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 symbolS1=00, S2=01, S3=10, S4=11

• Symbols that represent 4 bits per symbolS1=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 Meaning

V.22 Provides 1200 bits per second at 600 baud. (state changes per second)V.22bis The first true world standard, it allows 2400 bits per second at 600 baudV.32 Provides 4800 and 9600 bits per second at 2400 baud

V.32bisProvides 14,400 bits per second or fallback to 12,000, 9600, 7200, and 4800 bits per second

V.32terbo

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

V.34Provides 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

V.34bis Provides up to 33,600 bits per second or fallback to 31,200 or V.34 transfer rates

V.35

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.42Same transfer rate as V.32, V.32bis, and other standards but with better error correction and therefore more reliable

V.90Provides 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 - ModemDUPLEX 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• 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• V.32 9600bps with fall back to 4800bps• V.32bis 14400bps with fall back to 12000bps, 9600bps, 7200bps and 4800bps• V.32terbo 19200bps, with fall back to 16800bps and V.32bis• V.34 28800bps. Approved 6/9/94. Previously called V.FAST. Includes:• o "line probing", to test reliability of a connection.• o 28800bps half-duplex transmission for FAXes.• o fallback to existing V-series modems.• o 200bps channel for modem control data.• o Trellis coding to correct for line noise.• o Handshaking with telephone network equipment. *• 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 Frequency Range

HF-band 1.8-30 MHz

VHF-band 50-146 MHz

P-band 0.230-1.000 GHz

UHF-band 0.430-1.300 GHz

L-band 1.530-2.700 GHz

FCC's digital radio 2.310-2.360 GHz

S-band 2.700-3.500 GHz

C-bandDownlink: 3.700-4.200 GHzUplink: 5.925-6.425 GHz

X-bandDownlink: 7.250-7.745 GHzUplink: 7.900-8.395 GHz

Ku-band (Europe)

Downlink: FSS: 10.700-11.700 GHzDBS: 11.700-12.50 0 GHzTelecom: 12.500-12.750 GHzUplink: FSS and Telecom: 14.000-14.800 GHz;DBS: 17.300-18.100 GHz

Ku-band (America)

Downlink: FSS: 11.700-12.200 GHzDBS: 12.200-12.700 GHzUplink: FSS: 14.000-14.500 GHzDBS: 17.300-17.800 GHz

Ka-band 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 sec0.0322 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 sec0.0054 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/706@307.asp#

• 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_SatelliteBasics.asp

• http://www.tbs-satellite.com/tse/online/mis_telecom_geo.html

• http://www.ssloral.com/products/satint.html