introduction to packet voice · pdf fileintroduction to packet voice technologies ... dtmf...

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


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


• 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


• 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 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)


(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


• 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


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,


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.


3. Filter the signal to remove any noise.

Nyquist Theorem


Voice Compression Techniques

• Waveform algorithms

PCM

ADPCM

• Source algorithms


• 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


Mean Opinion Score


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


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 · pdf fileintroduction to packet voice technologies ... dtmf...

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