Introduction to Packet Voice Technologies

Cisco Networking Academy Program

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–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

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