6/9/2009 1
Course 4: IP
Telephony and VoIP
Telecommunications Technical Curriculum Program 3: Voice Knowledge
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2
Telecommunications Technical Curriculum
z Program 1: General Industry Knowledge
− Course 1: General Industry Knowledge z Program 2: General Telecommunications Knowledge
− Course 1: Information and Transmission Concepts
− Course 2: Transmission Systems
− Course 3: Network and Test Equipment z Program 3: Voice Knowledge
− Course 1: PSTN Concepts and Operation
− Course 2: Voice Equipment
− Course 3: PSTN Design and Services
− Course 4: IP Telephony and VoIP z Program 4: Data Knowledge
− Course 1: Network Models and Suites
− Course 2: Physical and Data Link Layer Concepts
− Course 3: Network Layer Concepts
− Course 4: Transport and Application Services Layer Concepts
− Course 5: Security Concepts z Program 5: Audio/Video Knowledge
− Course 1: Analog Cable Television
− Course 2: Digital Cable Television
− Course 3: Audio/Video Equipment and Services
− Course 4: Audio/Video Impairments and Testing
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Instructor Introductions
Paul Whalen
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Senior MTS and CEO
Dave Train
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Senior MTS and CTO
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Agenda
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Lesson 1: Why Voice over IP?
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Lesson 2: An Introduction to VoIP and IPT
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Lesson 3: VoIP/IPT Service Models
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Lesson 1: Why VoIP?
Upon completing this lesson, you will be able to
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Discuss the motivation for voice over Internet Protocol (VoIP)
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Compare the VoIP architecture with the traditional
circuit-switched PSTN
Completion time: Approximately 25 minutes
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Voice Technology Evolution
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Telephone network technology has undergone major replacement every 20–30 years
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The Internet has superseded the telephone network in bandwidth availability and usage
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VoIP is the natural choice for the next generation of technology
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VoIP enables new capabilities through integration with data applications
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A Stylized Class 5 Switch
Loop Interfaces
Special Interfaces Loops
Trunks
Signaling, CentrexPBX, Switch
Network Control
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Media Gateway
The Transformation from TDM to VoIP
Control
Loop
Trunks
High-Speed SS7 ConnectionData
IP NetworkSwitch Network
Signaling Gateway
PSTN
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Access and Control in a VoIP Network
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The telephone
− IP phone with integral codec
− Client software on a PC
− Telephone with a media adapter
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The loop
− High-speed data connection, preferably with QoS
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Control processor
− Call processor (aka manager, server, media gateway controller, gatekeeper)
− Software on a server
− Requires signaling protocol
− Might integrate with other server-based applications (e.g., email)
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Switching in a VoIP Network and Connections to the PSTN
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Switching
− Switching is provided by the IP network
− Managed IP network ensures QoS
− The Internet offers no quality guarantees
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Connection to the PSTN
− Signaling gateway to interface with the PSTN
− Makes VoIP network appear like a PBX or class 5 switch
− Media gateway to convert to/from VoIP to TDM
− Protocol to manage gateway functions
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Lesson 2: An Introduction to VoIP and IPT
Upon completing this lesson, you will be able to
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Describe voice over Internet Protocol (VoIP)
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Describe Internet Protocol telephony (IPT)
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Discuss why voice over packet is feasible
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Describe the requirements for VoIP
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Identify key standards for VoIP and IPT
Completion time: Approximately 33 minutes
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Voice over IP and IP Telephony
z VoIP
− IP-based network to transmit packets containing digitally encoded, compressed voice information
z IP telephony (enterprise or public)
− Adds the intelligence, call signaling, and feature sets that truly deliver the services users want
− Ability to enhance that intelligence to deliver new services, operation effectiveness, and applications
IP Transport Network IP Transport
Network Phone NumbersCall BlockingSignalingCaller ID Conference CallingCall Forwarding4-Digit DialingCall TransferVoice Mail
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Why Packetize Voice?
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Fact: Only a small percentage of human speech is required for high quality voice communications
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Packet technology well-suited to this profile
Source: Cisco Systems, Inc.
Essential Components Redundancy
Pauses
22%
56% 22%
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The New Voice Stack
Voice UDP
Layer 2 IP
Layer 1
We already know how to digitize it and put it in a packet (PCM word)
Possible requirement for extra protocols such as RTP, RTCP, RSVP
Use of ancillary techniques such as IPSec (VPN) or ToS field for CoS
Examples: Frame relay, ATM, Ethernet, MPLS Slow, fast—Copper, Fiber, Air
Examples: xDSL, T-1/3, SONET, DWDM
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VoIP Network Components
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A router-based IP backbone
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Call manager and media gateway controller
− “Softswitch” is really software
− Receives call routing, service selection, deals with authentication, billing, service-level information from Signaling System 7 (SS7)
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Media gateway: Access device for traffic
− Convert telephony to IP (to/from PSTN)
− Analog → digital/digital → analog
− Convert audio formats and transmission schemes
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User devices: IP telephone or PC with IPT software
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IP Telephones
The CODEC plays a significant
role in VoIP / IPT!
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Voice Acceptability Factors
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Low delay
− Circuit switched voice delay ≈ 30–60 msec (acceptable)
− Satellite-based delay ≈ 500 msec (unacceptable)
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Low jitter → Predictable delay
− Actual delay varies by the amount of jitter
− High jitter → Staccato type speech
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No echo
− PSTN uses echo suppressors or cancellers
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High signal-to-noise ratio (noise is low)
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Some packet loss is acceptable
− Too much leads to lost information
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Voice over IP Acceptability
z Reduce delay due to network
− Use private network
− Install faster computers at network nodes
z Reduce jitter due to network
− Implement some form of QoS assurance
z Improve processing rate of conversion algorithms
− Better algorithms
− Improve processing power
z Improve apparent bandwidth
− Reduce bit rate required by voice conversion algorithms
− Get more bandwidth
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Key VoIP Standards
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ITU-T
− H.323
− H.225 (call signaling)
− H.245 (control)
− Audio/video codecs
− G.711, G.722, G.723, G.728, G.729
− T.120 (data conferencing) z
IETF
− Session Initiation Protocol (SIP)
− Real-time Transport Protocol (RTP) (RFC 1889/1890)
− Resource Reservation Protocol (RSVP) (RFC 2205)
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Media Gateway Control Protocol (MEGACO)
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Lesson 3: VoIP/IPT Service Models
Upon completing this lesson, you will be able to
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Identify three service models for VoIP and/or IPT deployment
Completion time: Approximately 26 minutes
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VoIP Services
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Internet telephony service provider (ITSP)
− Internet telephony
− PSTN replacement
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Telephone company
− Business services
− IP trunking
− IP Centrex
− PSTN replacement
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Multiple systems operator
− PSTN replacement
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HFC Access Network
eMTA Cable Modem
CMTS
Managed
IP Network PSTN
Call Management Server
Media Gateway
Media Gateway Controller
Signaling Gateway
MSO PSTN Replacement
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Provides high quality voice service
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Does not use the public Internet
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Reuses existing equipment and wiring
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Reliable
DOCSIS QoS
Battery Backup
Managed IP
IP with QoS
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Summary
Having completed this course, you are now able to
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Discuss the motivation for Voice over Internet Protocol (VoIP)
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Compare the VoIP architecture with the traditional circuit-switched PSTN
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Describe the requirements for VoIP
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Describe key standards for VoIP and IPT
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Describe voice over Internet Protocol (VoIP)
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Describe Internet Protocol telephony (IPT)
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Discuss why VoIP is feasible
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Identify three service models for
VoIP and/or IPT deployment
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Who We Are
z Company Information Hill Associates, Inc.
106 Highpoint Center, Colchester, VT 05446 +1.802.655.0940 (main) [email protected](email)
Website: http://www.hill.com
Newsletter: http://www.hill.com/newsletter Podcast: http://www.hill.com/podcast Blog: http://www.hill.com/blog Wiki: http://www.hill.com/wiki
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