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Voice over IPVoice over IP
Habib UllahHabib Ullah
Pros & Cons
Voice over Internet Protocol
(VoIP) is a technology that
enables one to make and
receive phone calls through
the Internet instead of using
the traditional analogy
PSTN (Public Switched
Telephone Network) lines.
What is VoIP?
VoIP is packetisation and transport of
classic public switched telephone system
audio over an IP network.
It allows 2-way voice transmission over
It is also called IP telephony, internet telephony, voice over
broadband, broadband telephony.
PSTN vs. INTERNET
Voice network use circuit
Dedicated path between
calling and called party.
Bandwidth reserved in
Cost is based on distance
Data network use packet
No dedicated path between
sender and receiver.
It acquires and releases
bandwidth, as it needed.
Cost is not based on
distance and time.
Circuit Switched Networks (Voice)
Packet Switched Networks (Data)
• Separated networks
• Separated applications/services
• Converged network
• Separated or integrated applications
VoIP – How does it work?
Converting the voice signal
ADC (analog to digital)
DAC (digital to analog)
Voice (source) - - ADC - - - Internet - - - DAC - -Voice (dest)
Transmission of voice traffic in packets
VoIP – How does it work?
The 1-2-3s of VoIP
1. Compression – voice is compressed
typically with one of the following codecs, G7.11
64k, G7.29AB 8k, G723.1 6.3k
2. Encapsulation – the digitized voice is
wrapped in an IP packet
3. Routing – the voice packet is routed thru
the network to its final destination
VoIP Network Model
RTP, RTCP, RTSP
Transport Layer (UDP, TCP)
Network Layer (IP, IP Multicast)
Data Link Layer
IP Protocol LayeringIP Protocol Layering
Physical Transport (e.g, Cable Modem)
IP (Internet Protocol)
Applications (e.g., email, web pages)
Email Data (1000 bytes)TCP Header
A Typical IP Datagram
A VoIP gateway is a gateway device that uses Internet
Protocols to transmit and receive voice communications
Codecs are used to convert an analog voice signal to
digitally encoded version. Codecs vary in the sound
quality, the bandwidth required, the computational
Do Companies Want VoIP?
76% Will!76% Will!
Not at all
Network World asked 500 readers to assess
whether they would consider using voice over IP:
Key Business Drivers for LAN-Based Telephony and VoIP
0 50 100
Save MoneySave Money
Better Utilization of BandwidthBetter Utilization of Bandwidth
Support MultimediaSupport Multimedia
Improve Network ManagementImprove Network Management
AsVoIP uses the Internet, for example, it is vulnerable to
the same type as security risks
Denial of service