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Lecture 2 Paul Flynn

Switching and the Local Loop. Lecture 2 Paul Flynn. Loop Start. Station. PBX or Central Office. Loop (Local or Station). +. Switch. –. +. DC Current. Switch. –. AC. Ringing. +. Switch. –. Balanced and Unbalanced Electrical Circuit. Terminology. AWG - American Wire Gauge

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Lecture 2 Paul Flynn

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  1. Switching and the Local Loop • Lecture 2 • Paul Flynn

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

  3. Balanced and Unbalanced Electrical Circuit

  4. Terminology • AWG - American Wire Gauge • Bridge Tap - an unused, open-circuited, parallel-connected cable pair on a loop Bridge Tap

  5. Cable Color Codes • Pair (2 wires) • Binder (25 pair) • Super Unit Binder (24 Binders) • 1-600 White • 601-1200 Red • 1201-1800 Black • 1801-2400 Yellow • 2401-3000 Violet • 3001-3600 Blue • 3601-4200 Orange

  6. Cable Construction • Sheath • Armored (gopher protection) - lead/steel • Dielectric • Fill • Air filled (pressurized?) • Gel-filled (icky-PIC) • Insulation • Paper pulp • Plastic

  7. Loading Coils • Used to extend useful length of loops for voice service • Counteracts the effects of cable capacitance • BAD NEWS for high-speed digital services - causes excessive attenuation at frequencies above voice-band

  8. Wire Centers and Cable Plant Political Boundary Wire Center 18kft Carrier Serving Area

  9. Carrier Systems DigitalRepeater • How do we serve customersoutside the loop limits? • Range extenders • Carrier systems (Subscriber Loop Carrier) • Analog (frequency division multiplexing) • Digital (time division multiplexing)

  10. Analogue Amplifier

  11. Regenerative Repeater Section

  12. Carrier System Block Diagram 1 CommonEquipment CommonEquipment 1 2 COR LR LR 2 3 3 4 4 . . . . 21 21 22 LR LR COR 22 23 23 24 24

  13. Digital Hierarchies

  14. T1 versus E1 • Two different Pulse Code Modulation (PCM) standards • T1, or DS1 PCM hierarchy • North American standard • E1, or “the European System” • E1 is used as close as Mexico • Japan uses a hybrid system

  15. Transmission Media

  16. Electromagnetic Spectrum

  17. Guided Transmission Media • Twisted Pair • Coaxial cable • Optical fiber

  18. Twisted Pair

  19. Twisted Pair - Applications • Most common medium • Telephone network • Between house and local exchange (subscriber loop) • Within buildings • To private branch exchange (PBX) • For local area networks (LAN) • 10Mbps or 100Mbps

  20. Twisted Pair - Pros and Cons • Cheap • Easy to work with • Low data rate • Short range

  21. Twisted Pair - Transmission Characteristics • Analog - Amplifiers every 5km to 6km • Digital • Use either analog or digital signals • repeater every 2km or 3km • Limited distance • Limited bandwidth (1MHz) • Limited data rate (100MHz) • Susceptible to interference and noise

  22. Unshielded and Shielded TP • Unshielded Twisted Pair (UTP) • Ordinary telephone wire • Cheapest • Easiest to install • Suffers from external EM interference • Shielded Twisted Pair (STP) • Metal braid or sheathing that reduces interference • More expensive • Harder to handle (thick, heavy)

  23. UTP Categories • Cat 3 • up to 16MHz • Voice grade found in most offices • Twist length of 7.5 cm to 10 cm • Cat 4 • up to 20 MHz • Cat 5 • up to 100MHz • Commonly pre-installed in new office buildings • Twist length 0.6 cm to 0.85 cm

  24. Near End Crosstalk • Coupling of signal from one pair to another • Coupling takes place when transmit signal entering the link couples back to receiving pair • i.e. near transmitted signal is picked up by near receiving pair

  25. Coaxial Cable

  26. Coaxial Cable Applications • Most versatile medium • Television distribution • Ariel to TV • Cable TV • Long distance telephone transmission • Can carry 10,000 voice calls simultaneously • Being replaced by fiber optic • Short distance computer systems links • Local area networks

  27. Coaxial Cable - Transmission Characteristics • Analog • Amplifiers every few km • Closer if higher frequency • Up to 500MHz • Digital • Repeater every 1km • Closer for higher data rates

  28. Optical Fiber

  29. Optical Fiber - Benefits • Greater capacity • Data rates of hundreds of Gbps • Smaller size & weight • Lower attenuation • Electromagnetic isolation • Greater repeater spacing • 10s of km at least

  30. Optical Fiber - Applications • Long-haul trunks • Metropolitan trunks • Rural exchange trunks • Subscriber loops • LANs

  31. Optical Fiber - Transmission Characteristics • Act as wave guide for 1014 to 1015 Hz • Portions of infrared and visible spectrum • Light Emitting Diode (LED) • Cheaper • Wider operating temp range • Last longer • Injection Laser Diode (ILD) • More efficient • Greater data rate • Wavelength Division Multiplexing

  32. Optical Fiber Transmission Modes

  33. Wireless Transmission • Unguided media • Transmission and reception via antenna • Directional • Focused beam • Careful alignment required • Omnidirectional • Signal spreads in all directions • Can be received by many antennae

  34. Frequencies • 2GHz to 40GHz • Microwave • Highly directional • Point to point • Satellite • 30MHz to 1GHz • Omnidirectional • Broadcast radio • 3 x 1011 to 2 x 1014 • Infrared • Local

  35. Terrestrial Microwave • Parabolic dish • Focused beam • Line of sight • Long haul telecommunications • Higher frequencies give higher data rates

  36. Satellite Microwave • Satellite is relay station • Satellite receives on one frequency, amplifies or repeats signal and transmits on another frequency • Requires geo-stationary orbit • Height of 35,784km • Television • Long distance telephone • Private business networks

  37. Broadcast Radio • Omnidirectional • FM radio • UHF and VHF television • Line of sight • Suffers from multipath interference • Reflections

  38. Telecom Systems Circuit Switching Review Services vs. Operations Origins / Background of Circuit Switching Switch Stages Switch Dimensions Matrix Control Complexity

  39. Circuit SwitchingSystem Components Access Line Circuit Switch Circuit Switch A TRUNK GROUPS TERMINALS Cross-Connections B Circuit Switch Circuit Switch

  40. Circuit SwitchingBackground: A.G. Bell / Manual Switching

  41. Circuit SwitchingBackground: Almon Strowger / Automatic Switching

  42. Manual SwitchBasic Components Input/Output Channels Channel Terminations Manually Operated Cross-Connections

  43. Non-Blocking Switch Matrix 1 Switch i,j and j,i operate together 2 3 4 5 Input Lines 6 7 8 9 10 1 2 3 4 5 6 7 8 9 10 Output Lines

  44. Progressive Control Called Line Calling Line Line Circuit Line Finder Control Switch Control Switch Control Register Translation Register Progressive Control System

  45. Stored Program Control Other Offices Customer Lines Switching Network Address Address Distributor Scanner Central Control Address Call Store Program Store Stored Programs Translations Semi-Permanent Memory Call Processing Registers Temp Memory Maintenance Center

  46. Packet Switching Store and Forward

  47. Virtual Circuit vs. DatagramService vs. Operation

  48. Switching Services: - Connectionless (Datagram) - Connection Oriented (Virtual Circuit) Operations: - Circuit Switching - Store and Forward - Packet - Message

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