per day
– Prop delay = 22,300 miles/186,000 miles/sec = 0.1198 sec
0.1199 sec x 2 = 0.2398 seconds (one way delay)
– Freq. • C Band 4GHz-6-GHz - Interference from Microwave
• Ku 11GHz - 12 GHz - atmospheric attenuation
• Ka 14GHz - atmospheric attenuation
– Higher Frequencies used in uplink, lower loss for lower bands used in
downlink
Satellite Communications
• Orbits - MEO •
•
•
•
~6,000 miles
5,000-6,000 mile circular footprint
5 revolutions per day
Prop delay = 6,000 miles/186,000 miles/sec = 0.0322 sec
0.0322 sec x 2 = 0.0644seconds (one way delay)
• Freq. – Ranges from 300 MHz - 2200 MHz
– C, S, K Band
Satellite Communications
• Orbits - LEO•
•
•
•
>1,000 miles
1,000 - 3,500 mile circular footprint
~12 revolutions per day
Prop delay = 1,000 miles/186,000 miles/sec = 0.0054 sec
0.0054 sec x 2 = 0. 0108 seconds (one way delay)
• Freq. – Ranges from 300 MHz - 2200 MHz
– C, S, K Band
Satellite Communications
• Orbit Tracks
• http://liftoff.msfc.nasa.gov/realtime/jtrack/3d/JTrack3d.html
Satellite Communications
• Power and Footprint
–
–
–
–
Low Power - 10’s to 100 watts
Free Space Loss ~200 dB for GEOs
Very low power at receiver
Restricting radiated energy to specific area
allow power to be concentrated
– Antenna design - Gain
• Effective/Equivalent Isotropic Radiated Power : It is the ouptut power
at the transmitter terminal, minus feeder and mismatch losses, plus
average antenna gain relative to an isotropic radiator in the horizontal
direction in dBW
– Spot Beam
Satellite Communications
• http://www.intelsat.com/satellites/covmaps/[email protected]#
• http://liftoff.msfc.nasa.gov/realtime/jtrack/3d/JTrack3d.html
Satellite Communications
• Transponder
– Satellites have some number of transponders
– receives a signal, amplifies it, and retransmits it
(typically at 8.5 to 60 watts
– new direct broadcast satellites use up to 120
watts so that very small receiving antennas can
be used)
– Transponders typically have a bandwidth of 36
to 72 MHz each (though newer satellites have
up to 108-MHz transponder bandwidths).
•
http://www.oreilly.com/reference/dictionary/terms/S/Satellite.htm
Satellite Communications
• Transponder
– NTSC standard analog television video (with audio)
signal requires 24 to 36 MHz of transponder bandwidth
– Each transponder typically carries one, two, or three
television signals (two for a 54-MHz transponder, three
for a 72-MHz transponder).
– Video signal digitization and compression schemes
allow up to eight television signals to share the
bandwidth required by a single uncompressed video
signal.
•
http://www.oreilly.com/reference/dictionary/terms/S/Satellite.htm
Satellite Communications
• VSAT
Satellite Communications
Satellite Communications
• http://www.gilat.com/Technology_Satellite
Basics.asp
• http://www.tbssatellite.com/tse/online/mis_telecom_geo.ht
ml
• http://www.ssloral.com/products/satint.html