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TDC 461: Basic Telecommunications

This document provides an in-depth overview of telephone systems, exploring the intricacies of telephone numbering formats, signaling, and the technologies used in central office switches. It discusses how a voice call is initiated and transmitted through both analog and digital channels, the structure of the Public Switched Telephone Network (PSTN), and details on subscriber loops, service requests, and various trunking types. Additionally, the document covers the evolution of business station set features and the advantages of digital trunks over analog trunks in telecommunications.

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TDC 461: Basic Telecommunications

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  1. TDC 461: Basic Telecommunications DePaul University 9 April, 2001 LoriLee M. Sadler

  2. Telephone Network Telephone Numbering Format Signaling on Subscriber Loop Analog vs. Digital Information Central Office Switch Technologies How is a Voice Call Made? Carrier Services Agenda

  3. Public Switched Telephone Network: POP = Point of Presence PBX = Private Branch Exchange

  4. The PSTN: • Topology of Connections • Network=> • Demarcation point (Demarc)=>also called station drop.

  5. Network Configuration • Star configuration from the Central Office (CO) to the demarc • Star or ring configuration from the Central Office to other COs or higher-level offices • Wire Center or FrameSwitch • Physical vs. logical connections • Facilities

  6. The Subscriber (Local) Loop

  7. Outside Plant • Demarcation Point (Demarc) • Feeders: • Lateral distribution: • Branch feeders:

  8. Subscriber Loop Signaling • Carrier Sense=>

  9. The Subscriber Loop • The Subscriber Line or Subscriber Loop is made up of 2 copper wires twisted together (wires called “tip” and “ring”)

  10. The Subscriber LoopIdle Line • Central Office provides battery power (48 volts DC) to subscriber loop. • When telephone is ON-HOOK, it keeps loop open (wires are not connected) and there is no current flow.

  11. The Subscriber LoopService Request • Off-Hook signals request • Request fulfilled by CO

  12. North American Numbering Plan (NANP) • Determines format for dialed numbers. • Administered by BellCore • Format before 1995: Prefix + 0/1 + N(0/1)X - NNX - XXXX (N digits are 2-9, X digits are 0-9) • Format as of January, 1995: Prefix + 0/1 + NXX - NXX - XXXX (N digits are 2-9, X digits are 0-9)

  13. Address Signaling • Rotary Pulse Dial • After pulling dial for digit ‘N’, telephone opens and closes subscriber loop ‘N’ times as dial returns to its original position. • Dual Tone Multifrequency (DTMF) or Touch Tone • One frequency assigned to each row and each column. • Pressing any key sends a 2-frequency signal tone.

  14. Business Station Set Features • Access to multiple lines: • Multiple Directory Numbers • Multiple Access to single Directory Number (MADN) • Call Pickup privileges to other lines • Call status indicator lamps and display • Intercom dialing • Speakerphone • Voice Mail Access • Message Waiting lamp

  15. Business Station Set Features • Calling Features: • Hold • Drop • Conference • Transfer • Speed Dial • Call Forward • Call Waiting

  16. Trunks

  17. Analog Trunks • Trunk types: • 2-wire analog trunk • 4-wire analog trunk

  18. Digital Trunks • 1962 (T-1 carrier)

  19. Digital Trunks • Advantages of Using Digital Trunks:

  20. Voice Digitization1 Voice Channel = 64,000 bits/second Sample Quantize 100111011 8000 samples/sec 8 bits/sample

  21. Call over Digital Trunk • Codec (Coder/decoder) circuits in COs do analog-digital conversion. • Analog Central Office Switch: • Analog signal is switched internally. • Digital Central Office Switch: • Digital signal is switched internally.

  22. Channel Banks • T-1 Channel Bank converts between 24 analog voice channels and a single T-1 trunk. • Digitizes 24 voices (codec function) • Combines 24 DS0 signals into a DS1 signal (multiplexing function)

  23. Central Office Switch Technologies

  24. Wire Center Components • Central Office Switches • Main Distribution Frame (MDF) • Cable Vault

  25. Wire Center Components • Central Office Switch Components • Common Control • Data Store • Service Circuits

  26. Wire Center Components • Central Office Switch Components • Switch Matrix • Line Cards • Trunk Cards

  27. Wire Center Components • Distribution Frame • Cable Vault • Outside Plant

  28. How is a Voice Call Made?

  29. A Voice Call • Originating phone goes off-hook.

  30. A Voice Call • Customer dials number.

  31. A Voice Call • Phones go on-hook.

  32. Inter-Office Calls

  33. Network Structure POP = Point of Presence PBX = Private Branch Exchange

  34. Residential Services • Direct Distance Dialing or DDD service • Party Line Service

  35. Business Services • Line vs. Trunk Service • Private vs. Switched Service

  36. Private Line Services • Private Line Service provides a dedicated circuit between two locations

  37. Private Line Services • Private Line / Leased Line / Dedicated Line

  38. Private Line Services • Foreign Exchange (FX) Line • Off Premises Extension (OPX)

  39. Private Line Services • Foreign Exchange (FX) Line

  40. Private Line Services • Off Premises Extension (OPX)

  41. FX Line Example • LhasaLabs Corporation in Chicago has many customers in New York • DDD Chgo-NY costs 15 cents per minute • FX line Chgo-NY costs $800 per month • LhasaLabs makes about 25 calls to NY each day, each call lasting about 10 minutes • SHOULD LhasaLabs GET AN FX LINE?

  42. Private Line Services • Tie Line • Dedicated Access Line to IXC POP

  43. Private Line Services • Tie Line

  44. Private Line Services • Dedicated access to IXC POP

  45. Switched Line Services • Direct Distance Dialing (DDD) • Wide Area Telecommunications Service (WATS) • IN-WATS (800, 888 services)

  46. WATS, IN-WATS • WATS=>Wide-area telecommunications services; Refers to outbound calls only, not inbound. • old style with banded service rates • Full-time WATS=> • Measured WATS=>

  47. WATS Example • Lhasa Labs is located in Chicago and many customers in New York. Lhasa Labs wants to offer a toll free number to its New York customers. Lhasa Labs anticipates using 200 hours per month. • $37.50 per line per month; additional usage at $.15 a minute • Compare to DDD? • Compared to a T1?

  48. Switched Line Services • 900 Services • International WATS • Remote Call Forwarding

  49. Switched Line Services • Directory Services • Wide Area Telecommunications Service (WATS) • IN-WATS (800, 888 services)

  50. RCF Example • LhasaLabs Corporation in Chicago has many customers in New York. LhasaLabs wants to offer a local New York number. • DDD Chgo-NY costs 15 cents per minute • RCF service costs $50 per month • FX line Chgo-NY costs $800 per month • Customers in NY make about 10 calls to LhasaLabs each day, each call lasting about 10 minutes • SHOULD LhasaLabs GET AN FX LINE?

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