Introduction to VoIPIntroduction to VoIP

Dr. Farid Farahmand Dr. Farid Farahmand

CET479CET479Updated 5/15/2007Updated 5/15/2007

OutlineOutline

What is VoIP?What is VoIP? Voice-Over-IP (VoIP)Voice-Over-IP (VoIP)

• Sounds like (toy-p!)Sounds like (toy-p!)• Transport of voice traffic using the Transport of voice traffic using the Internet ProtocolInternet Protocol (IP) (IP)• Not necessarily IP – But only IP provides ubiquitous presenceNot necessarily IP – But only IP provides ubiquitous presence

VoFR (Voice-over frame relay)VoFR (Voice-over frame relay) VoATM VoATM

• Also referred to as IP Telephony (IPT)Also referred to as IP Telephony (IPT) IPT traditionally referred to LAN-based VoIPIPT traditionally referred to LAN-based VoIP

VoIP three major challenges VoIP three major challenges • Voice quality due to available bandwidth Voice quality due to available bandwidth • The Internet, inherently, does not provide the best managed The Internet, inherently, does not provide the best managed

networknetwork No network managementNo network management No Quality-of-Service (QoS) solutionsNo Quality-of-Service (QoS) solutions No Service-level agreement (SLAs) between users No Service-level agreement (SLAs) between users

• Security issues are also importantSecurity issues are also important

A Short Introduction – A Short Introduction – Transmitting VoiceTransmitting Voice

The first telephone invented in 1876 by Alexander Graham Bell The first telephone invented in 1876 by Alexander Graham Bell The first phone company started in 1879 (AT&T)The first phone company started in 1879 (AT&T)

• Slogan: A phone for every single household!Slogan: A phone for every single household! Early phones where analog-based with analog transmissionEarly phones where analog-based with analog transmission

• Noisy when calling long distance Noisy when calling long distance • Amplification of the signal caused more noise Amplification of the signal caused more noise

First phone systems where point-to-pointFirst phone systems where point-to-point• Referred to as POTS (Plain old telephone service) Referred to as POTS (Plain old telephone service)

Later switches where introduced Later switches where introduced • PSTN: Public switched telephone networkPSTN: Public switched telephone network

Then came digital telephonyThen came digital telephony• Voice signals can be digitizedVoice signals can be digitized

The existing telephone system is a circuit-based switched networkThe existing telephone system is a circuit-based switched network• Circuits must be established between users prior to their Circuits must be established between users prior to their

communication communication • Circuits are in place even if no data is passing through Circuits are in place even if no data is passing through

Analog TechnologyAnalog Technology

Analog TechnologyAnalog Technology

•Trunks: A line or link designed to handle many signals simultaneouslyTrunks: A line or link designed to handle many signals simultaneously•PSTN: Public Switched Telephone Network - Collection of interconnected voice-oriented public telephone networksPSTN: Public Switched Telephone Network - Collection of interconnected voice-oriented public telephone networks•Circuit Switching: Physical path is obtained for a single connection / Connection-orientedCircuit Switching: Physical path is obtained for a single connection / Connection-oriented

SLIC. Subscriber-Loop-Interface-Circuit: A telephone line interface

Call routing in PSTNCall routing in PSTN

(p.26)(p.26)

Local Switch Regional Switch Long distance switch regional Local

A Little History – Digital TechnologyA Little History – Digital Technology Analog to Digital ConversionAnalog to Digital Conversion

• Pulse Amplitude Modulation (PAM)Pulse Amplitude Modulation (PAM)• Pulse Code Modulation (PCM)Pulse Code Modulation (PCM)• The output of ADC has only two states The output of ADC has only two states

which are called Binary in form of 1’s which are called Binary in form of 1’s and 0’sand 0’s

Digital Packets Digital Packets • Small units of data (ones and zeros) Small units of data (ones and zeros)

routed through the network with routed through the network with destination address within each packetdestination address within each packet

Voice Conversion to DigitalVoice Conversion to Digital

A Little History – A Little History – Packetizing VoicePacketizing Voice

The concept of packetized voice The concept of packetized voice goes back to 1974 goes back to 1974 • No Internet; just sending voice No Internet; just sending voice

signals in packet form between signals in packet form between two universitiestwo universities

Based on Packet Switching Based on Packet Switching concepts concepts • Data path is shared and Data path is shared and

connectionlessconnectionless• No longer dedicated paths as in No longer dedicated paths as in

circuit switching circuit switching First Internet Telephony software First Internet Telephony software

platform (Softphone) introduced platform (Softphone) introduced in 1994in 1994

Initial VOIP systems where phone-Initial VOIP systems where phone-centriccentric• Using the PSTN to get connected Using the PSTN to get connected

to the Internetto the Internet

Internet

PSTN (Circuit Switching)

Modem Modem

PC PC

Call routing across a VoIP networkCall routing across a VoIP network

Long distance calls can be carried on the Long distance calls can be carried on the dedicated dedicated networknetwork

PSTN can be used for local callsPSTN can be used for local calls PSTN PSTN gateway interfacegateway interface is POTS/T1/DSL/ISDN-PRI is POTS/T1/DSL/ISDN-PRI

Internet Access using other Internet Access using other networksnetworks

ISDN –PRI/ interface with the

PSTN along w/Gateway

Renting the dedicated

linesInter

network

Internet

VoIP Motivation VoIP Motivation

Network convergence Network convergence • Having a single infrastructure! Having a single infrastructure! • Bringing together two or more diverse Bringing together two or more diverse

networks networks • Integrating Voice and data networksIntegrating Voice and data networks

Voice is still the killer application / Voice is a Voice is still the killer application / Voice is a major business! / Largest portion of major business! / Largest portion of revenues still come from voice servicesrevenues still come from voice services

Data applications are growing and new Data applications are growing and new services are emergingservices are emerging

Unifying the network so the Unifying the network so the voice transmission is seamlessvoice transmission is seamless

Why Voice over IP?Why Voice over IP? Circuit switching was designed for voiceCircuit switching was designed for voice

• Expensive yet solidExpensive yet solid Today's networkToday's network

• Many new applications have emerged (email, web, video, IM, etc.)Many new applications have emerged (email, web, video, IM, etc.)• Higher network flexibility is demanded by providers (mix-and-matching Higher network flexibility is demanded by providers (mix-and-matching

equipments)equipments) Offering a single network for wide range of applications Offering a single network for wide range of applications IP is an attractive choice for voice transport IP is an attractive choice for voice transport

• Lower equipment & operation costsLower equipment & operation costs Openness and standardized equipment Openness and standardized equipment Full compatibility Full compatibility Distributed network rather than centralized Distributed network rather than centralized

• Integration of voice and data applications Integration of voice and data applications Providing more advanced services Providing more advanced services Calling from your web browser? Calling from your web browser?

• Potentially lower BW requirements Potentially lower BW requirements VoIP transmission is inherently more transmission efficient VoIP transmission is inherently more transmission efficient Development of new coding schemes (can also be used for PSTN!)Development of new coding schemes (can also be used for PSTN!)

• Widespread availability of IP Widespread availability of IP only IP provides ubiquitous presenceonly IP provides ubiquitous presence Other alternatives are Other alternatives are VoFR (Voice-over frame relay) and VoATM VoFR (Voice-over frame relay) and VoATM

Spend the money on better

circuit-basedTelephone systems?

VoIP MarketVoIP Market According to the second quarter update of the US VoIP Report from According to the second quarter update of the US VoIP Report from

TeleGeography.com, 1.23 Million new customers signed up for wire-line replacement TeleGeography.com, 1.23 Million new customers signed up for wire-line replacement VoIP services during the second quarter of 2006. VoIP services during the second quarter of 2006.

www.voipwiki.com/blog/?cat=34

It pays to know about VoIP!

VoIP MarketVoIP Market

There were 5.1 There were 5.1 million cable million cable voice users at voice users at the end of the end of 2005, up 63% 2005, up 63% annuallyannually

http://gigaom.com/2006/02/27/cable-voip-hotter-than-ever/

VoIP Challenges VoIP Challenges

Offering credible alternative to Offering credible alternative to traditional circuit-switched telephony traditional circuit-switched telephony • High reliability High reliability

Five nine availability (99.99999%)Five nine availability (99.99999%)

• High quality of voice High quality of voice Toll-quality Toll-quality 4.0 or better4.0 or better

• High level of security High level of security

ITU-U Recommendation (P.800)1-bad2-Poor3-Fair4-Good 5-Excellent

Speech Quality Speech Quality Data traffic characteristicsData traffic characteristics

• Asynchronized (it can tolerate delay)Asynchronized (it can tolerate delay)• Sensitive to packet loss (ACK is required)Sensitive to packet loss (ACK is required)

Voice traffic characteristicsVoice traffic characteristics• Considered as a real time application Considered as a real time application • Very sensitive to delay Very sensitive to delay • Fewer than 5 percent loss can be toleratedFewer than 5 percent loss can be tolerated

Speech quality Speech quality • Delay Delay • JitterJitter• Packet lossPacket loss

Speech Quality - DelaySpeech Quality - Delay

Voice packets are very sensitive to delayVoice packets are very sensitive to delay• Less than 300 msec for telephonyLess than 300 msec for telephony• In case of satellite communications: In case of satellite communications:

2x120 msec + 200 TCP/IP msec > 300 msec2x120 msec + 200 TCP/IP msec > 300 msec

Delay is due to packet queuing time Delay is due to packet queuing time • The processor is busy processing other packets The processor is busy processing other packets • Upper bounds must be established Upper bounds must be established • Shortest path is the path with the least end-to-Shortest path is the path with the least end-to-

end transmission delay time end transmission delay time

Delay or Latency DefinitionsDelay or Latency Definitions The time from when words are The time from when words are

spoken until they are heard at the spoken until they are heard at the other endother end• Measure of delay in a callMeasure of delay in a call

Delay is also referred to the time that Delay is also referred to the time that it takes a packet to make its way it takes a packet to make its way through the network to the through the network to the destination or terminating devicedestination or terminating device

LatencyLatency Impact Impact Large latency values do not necessarily Large latency values do not necessarily

degrade the sound quality of phone call but degrade the sound quality of phone call but large latency values can result in a lack of large latency values can result in a lack of synchronization between the speakers. This synchronization between the speakers. This can cause hesitations during the voice can cause hesitations during the voice conversation make it difficult to interactconversation make it difficult to interact

Latency greater than 150 milliseconds is Latency greater than 150 milliseconds is unacceptable in most casesunacceptable in most cases

One-way latency is used for diagnosing One-way latency is used for diagnosing network problemsnetwork problems

Latency (Delay)Latency (Delay)

Factors contribute to DelayFactors contribute to Delay The time it takes for the endpoints to create The time it takes for the endpoints to create

the packets used in voice service, known as the packets used in voice service, known as packet creation latencypacket creation latency..

The time it takes to serialize the digital data The time it takes to serialize the digital data onto the physical links of the interconnecting onto the physical links of the interconnecting equipment, known as equipment, known as serialization delayserialization delay..

The time it takes an electrical signal to travel The time it takes an electrical signal to travel the length of a conductor, known as the length of a conductor, known as propagation delaypropagation delay..

The time that a network device to buffer a The time that a network device to buffer a packet and make the forwarding decision, packet and make the forwarding decision, known as known as packet forwarding delaypacket forwarding delay..

Latency TypesLatency Types

Fixed delayFixed delay CodecCodec

Time it takes to sample Time it takes to sample and digitize the voice and digitize the voice signalsignal

PacketizationPacketization Time it takes to convert Time it takes to convert

voice into IP packetsvoice into IP packets NetworkNetwork

component propagation component propagation due to manufacturingdue to manufacturing

Jitter bufferJitter buffer

Variable delayVariable delay Queuing delayQueuing delay Network delayNetwork delay

Speech Quality - JitterSpeech Quality - Jitter Jitter Jitter

• Defined as delay variation (lack of predictability Defined as delay variation (lack of predictability – high variance) – way to adjust – high variance) – way to adjust

• Jitter buffers are used to lower the delay Jitter buffers are used to lower the delay variance variance

Speech packets are buffered and transmitted at a Speech packets are buffered and transmitted at a steady rate steady rate

• Jitter is due to two factorsJitter is due to two factors packet routing (Different routs can produce different packet routing (Different routs can produce different

packet delays)packet delays) Different packet queuing time Different packet queuing time

There is no jitter Problems incircuit-switching!

Example of JitterExample of Jitter

For example, given a constant packet transmission rate For example, given a constant packet transmission rate of every 20 ms, new packets would be expected to of every 20 ms, new packets would be expected to arrive at the destination exactly over 20ms but arrive at the destination exactly over 20ms but unfortunately this is not always the case.unfortunately this is not always the case.

The figure shows packet one (P1) and packet three (P3) The figure shows packet one (P1) and packet three (P3) arriving when expected, but packet two (P2) arriving arriving when expected, but packet two (P2) arriving 12ms later then expected and packet four (P4) arriving 12ms later then expected and packet four (P4) arriving 5ms late.5ms late.

Jitter CausesJitter Causes The main cause of jitter is queuing The main cause of jitter is queuing

variations caused by dynamic variations caused by dynamic changes in network traffic loadchanges in network traffic load

Another cause is equal-cost links Another cause is equal-cost links do not have the same physical do not have the same physical lengthlength

Fixing Jitter ImpactFixing Jitter Impact The jitter buffer deliberately delays The jitter buffer deliberately delays

incoming packets in order to present incoming packets in order to present them to the decompression algorithm at them to the decompression algorithm at fixed spacingfixed spacing

The jitter buffer will also fix any out-of-The jitter buffer will also fix any out-of-order errors by looking at the sequence order errors by looking at the sequence number in the RTP framesnumber in the RTP frames

Speech Quality – Packet LossSpeech Quality – Packet Loss

Some packets are lost during transmission Some packets are lost during transmission • Buffer overflow Buffer overflow

Real-time applications cannot utilize the Real-time applications cannot utilize the same packet loss avoidance protocolssame packet loss avoidance protocols• The communication between the two ends take The communication between the two ends take

too long too long • Retransmission time is very longRetransmission time is very long

Five percent loss is tolerable Five percent loss is tolerable

Packet LossPacket Loss

VOIP is highly sensitive to packet lossVOIP is highly sensitive to packet loss• Loss Rates as low as 1% can garble Loss Rates as low as 1% can garble

communicationscommunications Latency and Jitter can contribute to Latency and Jitter can contribute to

“virtual packet loss” as packets “virtual packet loss” as packets arriving after their deadline are as arriving after their deadline are as good as “lost”good as “lost”

5% - Packet Loss5% - Packet Loss

http://www.networkcomputing.com/1001/1001ws2.html

10% - Packet Loss10% - Packet Loss

20% - Packet Loss20% - Packet Loss

40% - Packet Loss40% - Packet Loss

ExamplesExamples 10 percent packet loss/G.711 10 percent packet loss/G.711

G71110.wav (602 KB) G71110.wav (602 KB) 20 percent packet loss/G.711 20 percent packet loss/G.711

G71120.wav (512 KB) G71120.wav (512 KB) 50 percent packet loss/G.711 50 percent packet loss/G.711

G71150.wav (497 KB) G71150.wav (497 KB) 10 percent packet 10 percent packet

loss/G.723.1 G72310.wav loss/G.723.1 G72310.wav (632 KB) (632 KB)

20 percent packet 20 percent packet loss/G.723.1 G72320.wav loss/G.723.1 G72320.wav (592 KB) (592 KB)

50 percent packet 50 percent packet loss/G.723.1 G72350.wav loss/G.723.1 G72350.wav (776 KB) (776 KB)

Next step….Next step….

RADCOM SoftwareRADCOM Software

RADCOM SoftwareRADCOM Software

Critical Factors -OverviewCritical Factors -Overview

Network management Network management Speech codingSpeech coding Network reliability Network reliability Network scalability Network scalability

Network Management Network Management

Network convergence is beneficial but also Network convergence is beneficial but also introduces new challengesintroduces new challenges• Handling voice and data which have different Handling voice and data which have different

characteristics characteristics Network requirementsNetwork requirements

• Voice calls should not be connected if not Voice calls should not be connected if not enough resources are available enough resources are available

Check sufficient BW Check sufficient BW

• Support traffic prioritization Support traffic prioritization Ensure the most critical traffic is least effected when Ensure the most critical traffic is least effected when

network congestion occurs network congestion occurs Handle traffic management and QoS Handle traffic management and QoS

Speech-Coding TechniquesSpeech-Coding Techniques

Choice of speech coding is critical to Choice of speech coding is critical to having high-quality voice having high-quality voice

Two conflicting objectivesTwo conflicting objectives• Reducing bandwidth Reducing bandwidth • Maintaining the natural-sounding speech Maintaining the natural-sounding speech

(toll quality)(toll quality) A major advantage of VoIP is its A major advantage of VoIP is its

distributed characteristic distributed characteristic

Reliability & Scalability Reliability & Scalability

Commercial challenge to to having a Commercial challenge to to having a telephony network is to ensure five nine telephony network is to ensure five nine availabilityavailability

Today’s VoIP systemsToday’s VoIP systems• Provide sufficient reliability Provide sufficient reliability • Enable redundancy and load-sharing Enable redundancy and load-sharing

Good balance between cost and redundancyGood balance between cost and redundancy

• Offer scalabilityOffer scalability Scalability refers to supporting higher capacity Scalability refers to supporting higher capacity Handling millions of simultaneous callsHandling millions of simultaneous calls

VoIP Standardization ProcessVoIP Standardization Process Basic architectural issues in VoIPBasic architectural issues in VoIP

• Transporting Voice by using IP Transporting Voice by using IP • Decoding voice Decoding voice

Various standards have been proposed Various standards have been proposed Internet standards and specifications are handled by the Internet standards and specifications are handled by the

Internet Society Internet Society • Non-profit organization trying to keep the Internet alive and Non-profit organization trying to keep the Internet alive and

growing growing • The internet Architecture Board (IAB) – IS advisory group The internet Architecture Board (IAB) – IS advisory group • The Internet Engineering Task Force (IETF) – volunteer who The Internet Engineering Task Force (IETF) – volunteer who

collaborate in the development of Interne t standards collaborate in the development of Interne t standards • The Internet Engineering Steering Group (IESG) – responsible The Internet Engineering Steering Group (IESG) – responsible

for management of IETF’s activities and their approvalsfor management of IETF’s activities and their approvals• The Internet Assigned Numbers Authority (IANA) – responsible The Internet Assigned Numbers Authority (IANA) – responsible

for the administration of unique numbers and parameters used for the administration of unique numbers and parameters used in the Internet Standards in the Internet Standards

StatsStats

Today there are over 150 million cell phones in the U.S

21 million people registered broadband phones with Skype

DefinitionsDefinitions

ProtocolsProtocols• Set of rules to allow orderly communications Set of rules to allow orderly communications

POTS: Plain old telephone service POTS: Plain old telephone service PSTN: Public switched telephone network PSTN: Public switched telephone network ITU-T: International Telecommunication ITU-T: International Telecommunication

Union Telecommunications Solutions –Union Telecommunications Solutions –Standardization Sector Standardization Sector

ReferencesReferences

Carrier Grade Voice Over IP, second Carrier Grade Voice Over IP, second Edition, D. Collins Edition, D. Collins

Reference – Packet loss and jitterReference – Packet loss and jitter

www.radcom.comwww.radcom.com http://www.voiptroubleshooter.com/http://www.voiptroubleshooter.com/

problems/plc.htmlproblems/plc.html http://www.protocols.com/papers/http://www.protocols.com/papers/

voip2.htmvoip2.htm http://www.juniper.net/solutions/http://www.juniper.net/solutions/

literature/white_papers/200087.pdf literature/white_papers/200087.pdf