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!!!
Top Related