the all Collision Domain is the place where collision occurs.

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

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IP Telephony v1.0
Traditional Telephony

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IP Telephony v1.0
Basic Components of a Telephony Network

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IP Telephony v1.0
Central Office Switches

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IP Telephony v1.0
What Is a PBX?

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IP Telephony v1.0
Basic Call Setup

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IP Telephony v1.0
Supervisory Signaling

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IP Telephony v1.0
Address Signaling
Tone telephone
DTMF dialing
• Rotary telephone
– Pulse dialing

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IP Telephony v1.0
Informational Signaling

10. 10
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IP Telephony v1.0
Digital vs. Analog Connections

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IP Telephony v1.0
Time-Division Multiplexing

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IP Telephony v1.0
Frequency-Division Multiplexing

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IP Telephony v1.0
Packetized Telephony Networks

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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

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IP Telephony v1.0
Call Control

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IP Telephony v1.0
Distributed Call Control

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IP Telephony v1.0
Centralized Call Control

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IP Telephony v1.0
Packet Telephony Components

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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.

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IP Telephony v1.0
Foreign Exchange Station Interface

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IP Telephony v1.0
Foreign Exchange Office Interface

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IP Telephony v1.0
E&M Interface

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IP Telephony v1.0
T1 Interface

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IP Telephony v1.0
E1 Interface

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IP Telephony v1.0
BRI

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IP Telephony v1.0
Physical Connectivity Options

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IP Telephony v1.0
Cisco IP Phone

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IP Telephony v1.0
Analog Voice Basics

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IP Telephony v1.0
Local Loops

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IP Telephony v1.0
Types of Local-Loop Signaling
• Supervisory signaling
• Address signaling
• Informational Signaling

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IP Telephony v1.0
On Hook

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IP Telephony v1.0
Off Hook

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IP Telephony v1.0
Ringing

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IP Telephony v1.0
Ringing (Cont.)

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IP Telephony v1.0
Pulse Dialing

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IP Telephony v1.0
Dual Tone Multifrequency

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IP Telephony v1.0
Informational Signaling with
Call-Progress Indicators

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IP Telephony v1.0
Trunks

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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

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IP Telephony v1.0
Types of Trunk Signaling
• Loop start
• Ground start
• E&M Wink Start
• E&M immediate start
• E&M delay start

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IP Telephony v1.0
Loop-Start Signaling

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IP Telephony v1.0
Ground-Start Signaling

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IP Telephony v1.0
E&M Signaling
• Separate signaling
leads for each direction
• E-lead
(inbound direction)
• M-lead
(outbound direction)
• Allows independent
signaling

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IP Telephony v1.0
E&M Type I

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IP Telephony v1.0
E&M Type V

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IP Telephony v1.0
E&M Type II

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IP Telephony v1.0
E&M Type III

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IP Telephony v1.0
E&M Type IV

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IP Telephony v1.0
Trunk Supervisory Signaling—
Wink Start

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IP Telephony v1.0
Trunk Supervisory Signaling—
Immediate Start

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IP Telephony v1.0
Trunk Supervisory Signaling—
Delay Start

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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.

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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.

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IP Telephony v1.0
Echo Suppression

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IP Telephony v1.0
Echo Cancellation

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IP Telephony v1.0
Analog-to-Digital Voice Encoding

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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.

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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.

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IP Telephony v1.0
Nyquist Theorem

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IP Telephony v1.0
Voice Compression Techniques
• Waveform algorithms
PCM
ADPCM
• Source algorithms
LDCELP
CS-ACELP

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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

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IP Telephony v1.0
Compression Bandwidth Requirements

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IP Telephony v1.0
Perceptual Speech Quality Measurement

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IP Telephony v1.0
Signaling Systems

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IP Telephony v1.0
T1 Digital Signal Format

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IP Telephony v1.0
Robbed-Bit Signaling

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IP Telephony v1.0
Channel Associated Signaling—T1

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IP Telephony v1.0
E1 Framing and Signaling

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IP Telephony v1.0
Channel Associated Signaling—E1

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IP Telephony v1.0
Common Channel Signaling

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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

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IP Telephony v1.0
ISDN Network Architecture

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IP Telephony v1.0
Layer 3 (Q.930/931) Messages

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IP Telephony v1.0