Abdellatif O. Abdellatif
Sudatel Telecom Group
Voice
Over
IP
1
Why An Organization Would Use IPT
2
Definition
3
IP Telephony QoS
4
How Your Voice Becomes A Packet
5
MOS
6
SIP & H.323
7
Contrast between PSTN and NGN / Smooth Migration
Why an organization would use IPT
Trackable Cost Saving :
o Moves, Adds, and Changes (MACS)
o Bandwidth and equipment efficiency
o Lower cost of transmission
o New applications and devices
1
Why An Organization Would Use IPT
2
Definition
3
IP Telephony QoS
4
How Your Voice Becomes A Packet
5
MOS
6
SIP & H.323
7
Contrast between PSTN and NGN / Smooth Migration
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
ISP
Internet
ISP
PSTN
USER A
PSTN
USER B
USER
BModem
Modem
Server
PC-to-Phone
IP Telephony
Provider
ISP
Internet
IPTP
Gateway
PSaTN
PSTN
USER A
Modem
USER B
Phone-to-Phone
Management IP Network
Gateway
Gateway
Network of IP Telephony Service
Provider
PSTN
USER A USER B
USER B
USER B
USER A
PSTN
Public Switched
Telephone Network
Initially, PC to PC
voice calls over the
Internet
Gateways allow PCs
to also reach phones
PSTN
Gate
way
Multimedia
PC
IP Network
Gate
way
PSTN
Multimedia
PC
…or phones to reach
phones
1
Why An Organization Would Use IPT
2
Definition
3
IP Telephony QoS
4
How Your Voice Becomes A Packet
5
MOS
6
SIP & H.323
7
Contrast between PSTN and NGN / Smooth Migration
IP Telephony QoS
Packet loss (%)
10
9
8
Unacceptable for
Voice or Fax
7
ITU G.114
Utility
Recommendation
6
5
4
3
2
Possibly Tolerable
for Voice
Operational Target
for Voice and Fax
1
0
10
0
20
0
30
0
40
0
50
0
Delay (ms)
The Three Current Models OF QOS
o Best Effort
o Integrated Services (INTSERV )
o Differentiated Services (DIFF SERV)
QoS: Delays-1
1

Coding delay
2
Receiver Delay:
Decoding delay
Packeting delay
DePacketing delay
Transmission delay …
Receiver delay …
3
4
5
6
IP Network

Network Delay
Sender Delay:
1
3
5
Loss Packet
T"#T’#T
T
Sender
Network
Receiver
4
6
Delay-2
Fixed Delay Components
• Propagation
• Serialization
• Processing: (coding, compression, decompression, decoding)
Delay-3
Variable Delay Components
• Queuing delay
• Dejitter buffers
• Variable packet sizes
1
Why An Organization Would Use IPT
2
Definition
3
IP Telephony QoS
4
How Your Voice Becomes A Packet
5
MOS
6
SIP & H.323
7
Contrast between PSTN and NGN / Smooth Migration
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
1
Why An Organization Would Use IPT
2
Definition
3
IP Telephony QoS
4
How Your Voice Becomes A Packet
5
MOS
6
SIP & H.323
7
Contrast between PSTN and NGN / Smooth Migration
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
1
Why An Organization Would Use IPT
2
Definition
3
IP Telephony QoS
4
How Your Voice Becomes A Packet
5
MOS
6
SIP & H.323
7
Contrast between PSTN and NGN / Smooth Migration
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
Gatekeeper
Multipoint
Control Unit
Circuit
Switched
Networks
Packet Based
Network
Gateway
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
SIP Components
Location
Server
Redirect
Server
Registrar
Server
PSTN
User Agent
Gateway
Proxy
Server
Proxy
Server
Contents
1
Why An Organization Would Use IPT
2
Definition
3
IP Telephony QoS
4
How Your Voice Becomes A Packet
5
MOS
6
SIP & H.323
7
Contrast between PSTN and NGN / Smooth Migration
Smooth Migration
Soft switch
Tandem /toll
exchange
Packet core
network
LE
IN
App Server
NMS
Soft switch
ISUP
STP
LE
Policy Service
Soft switch
Packet core
network
SG
TMG
WMG
switch
PSTN
AMG
IAD
PC
Phone
SIP
H.323
Phone Phone
PLMN
Contrast between PSTN and NGN
Intelligent Service Server
SoftSwitch
Service Server
CPU
Switching Array
Signaling
Module
IP Core
Trunk Module
SS7
Signaling
Gateway
User
Access Module
Trunk
Gateway
Trunk
Gateway
Trunk
Gateway
User Access
Gateway
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.htm
o http:// communication howstuffworks.com/iptelephony
o http://www.networkmagazine.com/encyclopedia/
search?term=IPtelephony
o CCNA_voice_cbt_nuggets
o CCNP-ngts-VoIP
Thanks!!!