1. 1 Introduction to Telecommunications •Lecture 1 •Paul Flynn

2. 2 The Public Switch Telephone Network (PSTN) Composed of the following major network elements : lines trunks repeater transmission equipment (e.g. repeaters, multiplexers, DCS) switch switches PBX SS7 & IN network signaling and control (e.g. SS7 and IN) PC MODEM station equipment (e.g. telephone sets, MODEMs, FAX machines, …)

3. 3 Telephony Equipment •Telephone set •PBX (Private Branch Exchange) Advanced features and call routing 10s to 100s of telephone sets •Telephone Exchange

4. 4 Basic Call Progress: On-Hook Telephone Exchange Local Loop 2 wires Local Loop -48 DC Voltage DC Open Circuit No Current Flow

5. 5 Telephone Exchange Local Loop Local Loop Basic Call Progress: Off-Hook DC Current Dial Tone Off-Hook Closed Circuit

6. 6 Basic Call Progress: Dialing Dialed Digits Pulses or Tones DC Current Telephone Exchange Local Loop Off-Hook Closed Circuit

7. 7 DC Current Telephone Exchange Local Loop Basic Call Progress: Switching AddresstoPortTranslation Local Loop Off-Hook Closed Circuit

8. 8 Basic Call Progress: Ringing Ring Back Tone DC Current DC Open Cct. Ringing Tone Telephone Exchange Local Loop Local Loop Off-Hook Closed Circuit

9. 9 Basic Call Progress: Talking Voice Energy DC Current Voice Energy DC Current Telephone Exchange Local Loop Local Loop Off-Hook Closed Circuit

10. 10 Analog Telephony—Signaling •Supervisory •Addressing •Call progress

11. 11 Off-Hook Signaling •Loop Start (almost all telephones) Seizure is detected when current flows through local loop, due to off-hook

12. 12 Analog Telephony— Supervisory Signaling •Loop start Current flow sensed SwitchSwitch

13. 13 Loop Start Loop (Local or Station) + – + – AC + – StationPBX or Central Office DC Current Ringing Switch Switch Switch

14. 14 Signaling and Addressing Analog Transmission “In-Band” Signaling 0–9, *, # (12 Digits) Digital Transmission “Out-of-Band” Message-Based Signaling ISDN Dial Pulse DTMF

15. 15 Pulse Dialing Make (Circuit Closed) Break (Circuit Open) Off-HookDialingInter-DigitNext Digit Pulse Period (100 ms) US:60/40 Break/Make 700 ms

16. 16 Tone Dialing 123A 456B 789C *0#D Dual Tone Multifrequency (DTMF) 1209133614771633 697 770 852 941 Timing: 60 ms Break 40 ms Make

17. 17 Network Call Progress Tones Tone Frequency (Hz) On Time Off Time DialBusy Ringback, Normal Ringback, PBX Congestion (Toll) Reorder (local) Receiver Off-hook No Such Number 350 + 440 480 + 620 440 + 480 480 + 620 1400 + 2060 + 2450 +2600 200 to 400 Continuous 0.5O.5 24 13 0.20.3 0.30.2 0.10.1 Continuous, Freq. Mod 1Hz

18. 18 Voice Channel Bandwidth Output Voltage or Energy Frequency (K-Hertz) 1234.2 Voice Signal Voice Channel Tone Dialing Signals Systems Control Signals

19. 19 Local Access Network Telephone Exchange Feeder Route Boundary 40,000 to 50,000 Lines Serving Area Boundary

20. 20 Summary •Analog voice technology dates back to the 1900’s •Information exchange based on voltage, current flow, grounding, etc.

21. 21 Digital Telephony Digital Trunking ExchangeExchange Analog LoopDigital Network POTS Exchange L.E. Digital Loop Digital Network ISDN Switch

22. 22 Digital Telephony = Sample 8 kHz (8,000 Samples/Sec) Codec Technique Sampling StageAnalog Audio Source Pulse Code Modulation—Nyquist Theorem Voice Bandwidth = 300 Hz to 3400 Hz

23. 23 Pulse Code Modulation— Analog to Digital Conversion Stage 1 Quantizing Stage Quantizing Noise 100100111011001 A—Law (Europe) µ—Law (USA–Japan)

24. 24 Digital Telephony Summary •Analog telephony emulation Voice encoding Limited signaling Loop consolidation

25. 25 Voice Coding and Compression •Speech coding schemes •Digitizing voice •Voice compression

26. 26 Voice Compression Technologies Bandwidth (Kbps) Quality Unacceptable Business Quality Business Quality Toll Quality Toll Quality 8 16 32 24 64 0 * PCM (G.711) * PCM (G.711) * ADPCM 32 (G.726) * ADPCM 32 (G.726) * ADPCM 24 (G.726) * ADPCM 24 (G.726) * ADPCM 16 (G.726) * ADPCM 16 (G.726) * LDCELP 16 (G.728) * LDCELP 16 (G.728) * CS-ACELP 8 (G.729) * CS-ACELP 8 (G.729) * LPC 4.8 * LPC 4.8 (Cellular)

27. 27 Digitizing Voice: PCM Waveform Encoding •Nyquist Theorem: sample at twice the highest frequency Voice frequency range: 300-3400 Hz Sampling frequency = 8000/sec (every 125us) Bit rate: (2 x 4 Khz) x 8 bits per sample = 64,000 bits per second (DS-0) •By far the most commonly used method CODEC PCM 64 Kbps = DS-0

28. 28 Waveform Coders Sampling Filtering Encoding Quantizing 1110010010010110 Waveform ENCODER Waveform DECODER

29. 29 Voice Compression •Objective: reduce bandwidth consumption Compression algorithms are optimized for voice Unlike data compression: these are “loose” •Drawbacks/tradeoffs Quantization distortion Tandem switching degradation Delay (echo)

30. 30 Digital Speech Interpolation (DSI) •Voice Activity Detection (VAD) •Removal of voice silence •Examines voice for power, change of power, frequency and change of frequency •All factors must indicate voice “fits into the window” before cells are constructed •Automatically disabled for fax/modem

31. 31 Voice Activity Detection Voice “Spurt” Silence Pink Noise Time Voice Activity (Power Level) SID Buffer SID Hang Timer No Voice Traffic Sent B/W Saved - 54 dbm - 31 dbm Voice “Spurt”

32. 32 Bandwidth Requirements Voice Band Traffic Encoding/Compression Result Bit Rate G.711 PCM A-Law/u-Law 64 kbps (DS0) G.726 ADPCM 16, 24, 32, 40 kbps G.729 CS-ACELP 8 kbps G.728 LD-CELP 16 kbps G.723.1 CELP 6.3/5.3 kbps Variable

33. 33 Voice Quality Compression Method MOS Score Delay (msec) 64K PCM (G.711) 4.40.75 32K ADPCM (G.726) 4.21 16K LD-CELP (G.728) 8K CS-ACELP (G.729) 4.215 8K CS-ACELP (G.729a) 15 3–5 4.2 3.6 Anything Above an MOS of 4.0 Is “Toll” Quality

34. 34 Voice Network Transport •Voice Network Transport is typically TDM circuit-based: T1/E1 DS3/E3 SONET (OC3, OC12, etc.) •But can also be packet-based: ATM Frame Relay IP

35. 35 Voice Transport and Delay Time (msec) 0100200300400 CB Zone Cumulative Transmission Path Delay Satellite Quality Fax Relay, Broadcast High Quality Delay Target 500600700800

36. 36 The Public Switch Telephone Network (PSTN) Composed of the following major network elements :  lines  trunks repeater  transmission equipment (e.g. repeaters, multiplexers, DCS) switch  switches PBX SS7 & IN  network signaling and control (e.g. SS7 and IN) PC MODEM  station equipment (e.g. telephone sets, MODEMs, FAX machines, …)

37. Structure of the tel. network Telephone networks

39. Fiber to the curb (FTTC)

40. 40 European Numbering Plan  defines format for dialed numbers in Europe  As of 1/95 00 + 353 + 71 - 91 - 55363 (N digits are 2-9, X digits are 0-9)  international calls are initiated by dialing 00, followed by country and city code (if any)  phone number shortage crisis – Why? International preliminary code Station number Exchange code Area code (geographic region) International Country Code

41. 41 Network Architecture •ISDN is an access specification to a network ISDN PBX PRA NT1 BRA Common Channel Signalling Network and Database Circuit Switched Services Dedicated Circuit Services Public Packet Network TelcoSwitch TelcoSwitch

42. 42 Public ISDN and SS7 Transmission Network PBX 2 PBX 1 Signaling System 7DSS1 SwitchSwitch Signaling Network BRI PRI DSS1 is a Public ISDN Protocol

43. 43 ISDN and SS7 “The Bridge Between the Islands” Exchange ISDN— PRI SS7 Signaling Network Voice Transmission Voice Transmission PBX 1 Voice and Signaling SCP SSP SCP STP

44. 44 Convergence