Presentation is loading. Please wait.

Presentation is loading. Please wait.

Telephony Slide 1 ear T R mouth DTMF ringer C dial switch SLIC Telephone Subscriber Line CO (Local Exchange) cradle switch off-hook on-hook tip (+) ring.

Similar presentations

Presentation on theme: "Telephony Slide 1 ear T R mouth DTMF ringer C dial switch SLIC Telephone Subscriber Line CO (Local Exchange) cradle switch off-hook on-hook tip (+) ring."— Presentation transcript:

1 telephony Slide 1 ear T R mouth DTMF ringer C dial switch SLIC Telephone Subscriber Line CO (Local Exchange) cradle switch off-hook on-hook tip (+) ring ( - ) Basic Telephone

2 telephony Slide 2 hybrid T Telephone current detector ~ ring switch ring generator (100V rms 25 Hz) -48 VDC Subscriber Line crossconnect switch Subscriber Line Interface Circuit Processor control channel Call States idle on hook dialing dialing in progress calling after dialing ringing incoming call called call in progress tip (+) ring ( - ) Subscriber Line Interface

3 telephony Slide 3 The PSTN circa 1900 pair of copper wires local loop manual routing at local exchange office (CO) Analog voltage travels over copper wire end-to-end Voice signal arrives at destination severely attenuated and distorted Routing performed manually at exchanges office(s) Routing is expensive and lengthy operation Route is maintained for duration of call PSTN Review

4 telephony Slide 4 Multiplexing 1900: 25% of telephony revenues went to copper mines standard was 18 gauge, long distance even heavier two wires per loop to combat cross-talk needed method to place multiple conversations on a single trunk 1918: Carrier system (FDM) 5 conversations on single trunk later extended to 12 (group) still later supergroups, master groups, supermaster groups 1963: T-carrier system (TDM) T1 = 24 conversations per trunk later T3 = 28 T1s still later SDH rates with 1000s of conversations per trunk PSTN Review f channels t timeslots

5 telephony Slide 5 Cross-connect switch Complexity increases rapidly with size Analog Crossbar switch Digital Cross-connect (DXC) processor t t 21543

6 telephony Slide 6 SLIC PCM MUX HybridSLIC TDM port TDM port TDM port TDM port Tone & Ann DTMF decode Processor Subscriber Lines Hybrid 2w 4w DXC E1/T1 Basic TDM CO

7 telephony Slide 7 PSTN Topology Many local telephone exchanges had sprung up Bell Telephone acquired them and interconnected them for long distance Local Exchange Local Exchange Local Exchange local loop Long distance network trunk circuit subscriber line PSTN Review

8 telephony Slide 8 Old US PSTN Class 3 Class 2 Class 1 Class 3 Regional centers Sectional centers Primary centers Toll (tandem) offices Central (end) offices Class 4 last mile subscriber lines local loop circuits,trunks Class 5 switch is the sole interface to the subscriber lines PSTN Review Class 5 Class 4

9 telephony Slide 9 Numbering Plans An E.164 International Number has the format : Country-Code Area-Code Exchange-Code Line-Number EX: Country-Codes 1 : N America (US, CA, Caribbean) 1 digit 2 : Africa 2 or 3 digits 20 Egypt 27 South Africa 235 Chad 3 : Europe 2 or 3 digits 31 Netherlands 354 Iceland 4 : Europe 2 or 3 digits 44 UK 49 Germany 420 Czech Republic 5 : S America 2 or 3 digits 54 Argentina 595 Paraguay 6 : Australia & S Pacific 2 or 3 digits 61 Australia 675 Papua 7 : Russia 1 digit 8 : China & N Pacific 2 or 3 digits 86 PR China 855 Cambodia 9 : Middle East 2 or 3 digits 90 Turkey 972 Israel MAXIMUM 15 DIGITS

10 telephony Slide 10 Signaling PSTN with automatic switching requires signaling The present PSTN has thousands of features and all require signaling support Examples: On-hook / off-hook Pulse / Tone dialing Receiver off-hook Call waiting Caller number identification Call forwarding Hook-flash Fax transmission detect Inter-CO messaging Echo cancellation Voice mail Conference calls Coin-drop Billing PSTN Review

11 telephony Slide 11 Signaling Methods Signaling can be performed in many ways Analog voltage signaling loop-start, ground-start, E&M In-band signaling DTMF, MFR1, MFR2 Channel associated signaling (CAS) AB bits, ABCD bits Common channel signaling (CCS) SS7, QSIG –Trunk Associated CCS –Separate signaling network CCS PSTN Review

12 telephony Slide 12 Subscriber - Exchange Signaling* On/off hook DC current flow Dial-tone continuous Pulse Dialing DTMF L1 697 L2 770 L3 852 L4 941 H H H H Ring AC with cadence Ring-back with 2:4 cadence Busy with 1/2:1/2 cadence Trunk busy but 0.2:0.3 cadence Receiver off-hook with ).1:0.1 cadence Invalid (nonworking, unobtainable) number announcement, SIT-tone * US cadences - national differences H1 H2 H3 H4 L A L B L C L4 * 0 # D make break >700ms >100ms (60:40) off-hook

13 telephony Slide 13 Subscriber - Subscriber Subscriber - Exchange Signaling Hook-flash on-hook for sec Echo suppressor disabler 2100 continuous –FAX CED sec –Modem ANS 2100 with phase reversals every 450 ms for 3.3 s –ANSAM 2100 with phase reversals and 15 Hz AM modulation CNG –FAX 1100 with 0.5:3 cadence –Modem 1300 with 0.5:2 cadence Caller Line Identification (CLI/CND) –1200 bps FSK (V.23) data signal 1300 = = 0 –Between 1st and 2nd rings RING CLI >300 ms > 475 ms

14 telephony Slide 14 Supervision procedures FXO/FXS Foreign Exchange Office / Foreign Exchange Subscriber FXS is like exchange - provides voltage, ringing, dialtone FXO is like a phone - requires voltage, detect ring, etc. When connecting PBX to CO, PBX is FXO, CO is FXS Analog loop start Digital loop start Analog ground start Digital ground start E&M (wink)

15 telephony Slide 15 Interexchange Signaling CAS - R2 CAS - R1 CCS - SS7

16 telephony Slide 16 Optimized Telephony Routing Circuit switching (route is maintained for duration of call) Route set-up is an expensive operation, just as it was for manual switching Today, complex least cost routing algorithms are used Call duration consists of set-up, voice and tear-down phases PSTN Review

17 telephony Slide 17 The PSTN circa 1960 local loop subscriber line automatic routing through universal telephone network Analog voltages used throughout, but extensive Frequency Division Multiplexing Voice signal arrives at destination after amplification and filtering to 4 KHz Automatic routing Universal dial-tone Voltage and tone signaling Circuit switching (route is maintained for duration of call) trunks circuits PSTN Review

18 telephony Slide 18 The Digitalization of the PSTN Shannon (Bell Labs) proved is better than and the PSTN became digital Better means More efficient use of resources (e.g. more channels on trunks) Higher voice quality (less noise, less distortion) Added features Digital Communications Analog Communications PSTN Review

19 telephony Slide 19 Timing In addition to voice, the digital PSTN transports timing This timing information is essential because of –the universal use of TDM –the requirement of accurate playback (especially for fax/modem) Receiving switches can recover the clock of the transmitting switch Every telephony network has an accurate clock called stratum 1 Clocks synchronized to it are called stratum 2 Clocks synchronized to them are called stratum 3 and so on PSTN Review

20 telephony Slide 20 The Present PSTN subscriber line Analog voltages and copper wire used only in last mile, but core designed to mimic original situation Voice signal filtered to 4 KHz at input to digital network Time Division Multiplexing of digital signals in the network Extensive use of fiber optic and wireless physical links T1/E1, PDH and SONET/SDH synchronous protocols Signaling can be channel/trunk associated or via separate network (SS7) Automatic routing Circuit switching (route is maintained for duration of call) Complex routing optimization algorithms (LP, Karmarkar, etc) PSTN Network core backbone PSTN Review

21 telephony Slide 21 Nonvoice services The PSTN can even be used to transport non-voice signals such as FAX or DATA These services disguise themselves as voice by using a modem Proper timing is essential Special signaling is required –turn off LEC –turn off call waiting –service recognition PSTN VoP course PSTN Review – capabilities negotiation – mutual identification – end of page/document – modem recognition – modem training – data compression

22 telephony Slide 22 Digital Loop Carrier Pushes the digital PSTN closer to customer AT&T SLC-40, SLC-96, Nortel DMS P-phone,pair-gain TR-08 multiplex 96 lines on: Mode 1 : 4 T1s Mode 2 : 2 T1s (2:1 concentration) GR303/V5.1/V5.2 multiplex up to 2048 lines CLASS 5 Street cabinet UTP/coax/fiber UTP pedestal TR-08 Mode 1 pair-gain: Replace 96 pairs with 5 T1s (one spare for span protection) 96 – 10 = 86 TR-08 Mode 2 pair-gain: Replace 96 pairs with 2 T1s (without span protection) 96 – 4 = 92 Access Network CPE FTTB/FTTC PSTN Review

Download ppt "Telephony Slide 1 ear T R mouth DTMF ringer C dial switch SLIC Telephone Subscriber Line CO (Local Exchange) cradle switch off-hook on-hook tip (+) ring."

Similar presentations

Ads by Google