Course 4: IP Telephony and VoIP Telecommunications Technical Curriculum Program 3: Voice Knowledge 6/9/2009 1
Telecommunications Technical Curriculum Program 1: General Industry Knowledge Course 1: General Industry Knowledge Program 2: General Telecommunications Knowledge Course 1: Information and Transmission Concepts Course 2: Transmission Systems Course 3: Network and Test Equipment 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 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 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 2 6/9/2009 2
Instructor Introductions Paul Whalen Senior MTS and CEO Dave Train Senior MTS and CTO 3 6/9/2009 3
Agenda Lesson 1: Why Voice over IP? Lesson 2: An Introduction to VoIP and IPT Lesson 3: VoIP/IPT Service Models 4 6/9/2009 4
Lesson 1: Why VoIP? Upon completing this lesson, you will be able to Discuss the motivation for voice over Internet Protocol (VoIP) Compare the VoIP architecture with the traditional circuit-switched PSTN Completion time: Approximately 25 minutes 6/9/2009 5
Voice Technology Evolution Telephone network technology has undergone major replacement every 20 30 years The Internet has superseded the telephone network in bandwidth availability and usage VoIP is the natural choice for the next generation of technology VoIP enables new capabilities through integration with data applications 6 6/9/2009 6
A Stylized Class 5 Switch Loops Control Switch Network Trunks Special Interfaces Loop Interfaces Signaling, PBX, Centrex 7 6/9/2009 7
The Transformation from TDM to VoIP Control Trunks Loop High-Speed Data Connection IP Network Switch Network Signaling Gateway Media SS7 Gateway PSTN 8 6/9/2009 8
Access and Control in a VoIP Network The telephone IP phone with integral codec Client software on a PC Telephone with a media adapter The loop High-speed data connection, preferably with QoS 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) 9 6/9/2009 9
Switching in a VoIP Network and Connections to the PSTN Switching Switching is provided by the IP network Managed IP network ensures QoS The Internet offers no quality guarantees 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 10 6/9/2009 10
Lesson 2: An Introduction to VoIP and IPT Upon completing this lesson, you will be able to Describe voice over Internet Protocol (VoIP) Describe Internet Protocol telephony (IPT) Discuss why voice over packet is feasible Describe the requirements for VoIP Identify key standards for VoIP and IPT Completion time: Approximately 33 minutes 6/9/2009 11
Voice over IP and IP Telephony VoIP IP-based network to transmit packets containing digitally encoded, compressed voice information Conference Phone 4-Digit Call Voice Signaling Caller IP Forwarding Blocking Transfer Transport Numbers Dialing Mail ID Calling Network 12 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 6/9/2009 12
Why Packetize Voice? Fact: Only a small percentage of human speech is required for high quality voice communications 56% 22% 22% Pauses Essential Components Redundancy Packet technology well-suited to this profile Source: Cisco Systems, Inc. 13 6/9/2009 13
The New Voice Stack Voice UDP IP Layer 2 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 14 6/9/2009 14
VoIP Network Components A router-based IP backbone 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) Media gateway: Access device for traffic Convert telephony to IP (to/from PSTN) Analog digital/digital analog Convert audio formats and transmission schemes User devices: IP telephone or PC with IPT software 15 6/9/2009 15
IP Telephones The CODEC plays a significant role in VoIP / IPT! 16 6/9/2009 16
Voice Acceptability Factors Low delay Circuit switched voice delay 30 60 msec (acceptable) Satellite-based delay 500 msec (unacceptable) Low jitter Predictable delay Actual delay varies by the amount of jitter High jitter Staccato type speech No echo PSTN uses echo suppressors or cancellers High signal-to-noise ratio (noise is low) Some packet loss is acceptable Too much leads to lost information 17 6/9/2009 17
Voice over IP Acceptability Reduce delay due to network Use private network Install faster computers at network nodes Reduce jitter due to network Implement some form of QoS assurance Improve processing rate of conversion algorithms Better algorithms Improve processing power Improve apparent bandwidth Reduce bit rate required by voice conversion algorithms Get more bandwidth 18 6/9/2009 18
Key VoIP Standards 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) IETF Session Initiation Protocol (SIP) Real-time Transport Protocol (RTP) (RFC 1889/1890) Resource Reservation Protocol (RSVP) (RFC 2205) Media Gateway Control Protocol (MEGACO) 19 6/9/2009 19
Lesson 3: VoIP/IPT Service Models Upon completing this lesson, you will be able to Identify three service models for VoIP and/or IPT deployment Completion time: Approximately 26 minutes 6/9/2009 20
VoIP Services Internet telephony service provider (ITSP) Internet telephony PSTN replacement Telephone company Business services IP trunking IP Centrex PSTN replacement Multiple systems operator PSTN replacement 21 6/9/2009 21
MSO PSTN Replacement Provides high quality voice service Does not use the public Internet Reuses existing equipment and wiring Reliable Cable emtabattery Backup Modem CMTS DOCSIS HFC QoS Access Network 22 IP with Managed Managed QoS IP IP Network Call Management Server Media Gateway Controller Media Gateway Signaling Gateway PSTN 6/9/2009 22
Summary Having completed this course, you are now able to Discuss the motivation for Voice over Internet Protocol (VoIP) Compare the VoIP architecture with the traditional circuit-switched PSTN Describe the requirements for VoIP Describe key standards for VoIP and IPT Describe voice over Internet Protocol (VoIP) Describe Internet Protocol telephony (IPT) Discuss why VoIP is feasible Identify three service models for VoIP and/or IPT deployment 23 6/9/2009 23
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