Cisco - Introduction to Voice and Telephone Technology 401

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© 1999, Cisco Systems, Inc.

Introduction to Voice and Telephone Technology Session 401

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© 1999, Cisco Systems, Inc.

Cisco Systems Confidential

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Voice Is Not A Network

• Voice is an Application • Complete understanding of Voice Application fundamentals helps us to design and build better Networks

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© 1999, Cisco Systems, Inc.

Objective

To Prepare the Data Communications Professional for Voice and Data Network Integration by Providing Voice Technology Fundamentals

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© 1999, Cisco Systems, Inc.

Cisco Systems Confidential

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Agenda • Basic Analog Telephony • Basic Digital Telephony • Voice Coding and Compression Techniques • Voice Transport and Delay • Supplemental Slides: Digital Voice Signaling Techniques 401 0985_05f9_c1

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© 1999, Cisco Systems, Inc.

Telephony Equipment • Telephone set • Key system Optimizes use of telephone sets to lines Mechanical to electronic Two to ten telephone handsets is typical

• PBX (Private Branch Exchange) Advanced features and call routing Tens to hundreds of telephone handsets

• Central office switch 401 0985_05f9_c1

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Cisco Systems Confidential

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Analog Telephony— Connection Basics Tip Ring

Sleeve

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Basic Call Progress: On-Hook

Telephone Switch Local Loop

Local Loop

DC Voltage Open Circuit No Current Flow 401 0985_05f9_c1

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Cisco Systems Confidential

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Basic Call Progress: Off-Hook Off-Hook Closed Circuit

DC Current Dial Tone

Telephone Switch

Local Loop

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Local Loop

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Basic Call Progress: Dialing Off-Hook Closed Circuit Dialed Digits

Pulses or Tones DC Current

Telephone Switch Local Loop

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Basic Call Progress: Switching Off-Hook Closed Circuit

Telephone Switch

DC Current Local Loop

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Address to Port Translation

Local Loop

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Basic Call Progress: Ringing Off-Hook Closed Circuit Ring Back Tone DC Current Local Loop

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DC Open Cct. Ringing Tone Telephone Switch Local Loop

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Basic Call Progress: Talking Off-Hook Closed Circuit Voice Energy DC Current

Telephone Switch

Voice Energy DC Current

Local Loop

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Local Loop

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Analog Telephony—Signaling

• Supervisory • Addressing • Call progress

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Analog Telephony— Supervisory Signaling Switch

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Switch

• Loop start

• Ground start

Almost all telephones

Switch Trunk Lines

Current flow sensed

Momentary ground ring lead 15

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Loop Start Station

PBX or Central Office Loop (Local or Station)

DC Current

Ringing

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AC

Switch

+ –

Switch

+ –

Switch

+ – 16

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E&M Signaling • PBXs, switches Separate signaling leads for each direction E-Lead (inbound direction) M-Lead (outbound direction) Allows independent signaling

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State

E-Lead

M-Lead

On-Hook

Open

Ground

Off-Hook

Ground

Battery Voltage

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Signaling and Addressing

Dial Pulse

DTMF

Analog Transmission “In-Band” Signaling 0–9, *, # (12 Digits)

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ISDN

Digital Transmission “Out-of-Band” Message-Based Signaling

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Pulse Dialing Off-Hook

Dialing

Inter-Digit

Next Digit

Make (Circuit Closed)

Break (Circuit Open)

700 ms

US:60/40 Break/Make Pulse Period (100 ms) 401 0985_05f9_c1

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Tone Dialing Dual Tone Multifrequency (DTMF)

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1209

1336

1477

1633

697

1

2

3

A

770

4

5

6

B

852

7

8

9

C

941

*

0

#

D

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Cisco Systems Confidential

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Voice Channel Bandwidth Voice Channel Voice Signal Output Voltage or Energy

.2

1

Tone Dialing Signals 401 0985_05f9_c1

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3

4

Frequency (K-Hertz)

Systems Control Signals 21

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Switching Systems Manual Control—Switch/Cord Boards Off-Hook Indicator Tip Ring

Patch Cord Pairs Manual Ring

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Local Access Network Feeder Route Boundary

Central Office

40,000 to 50,000 Lines

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Serving Area Boundary

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PSTN Network Hierarchy 1

1

1

Class Name 2

4C

4P

3

3

5

4C

4C

4X

4P

5

5

4P

5

5R

5R

5

4X

1

Regional Center

2

Sectional Center

3

Primary Center

4C

Toll Center

4P

Toll Point

4X

Interm. Point

5

End Office

5R

EO w/ RSU

R

Remote Sw. Unit

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Types of Voice Circuits Serving Area 415-NXX-XXX 415-577-3800

Serving Area 510-NXX-XXX

Class 5

Class 5

Switch

Switch

OPX Off-Premises Ext. 415-577-3801

510-655-1400

FX Foreign Exchange

ARD Auto Ring Down 401 0985_05f9_c1

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© 1999, Cisco Systems, Inc.

Echo in Voice Networks Talker

Listener

Delay

Talker Echo

Listener Echo

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Normal Signal Flow Two-Wire Local Loop

Central Office

Receive Direction

2w-4w Hybrid Transmit Direction

• Two- to four-wire hybrid combines receive-and transmit-signals over the same pair • Two-wire impedance must match four-wire impedance 401 0985_05f9_c1

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© 1999, Cisco Systems, Inc.

How Does Echo Happen? Echo Is Due to a Reflection Echo Is Experienced here

Transmit Direction

Impedance Mismatch is here

2w-4w Hybrid

2w-4w Hybrid Central Office

Central Office

Reflected Signal

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Receive Direction

Impedance Mismatch at the 2w-4w Hybrid Is the Most Common Reason for Echo 28

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Echo Is Always Present Echo as a Problem Is a Function of the Echo Delay, and the Magnitude of the Echo Echo Is Unnoticeable (dB) Echo Path Loss Echo Is a Problem

Echo Path Delay (ms) 401 0985_05f9_c1

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© 1999, Cisco Systems, Inc.

Ways to Defeat Echo • Increase the loss in the echo path Can often be the solution Disadvantage: static setting and reduces the signal strength of the speaker

• Echo suppresser Acts like a noise gate, effectively making communications half-duplex 401 0985_05f9_c1

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Echo Canceler Most Effective Means for Removing Echo Echo “Cancelled” Here

Voice Endpoint

E/C Received Voice Signal

+ Echo Canceler Block Diagram

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Adaptive Filter

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Summary

• Information exchange based on voltage, current flow, grounding, and so on • Analog voice technology dates back to the late 1800s

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Agenda • Basic Analog Telephony • Basic Digital Telephony • Voice Coding and Compression Techniques • Voice Transport and Delay • Supplemental Slides: Digital Voice Signaling Techniques 401 0985_05f9_c1

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© 1999, Cisco Systems, Inc.

Digital Telephony Digital Trunking Switch

Switch

Analog Loop

Digital Network Switch

POTS A to D Conversion

Digital Loop Digital Network Switch

ISDN 401 0985_05f9_c1

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Digital Telephony Pulse Code Modulation—Nyquist Theorem Voice Bandwidth = 200 Hz to 3400 Hz

Analog Audio Source

Sampling Stage = Sample

Codec Technique 401 0985_05f9_c1

8 bits per sample 8 kHz (8,000 Samples/Sec) 35

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Pulse Code Modulation— Analog to Digital Conversion Quantizing Noise

A—Law (Europe)

10010011011

Stage 1

µ—Law (USA) Quantizing Stage 401 0985_05f9_c1

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Time Division Multiplexer Example: T1 Channel Bank INPUTS

OUTPUT 8,000 Frames per Second (1 Frame per 125 µs)

Analog or Digital Interface Cards Ch. 1 Ch. 2 Ch. 3 Ch. 4 Ch. 5 Ch. 6

Framing Bit (8000 per Second)

Ch 1 Ch 2 Ch 3

Ch 4 Ch 5

Ch 6

Next Frame Framing Bit

Ch 24

Chs 7-23

Ch 1, etc

T1 Multiplexer

Chs. 7-23

64 kbps x 24 = 1.536 Mbps Add Framing Bits = 8 Kbps Total Bit Rate: 1.544 Mbps

Ch. 24

Each Input Represents 64 kbps 401 0985_05f9_c1

Eight Bits from Each Channel Input In Sequential Order

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DS1 Superframe (D4) Format • 193rd bit of each frame used for frame synchronization • D4 framing is 12 frames • D4 framing pattern is: 100011011100 • Channel Associated Signaling (CAS) robs the LSB of every byte in frames 6 and 12 for AB bits

Framing Bits Frame Number 1 2 3 4 5 6 7 8 9 10 11 12

Framing Bit Value

1 0 0 0 1 1 0 1 1 1 0 0

Bit Use in Each Channel Time Slot

Signaling—Bit Use Options

Traffic

Signaling

T

2

4

Bits 1–7

Bit 8

*

A

A

Bits 1–7

Bit 8

*

A

B

• Common Channel Signaling (ISDN) uses TS 24

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Extended Superframe (ESF) S Bits Frame Number 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 401 0985_05f9_c1

Bit Use in Each Channel Time Slot

Fe

DL

BC

– – – 0 – – – 0 – – – 1 – – – 0 – – – 1 – – – 1

m – m – m – m – m – m – m – m – m – m – m – m –

– C1 – – – C2 – – – C3 – – – C4 – – – C5 – – – C6 – –

Signaling—Bit Use Options

Traffic

Signaling

T

2

4

16

Bits 1–7

Bit 8

*

A

A

A

Bits 1–7

Bit 8

*

A

B

B

Bits 1–7

Bit 8

*

A

A

C

Bits 1–7

Bit 8

*

A

B

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Digital Signaling Schemes Channel Associated Signaling Extended Superframe

“In-Band” Audio Address Signaling (DTMF)

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Bit A B C D Supervision On/Off Hook

Frame 6th 12th 18th 24th

Address Signaling (Dial Pulse)

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Digital Signaling Schemes Common Channel Signaling Extended Super Frame

64 Kbps Signaling Channel in TS24 of Each Frame (e.g. ISDN D Channel Q.931 Messages)

“In-Band” Audio Address Signaling (DTMF) 401 0985_05f9_c1

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Digital Telephony— Synchronization • Bit synchronization Primary reference source Ones density

• Time-slot synchronization Bits/bytes/channels

• Frame alignment 193rd Bit Pattern 401 0985_05f9_c1

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Digital Telephony— Synchronization One Multiframe (ESF) 3 ms 12

1

24

1 Frame, 125µs, 193bits 24 Time Slots 1

12

24

1 Channel Time Slot, 5.18µs

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Synchronization—Traditional Network Clocking Strata Master Clock

Stratum

PRS

1

Timing Toll Office

Timing

2

Timing Timing

End Office

End Office

DCS

3 PBX

PBX

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© 1999, Cisco Systems, Inc.

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Agenda • Basic Analog Telephony • Basic Digital Telephony • Voice Coding and Compression Techniques • Voice Transport and Delay • Supplemental Slides: Digital Voice Signaling Techniques 401 0985_05f9_c1

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© 1999, Cisco Systems, Inc.

Voice Coding and Compression • Speech-coding schemes • Subjective impairment analysis: mean opinion scores • Digitizing voice • Voice compression ADPCM CELP (LD-CELP and CSA-CELP) Silence removal techniques (DSI using VAD) 401 0985_05f9_c1

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Voice Compression Technologies Unacceptable

Business Quality

Toll Quality * PCM (G.711)

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PCM (G.711)

(Cellular)

Bandwidth (Kbps) 32

*

* (G.726) ADPCM 32 *

24 16

ADPCM 24 (G.726)

*

* * ADPCM 16 (G.726) LDCELP 16 (G.728)

8 0

*

CS-ACELP* 8 (G.729)

* LPC 4.8

Quality 401 0985_05f9_c1

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© 1999, Cisco Systems, Inc.

Speech-Coding Schemes • Waveform coders Non-linear approximation of the actual waveform Examples: PCM, ADPCM

• Vocoders Synthesized voice Example: LPC

• Hybrid coders Linear waveform approximation with synthesized voice Example: CELP 401 0985_05f9_c1

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Subjective Impairment Analysis: Mean Opinion Scores 5 Hybrid Coders

4

Waveform Coders

Subjective Quality 3 (MOS) 2

Vocoders

1 2 Score 5 4 3 2 1 401 0985_05f9_c1

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8

16

Kbps

32

Quality

Description of Impairment

Excellent Good Fair Poor Bad

Imperceptible Just Perceptible, not Annoying Perceptible and Slightly Annoying Annoying but not Objectionable Very Annoying and Objectionable

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Measuring Mean Opinion Scores: ITU P.800 Series Source

Channel Simulation

Impairment Codec ‘X’

1

2

3

4

5

1

2

3

4

5

“Nowadays, a chicken leg is a rare dish” Rating Rating

Level Level of of Speech Speech Quality Quality

Distortion Distortion

5

Excellent

Imperceptible

4

Good

Just perceptible but not annoying

3

Fair

Perceptible and slightly annoying

2

Poor

Annoying but not objectionable

1

Unsatisfactory

Very annoying and objectionable

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Digitizing Voice: PCM Waveform Encoding Review • Nyquist Theorem: sample at twice the highest frequency Voice frequency range: 200-3400 Hz Sampling frequency = 8000/sec (every 125µs) Bit rate: (2 x 4 kHz) x 8 bits per sample = 64,000 bits per second (DS-0)

• By far the most commonly used method CODEC PCM = DS-0 64 Kbps

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Nonlinear vs. Linear Encoding Output

Output

Input

Input

Nonlinear Encoding

Linear Encoding

Closely Follows Human Voice Characteristics. High Amplitude Signals have More Quantization Distortion.

Relatively Easy to Analyze, Synthesize and Regenerate. All Amplitudes Have Roughly Equal Quantization Distortion.

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Encoding

Quantizing

Filtering

Sampling

Voice CODECs: Waveform Coders

1110010010010110

Waveform ENCODER

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Waveform DECODER

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Voice Compression • Objective: reduce bandwidth consumption Compression algorithms are optimized for voice Unlike data compression: these are “loose”

• Drawbacks/tradeoffs Quantization distortion Tandem switching degradation Delay (echo) 401 0985_05f9_c1

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Voice Compression—ADPCM • Adaptive Differential Pulse Code Modulation Waveform coding scheme Adaptive: automatic companding Differential: encode the changes between samples only Rates and bits per sample: 32 Kbps = 8 Kbps x 4 bits/sample 24 Kbps = 8 Kbps x 3 bits/sample 16 Kbps = 8 Kbps x 2 bits/sample 401 0985_05f9_c1

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Voice Compression—CELP • Code excited linear predictive • Very high voice quality at low-bit rates, processor intensive, use of DSPs • G.728: LD-CELP—16 Kbps • G.729: CSA-CELP—8 Kbps G.729a variant— “stripped down” 8 kbps (with a noticeable quality difference) to reduce processing load, allows two voice channels encoded per DSP 401 0985_05f9_c1

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Voice CODECs: Hybrid Coders PCM Encoder

PCM Decoder

Filtering 11100100100101 Sampling 1 Quantizing Sample Encoding

Frames

VocalCords Throat Nose Mouth

Human Speech Model 401 0985_05f9_c1

Model Parameters

Model Parameters

10110010

Parameters

Analysis

Synthesis 57

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G.729 Cake A/D

Cake

Code DSP Packet Recipe 10.1.1.1

16-Bit Linear PCM Code Look-up

IngredientsDirections A-sound Play K, A, K-sound and K

Recipe or Code Book 401 0985_05f9_c1

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Digital Speech Interpolation (DSI) • Voice Activity Detection (VAD) • Removal of voice silence • Examines voice for power, change of power, frequency and change of frequency • All factors must indicate voice “fits into the window” before cells are constructed • Automatically disabled for fax/modem 401 0985_05f9_c1

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© 1999, Cisco Systems, Inc.

Voice Activity Detection

- 31 dbm B/W Saved Voice Activity (Power Level)

Hang Timer

No Voice Traffic Sent SID

SID Buffer

- 54 dbm Pink Noise Voice “Spurt”

Silence

Voice “Spurt”

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Bandwidth Requirements Voice Band Traffic Encoding/ Compression G.711 PCM A-Law/µ A-Law/ µ-Law

64 kbps (DS0)

G.726 ADPCM

16, 24, 32, 40 kbps

G.729 CS-ACELP

8 kbps

G.728 LD-CELP

16 kbps

G.723.1 CELP 401 0985_05f9_c1

Result Bit Rate

6.3/5.3 kbps Variable 61

© 1999, Cisco Systems, Inc.

Agenda • Basic Analog Telephony • Basic Digital Telephony • Voice Coding and Compression Techniques • Voice Transport and Delay • Supplemental Slides: Digital Voice Signaling Techniques 401 0985_05f9_c1

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Voice Network Transport • Voice Network Transport is typically TDM circuit-based: T1/E1 DS3/E3 SONET (OC-3, OC-12, etc.)

• But can also be packet-based: ATM Frame Relay IP 401 0985_05f9_c1

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Data Is Overtaking Voice Evolution from TDM-based transport to packets/cells or a combination

Relative Load Data Is 23x Voice Traffic

30 25 20

Data 15 10

Data Is 5x Voice Traffic

5 0 1990

Voice 1995

2000

2005

Year Source: Electronicast 401 0985_05f9_c1

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The Tyranny of the DS0 • Switching and transport based on circuits • Rigid structure yields high cost for packet Customer Premise

Local CO Class-5 DS0 Switch DS1

DS0

Class-4 Switch

DS3

DS0

Switching

Class-4 Switch

DS1

DS3

DS0

DS3

DS3

401 0985_05f9_c1

Customer Premise DS0

DS1 DS0

3/1 DACS DS3

DS3

DS1

SONET ADM

SONET ADM

OC-3/12

Class-5 Switch

DS1

Transport

3/1 DACS

DS1

Local CO

Interexchange

OC-48

OC-48

OC-48

OC-3/12

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TDM Transport Efficiency Types of Traffic Voice

Utilization

PBX

Wasted Bandwidth

Legacy

50–60%

LAN

Video

Single WAN Link

Time Slot Assignments

• Wasted bandwidth • No congestion 401 0985_05f9_c1

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Packet Transport Efficiency Types of Traffic Voice PBX

Utilization

Q U E U E

Legacy

90–95%

LAN

Cells/Frames/Packets

Video

Individual Packets

• High bandwidth efficiency • Congestion management 401 0985_05f9_c1

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Delay Sender PBX

Receiver Network

PBX

First Bit Transmitted

Last Bit Received

A Processing Delay

A Network Transit Delay

t Processing Delay

End-to-End Delay 401 0985_05f9_c1

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Delay Variation—“Jitter” Sender

Receiver Network

A

B

C

Sender Transmits

t A

B

D1 401 0985_05f9_c1

D2 = D1

C

Sink Receives

D3 = D2

t

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© 1999, Cisco Systems, Inc.

Voice Delay Guidelines One Way Delay (msec)

Description

0–150

Acceptable for Most User Applications

150–400

Acceptable Provided That Administrations Are Aware of the Transmission Time Impact on the Transmission Quality of User Applications

400+

Unacceptable for General Network Planning Purposes; However, It Is Recognized That in Some Exceptional Cases This Limit Will Be Exceeded

ITU’s G.114 Recommendation 401 0985_05f9_c1

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Delay in Perspective Cumulative Transmission Path Delay CB Zone Satellite Quality Fax Relay, Broadcast

High Quality 0

100

200

300

400

500

600

700

800

Time (msec) Delay Target

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Fixed Delay Components Propagation Delay Serialization Delay— Buffer to Serial Link Processing Delay

• Propagation—Six microseconds per kilometer • Serialization • Processing Coding/compression/decompression/decoding Packetization 401 0985_05f9_c1

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Variable Delay Components Queuing Delay

Queuing Delay

Queuing Delay

Dejitter Buffer

• Queuing delay • Dejitter buffers • Variable packet sizes 401 0985_05f9_c1

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An Example • Assumptions: We have eight trunks We are going to use CS-ACELP that uses 8 Kbps per voice channel Our uplink is 64 Kbps Voice is using a high priority queue and no other traffic is being used 401 0985_05f9_c1

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Delay Calculation Los Coder Delay Queuing Delay Angeles 25 ms 6 ms Propagation Delay—32 ms

Dejitter Buffer 50 ms

Munich

(Private Line Network) Serialization Delay 3 ms Fixed Delay Coder Delay G.729 (5 msec Look Ahead) Coder Delay G.729 (10 msec per Frame) Packetization Delay—Included in Coder Delay

Variable Delay

5 msec 20 msec

21 msec

Max Queuing Delay 64 kbps Trunk Serialization Delay 64 kbps Trunk

3 msec

Propagation Delay (Private Lines)

32 msec

Variable Delay Component

Network Delay (e.g., Public Frame Relay Svc) Dejitter Buffer 401 0985_05f9_c1

Total

50 msec

110 msec 75 82

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Variable Delay Calculation • We have eight trunks, so in the worst case we will have to wait for seven voice calls prior to ours • To put one voice frame out on a 64Kbps link takes 3msec • 1 byte over a 64Kbps link takes 125 microseconds. We have a 20 byte frame relay frame with 4 bytes of overhead. 125 * 24 = 3000 usecs or 3 msec • Does not factor in waiting for a possible data packet or the impact of variable sized frames • Assumes voice prioritization of frames 401 0985_05f9_c1

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Delay Calculation Site B Fixed Delay

Variable Delay

Site A

Delay #1

DELAY #1 Coder Delay G.729 Packetization Delay

25 msec

(Included in Coder Delay) Max Queuing Delay 64 kbps Trunk Serialization Delay 64 kbps Trunk

3 msec

Propagation Delay (Private Lines) Dejitter Buffer

32 msec 50 msec

Private Line Network

21msec

Delay #2 Tandem Switch Delay #1 Total

— 110 msec

Site C 401 0985_05f9_c1

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Delay Calculation Site B Fixed Delay DELAY #1 Total

Variable Delay

Site A

Delay #1

110 msec

DELAY #2 Coder Delay G.729 Packetization Delay

25 msec

Private Line Network

(Included in Coder Delay) Max Queuing Delay 2 Mbps Trunk Serialization Delay 2 Mbps Trunk

0.1 msec

.7 msec

Propagation Delay (Private Lines) Dejitter Buffer

5 msec 50 msec

Delay #2 Total

80 msec

Total Delay

190 msec

Delay #2

Site C 401 0985_05f9_c1

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Other Useful Voice QoS Schemes in IP • Custom Queuing, Priority Queuing and Weighted Fair Queuing (WFQ) • Resource Reservation Protocol (RSVP) • IP Precedence Bit setting in the ToS Field of the IP Header • Compressed Real Time Protocol (CRTP) 401 0985_05f9_c1

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Summary • Voice traffic engineering principles still apply • Packet-based voice trunks can provide efficiency with high quality if properly engineered • The biggest impact on voice quality over a data network will be as a result of the delay and delay variation 401 0985_05f9_c1

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Repeat: Voice Is Not A Network

• Voice is an Application • Complete understanding of Voice Application fundamentals helps us to design and build better Networks

401 0985_05f9_c1

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Agenda • Basic Analog Telephony • Basic Digital Telephony • Voice Coding and Compression Techniques • Voice Transport and Delay • Supplemental Slides: Digital Voice Signaling Techniques 401 0985_05f9_c1

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Cisco Systems Confidential

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Digital Voice Signaling Techniques

• ISDN • Q.930/Q.931 • Signaling System 7 • Voice addressing

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ISDN • Integrated Services Digital Network Part of a network architecture Definition for the access to the network Allows access to multiple services through a single access

• Standards-based ITU recommendations Proprietary implementations 401 0985_05f9_c1

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Network Access Traditional Access Public Packet-Switched Network PSTN (CO Lines) 800 Tie Trunks FX Private Lne Data

Customer Equipment (PBX)

ISDN Access Customer Equipment (PBX)

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Telephone Switch

Public Packet-Switched Network PSTN (CO Lines) 800 Tie Trunks FX Private Line Data

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Terminology

• B channel “bearer channel” 64 kbps Carries information (voice, data, video, etc.) DS-0

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Terminology (Cont.)

• D channel “signaling channel” 16 Kbps or 64 Kbps Carries instructions between customer equipment and network Carries information Can also carry packet switch data (X.25) for the public packet switched network 401 0985_05f9_c1

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Terminology (Cont.)

• BRA/BRI (Basic Rate Access/ Basic Rate Interface) 2B+D 2 x 64 Kbps + 16 Kbps = 144 Kbps (not including overhead) Designed to operate using the average local copper pair 401 0985_05f9_c1

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Terminology (Cont.)

• PRA/PRI (Primary Rate Access/Primary Rate Interface) 23 B + D 23 x 64 Kbps + 64 Kbps (D Channel) + 8 Kbps (Frame Alignment bit) = 1.544 Mbps Designed to operate using T1/E1 In E1 environments: 30 B + D 401 0985_05f9_c1

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ISDN Reference Points TE1

.

TE1

NT1

S/T

.

TE2

.

BRA

U

TA

R TE1

Carrier

. . R S

TE2

TE2

.

TA

R

NT2 (PBX)

.T

. U

PRA

.

S

Customer Premises 401 0985_05f9_c1

NT1

Local Loop 90

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ISDN Reference Points

• NT1 Terminates local loop Coding and transmission conversion Maintenance and performance monitoring Functions as a CSU 401 0985_05f9_c1

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ISDN Reference Points (Cont.) • TE1 ISDN compatible equipment

• TE2 Non-ISDN compatible equipment Requires TA

• TA Interfaces available for different TE2 E.g. RS-232, X.21, V.35, PC-Bus, video, etc. 401 0985_05f9_c1

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ISDN Reference Points (Cont.)

• NT2 Typically a PBX Provides switching functions Handles Layer 2 and Layer 3 protocols

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Access to ISDN • At the S-reference point: RJ-45 (receive and transmit pair) Optional power can be provided for TE devices Distance: 1 Km (1 x TE only), 200 m (8 x TE), 500 m (4 x TE)

When more than one TE, wires act as a bus CSMA/CD

Limitation: cannot have an extension phone 401 0985_05f9_c1

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Access to ISDN • At the U-Reference point (BRA) Standards differ NA, France, UK vs. Germany vs. Japan In North America, designed to use as much of existing copper plant available Two wire, unloaded local loops are 99% of total Up to 5.5 Km loop length

• At the U-Reference point (PRA) T1/E1 standard 401 0985_05f9_c1

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D Channel • ISDN Access Protocols are carried in the D channel • Layer 2 and Layer 3 protocol specifications Protocol specifications are identical for BRA and PRA

• Layer 2, Q.920/921, LAP-D Supports the communications for Layer 3 Maintains the connections between devices

• Layer 3, Q.930/931 Call setup, call supervision, call tear down, and supplementary services Uses standard set of messages to communicate 401 0985_05f9_c1

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D-Channel Encapsulation

Layer 3

Layer 2

Protocol Length of Discriminator Call Reference

Flag

Address Control

Layer 1

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Call Reference

Message Type

Information

CRC

Information Elements

Flag

D Channel (16 Kbps or 64 Kbps)

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ISDN CCS (Q.930/931) Messages Call Establishment

Call Information

Call Clearing

• • • • • • •

• • • • • • • • • • • • •

• • • • •

Alerting Call proceeding Connect Connect ack Progress Setup Setup ack

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Hold Hold ack Hold reject Resume Resume ack Resume reject Retrieve Retrieve ack Retrieve reject Suspend Suspend ack Suspend reject User information

Disconnect Release Release complete Restart Restart ack

Miscellaneous • • • • • • •

Congestion control Facility Information Notify Register Status Status inquiry 98

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Public ISDN and Signaling System 7 Signaling Network BRI

PBX1

BRI

Switch

PRI

DSS1

Transmission Network

Switch

PRI

Signaling System 7

PBX2

DSS1

DSS1 Is a Public ISDN Protocol 401 0985_05f9_c1

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ISDN and SS7 “The Bridge Between the Islands” Voice Transmission STP

Switch

SSP

Switch

SSP

SS7

SCP

Signaling Network Voice Transmission

Switch

STP

STP

STP

STP

PBX1

SSP STP

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Voice and ISDN— Signaling PRI

SCP

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SS7 Components SCP

Network 1

SCP

SSP

Network 2

STP

STP

STP

STP

SCP SCP

SSP SSP

SSP

Voice Trunk Signaling Link 401 0985_05f9_c1

SSP: Signal Switching Point STP: Signal Transfer Point SCP: Signal Control Point 101

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Network Addressing

LEC 1-609-555-1234

IXC

555-1234

LEC

PSTN E.164 Addressing

1-609-5551234 Dials: 9+1-609-555-1234

555-1234

PBX PBX Dials: 8+555-1234

555-1234

555-1234

VCI/VPI

1234 1234

VCI/VPI

WAN 401 0985_05f9_c1

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Agenda • Basic Analog Telephony • Basic Digital Telephony • Voice Coding and Compression Techniques • Voice Transport and Delay • Supplemental Slides: Digital Voice Signaling Techniques 401 0985_05f9_c1

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Thank You!

•Q & A • Please Fill Out Evaluation Forms • THANK YOU!

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Please Complete Your Evaluation Form Session 401

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