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 –Signaling Rate / Second - (Baud) symbols per second –Data Rate / Second - bits per second Nyquists Limit for Signaling Rate - twice passband (2B) - not achievable in practice
Analog - Modem Nyquists 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 Nyquists Limit for Signaling Rate –page 297 data stream vs. symbols
Analog - Modem Nyquists Limit for Signaling Rate –Multi-level signaling Amplitude Phase –Figure 7.2
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 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 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.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 Orbits - GEO - –35,786 kilometers 22,241 statute miles –6,900 mph –7,000 circular footprint –Spacing >= 2 o degrees, or >= 9 o (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 Power and Footprint –Low Power - 10s 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 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
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