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Telecommunications Concepts

Chapter 2.1 The Circuit Switched Telephone Network. Telecommunications Concepts. Traditional Overall structure Access network Fixed lines Wireless access GSM UMTS Trunk network Primary multiplexing : E1 / T1 lines Higher order multiplexing Plesiochronous Data Hierarchy

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Telecommunications Concepts

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  1. Chapter 2.1 The Circuit Switched Telephone Network TelecommunicationsConcepts

  2. Traditional Overall structure Access network Fixed lines Wireless access GSM UMTS Trunk network Primary multiplexing : E1 / T1 lines Higher order multiplexing Plesiochronous Data Hierarchy Synchronous Data Hierarchy Exchanges and signaling General purpose SDH networks Contents

  3. Traditional Overall structure Access network Fixed lines Wireless access GSM UMTS Trunk network Primary multiplexing : E1 / T1 lines Higher order multiplexing Plesiochronous Data Hierarchy Synchronous Data Hierarchy Exchanges and signaling General purpose SDH networks Contents

  4. PABX PABX The Telephone Network Analog / Digital SW SW SW SW SW SW SW

  5. Traditional Overall structure Access network Fixed lines Wireless access GSM UMTS Trunk network Primary multiplexing : E1 / T1 lines Higher order multiplexing Plesiochronous Data Hierarchy Synchronous Data Hierarchy Exchanges and signaling General purpose SDH networks Contents

  6. The Fixed Access NetworkAnalog phone on analog switch Analog switch twisted pair, average length 2.5 Km Signaling (DTMF or pulse) and voice multiplexed Line circuit In Belgium : last one went out of service in 2002

  7. The Fixed Access Network Analog phone on digital switch Digital switch Digital Analog twisted pair, average length 2.5 Km Signaling (DTMF or pulse) and voice multiplexed Line circuit In Belgium : the most common situation

  8. The Fixed Access Network The ISDN Basic Access Digital switch S bus twisted pair, average length 2.5 Km 144Kb/s modem 144Kb/s modem 2 * 64 Kb/s + 16 Kb/s TDM In Belgium : e.g. the Belgacom TWIN

  9. Traditional Overall structure Access network Fixed lines Wireless access GSM UMTS Trunk network Primary multiplexing : E1 / T1 lines Higher order multiplexing Plesiochronous Data Hierarchy Synchronous Data Hierarchy Exchanges and signaling General purpose SDH networks Contents

  10. The Mobile Access NetworkMobility Management HLR : Home Location Register VLR : Visitors Location Register MSC : Mobile Switching Center PSTN NSS MSC 13 Kb/s 16 Kb/s 64 Kb/s BSS VLR HLR NSS BSS : Base Station Subsystem NSS : Network & Switching Subsystem

  11. Mobile terminal identification SIM card with unique id. Data about SIM stored in HLR of operator who owns SIM Phone calls directed to HLR of operator Mobile terminal localization BSS regularly makes broadcasts in its cells Mobile selects best cell and sends its SIM id. Presence of mobile recorded in local VLR SIM’s owner HLR updated with applicable VLR Handover When location of mobile changes during conversation Circuit routing modified “on the fly” Sound quality briefly degraded Handover not available between different operators The Mobile Access NetworkMobility Management

  12. Traditional Overall structure Access network Fixed lines Wireless access GSM UMTS Trunk network Primary multiplexing : E1 / T1 lines Higher order multiplexing Plesiochronous Data Hierarchy Synchronous Data Hierarchy Exchanges and signaling General purpose SDH networks Contents

  13. The Mobile Access NetworkGSM radio system • A combination of FDM and TDM • Two separate frequency bands used for Tx and Rx • Slow frequency hopping for propagation diversity • Sender and receiver sequences shifted by 45MHz and 3 slots • Predefined time slot for signaling channel frequency 200 KHz Tx 45 MHz Rx 3 radio slots 15/26 ms time

  14. Traditional Overall structure Access network Fixed lines Wireless access GSM UMTS Trunk network Primary multiplexing : E1 / T1 lines Higher order multiplexing Plesiochronous Data Hierarchy Synchronous Data Hierarchy Exchanges and signaling General purpose SDH networks Contents

  15. Considerable room for improvements by controlling interferences : Fast frequency hopping spread spectrum radio with Code Domain Multiple Access Third generation mobile networks (UMTS) The Mobile Access Network Wireless interference margins cause considerable loss in transmission capacity Frequency Time Space

  16. Data combined with known higher frequency pseudo random sequence Resulting modulated radio signal has high bandwidth Shannon : low data rate combined with high bandwidth = excellent noise margins! The Mobile Access Network Fast hopping Spread Spectrum n b/s Modulated signal Large bandwidth ≈ m times bandwidth needed for data Data xor Pseudo-random sequence m * n b/s HF carrier

  17. D1 D2 Tx1 xor xor Correl -ator Correl -ator S2 S1 S2 S1 HF HF D2 D1 Rx1 Rx2 HF HF Tx2 The Mobile Access Network Spread Spectrum and CDMA For radio link Tx1-Rx1, emission by Tx2 is just another source of noise

  18. The Mobile Access NetworkMulti-path Interference Different paths have different lengths and different delays GSM : interference = noise UMTS : correlator adds similar input signals with appropriate delays so that they reinforce each other

  19. The Mobile Access NetworkThird Generation Handover When a receiver is between two cells, both transmitters send the same signal. These two signals reinforce each other, as multipath propagation does.

  20. Traditional Overall structure Access network Fixed lines Wireless access GSM UMTS Trunk network Primary multiplexing : E1 / T1 lines Higher order multiplexing Plesiochronous Data Hierarchy Synchronous Data Hierarchy Exchanges and signaling General purpose SDH networks Contents

  21. 1 0 0 1 0 1 0 1 0 0 1 1 XX 0 1 0 1 Unique bit pattern to delimit frames Time Domain Multiplexing Synchronous multiplexing

  22. Primary MultiplexingTrunk Network (E1 = CEPT30) Digital switch Digital switch n*30*64 Kb/s n*2048 Kb/s

  23. Primary MultiplexingTrunk Network (T1 = Bell D2) Digital switch Digital switch n*23*64 Kb/s n*1544 Kb/s

  24. pabx The ISDN Primary Ratefor connecting Private Branch Exchanges Digital switch PABX E1 Optical Fiber or Microwave Link 2048 Kb/s (CEPT30) e.g: VUB : 4 E1 lines = 120 simultaneous calls

  25. Traditional Overall structure Access network Fixed lines Wireless access GSM UMTS Trunk network Primary multiplexing : E1 / T1 lines Higher order multiplexing Plesiochronous Data Hierarchy Synchronous Data Hierarchy Exchanges and signaling General purpose SDH networks Contents

  26. Higher Order Multiplexing Digital switch Digital switch Optical Fiber or Microwave Link

  27. T S R Q P Synchronous Multiplexingof almost synchronous data flows Primary rate dataflows to be multiplexed can be derived from independent clocks ! 1 Frame F E D C B A T F S E D 1 0 R C Q B P A S C fout > n * MAX(fin)

  28. Traditional Overall structure Access network Fixed lines Wireless access GSM UMTS Trunk network Primary multiplexing : E1 / T1 lines Higher order multiplexing Plesiochronous Data Hierarchy Synchronous Data Hierarchy Exchanges and signaling General purpose SDH networks Contents

  29. Each multiplexed section has its own clock Each level of multiplexing has its own clock Frame structure from multiplexed signals is not explicitly present in the multiplexed stream Full demultiplexing required at each node ! Plesiochronous Digital Hierarchy

  30. Traditional Overall structure Access network Fixed lines Wireless access GSM UMTS Trunk network Primary multiplexing : E1 / T1 lines Higher order multiplexing Plesiochronous Data Hierarchy Synchronous Data Hierarchy Exchanges and signaling General purpose SDH networks Contents

  31. Synchronous Digital Hierarchy • The entire trunk network has one clock • Multiplexed stream based on 125 S frames • Different channels can each have their own asynchronous clock. • Add-drop multiplexers STM-1 STM-1 Up to 63 channels at 2 Mb/s

  32. Data rate CCITT USA-Elec. USA-Opt. 51.84 STS-1 OC-1 155.52 STM-1 STS-3 OC-3 466.56 STM-3 STS-9 OC-9 622.08 STM-4 STS-12 OC-12 933.12 STM-6 STS-18 OC-18 1244.16 STM-8 STS-24 OC-24 1866.24 STM-12 STS-36 OC-36 2488.32 STM-16 STS-48 OC-48 ... ... ... ... Synchronous Digital HierarchySDH - SONET

  33. 34 Mb/s 2 Mb/s SDH Rings

  34. SDH Rings

  35. SDH Rings

  36. SDH RingsThe MCI Belgian Network

  37. SDH Rings CUT !

  38. Traditional Overall structure Access network Fixed lines Wireless access GSM UMTS Trunk network Primary multiplexing : E1 / T1 lines Higher order multiplexing Plesiochronous Data Hierarchy Synchronous Data Hierarchy Exchanges and signaling General purpose SDH networks Contents

  39. Line Circuit Line Circuit Line Circuit Line Circuit Line Circuit Register Register Register Register Switching Matrix Telephone Exchange(Conceptual Model) trunk lines + Inter-office signaling Control Computer

  40. SS1 - SS5 : Analog call forwarding between exchanges SS6 : First digital signaling system monolithic communications system (no layers) Full mesh of virtual circuits, based on 2400 b/s links SS7 : Signaling system for the intelligent network uses any digital link, satellites included layered, OSI inspired, network architecture supports "intelligent network" applications Non-geographic numbers (800) CLIP, Call forwarding, Conference calls, etc... Number portability, Carrier selection Mobility & roaming IP ??? Signaling system generations

  41. 477 The Telephone Network Non-geographic Numbering 4776970 6234567 database 0800 62X 538 673 6736476 643 629 64X 6433180 0800 12345 6292905

  42. The Telephone Network Number portability Ported numbers

  43. Traditional Overall structure Access network Fixed lines Wireless access GSM UMTS Trunk network Primary multiplexing : E1 / T1 lines Higher order multiplexing Plesiochronous Data Hierarchy Synchronous Data Hierarchy Exchanges and signaling General purpose SDH networks Contents

  44. PABX PABX General Purpose SDH Networks

  45. John C. BELLAMY Digital Telephony Third edition John Wiley, 2000. ISBN : 0-471-34571-7 BibliographyTo know More about Telephony Recommended for this chapter

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