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Lecture 1 Intro to Telecommunications

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Lecture 1 Intro to Telecommunications Powered By Docstoc
					   Introduction to
Telecommunications


      • Lecture 1




      • Paul Flynn

                     1
The Public Switch Telephone Network
(PSTN)

     Composed of the following major network elements:
  switches
  trunks
  lines
  station equipment (e.g. telephone sets, MODEMs, FAX machines, …)
  transmission equipment (e.g. repeaters, multiplexers, DCS)
  network signaling and control (e.g. SS7 and IN)


                             SS7 & IN


                    switch              switch

                                                            PBX

                  repeater    switch

                                                    MODEM    PC

                                                                     2
Telephony Equipment


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

  • Telephone Exchange



                                         3
Basic Call Progress: On-Hook

                   Telephone
                   Exchange




    Local Loop                     Local
      2 wires                      Loop


                  -48 DC Voltage
                 DC Open Circuit
                 No Current Flow


                                           4
Basic Call Progress: Off-Hook
 Off-Hook
 Closed
                         Telephone
 Circuit
                         Exchange
            DC Current
             Dial Tone

             Local                   Local
             Loop                    Loop




                                             5
Basic Call Progress: Dialing
 Off-Hook
 Closed
                         Telephone
 Circuit Dialed Digits
          Pulses or      Exchange
            Tones
         DC Current

                                     Local
                                     Loop




                                             6
Basic Call Progress: Switching
 Off-Hook
 Closed
                     Telephone
 Circuit
                     Exchange


        DC Current    Address
                         to
                        Port
            Local    Translation   Local
            Loop                   Loop




                                           7
Basic Call Progress: Ringing
 Off-Hook
 Closed
                     Telephone
 Circuit
                     Exchange
        Ring Back
          Tone                   DC Open Cct.
        DC Current               Ringing Tone


            Local                    Local
            Loop                     Loop




                                                8
Basic Call Progress: Talking
 Off-Hook
 Closed
                      Telephone
 Circuit
                      Exchange
       Voice Energy               Voice Energy
        DC Current                 DC Current


            Local                     Local
            Loop                      Loop




                                                 9
Analog Telephony—Signaling



        • Supervisory
        • Addressing
        • Call progress




                             10
Off-Hook Signaling



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




                                           11
Analog Telephony—
Supervisory Signaling
 • Loop start
   Current flow
   sensed


         Switch         Switch




                                 12
Loop Start
      Station                         PBX or Central Office
                      Loop
                 (Local or Station)
                                       Switch     +
                                                  –


                DC Current             Switch     +
                                                  –


                             AC
                 Ringing               Switch     +
                                                  –

                                                              13
Signaling and Addressing



Dial Pulse      DTMF            ISDN

Analog Transmission      Digital Transmission
―In-Band‖ Signaling         ―Out-of-Band‖
 0–9, *, # (12 Digits)     Message-Based
                               Signaling



                                                14
    Pulse Dialing
                   Off-Hook    Dialing   Inter-Digit Next Digit

Make
(Circuit Closed)



Break                                      700 ms
(Circuit Open)

                                          US:60/40 Break/Make
                         Pulse Period
                           (100 ms)


                                                             15
Tone Dialing
         Dual Tone Multifrequency (DTMF)

         1209    1336     1477     1633

   697    1        2       3        A

                                           Timing:
   770    4        5       6        B      60 ms Break
                                           40 ms Make
   852    7        8       9        C


   941    *        0       #        D



                                                         16
   Network Call Progress Tones

Tone                Frequency (Hz)           On Time      Off Time
Dial                350 + 440                Continuous
Busy                480 + 620                0.5          O.5
Ringback, Normal    440 + 480                2            4
Ringback, PBX       440 + 480                1            3
Congestion (Toll)   480 + 620                0.2          0.3
Reorder (local)     480 + 620                0.3          0.2
Receiver Off-hook   1400 + 2060 + 2450 +2600 0.1          0.1
No Such Number      200 to 400               Continuous, Freq. Mod 1Hz




                                                                     17
 Voice Channel Bandwidth
                    Voice Channel

Output         Voice Signal
Voltage
     or
Energy



                                                    Frequency
                                                    (K-Hertz)
          .2        1         2         3       4


               Tone Dialing       Systems Control
                 Signals              Signals


                                                                18
   Local Access Network
               Feeder Route Boundary


Telephone
Exchange




 40,000 to                             Serving
50,000 Lines                           Area
                                       Boundary




                                                  19
Summary


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



                                           20
Digital Telephony
                        Digital Trunking
        Exchange                               Exchange




                   Analog Loop             Digital Network
                                               Exchange
POTS
                                   L.E.


                     Digital Loop Digital Network
                                                Switch
 ISDN


                                                             21
 Digital Telephony
Pulse Code Modulation—Nyquist Theorem
Voice Bandwidth =
 300 Hz to 3400 Hz




               Analog Audio Source       Sampling Stage

                                  = Sample
  Codec Technique                8 kHz (8,000 Samples/Sec)



                                                             22
  Pulse Code Modulation—
  Analog to Digital Conversion
A—Law (Europe)       Quantizing Noise




                                        100100111011001



  Stage 1




µ—Law (USA–Japan)   Quantizing Stage
                                                     23
 Digital Telephony Summary


• Analog telephony emulation
  Voice encoding
  Limited signaling
  Loop consolidation




                               24
Voice Coding and Compression



    • Speech coding schemes
    • Digitizing voice
    • Voice compression




                               25
     Voice Compression
     Technologies
                Unacceptable      Business              Toll
                                   Quality             Quality
           64                                            *
                                (Cellular)            PCM (G.711)


Bandwidth
  (Kbps)


           32                                            *
                                               ADPCM 32 (G.726)
           24                         *
                              ADPCM 24 (G.726)
           16             *                       *
                  ADPCM 16 (G.726)        LDCELP 16 (G.728)
            8
                   *                                    *
                LPC 4.8                       CS-ACELP 8 (G.729)
            0
                                                 Quality

                                                                    26
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
                                                  = DS-0
                                          64 Kbps


                                                           27
Waveform Coders

                        Quantizing
                                     Encoding
             Sampling
 Filtering




                                                1110010010010110




 Waveform                                                          Waveform
 ENCODER                                                           DECODER




                                                                              28
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)


                                                   29
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



                                                   30
   Voice Activity Detection

- 31 dbm

                                    B/W Saved
  Voice
 Activity           Hang Timer       No Voice
 (Power                             Traffic Sent
  Level)
            SID Buffer                              SID
- 54 dbm
                                    Pink Noise

                 Voice ―Spurt‖       Silence       Voice ―Spurt‖

                             Time
                                                                   31
Bandwidth Requirements
        Voice Band Traffic
    Encoding/           Result
    Compression         Bit Rate
    G.711 PCM         64 kbps (DS0)
    A-Law/u-Law

    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


                                           32
Voice Quality
Anything Above an MOS of 4.0 Is ―Toll‖ Quality

     Compression Method     MOS Score    Delay
                                        (msec)

     64K PCM (G.711)          4.4        0.75

     32K ADPCM (G.726)        4.2         1

     16K LD-CELP (G.728)      4.2        3–5

     8K CS-ACELP (G.729)      4.2         15

     8K CS-ACELP (G.729a)     3.6         15



                                                 33
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


                                         34
     Voice Transport and Delay
     Cumulative Transmission Path Delay


                                                    CB Zone
                         Satellite Quality
    High Quality                                    Fax Relay, Broadcast

0         100      200    300        400      500        600        700    800

                                Time (msec)
Delay Target




                                                                             35
             The Public Switch Telephone Network
                                     (PSTN)

Composed of the following major network elements:
        switches
        trunks
        lines
        station equipment (e.g. telephone sets, MODEMs, FAX machines, …)
        transmission equipment (e.g. repeaters, multiplexers, DCS)
        network signaling and control (e.g. SS7 and IN)


                                SS7 & IN


                       switch              switch

                                                              PBX

                     repeater    switch

                                                      MODEM    PC
                                                                            36
Structure of the tel. network




                         Telephone networks
Fiber to the curb
    (FTTC)




                    Telephone networks
         European Numbering Plan
   defines format for dialed numbers in Europe
   As of 1/95
            00 + 353 + 71 -               91 -        55363
                                                              Station number
                                                              Exchange code


                                                              Area code (geographic region)

                                                              International Country Code

                                                              International preliminary code


                       (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?




                                                                                               40
Network Architecture
       • ISDN is an access specification
         to a network
                            Common Channel
                         Signalling Network and
                                Database



              Telco
ISDN    PRA          Circuit Switched Services    Telco
                                                           BRA
              Switch                              Switch         NT1
 PBX
                     Dedicated Circuit Services

                           Public Packet
                             Network




                                                                       41
Public ISDN and SS7

                            Signaling
                            Network
         BRI                                      BRI



               Switch     Transmission   Switch
PBX1    PRI                                         PRI   PBX2
                             Network


       DSS1             Signaling System 7          DSS1


   DSS1 is a Public ISDN Protocol

                                                                 42
    ISDN and SS7 ―The Bridge
    Between the Islands‖
                  Voice Transmission
                                        STP
     Exchange                                         Exchange
                SSP                             SSP
                      SCP         SS7
                            Signaling Network
   Voice                                                   Voice
Transmission                         STP                    and
                            STP                                    ISDN—
                                                         Signaling
                                                                   PRI

                        STP          STP
     Exchange                                         PBX1
                SSP
                        STP                   SCP



                                                                      43

				
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posted:9/24/2011
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