TDC 461: Basic Telecommunications

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?