introduction to packet voice technologies

1© 2005 Cisco Systems, Inc. All rights reserved. Cisco PublicIP Telephony

Introduction to Packet Voice Technologies

Cisco Networking Academy Program

2© 2005 Cisco Systems, Inc. All rights reserved. Cisco PublicIP Telephony v1.0

Traditional Telephony


Basic Components of a Telephony Network


Central Office Switches


What Is a PBX?


Basic Call Setup


Supervisory Signaling


Address Signaling

Tone telephone

DTMF dialing• Rotary telephone

– Pulse dialing


Informational Signaling


Digital vs. Analog Connections


Time-Division Multiplexing


Frequency-Division Multiplexing


Packetized Telephony Networks


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


Call Control


Distributed Call Control


Centralized Call Control


Packet Telephony Components


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.


Foreign Exchange Station Interface


Foreign Exchange Office Interface


E&M Interface


T1 Interface


E1 Interface


BRI


Physical Connectivity Options


Cisco IP Phone


Analog Voice Basics


Local Loops


Types of Local-Loop Signaling

• Supervisory signaling

• Address signaling

• Informational Signaling


On Hook


Off Hook


Ringing


Ringing (Cont.)


Pulse Dialing


Dual Tone Multifrequency


Informational Signaling with Call-Progress Indicators


Trunks


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


Types of Trunk Signaling

• Loop start

• Ground start

• E&M Wink Start

• E&M immediate start

• E&M delay start


Loop-Start Signaling


Ground-Start Signaling


E&M Signaling

• Separate signaling leads for each direction

• E-lead (inbound direction)

• M-lead (outbound direction)

• Allows independent signaling


E&M Type I


E&M Type V


E&M Type II


E&M Type III


E&M Type IV


Trunk Supervisory Signaling—Wink Start


Trunk Supervisory Signaling—Immediate Start


Trunk Supervisory Signaling—Delay Start


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.


Echo Is Always Present

• Echo as a problem is a function of the echo delay and the loudness of the echo.


Echo Suppression


Echo Cancellation


Analog-to-Digital Voice Encoding


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.


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.


Nyquist Theorem


Voice Compression Techniques

• Waveform algorithms

PCM

ADPCM

• Source algorithms

LDCELP

CS-ACELP


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





Compression Bandwidth Requirements


Perceptual Speech Quality Measurement


Signaling Systems


T1 Digital Signal Format


Robbed-Bit Signaling


Channel Associated Signaling—T1


E1 Framing and Signaling


Channel Associated Signaling—E1


Common Channel Signaling


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


ISDN Network Architecture


Layer 3 (Q.930/931) Messages

introduction to packet voice technologies

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