Voice over IPVoice over IP

Habib UllahHabib Ullah

12-MS-CSc-1212-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. INTERNETPSTN

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 NetworksCircuit Switched Networks (Voice)

COPBX

CO CO

Packet Switched Networks (Data)Router

RouterRouter

Router

Router

• Separated networks• Separated applications/services

PBX

IP Phone

Converged Network

PSTN

CO

Gateway

RouterRouter

RouterRouter

• 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

LTS©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

SIPRTP, RTCP, RTSP

Transport Layer (UDP, TCP)Network Layer (IP, IP Multicast)

Data Link LayerPhysical Layer

PURC 2004

IP Protocol LayeringIP 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!

Unsure

4%Not at all

likely

4%Not very

likely

16%

Likely

28%

Very likely

32%

Extremely

likely

16%

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 MoneySave Money

Better Utilization of BandwidthBetter Utilization of Bandwidth

Support MultimediaSupport Multimedia

Improve Network ManagementImprove 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?