Abdellatif O. Abdellatif Sudatel Telecom Group

Voice Over

IP

6

7

1 Why An Organization Would Use IPT

3 IP Telephony QoS

4 How Your Voice Becomes A Packet

5 MOS

2 Definition

Contrast between PSTN and NGN / Smooth Migration

SIP & H.323

Why an organization would use IPT

Trackable Cost Saving :o Moves, Adds, and Changes (MACS)o Bandwidth and equipment efficiencyo Lower cost of transmission o New applications and devices

6

7

2 Definition

3 IP Telephony QoS

4 How Your Voice Becomes A Packet

5 MOS

Contrast between PSTN and NGN / Smooth Migration

SIP & H.323

1 Why An Organization Would Use IPT

Definition

• IP Telephony– Transmission of voice, fax, and related services

over packet-switched IP- based networks.• Internet Telephony

– Specific sub-set of IP Telephony in which the principal transmission network is the public Internet.

– Voice-over-the-Net (VoN); Internet Phone; Net Telephony.

Definition

• Voice-over-IP (VoIP)– Specific sub-set of IP Telephony in which the

principal transmission network(s) is (are) private, managed IP-based network(s).

– Voice-over-DSL (VoDSL)

IP Telephony

Instead of using traditional circuit switch systems for voice communications, IP Telephony uses a packet protocol originally designed for data communications

Circuit Switched - PSTN

Packet Switched – Data Network

Configuration Options PC-to-PC

PSTN

Internet ISP

Modem

USER B

Server

PSTN

ISP

USER BModem

USER A

PC-to-Phone

PSaTN

PSTN

InternetISP IPTP

Modem

USER A

USER B

Gateway

IP Telephony Provider

Phone-to-Phone

PSTN

USER A USER B

USER B

Gateway

Network of IP Telephony Service Provider

PSTN

USER B

USER A

Gateway

Management IP Network

IP NetworkMultimedia PC

Multimedia PC

Initially, PC to PC voice calls over the

Internet

PSTN

Gateway

PSTN

Gateway

Public Switched Telephone Network

Gateways allow PCs to also reach phones

…or phones to reach phones

6

7

4 How Your Voice Becomes A Packet

5 MOS

2 Definition

Contrast between PSTN and NGN / Smooth Migration

SIP & H.323

3 IP Telephony QoS

1 Why An Organization Would Use IPT

IP Telephony QoS

100

200

300

400

500

0

4

3

5

2

1

9

8

10

7

6

Operational Target for Voice and Fax

Possibly Tolerable for Voice

Unacceptable for Voice or Fax ITU G.114

Utility Recommendation

Delay (ms)

Packet loss (%)

The Three Current Models OF QOS

o Best Effort

o Integrated Services (INTSERV )

o Differentiated Services (DIFF SERV)

QoS: Delays-1

1 2 3 4 5 6 1 3 5 4 6

T

Loss Packet

T"#T’#T

IP N

etw

ork

Network Delay

SenderNetwork

Receiver

Sender Delay:

Coding delay

Packeting delay

Transmission delay …

Receiver Delay:

Decoding delay

DePacketing delay

Receiver delay …

Delay-2

Fixed Delay Components

• Propagation• Serialization• Processing: (coding, compression, decompression, decoding)

Delay-3

Variable Delay Components

• Queuing delay• Dejitter buffers• Variable packet sizes

6

7

5 MOS

2 Definition

Contrast between PSTN and NGN / Smooth Migration

SIP & H.323

4 How Your Voice Becomes A Packet

1 Why An Organization Would Use IPT

3 IP Telephony QoS

How Your Voice Becomes A Packet

• Voice Encoding : Analog to Digital• The Nyquist Theorem• Quantization and Quantization Techniques• Compressing Voice

- compression Techniques

- CODECs

How to Turn Voice Into Bits

The 4 Step Recipe :

1. Take Many Sample Of The Analog Signal

2. Calculate A number Representing Each Sample (quantization )

3. Convert The Number To Binary

4. (Optional) compression

The Nyquist Theorem

• A tribute to Dr Nyquist

o The Nyquist Theorem :

“ if you sample a signal in regular intervals at least twice the highest Channel frequency the samples will contain enough information to accurately reconstruct the signal”

The Nyquist Theorem

o Some Important Frequencies :

The Human Ear : 20-20,000 Hz

Human speech : 200- 9,000 Hz

Telephone Channels : 300- 3, 400 Hz

Nyquist Theorem : 300- 4,000 Hz

Quantization Techniques

o Waveform Algorithms ( Encode everything )

- PCM

- AD PCM

o Source Algorithms ( Encode changes )

- CS- ACELP

- LDCELP

CODECs

• Waveform CODECs

- G.711 Uses PCM coding and chomps up 64 kbps

- G.726 Used AD PCM Coding and eats 32 kbps

… or 24 kbps

… or 16 kbps

6

7

2 Definition

Contrast between PSTN and NGN / Smooth Migration

SIP & H.323

5 MOS

1 Why An Organization Would Use IPT

3 IP Telephony QoS

4 How Your Voice Becomes A Packet

Mean opinion score MOS How Good Do They Sounds ? Based On Mean Opinion Score Scale Of 1-5 Toll Quality Is 4,0 MOS

Compression Method Bit Rate(kbps ) MOS score Compression delay (ms)

G.711 PCM 64 4.1 0.75

G.726 ADPCM 32.0 3.2 1

G.728 LD-CELP 16.0 3.61 3-5

G.729 CS-ACELP 8 3.92 10

G.729a CS-ACELP 8 3.7 10

G.723 1 MP-MLQ 06.3 3.9 30

G.723 1 ACELP 05.3 3.65 30

iLBC 15.2 4.1

DSP

o Digital signal processors are the engines behind a voice network

o Perform the following:

- Analog to digital conversion

- conferencing

- Echo cancellation

- Voice activity Detect

- Comfort noise

- Transcoding

7

2 Definition

Contrast between PSTN and NGN / Smooth Migration

6 SIP & H.323

1 Why An Organization Would Use IPT

3 IP Telephony QoS

4 How Your Voice Becomes A Packet

5 MOS

IP Telephony Signaling Protocols: H.323

Describes terminals and other entities that provide multimedia communications services over Packet Based Networks (PBN) which may not provide a guaranteed Quality of Service.

H.323 entities may provide real-time audio, video and/or data communications.

H.323 Components

Gateway

Multipoint Control Unit

Gatekeeper

Circuit Switched Networks

Packet Based Network

Terminal

SIP: Session Initiation Protocol

Session Initiation Protocol - An application

layer signaling protocol that defines initiation,

modification and termination of interactive,

multimedia communication sessions between

users.

IETF RFC 2543 Session Initiation Protocol

SIP Distributed Architecture

Redirect Server

Location Server

Registrar Server

User AgentProxy Server

Gateway

SIP Components

Proxy Server

PSTN

Contents

2 Definition

Contrast between PSTN and NGN / Smooth Migration

1 Why An Organization Would Use IPT

3 IP Telephony QoS

4 How Your Voice Becomes A Packet

5 MOS

6 SIP & H.323

7

Smooth Migration

Tandem /toll exchange

LE

Packet core network

LE

Soft switch

IN NMS App Server Policy Service

ISUP SG

PSTN

switch

STPTMG

PLMN

WMG

SIPPhone

H.323Phone

PCPhone

IADAMG

Packet core network

Soft switchSoft switch

Contrast between PSTN and NGN

SignalingModule

Trunk Module UserAccess Module

Service ServerSoftSwitch

TrunkGateway

TrunkGateway Trunk

Gateway

SS7SignalingGateway

User AccessGateway

CPU

Switching Array

Intelligent Service Server

IP Core

Final Thoughts

• One approach, which is hotly debated in the VoIP market, is to rip out your old PBX, phones and wiring and replace everything with IP phones. That might work in some cases, particularly where the old PBX is long past its expiration date, but it isn't always the best approach.

• Consider deploying IP Telephony based on a Phased Approach

• Understand the benefits that the technology offers, not just the costs

• Have a Plan

References

o http://www.protocols.com/papers/voip.htmo http:// communication howstuffworks.com/ip-

telephonyo http://www.networkmagazine.com/encyclopedia/

search?term=IPtelephonyo CCNA_voice_cbt_nuggetso CCNP-ngts-VoIP

Thanks!!!