The document discusses traditional telephony and packet voice technologies, including an overview of analog telephone networks, components, signaling, encoding, compression techniques, and standards such as ISDN. It covers topics such as circuit switching versus packet switching, call control methods, quality of service for real-time traffic, voice coding algorithms, and signaling protocols.

1. 1
© 2005 Cisco Systems, Inc. All rights reserved. Cisco Public
IP Telephony
Introduction to Packet Voice
Technologies
Cisco Networking Academy Program

2. 2
© 2005 Cisco Systems, Inc. All rights reserved. Cisco Public
IP Telephony v1.0
Traditional Telephony

3. 3
© 2005 Cisco Systems, Inc. All rights reserved. Cisco Public
IP Telephony v1.0
Basic Components of a Telephony Network

4. 4
© 2005 Cisco Systems, Inc. All rights reserved. Cisco Public
IP Telephony v1.0
Central Office Switches

5. 5
© 2005 Cisco Systems, Inc. All rights reserved. Cisco Public
IP Telephony v1.0
What Is a PBX?

6. 6
© 2005 Cisco Systems, Inc. All rights reserved. Cisco Public
IP Telephony v1.0
Basic Call Setup

7. 7
© 2005 Cisco Systems, Inc. All rights reserved. Cisco Public
IP Telephony v1.0
Supervisory Signaling

8. 8
© 2005 Cisco Systems, Inc. All rights reserved. Cisco Public
IP Telephony v1.0
Address Signaling
Tone telephone
DTMF dialing
• Rotary telephone
– Pulse dialing

9. 9
© 2005 Cisco Systems, Inc. All rights reserved. Cisco Public
IP Telephony v1.0
Informational Signaling

10. 10
© 2005 Cisco Systems, Inc. All rights reserved. Cisco Public
IP Telephony v1.0
Digital vs. Analog Connections

11. 11
© 2005 Cisco Systems, Inc. All rights reserved. Cisco Public
IP Telephony v1.0
Time-Division Multiplexing

12. 12
© 2005 Cisco Systems, Inc. All rights reserved. Cisco Public
IP Telephony v1.0
Frequency-Division Multiplexing

13. 13
© 2005 Cisco Systems, Inc. All rights reserved. Cisco Public
IP Telephony v1.0
Packetized Telephony Networks

14. 14
© 2005 Cisco Systems, Inc. All rights reserved. Cisco Public
IP Telephony v1.0
Packet Telephony vs.
Circuit-Switched Telephony
• More efficient use of bandwidth and equipment
• Lower transmission costs
• Consolidated network expenses
• Increased revenue from new services
• Service innovation
• Access to new communications devices
• Flexible new pricing structures

15. 15
© 2005 Cisco Systems, Inc. All rights reserved. Cisco Public
IP Telephony v1.0
Call Control

16. 16
© 2005 Cisco Systems, Inc. All rights reserved. Cisco Public
IP Telephony v1.0
Distributed Call Control

17. 17
© 2005 Cisco Systems, Inc. All rights reserved. Cisco Public
IP Telephony v1.0
Centralized Call Control

18. 18
© 2005 Cisco Systems, Inc. All rights reserved. Cisco Public
IP Telephony v1.0
Packet Telephony Components

19. 19
© 2005 Cisco Systems, Inc. All rights reserved. Cisco Public
IP Telephony v1.0
Real-Time vs. Best-Effort Traffic
• Real-time traffic needs guaranteed delay and
timing.
• IP networks are best-effort with no guarantees of
delivery, delay, or timing.
• Solution is quality of service end-to-end.

20. 20
© 2005 Cisco Systems, Inc. All rights reserved. Cisco Public
IP Telephony v1.0
Foreign Exchange Station Interface

21. 21
© 2005 Cisco Systems, Inc. All rights reserved. Cisco Public
IP Telephony v1.0
Foreign Exchange Office Interface

22. 22
© 2005 Cisco Systems, Inc. All rights reserved. Cisco Public
IP Telephony v1.0
E&M Interface

23. 23
© 2005 Cisco Systems, Inc. All rights reserved. Cisco Public
IP Telephony v1.0
T1 Interface

24. 24
© 2005 Cisco Systems, Inc. All rights reserved. Cisco Public
IP Telephony v1.0
E1 Interface

25. 25
© 2005 Cisco Systems, Inc. All rights reserved. Cisco Public
IP Telephony v1.0
BRI

26. 26
© 2005 Cisco Systems, Inc. All rights reserved. Cisco Public
IP Telephony v1.0
Physical Connectivity Options

27. 27
© 2005 Cisco Systems, Inc. All rights reserved. Cisco Public
IP Telephony v1.0
Cisco IP Phone

28. 28
© 2005 Cisco Systems, Inc. All rights reserved. Cisco Public
IP Telephony v1.0
Analog Voice Basics

29. 29
© 2005 Cisco Systems, Inc. All rights reserved. Cisco Public
IP Telephony v1.0
Local Loops

30. 30
© 2005 Cisco Systems, Inc. All rights reserved. Cisco Public
IP Telephony v1.0
Types of Local-Loop Signaling
• Supervisory signaling
• Address signaling
• Informational Signaling

31. 31
© 2005 Cisco Systems, Inc. All rights reserved. Cisco Public
IP Telephony v1.0
On Hook

32. 32
© 2005 Cisco Systems, Inc. All rights reserved. Cisco Public
IP Telephony v1.0
Off Hook

33. 33
© 2005 Cisco Systems, Inc. All rights reserved. Cisco Public
IP Telephony v1.0
Ringing

34. 34
© 2005 Cisco Systems, Inc. All rights reserved. Cisco Public
IP Telephony v1.0
Ringing (Cont.)

35. 35
© 2005 Cisco Systems, Inc. All rights reserved. Cisco Public
IP Telephony v1.0
Pulse Dialing

36. 36
© 2005 Cisco Systems, Inc. All rights reserved. Cisco Public
IP Telephony v1.0
Dual Tone Multifrequency

37. 37
© 2005 Cisco Systems, Inc. All rights reserved. Cisco Public
IP Telephony v1.0
Informational Signaling with
Call-Progress Indicators

38. 38
© 2005 Cisco Systems, Inc. All rights reserved. Cisco Public
IP Telephony v1.0
Trunks

39. 39
© 2005 Cisco Systems, Inc. All rights reserved. Cisco Public
IP Telephony v1.0
Foreign Exchange Trunks
• Foreign Exchange Office
Connects directly to office equipment
Used to extend connections to another location
• Foreign Exchange Station
Connects directly to station equipment
Used to provision local service

40. 40
© 2005 Cisco Systems, Inc. All rights reserved. Cisco Public
IP Telephony v1.0
Types of Trunk Signaling
• Loop start
• Ground start
• E&M Wink Start
• E&M immediate start
• E&M delay start

41. 41
© 2005 Cisco Systems, Inc. All rights reserved. Cisco Public
IP Telephony v1.0
Loop-Start Signaling

42. 42
© 2005 Cisco Systems, Inc. All rights reserved. Cisco Public
IP Telephony v1.0
Ground-Start Signaling

43. 43
© 2005 Cisco Systems, Inc. All rights reserved. Cisco Public
IP Telephony v1.0
E&M Signaling
• Separate signaling
leads for each direction
• E-lead
(inbound direction)
• M-lead
(outbound direction)
• Allows independent
signaling

44. 44
© 2005 Cisco Systems, Inc. All rights reserved. Cisco Public
IP Telephony v1.0
E&M Type I

45. 45
© 2005 Cisco Systems, Inc. All rights reserved. Cisco Public
IP Telephony v1.0
E&M Type V

46. 46
© 2005 Cisco Systems, Inc. All rights reserved. Cisco Public
IP Telephony v1.0
E&M Type II

47. 47
© 2005 Cisco Systems, Inc. All rights reserved. Cisco Public
IP Telephony v1.0
E&M Type III

48. 48
© 2005 Cisco Systems, Inc. All rights reserved. Cisco Public
IP Telephony v1.0
E&M Type IV

49. 49
© 2005 Cisco Systems, Inc. All rights reserved. Cisco Public
IP Telephony v1.0
Trunk Supervisory Signaling—
Wink Start

50. 50
© 2005 Cisco Systems, Inc. All rights reserved. Cisco Public
IP Telephony v1.0
Trunk Supervisory Signaling—
Immediate Start

51. 51
© 2005 Cisco Systems, Inc. All rights reserved. Cisco Public
IP Telephony v1.0
Trunk Supervisory Signaling—
Delay Start

52. 52
© 2005 Cisco Systems, Inc. All rights reserved. Cisco Public
IP Telephony v1.0
2-Wire to 4-Wire Conversion and Echo
• Echo is due to a
reflection.
• Impedance
mismatch at the
2-wire to 4-wire
hybrid is the
most common
reason for echo.

53. 53
© 2005 Cisco Systems, Inc. All rights reserved. Cisco Public
IP Telephony v1.0
Echo Is Always Present
• Echo as a
problem is a
function of the
echo delay and
the loudness
of the echo.

54. 54
© 2005 Cisco Systems, Inc. All rights reserved. Cisco Public
IP Telephony v1.0
Echo Suppression

55. 55
© 2005 Cisco Systems, Inc. All rights reserved. Cisco Public
IP Telephony v1.0
Echo Cancellation

56. 56
© 2005 Cisco Systems, Inc. All rights reserved. Cisco Public
IP Telephony v1.0
Analog-to-Digital Voice Encoding

57. 57
© 2005 Cisco Systems, Inc. All rights reserved. Cisco Public
IP Telephony v1.0
Digitizing Analog Signals
1. Sample the analog signal regularly.
2. Quantize the sample.
3. Encode the value into a binary expression.
4. Compress the samples to reduce bandwidth,
optional step.

58. 58
© 2005 Cisco Systems, Inc. All rights reserved. Cisco Public
IP Telephony v1.0
Basic Voice Encoding:
Converting Digital to Analog
1. Decompress the samples, if compressed.
2. Decode the samples into voltage amplitudes,
rebuilding the PAM signal.
3. Filter the signal to remove any noise.

59. 59
© 2005 Cisco Systems, Inc. All rights reserved. Cisco Public
IP Telephony v1.0
Nyquist Theorem

60. 60
© 2005 Cisco Systems, Inc. All rights reserved. Cisco Public
IP Telephony v1.0
Voice Compression Techniques
• Waveform algorithms
PCM
ADPCM
• Source algorithms
LDCELP
CS-ACELP

61. 61
© 2005 Cisco Systems, Inc. All rights reserved. Cisco Public
IP Telephony v1.0
Example: Waveform Compression
• PCM
Waveform coding scheme
• ADPCM
Waveform coding scheme
Adaptive: automatic companding
Differential: encode changes between
samples only
• ITU standards:
G.711 rate: 64 kbps = (2 * 4 kHz) * 8 bits/sample
G.726 rate: 32 kbps = (2 * 4 kHz) * 4 bits/sample
G.726 rate: 24 kbps = (2 * 4 kHz) * 3 bits/sample
G.726 rate: 16 kbps = (2 * 4 kHz) * 2 bits/sample

62. 62
© 2005 Cisco Systems, Inc. All rights reserved. Cisco Public
IP Telephony v1.0
Compression Bandwidth Requirements

63. 64
© 2005 Cisco Systems, Inc. All rights reserved. Cisco Public
IP Telephony v1.0
Perceptual Speech Quality Measurement

64. 65
© 2005 Cisco Systems, Inc. All rights reserved. Cisco Public
IP Telephony v1.0
Signaling Systems

65. 66
© 2005 Cisco Systems, Inc. All rights reserved. Cisco Public
IP Telephony v1.0
T1 Digital Signal Format

66. 67
© 2005 Cisco Systems, Inc. All rights reserved. Cisco Public
IP Telephony v1.0
Robbed-Bit Signaling

67. 68
© 2005 Cisco Systems, Inc. All rights reserved. Cisco Public
IP Telephony v1.0
Channel Associated Signaling—T1

68. 69
© 2005 Cisco Systems, Inc. All rights reserved. Cisco Public
IP Telephony v1.0
E1 Framing and Signaling

69. 70
© 2005 Cisco Systems, Inc. All rights reserved. Cisco Public
IP Telephony v1.0
Channel Associated Signaling—E1

70. 71
© 2005 Cisco Systems, Inc. All rights reserved. Cisco Public
IP Telephony v1.0
Common Channel Signaling

71. 72
© 2005 Cisco Systems, Inc. All rights reserved. Cisco Public
IP Telephony v1.0
ISDN
• ISDN
Part of network architecture
Definition for access to the network
Allows access to multiple services through
a single access
Used for data, voice, or video
• Standards-based
ITU recommendations
Proprietary implementations

72. 73
© 2005 Cisco Systems, Inc. All rights reserved. Cisco Public
IP Telephony v1.0
ISDN Network Architecture

73. 74
© 2005 Cisco Systems, Inc. All rights reserved. Cisco Public
IP Telephony v1.0
Layer 3 (Q.930/931) Messages

74. 75
© 2005 Cisco Systems, Inc. All rights reserved. Cisco Public
IP Telephony v1.0