Voice over Internet Protocol

Presenter: Devesh Patidar

August 2, 2009

Introduction• What is Voice Over Internet Protocol (VoIP)?

• The two-way transmission of audio over a packet-switched IP network.

• When used in a private intranet or WAN, it is generally known as 'voice over IP,' or 'VoIP.'

• When the transport is the public Internet or the Internet backbone from a major carrier, it is generally called 'Internet telephony’.

Introduction• Voice Over Internet Protocol (VoIP)

– History– Implementation– Service Types– Benefits– Drawbacks– Current and Projected Use

History of VoIP• Network Voice Protocol

– Created in 1973 by Danny Cohen at USC– Project Goals

• Wanted to create digital high-quality, low-bandwidth, secure voice handling capability

– Control Protocol– Data Transport Protocol

Circuit Switching• Current Phone Systems

• Dedicated line with a constant connection

• Originally very expensive

• Each call transmits at 64 kilobits per second– 64 kbps x 2 directions = 128 kbps– 128 kbps = 16 kilobytes per second– During a 10 minute call, about 10 MB– Highly inefficient

Circuit Switching• Example: Circuit Switching

Packet Switching• VoIP Phone Systems

• Connection only long enough to send a packet of information

• Thousands of possible paths for packet to go

• Network uses cheapest and least congested paths

• Quality of Service (QoS)

• A 10 minute call transfers only about 2 MB

Packet Switching• Example: Packet Switching

Quality of Service (QoS)• Defined in the International

Telecommunication Union standard X.902

• A set of quality requirements on the collective behavior of one or more objects.

• Control mechanisms to provide different priorities to different users or data flows

• Important for real-time streaming applications

VoIP Implementation• Sender picks up the phone

• Analog telephone adapter (ATA)– Data converted by a codec

• Soft Switch

• Receiver picks up ringing phone

• Data transfer during calls is handled by current internet infrastructure

Analog Telephone Adapter (ATA)

• Converts audio between analog and digital signals

• Need one on each end of the call

• Sends signal to handle connect and disconnect

Codecs• Coder-decoder or codecs

• Conversion from analog audio signal to digital signal

• Most common codec is the G.729A– sampling rate of 8,000 times per second

• Conjugate-structure Algebraic-code-excited Linear Prediction algorithm (CS-ACELP)

• Responsible for the large gap in performance

Soft Switches• Database mapping program

• Endpoint-to-Endpoint– Location– Phone Number– IP address

• Allows phones, computers, and WiFi phones to work together

Industry Protocol Standards• H.323 Protocol Suite

• Main flaw – not designed for VoIP

Industry Protocol Standards• Session Initiation Protocol (SIP)

– Smaller, more efficient– Designed specifically for VoIP

• Handles– User location– User capabilities– User availability – Call setup– Call handling

VoIP Service Types• Home Phones

– Requires an ATA– Usually provided for free

• IP Phones– ATA technology built in– Ethernet Phones– WiFi Phones

• Computer-to-Computer calls

Computer-to-Computer VoIP• Simplest and cheapest way to use VoIP• Requires

– Microphone– Speaker– Sound card– Broadband internet

• Costs: Software and ISP service• Calls: Free• Example: Skype Download Service

Benefits• Uses technology already in common use• Cost• Bundled Services

– Caller ID– Voice Mail– Call Waiting – Call Forwarding– Many Others

• Long Distance and International Rates

Benefits

Cost of Calls Made from US to Foreign Countries

Drawbacks• 911 Emergency Calls• Dependence on Wall Power• Latency issues, jitter, and packet loss• Viruses, worms, and hackers• Integration with land-line dependant

hardware– DVRs, digital television service, and home

security systems

Drawbacks• Security• Problems sending faxes• Dependence on Internet Service Providers• Requirement of broadband connectivity• WiFi hotspot dependence

Current and Projected Use• Roughly 6 million in US in 2006• Expected to climb to 24 million by the end of

2008• Increase in service providers

– Traditional phone companies• At&T, Sprint, Nextel, Time Warner, Reliance info.

– VoIP companies• Skype, Vonage, VoIP Inc.

Conclusion• VoIP will be a dominate force in the 21st

century• Probably at least another 10 years before

possibly replacing current phone systems• If the current flaws are fixed sooner rather

than later, it could be much sooner than a decade

Thank you