9/18/2015© 2012 Raymond P. Jefferis IIILect Forms of Communication

9/18/2015© 2012 Raymond P. Jefferis IIILect Internet Communications Largely carried on telephone network Lately quite a bit of privately owned fiber –communication carriers –electric companies –private organizations Some carried over television cables New conveyance by wireless providers

9/18/2015© 2012 Raymond P. Jefferis IIILect Present Telephone Conveyance ATM backbone (long distance) ATM switching at core T1 data lines to businesses (1.544 Mb/s) Copper “last mile” –voice grade lines –DSL possible using residual bandwidth outside the voice channel - has distance limitations

Telephone on Internet (VOIP) Voice messaging using IP packets –Session layer setup and closing of “call” –Voice is digitized using CODEC –Encoded and packaged into frames –Encryption can be arranged (SRTP) –Transmitted over packet network (e.g. Internet) Uses Internet transport (IP) 9/18/2015© 2012 Raymond P. Jefferis IIILect

9/18/2015© 2012 Raymond P. Jefferis IIILect Terms ATM - Asynchronous Transfer Mode DSL - Digital Subscriber Line DSLM - DSL Modem DSLAM - DSL Access Module POTS - Plain Ordinary Telephone System SONET - Synchronous Optical NETwork

ATM Asynchronous Transfer Mode –Bakbone of telephone system –Data in packets (48-bit cells) –Uses time-division multiplexing 8000 samples/second (CODEC) 9/18/2015© 2012 Raymond P. Jefferis IIILect

DSL Digital transmission over phone lines Uses frequency channels above phone Channel filters separate Up/Down bands –Uses DSL Modem (DSLM) for this Speed depends on distance to TelCo station –256 kb/s to 24 Mb/s data rate Becoming obsolete due to fiber and cable 9/18/2015© 2012 Raymond P. Jefferis IIILect

9/18/2015© 2012 Raymond P. Jefferis IIILect TelCo Network Interface

9/18/2015© 2012 Raymond P. Jefferis IIILect Residential Data Lines POTS line with modem –56 kb/s –rate depends on line quality DSL line with splitter/modem* – Advanced, up to 1.5M / 128K$59.95/month –Premium, up to 384K / 384K $69.95/month –Professional, up to 1.5M / 384K$79.95/month *Speed depends on distance to TelCo office

9/18/2015© 2012 Raymond P. Jefferis IIILect Digital Data Transmission Binary data Transmitted as pulses Pulses shaped by line bandwidth Pulses have high frequency components Limiting bandwidth limits data rate

9/18/2015© 2012 Raymond P. Jefferis IIILect Fourier Series of Bandlimited Pulse

9/18/2015© 2012 Raymond P. Jefferis IIILect Fourier Transform of Pulse

9/18/2015© 2012 Raymond P. Jefferis IIILect Notes: First crossover of spectral amplitude is at B 2B is effective bandwidth needed to transmit through noiseless channel.

9/18/2015© 2012 Raymond P. Jefferis IIILect Nyquist Bit Rate Relates three transmission variables: –Channel Capacity (C) –Bandwidth (B) –Signal levels (L) – quantization levels –Formula: C = 2Blog 2 [L] Noise-free channel assumed

9/18/2015© 2012 Raymond P. Jefferis IIILect Nyquist Example: Formula: 2BLog 2 [L] Example: L = 2 (binary signals), (Log 2 [L] = 1) B = 3000 Hz (300 – 3300 Hz) C = 2*3000*1 = 6000 [bits/s] Note: Applies to noise-free channel only

9/18/2015© 2012 Raymond P. Jefferis IIILect Shannon Formula C = B log 2 (1 + SNR) Example: –B = 3000 Hz (300 – 3300 Hz) –SNR = 3163 (35 dB power ratio) –C = 34,882 [bits/s]

9/18/2015© 2012 Raymond P. Jefferis IIILect All Digital Telephony Voice-to-Digital conversion coding at transmitter Digital transmission Digital-to-Voice code conversion at receiver Conversions performed by COder-DECoder (CODEC) module at each end of line

9/18/2015© 2012 Raymond P. Jefferis IIILect Voice-Data Conversion CODEC VoiceDataVoice (8 bits)

9/18/2015© 2012 Raymond P. Jefferis IIILect Digital Data Frame on T1 Line Voice lines are low-pass filtered to 3.1 KHz –Why? (Anti-Aliasing) CODEC output is 8 bits wide Sampling rate is about 8000 samples/s Data rate is thus about bits/sec 24 lines carried on T1 link (1.544 Mb/s)

9/18/2015© 2012 Raymond P. Jefferis IIILect T1 Time-Division Multiplexing Data frame starts with framing bit Data samples (8 bits each) 24 lines each supply a data sample every 125 microseconds ( sec) Samples are sequentially multiplexed 193 bits per data frame Mb/s total data rate

9/18/2015© 2012 Raymond P. Jefferis IIILect Time Division Multiplexing Multiplexer Line 1 Line 2 Line n... Line 1Line 1 Line 2Line 2 Line nLine n

9/18/2015© 2012 Raymond P. Jefferis IIILect Time Division De-Multiplexing De-Multiplexer Line 1 Line 2 Line n... Line 1Line 1 Line 2Line 2 Line nLine n

9/18/2015© 2012 Raymond P. Jefferis IIILect De-Multiplexing Data samples are redistributed into lines Low-pass filter recovers analog voice

9/18/2015© 2012 Raymond P. Jefferis IIILect High-Speed Backbone 28 T1 streams merged to T3 stream ATM cells repackage data at core –53 octets/cell 5 octets of header information 48 octets of data SONET frames –8 x 810 = 6480 bits sent 8000 times per second –51.85 Mb/s data rate (some frame overhead)

9/18/2015© 2012 Raymond P. Jefferis IIILect ATM Cell Transmission Time ATM Cell... ATM Cell

9/18/2015© 2012 Raymond P. Jefferis IIILect TelCo Standard Data Rates T Mb/s (24 voice circuits) T Mb/s (672 voice circuits) OC Mb/s (2430 voice circuits) OC Mb/s (9720 voice circuits) OC Mb/s (19440 voice circuits) OC Mb/s (38880 voice circuits)

9/18/2015© 2012 Raymond P. Jefferis IIILect Future Network Interface

9/18/2015© 2012 Raymond P. Jefferis IIILect  Network Backbone fiber combines 16 OC-192 lines Each is given a different wavelength All data streams merged into single fiber Streams split by wavelength 16 OC-192 lines out Switches to TelCo customers

9/18/2015© 2012 Raymond P. Jefferis IIILect Optical-Data Conversion LASERDIODE CopperFiberCopper ( )

9/18/2015© 2012 Raymond P. Jefferis IIILect Optical Data Conversion Data on wire drives tunable laser Laser emits photon pulses Photons propagate down fiber Photon energy activates receiving diode Diode produces voltage or current Amplifier drives wire

9/18/2015© 2012 Raymond P. Jefferis IIILect Transmission Problems Photons lost at fiber coupling Photons lost in fiber due to scattering Photons per pulse deteriorates with length Repeater amplifiers needed

9/18/2015© 2012 Raymond P. Jefferis IIILect Optical-Data Link LASERDIODE Copper Fiber Copper ( ) Repeater Fiber ( )

9/18/2015© 2012 Raymond P. Jefferis IIILect More Problems Repeaters require external power Photons need conversion to voltage, amplification, and then reconversion to photons - data rate bottleneck!

9/18/2015© 2012 Raymond P. Jefferis IIILect Repeater for Fiber Optic Line DiodeLaser Fiber Copper Fiber ( ) Amplifier Copper ( )

9/18/2015© 2012 Raymond P. Jefferis IIILect Wave Division Multiplexing Laser Line 1 Line 2 Line n... Laser WDM Fiber

9/18/2015© 2012 Raymond P. Jefferis IIILect Wave Division Multiplexing Incoming data converted to photons Photon streams have individual frequencies Streams can be merged onto single fiber Streams propagate without interference

9/18/2015© 2012 Raymond P. Jefferis IIILect WDM Problems Limited number of “colors” of photons –Fiber attenuation “windows” –Laser limitations (separation practicality) Repeaters must work on all “colors”

9/18/2015© 2012 Raymond P. Jefferis IIILect Repeaters for WDM Must amplify all photon “colors” Must not cause interaction between photon streams (intermodulation)

9/18/2015© 2012 Raymond P. Jefferis IIILect Pumped Laser Repeater Pumped Laser Fiber ( ) Pump PhotonEnergy

9/18/2015© 2012 Raymond P. Jefferis IIILect Pumped Laser Repeater Rare-earth doped glass Pumped by external light Photons receive excitation and are amplified Amplification of many photon “colors”

9/18/2015© 2012 Raymond P. Jefferis IIILect WDM De-multiplexing Photon stream split by “colors” Separated streams may be converted to voltage pulses

9/18/2015© 2012 Raymond P. Jefferis IIILect Wave Division De-Multiplexing Line 1 Line 2 Line n... WDM Fiber DIODE 1 2 n

9/18/2015© 2012 Raymond P. Jefferis IIILect WDM Routing Data streams must be switched Ideally this should be optical Optical switching of SONET frames? Electro-optics? State-of-the-art - developments taking place rapidly