Introduction

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Introduction Chapter 1

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Introduction. Chapter 1. Instructor Ming-Feng Chang, [email protected] EC 425, 5731812 Textbook “ Carrier Grade Voice over IP. ” D. Collins, 2nd ed., McGraw-Hill, 2003. Additional technique reports and papers Requirements Homework and machine problems25% - PowerPoint PPT Presentation

Transcript of Introduction

Page 1: Introduction

Introduction

Chapter 1

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2Internet Telephony

Instructor Ming-Feng Chang, [email protected] EC 425, 5731812

Textbook “Carrier Grade Voice over IP.” D. Collins, 2nd ed.,

McGraw-Hill, 2003. Additional technique reports and papers

Requirements Homework and machine problems 25% One mid-term exam                45% One term project                    30%

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Telephone

1876 Alexander Graham Bell transfered voice over wire for the first time.

Direct connection; telephones are sold in pair

A

B D

E

F

C

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Switches

As the number of users increases, switching centers are more economical

A

B D

E

F

C

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Digital Switches

Took more than 100 years from analog to digital voice transmission

Better quality for long distance calls

Demands to telephone network become constantly higher

World-wide communication network

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Mobile Communications

Bell Laboratories introduced the idea of cellular communications in 1947

Motorola and Bell Labs in the 60s and early 70s were in a race to design portable devices

Dr. Cooper, 2-pound Motorola handset (1973)

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The Internet

Data Networks since 1960’s ARPA*-Net 1969 Internet since early 1990’s

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What is VoIP?

Use a LAN and/or WAN to carry voice in the same way as the telephone system.

Why? Save costs Improve facilities.

IP WAN/INTERNET

VoIP

VoIP

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VoIP Gateway

The interface between VoIP and PSTN

•An essential feature for VoIP

Internet

PSTN to IPGateway

POTSVoIP

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Cheap phone-cards/voice carriers

IP Network(with QoS for voice)

PSTN to IPGateway

POTS

PSTN to IPGateway

POTS

e.g.Australia

e.g. UK

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Carrier Grade VoIP

Carrier grade and VoIP mutually exclusive A serious alternative with enhanced features

Carrier grade The last time when it fails 99.999%, five-nines reliability Verizon network supports 70M voice access

lines AT&T serves 300M voice calls a day Short call setup time, high speech quality no perceptible echos, noticeable delay or

annoying noises Self-healing, highly scalable and manageable

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VoIP

Transport voice traffic using IP Voice over the Internet?

Interconnected networks Applications: e-mail, file transfer, e-com

The greatest challenges Voice quality and bandwidth Control and prioritize the access

Internet: best-effort transfer The next generation VoIP != Internet telephony

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IP

A packet-based protocol Routing on a packet-by-packet base

Packet transfer with no guarantees May not receive in order May be lost ore severely delayed

TCP/IP Retransmission Assemble the packets in order Congestion control Useful for file-transfers and e-mail

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Data and Voice

Data traffic Asynchronous – can be delayed Extremely error sensitive

Voice traffic Synchronous – the stringent delay

requirements More tolerant of errors

IP is not for voice VoIP must

Match the PSTN Offer new and attractive capabilities at a

lower cost

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Why VoIP?

Why carry voice? Internet support instant access to anything

Everything can be done on the net? “Dot-com guy” Many new services and applications

However, voice services provide more revenues

Why use IP for voice? Why try to fix something that is not broken? Circuit-switching is not for datacom IP

Equipment cost, integrated access, less bandwidth, and widespread availability

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Lower Equipment Cost

PSTN switch Proprietary – hardware, OS, applications High operation and management cost Training, support and feature development cost

Mainframe computer The IP world

Standard hardware and mass-produced Application software is quite separate A horizontal business model

IN does not match the openness and flexibility of IP A few highly successful services

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Moore’s Law Processing power doubles every 18 months Frame 10 Router 20 ATM 40 Circuit 80

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Voice/Data Integration

Click to talk application Personal communication E-commerce CTI – Computer Telephony Integration

Web collaboration Shop on-line with a fried at another location

Video conferencing IP-based PBX IP-based call centers

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Lower Bandwidth Requirements

PSTN G.711 - 64 kbps Human speech bandwidth < 4K Hz The Nyquist Theorem: sample rate twice the bandwidth 8K * 8 bits

Sophisticated coders 32kbps, 16kbps, 8kbps, 6.3kbps, 5.3kbps GSM – 13kbps Save more by silence-detection

Traditional telephony networks can use coders too

But it is difficult So many switches

VoIP – two ends of the call negotiate the codec

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The Widespread Availability of IP

IP LANs and WANs The ubiquitous presence

VoFR or VoATM Only for the backbone of the carriers

Voice over WLAN Voice over WiFi for now Voice over WiMax could be a real threat for PLMN

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The VoIP Market

The revenue projection Value-added service

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Revenue breakdown VoIP Fax over IP

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VoIP Challenges

Speech quality Must be as good as PSTN Delay

The round-trip delay International calls through satellite – 500-600 ms G.114 – < 300 ms

Jitter Delay variation Different routes or queuing times Adjusting to the jitter is difficult Jitter buffers add delay

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Packet loss Traditional retransmission cannot meet the real-time

requirements Packets must be played in order

Speech-coding techniques MOS, Mean Opinion Score >= 4 P.800, but subjective in nature G.711 64kbps 4.3 G.726 32kbps 4.0 G.723 (celp) 6.3kbps 3.8 G.728 16kbps 3.9 G.729 8kbps 4.0 GSM 13kbps 3.7 iLBC 13.33/15.2kbps high robustness

to packet loss iSAC 10-32kbps wideband codec

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Network Reliability and Scalability

PSTN system fails Five-nines reliability

The office computer network fails Today’s VoIP solutions

Redundancy and load sharing Scalable too – easy to start small and expand Fiber-optic transport, gigabit router, high-speed

ATM base

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Managing Access and Prioritizing Traffic

A single network for a wide range of applications

Call admitted if sufficient resources available

Different types of traffic are handled in different ways

QoS has required huge efforts

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VoIP Implementations

IP-based PBX solutions A single network Enhanced services

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IP voice mail One of the easiest applications

Hosted PBX solutions For SOHO Internet and telephony access

IP call centers Use the caller ID Automatic call distribution Load the customer’s information on the

agent’s desktop Click to talk

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IP user devices VoIP protocols, SIP Integrated functions

Telephony, WWW, e-mail, voice mail, address-book

WiFi phone

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Skype A peer-to-peer VoIP client developed

by KaZaa in 2003 Skype can

work almost seamlessly across NATs and firewalls has better voice quality than the MSN and Yahoo IM

applications encrypts calls end-to-end, and stores user information

in a decentralized fashion SkypeOut, SkypeIn

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New applications

The networks are converging Possible applications

Video Phones Conferencing Collaboration Tools Distance Learning / Training Tele-medicine, tele-repair, tele-… On-line gaming Dating Applications

Skype is rolling out developer kits and programs to encourage innovation, similar to the wireless industry promoting application development on their platforms

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Why Internet Telephony?

The business case Integration of voice and data Bandwidth consolidation Tariff arbitrage

Universal presence of IP Maturation of technologies The shift to data networks

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VoIP Spectrum

Traditional Telecomm Segments in transition to VoIP International Low cost calling Internal networks of large carriers Numerous equipment makers, software providers Residential VoIP phone service

This area is exploding: Vonage, Packet8, Broadvoice … Office PBX systems

Using VoIP inside a company location, and between corporate branches

Call Center Instant Messaging

Not only the traditional big 3, but newcomers like Skype … Consumer and Business Application Areas

Voice applications Wireless Internet applications

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Course Overview

VoIP and RTP Voice codecs H.323 SIP – simple and flexible MGC and softswitch SS7, UMTS QOS Voice over WLAN P2P IP communications Charging and payments


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