bài thuyết trình về Voip

Voice over IP
Voice over IP
Habib Ullah
Habib Ullah
12-MS-CSc-12
12-MS-CSc-12
Contents

Abstract

What is VoIP

How VoIP works

VoIP Architecture

Components

Pros & Cons

Summary
Abstract

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
broadband connection.

It is also called IP telephony, internet telephony, voice
over broadband, broadband telephony.
PSTN vs. INTERNET
PSTN

Voice network use circuit
switching.

Dedicated path between
calling and called party.

Bandwidth reserved in
advance.

Cost is based on distance
and time.
INTERNET

Data network use packet
switching.


No dedicated path between
sender and receiver.

It acquires and releases
bandwidth, as it needed.

Cost is not based on
distance and time.
PBX
Yesterday’s Networks
Circuit Switched Networks (Voice)
CO
PBX
CO
CO
Packet Switched Networks (Data)
Router
Router
Router
Router
Router
• Separated networks
• Separated applications/services
PBX
IP Phone
Converged Network
PSTN
CO
Gateway
Router

Router
Router
Router
• Converged network
• Separated or integrated applications
PBX
IP Phone
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

LT
S
©Telcordia Technologies, Inc.
Slide 10
IP Network
Multimedia
PC
Multimedia
PC
Initially, PC to PC
voice calls over the
Internet
VoIP Architecture?
PSTN
(DC)
Gateway
PSTN
(NY)
Gateway
Public Switched
Telephone Network
Gateways allow PCs
to also reach phones
…or phones to reach
phones
Components

VoIP Protocols

VoIP Gateway


VoIP Codecs
VoIP Network Model
SIP
RTP, RTCP, RTSP
Transport Layer (UDP, TCP)
Network Layer (IP, IP Multicast)
Data Link Layer
Physical Layer
PURC 2004
IP Protocol Layering
IP Protocol Layering
Physical Transport (e.g, Cable Modem)
IP (Internet Protocol)
TCP UDP
Applications (e.g., email, web pages)
Email Data (1000 bytes)
TCP Header
(20 bytes)
IP Header
(20 bytes)
A Typical IP Datagram
VoIP SIP
VoIP Gateway

A VoIP gateway is a gateway device that
uses Internet Protocols to transmit and receive
voice communications (VoIP).
VoIP Codecs


Codecs are used to convert an analog voice
signal to digitally encoded version. Codecs vary
in the sound quality, the bandwidth required, the
computational requirements, etc.
Do Companies Want VoIP?
76% Will!
76% Will!
Network World asked 500 readers to assess
whether they would consider using voice over IP:
Key Business Drivers for LAN-Based Telephony and VoIP
81%
81%
59%
59%
38%
38%
26%
26%
0 50 100
Save Money
Save Money
Better Utilization of Bandwidth
Better Utilization of Bandwidth
Support Multimedia
Support Multimedia
Improve Network Management
Improve Network Management
Security Risks


As VoIP uses the Internet, for example, it is
vulnerable to the same type as security risks

Hacking

Denial of service

Eavesdropping
Summary
Questions?