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Introduction to Packet Voice Technologies
1© 2005 Cisco Systems, Inc. All rights reserved. Cisco PublicIP Telephony
Cisco Networking Academy Program
Traditional Telephony
2© 2005 Cisco Systems, Inc. All rights reserved. Cisco PublicIP Telephony v1.0
Basic Components of a Telephony Network
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Central Office Switches
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What Is a PBX?
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Basic Call Setup
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Supervisory Signaling
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Address Signaling
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Tone telephone
DTMF dialing• Rotary telephone
– Pulse dialing
Informational Signaling
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Digital vs. Analog Connections
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Time-Division Multiplexing
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Frequency-Division Multiplexing
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Packetized Telephony Networks
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Packet Telephony vs. Circuit-Switched Telephony
• More efficient use of bandwidth and equipment
• Lower transmission costs
• Consolidated network expenses
• Increased revenue from new services
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• Increased revenue from new services
• Service innovation
• Access to new communications devices
• Flexible new pricing structures
Call Control
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Distributed Call Control
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Centralized Call Control
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Packet Telephony Components
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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.
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• Solution is quality of service end-to-end.
Foreign Exchange Station Interface
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Foreign Exchange Office Interface
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E&M Interface
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T1 Interface
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E1 Interface
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BRI
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Physical Connectivity Options
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Cisco IP Phone
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Analog Voice Basics
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Local Loops
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Types of Local-Loop Signaling
• Supervisory signaling
• Address signaling
• Informational Signaling
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On Hook
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Off Hook
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Ringing
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Ringing (Cont.)
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Pulse Dialing
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Dual Tone Multifrequency
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Informational Signaling with Call-Progress Indicators
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Trunks
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Foreign Exchange Trunks
• Foreign Exchange Office
Connects directly to office equipment
Used to extend connections to another location
• Foreign Exchange Station
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• Foreign Exchange Station
Connects directly to station equipment
Used to provision local service
Types of Trunk Signaling
• Loop start
• Ground start
• E&M Wink Start
• E&M immediate start
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• E&M immediate start
• E&M delay start
Loop-Start Signaling
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Ground-Start Signaling
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E&M Signaling
• Separate signaling leads for each direction
• E-lead (inbound direction)
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(inbound direction)
• M-lead (outbound direction)
• Allows independent signaling
E&M Type I
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E&M Type V
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E&M Type II
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E&M Type III
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E&M Type IV
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Trunk Supervisory Signaling—Wink Start
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Trunk Supervisory Signaling—Immediate Start
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Trunk Supervisory Signaling—Delay Start
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2-Wire to 4-Wire Conversion and Echo
• Echo is due to a reflection.
• Impedance
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• Impedance mismatch at the 2-wire to 4-wire hybrid is the most common reason for echo.
Echo Is Always Present
• Echo as a problem is a function of the
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function of the echo delay and the loudness of the echo.
Echo Suppression
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Echo Cancellation
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Analog-to-Digital Voice Encoding
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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,
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4. Compress the samples to reduce bandwidth, optional step.
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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3. Filter the signal to remove any noise.
Nyquist Theorem
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Voice Compression Techniques
• Waveform algorithms
PCM
ADPCM
• Source algorithms
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• Source algorithms
LDCELP
CS-ACELP
Example: Waveform Compression
• PCM
Waveform coding scheme
• ADPCM
Waveform coding scheme
Adaptive: automatic companding
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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
Compression Bandwidth Requirements
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Mean Opinion Score
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Perceptual Speech Quality Measurement
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Signaling Systems
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T1 Digital Signal Format
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Robbed-Bit Signaling
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Channel Associated Signaling—T1
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E1 Framing and Signaling
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Channel Associated Signaling—E1
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Common Channel Signaling
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ISDN
• ISDN
Part of network architecture
Definition for access to the network
Allows access to multiple services through a single access
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a single access
Used for data, voice, or video
• Standards-based
ITU recommendations
Proprietary implementations
ISDN Network Architecture
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Layer 3 (Q.930/931) Messages
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