1.intro to packet voice technologies

7/28/2019 1.Intro to Packet Voice Technologies

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

Introduction to Packet VoiceTechnologies

Cisco Networking Academy Program


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

Traditional Telephony


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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


7/747 2005 Cisco Systems, Inc. All rights reserved. Cisco PublicIP Telephony v1.0

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 andtiming.

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


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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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I f ti l Si li ith


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Informational Signaling withCall-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 StationConnects directly to station equipment

Used to provision local service


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Types of Trunk Signaling

Loop start

Ground start

E&M Wink Start

E&M immediate start

E&M delay start


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Loop-Start Signaling


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Ground-Start Signaling


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E&M Signaling

Separate signalingleads for each direction

E-lead

(inbound direction)

M-lead(outbound direction)

Allows independent

signaling


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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

Trunk Supervisory Signaling


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Trunk Supervisory SignalingWink Start



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Trunk Supervisory SignalingImmediate Start



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Trunk Supervisory SignalingDelay Start


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2-Wire to 4-Wire Conversion and Echo

Echo is due to areflection.

Impedancemismatch at the2-wire to 4-wirehybrid is themost common

reason for echo.


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Echo Is Always Present

Echo as aproblem is a

function of theecho delay andthe loudnessof the echo.


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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,optional step.

Basic Voice Encoding:


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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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Nyquist Theorem


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Voice Compression Techniques

Waveform algorithms

PCM

ADPCM

Source algorithms

LDCELP

CS-ACELP


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Example: Waveform Compression

PCM

Waveform coding scheme

ADPCM

Waveform coding scheme

Adaptive: automatic compandingDifferential: encode changes betweensamples 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




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Compression Bandwidth Requirements


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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 SignalingT1


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E1 Framing and Signaling


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Channel Associated SignalingE1


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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 througha single access

Used for data, voice, or video

Standards-based

ITU recommendations

Proprietary implementations


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ISDN Network Architecture


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Layer 3 (Q.930/931) Messages


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