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Essentials of Real-Time Networking: How Real-Time Disrupts the Best-Effort ParadigmCopyright 2004 Nortel Networks, All Rights ReservedPrinted in the United States of America

NORTEL, NORTEL NETWORKS, NORTEL NETWORKS LOGO, the GLOBEMARK, BAYSTACK, CALLPILOT, CONTIVITY, DMS, MERIDIAN, MERIDIAN 1, NORSTAR, OPTERA, OPTIVITY, PASSPORT, SUCCESSION and SYMPOSIUM are trademarks of Nortel Networks.ALTEON is a trademark of Alteon WebSystems, Inc.ARIN is a trademark of American Registry of Internet Numbers, Ltd. APACHE is a trademark of Apache Micro Peripherals, Inc. APPLE, APPLETALK, MAC OS and QUICKTIME, are trademarks of Apple Computer Inc. CABLELABS, DOCSIS and PACKETCABLE are trademarks of Cable Television Laboratories, Inc. C7 and CALIX are trademarks of Calix Networks Inc.CANAL + is a trademark of Canal + Corporation KEYMILE is a trademark of Datentechnik Aktiengesellschaft MPEGABLE is a trademark of Dicas Digital Image Coding GmbH CINEPAK is a trademark of Digital Origin, Inc. ECI is a trademark of ECI Telecom Limited DIGICIPHER and GENERAL INSTRUMENT are trademarks of General Instrument Corporation INFOTECH is a trademark of Infotech, Inc. ESCON and LOTUS NOTES are trademarks of International Business Machines Corporation (dba IBM Corporation). IANA and ICANN are trademarks of Internet Corporation of Assigned Names and Numbers.NAGRA and NAGRAVISION are trademarks of Kudelski A.B. INDEO is a trademark of Ligos Corporation ENHYDRA is a trademark of Lutris Technologies, Inc. SIP is a trademark of Merrimac Industries, Inc. FORE SYSTEMS is a trademark of Marconi Communications, Inc. ACTIVEX, NETMEETING, MICROSOFT WINDOWS, OUTLOOK, WINDOWS, and WINDOWS MEDIA are trademarks of Microsoft CorporationNETIQ is a trademark of NetIQ Corporation TIMBUKTU is a trademark of Netopia, Inc. OPNET is a trademark of OPNET Technologies, Inc. ECAD is a trademark of Pentek, Inc. REALAUDIO, REALNETWORKS, REALPLAYER, REALPROXY, and REALVIDEO are trademarks of RealNetworks, Inc.PESQ is a trademark of Psytechnics LimitedPOWERTV and SCIENTIFIC ATLANTA are trademarks of Scientific-Atlanta, Inc.SILKROAD is a trademark of SilkRoad Technology, Inc. SPRINT is a trademark of Sprint Communications Company L.P. CDMA2000 is a trademark of Telecommunications Industry Association NETBSD is a trademark of The NetBSD Foundation THE YANKEE GROUP is a trademark of The Yankee Group VERIZON is a trademark of Verizon Trademark Services LLC BSD is a trademark of Wind River Systems, Inc. ZENITH is a trademark of Zenith Electronics Corporation Trademarks are acknowledged with an asterisk (*) at their first appearance in the document.

iContents 1Author Biographies ...........................................................................ix

Acknowledgments ................................................................................................ xiv

Chapter 1. Introduction ......................................................................1Section I: Real Time Applications and Services .....................................................3Section II: Legacy Networks ...................................................................................5Section III: Protocols for Real-time Applications .....................................................5Section IV: Packet Network Technologies ...............................................................6Section V: Network Design and Implementation .....................................................7Section VI: Examples ..............................................................................................8Lets Get Started .....................................................................................................9Reading the Transport Path Diagrams ..................................................................10Conclusion ............................................................................................................11

Section I: Real-Time Applications and Services ...........13

Chapter 2. The Real-Time Paradigm Shift ......................................15Concepts Covered ................................................................................................15Introduction ...........................................................................................................15What is convergence? ...........................................................................................16What do we mean by real time? ............................................................................19Service quality and performance requirements ....................................................25Conclusion ............................................................................................................31What You Should Have Learned ...........................................................................33References ............................................................................................................34

Chapter 3. Voice Quality ...................................................................35Concepts covered .................................................................................................35Introduction ...........................................................................................................36Voice calls through an IP network .........................................................................36Copyright 2004 Nortel Networks Essentials of Real-Time Networking

Factors affecting VoIP conversation quality ...........................................................38Quality metrics for voice ........................................................................................52What you should have learned ..............................................................................62References ............................................................................................................64

Chapter 4. Video Quality ..................................................................67Concepts covered .................................................................................................67

ii ContentsVideo .....................................................................................................................67Video Impairments ................................................................................................68Digital video impairments ......................................................................................68Causes of video signal impairments .....................................................................69Digital video ..........................................................................................................70Sequences of frames ............................................................................................74What you should have learned ..............................................................................79

Chapter 5. Codecs for Voice and Other Real-Time Applications .81Concepts Covered ................................................................................................81Introduction ...........................................................................................................82Basic Characteristics of Codecs ...........................................................................85Coding impairments ..............................................................................................88Speech Codecs for Voice Services .......................................................................98Audio Codecs ......................................................................................................105Video Codecs ......................................................................................................107What you should have learned ............................................................................116References ..........................................................................................................117

Section II: Legacy Networks .........................................121

Chapter 6. TDM Circuit-Switched Networking ..............................123Concepts covered ...............................................................................................124TDM principles ....................................................................................................124The importance of clock rate and synchronization in TDM .................................127Principles of digital switching, voice switches .....................................................128What you should have learned ............................................................................138

Chapter 7. SONET/SDH ..................................................................139Concepts covered ...............................................................................................139Introduction .........................................................................................................140Overview .............................................................................................................140SONET a practical introduction ...........................................................................141The copper DS0-DS1-DS3 (traditional services) ................................................142ATM and other traffic services .............................................................................142Optical Ethernet applications ..............................................................................142SONET terminology ............................................................................................143The network element ..........................................................................................147Network configurations .......................................................................................148Synchronization ..................................................................................................153What you should have learned ............................................................................158

Section III. Protocols for Real-Time Applications .......159

Chapter 8. Real-Time Protocols: RTP, RTCP, RTSP .....................161Concepts covered ...............................................................................................161Introduction .........................................................................................................162Real-Time Transport Protocol (RTP) ...................................................................162Real-Time Control Protocol .................................................................................167Essentials of Real-Time Networking Copyright 2004 Nortel Networks

Contents iiiRTP and TCP ......................................................................................................169Real-Time Streaming Protocol (RTSP) ...............................................................170RTSP and HTTP .................................................................................................175What you should have learned ............................................................................177References ..........................................................................................................178

Chapter 9. Call Setup Protocols: SIP, H.323, H.248 .....................179Concepts covered ...............................................................................................179Introduction .........................................................................................................180H.323 ..................................................................................................................182SIP ......................................................................................................................198Comparison of SIP and H.323 ............................................................................216Gateway Control protocols ..................................................................................219What you should have learned ............................................................................225References ..........................................................................................................227

Chapter 10. QoS Mechanisms .......................................................229Concepts Covered ..............................................................................................229Introduction .........................................................................................................230QoS and Network Convergence .........................................................................231Overview of QoS Mechanisms ............................................................................232DiffServ QoS Architecture ...................................................................................237DSCP Configuration Considerations ...................................................................239Ethernet IEEE 802.1Q ........................................................................................240Host DSCP or 802.1p Marking ............................................................................241Packet Fragmentation and Interleaving ...............................................................241Other methods to achieve QoS ...........................................................................243What you should have learned ............................................................................246References ..........................................................................................................247

Section IV: Packet Network Technologies ...................249

Chapter 11. ATM and Frame Relay ................................................251Concepts Covered ..............................................................................................251Introduction .........................................................................................................252Layered protocol .................................................................................................253ATM interfaces ....................................................................................................255ATM architecture .................................................................................................256AAL (ATM adaptation layer) ................................................................................261QoS and services in ATM networks ....................................................................264Voice and telephony over ATM ............................................................................269Frame relay and FRF.11/12 .................................................................................271Seven engineering best practices .......................................................................275What you should have learned ............................................................................280References ..........................................................................................................282

Chapter 12. MPLS Networks ..........................................................285Concepts covered ...............................................................................................285Introduction .........................................................................................................286Copyright 2004 Nortel Networks Essentials of Real-Time Networking

iv ContentsTraffic trunks and flows ........................................................................................287Motivations to move to MPLS .............................................................................287The label .............................................................................................................287Protocol components of MPLS ...........................................................................288How to build the LSRs MPLS forwarding table ...................................................290Label switched paths setup .................................................................................290LSP setup using explicit routes ...........................................................................291LSP setup, example using RSVP-TE signaling ...................................................291Integration MPLS and DiffServ ...........................................................................292Label merging .....................................................................................................293Label stacking .....................................................................................................293What you should have learned ............................................................................295References ..........................................................................................................296

Chapter 13. Optical Ethernet .........................................................297Concepts covered ...............................................................................................297Introduction .........................................................................................................297What is optical Ethernet? ....................................................................................298How does an optical Ethernet network operate? ................................................299How fast is optical Ethernet? ...............................................................................299Ethernet over fiber ..............................................................................................299Resilient packet ring ............................................................................................300Ethernet over DWDM ..........................................................................................303Optical Ethernet services ....................................................................................304Internet access services .....................................................................................305LAN extension .....................................................................................................305What you should have learned ............................................................................306

Chapter 14. Network Access: Wireless, DSL, Cable ................... 307Concepts covered ...............................................................................................307Introduction .........................................................................................................308Physical challenges to bandwidth and distance ..................................................309Wireless systems for broadband delivery ...........................................................310Networking solutions supporting nomadic and mobile users ..............................317xDSL technology .................................................................................................319Cable access technology ....................................................................................326What you should have learned ............................................................................339References ..........................................................................................................339

Chapter 15. The Future Internet Protocol: IPv6 ........................... 341Concepts covered ...............................................................................................341Renewing the Internet .........................................................................................342Key IPv6 Items affecting Real-Time Networking .................................................343Basics of the IPv6 network layer .........................................................................344Layers above the Network Layer .........................................................................355Control, Operations and Management ................................................................355IPv6 Transition Strategies ...................................................................................359What you should have learned ............................................................................365References ..........................................................................................................366Essentials of Real-Time Networking Copyright 2004 Nortel Networks

Contents vSection V: Network Design and Implementation ........369

Chapter 16. Network Address Translation ....................................371Concepts covered ...............................................................................................371Introduction .........................................................................................................372The swings and the roundabouts ........................................................................373Why do we need NATs? ......................................................................................375NATs as a middlebox ..........................................................................................376NAT terminology ..................................................................................................376The basics of Network Address Translation ........................................................377Network Address Translator taxonomy ...............................................................379Interactions with applications ..............................................................................383Packet translations needed to support NAT ........................................................383Using the varieties of NAT ...................................................................................385Issues with NAT ..................................................................................................387What you should have learned ............................................................................390References ..........................................................................................................391

Chapter 17. Network Reconvergence ...........................................393Concepts covered ...............................................................................................393Introduction .........................................................................................................394Achieving resiliency .............................................................................................394Redundancy to provide reliability ........................................................................394Path redundancy and recovery ...........................................................................395Protection schemes ............................................................................................396Protocols for the network edge ...........................................................................397Protocols for the core ..........................................................................................404What you should have learned ............................................................................415

Chapter 18. MPLS Recovery Mechanisms ...................................417Concepts covered ...............................................................................................417Introduction .........................................................................................................417MPLS protection schemes ..................................................................................418Components of an MPLS recovery solution ........................................................420Monitoring, detection and notification mechanisms ............................................422MPLS scope of recovery global and local ......................................................426MPLS recovery versus IP (IGP) recovery ...........................................................428What you should have learned ............................................................................430References ..........................................................................................................431Informative references ........................................................................................431

Chapter 19: Implementing QoS: Achieving Consistent Application Performance ...............................................................433

Concepts covered ...............................................................................................434Introduction .........................................................................................................434Mapping DiffServ to Link Layer (Layer 2) QoS ....................................................434Application Performance Requirements ..............................................................444Categorizing Applications ...................................................................................445Making QoS Simple via Networks Service Classes ............................................448Copyright 2004 Nortel Networks Essentials of Real-Time Networking

vi ContentsAdditional QoS Implementation Considerations .................................................456What you should have learned ............................................................................461References ..........................................................................................................462

Chapter 20. Achieving QoE: Engineering Network Performance.................................................................................... 463

Concepts covered ...............................................................................................463Introduction .........................................................................................................464QoE Engineering Methodology ...........................................................................464HRXs and QoS Mechanism Requirements .........................................................470Traffic Engineering & Resources Allocation .......................................................476SummaryNetwork Engineering Guidelines .......................................................495What you should have learned ............................................................................497

Section VI: Examples ....................................................499

Chapter 21. VoIP and QoS in a Global Enterprise .......................501Voice over IP: Raising the need for Quality of Service ........................................501The Quality of Service (QoS) design ..................................................................507Lessons learned ..................................................................................................514

Chapter 22. Real-Time Carrier Examples .....................................515Centrex IP ...........................................................................................................515Local ...................................................................................................................519Long distance ......................................................................................................522Multimedia ...........................................................................................................526Cable ...................................................................................................................529Broadband ..........................................................................................................534Conclusion ..........................................................................................................538References ..........................................................................................................540

Chapter 23. Private Network Examples ........................................541The data solution ................................................................................................541Introduction .........................................................................................................541Getting Started ....................................................................................................541Designing the Real-time Networking Solution Infrastructure ..............................543Content Delivery Networking ..............................................................................556Solutions Management .......................................................................................559Closets and Aggregation Points ..........................................................................560The voice solution ...............................................................................................561Voice and Multimedia Communication Services .................................................561VoIP architecture and requirements ....................................................................563Call Server ..........................................................................................................566Gateways ............................................................................................................576Clients .................................................................................................................578Applications .........................................................................................................580Conclusion ..........................................................................................................587Essentials of Real-Time Networking Copyright 2004 Nortel Networks

Contents viiChapter 24. IP Television Example ................................................589Introduction .........................................................................................................590The IP television system .....................................................................................593Core switch/router feature enhancements for IP multicast ..................................595Video on demand service extensions .................................................................600Summary .............................................................................................................610

Appendix A. Additional Details about TDM Networking .............611SONET/SDH hierarchy .......................................................................................611Stratum level clocks ............................................................................................612

Appendix B. RTP Protocol Structure ............................................615RTCP packet formats ..........................................................................................616

Appendix C. Additional Information on Voice Performance Engineering .....................................................................................619

Network jitter .......................................................................................................620Access/source jitter .............................................................................................620Jitter buffer dimensioning ....................................................................................621

Appendix D. Additional Information about IPv6 ..........................633Concepts covered ...............................................................................................633Introduction .........................................................................................................633Directing Packets in an IPv6 Network .................................................................633Control, Operations and Management ................................................................643Application Programming Interface .....................................................................653IPv6 Transition Mechanisms ...............................................................................656References ..........................................................................................................668

Appendix E. Virtual Private Networks: Extending the Corporate Network ............................................................................................671

Introduction .........................................................................................................671The development of VPNs ..................................................................................672Catering for the Road Warrior ...........................................................................674More Flexible VPNs ............................................................................................676Layer 2 VPNs ......................................................................................................678Layer 3 VPNs ......................................................................................................680VPN Scaling, Security and Performance ............................................................686Summary .............................................................................................................689References ..........................................................................................................690

Appendix F: IP Multicast ................................................................691IP television head-end system ............................................................................691Core feature enhancements for IP multicast .......................................................694Bandwidth factors at the network edge ...............................................................697Conditional access & content protection methods ..............................................699Web streaming methods and practices ...............................................................703

Appendix G. QoE Engineering ......................................................707Copyright 2004 Nortel Networks Essentials of Real-Time Networking

viii ContentsData QoE performance metrics & targets ...........................................................707Nodal QoS Mechanisms .....................................................................................710

Appendix H. PPP Header Overview ..............................................717

Glossary ..........................................................................................719Essentials of Real-Time Networking Copyright 2004 Nortel Networks

ixAuthor BiographiesDave Anderson is a Senior Manager of Nortel Networks Wireless Engineering and is responsible for the engineering aspects of Nortels responses to global Wireless proposals and network designs. Dave has been with Nortel since earning his B.S.E.E. in 1986 and has held a number of Engineering positions within the company, including customer supporting engineering roles for DMS switching, and more recently, Wireless Network Engineering including aspects of Radio as well as core network. He is familiar with the evolving global standards for wireless systems including CDMA, EV-DO, GSM, UMTS and Wireless LAN.

Cedric Aoun works as a Senior Network Architect in Nortel Networks Carrier VoIP business. For the past four years, he has been working on corporate strategy for solving NAT and Firewall Traversal application issues, as well as the introduction of IPv6 in VoIP networks. He holds a B.S. in Engineering and an M.S. in Mobile Communications. Cedric is a regular attendee and contributor to the IETF in the areas of NAT and Firewall Traversal solutions, with primary focus on the NSIS Working Group.

Franois Audet is an IP Telephony Subject Matter Expert at Nortel, where he is a System Architect in the Enterprise Business Networks division. Franoiss expertise is in telephony protocols, Voice over ATM, and Voice over IP. He is an active participant in many Standards Forums, such as ITU-T (for the H.323 suite of Recommendations), and IETF (for SIP and SIP-related standards).

Franois Blouin is an Engineer and Subject Matter Expert in modeling and simulation with the Solutions Ready Group in Nortels Ottawa Lab. Franois leads a team developing network models for the prediction of performance for real-time services running over packet networks, using tools based on the ITU-T E-Model and OPNET. He consults with Nortel account teams to specify target performance for customer networks. In 2001, Franois was presented with a gold pride award for his work on voice bearer channel design guidelines for Succession Networks.

Sandra Brown is the Manager of the Technology and New Product Introduction team in Nortel Networks Information Services, responsible for the evaluation and trialing of new product and technology onto the company's global network. Sandra has a B.S. and an M.B.A. and has extensive experience in managing corporate information services.Chris Busch is a Senior Network Architect for Nortel. He has more than eight years of network systems experience within Telecommunications and Copyright 2004 Nortel Networks Essentials of Real-Time Networking

x Author BiographiesHealthcare industries. While at Nortel, he has held leadership roles in Network Design, Product Integration, and Systems Engineering. Mr. Busch is recognized for end-to-end solutions approach to Wide Area, Core, Enterprise and Access Networks.

Peter Chapman has held positions as Development Manager, Product Line Manager and Business Unit Manager over more than thirty years in the telecommunications, aerospace, television technology and semiconductor industries. He currently holds a position in the Chief Technology Officer's organization of Nortel, with responsibility for end-to-end performance of networks, applications and services. He is a Chartered Electrical Engineer and holds a B.S.E.E. from Imperial College, London.

Hung-Ming Fred Chen is a Network Performance Consultant with Nortel. At Nortel, he conducts analytical modeling and simulations for various network architectures and products, including wireless and wireline networks. His work mainly investigates QoS for triple-play service. He completed his B.S, M.S., and Ph.D. with National Sun Yat-Sen University, National Taiwan University, and University of Durham, UK, respectively.

Robert L. Cirillo, Jr. is a Network Architect in the Wireline Global Operations division of Nortel. A native of Boston, he has been involved with Enterprise Networking and the Telecommunications Industry for fifteen years. Since joining Nortel in 1997, he has had extensive involvement with the evolution of circuit-switched voice systems into high performance, Next Generation packet-based networks.

Rob Dalgleish is responsible for 3G Access Strategy with Nortel Networks Wireless Network Engineering based in Richardson, USA. Rob has been with Nortel Wireless since 1995 in Engineering management and advisory roles, working with GSM and CDMA customers and Nortel core R&D and project teams in Asia and North America. Robert holds a B.S. in Engineering with Honors from the University of Tasmania and is a Chartered Professional Engineer.

Elwyn Davies is currently leading the CTO Office team setting the strategy for the introduction of IPv6 into Nortel products. His background includes an M.A. in Mathematics and research into aspects of Noise Reduction in electronic and other systems. He is a regular attendee and contributor to the IETF in a number of areas, including network layer signaling and to the IRTF in routing research.Essentials of Real-Time Networking Copyright 2004 Nortel Networks

Author Biographies xiStephen Dudley has 23 years experience as an engineer in the telecommunications business, working with fiber optic and digital switching systems. He holds a B.S.E.E. and an M.S.E.E. with a certificate in Computer Integrated Manufacturing. He is currently a Network Engineer for converged voice and data networks.

Stphane Duval is a Product Line Manager for OME Data. He has twelve years of experience with data infrastructure solutions design for private and public sector organizations and extensive customer interaction, which helped him develop his skills to deliver reliable and secure data infrastructures.

Gwyneth Edwards manages the Information Services (IS) product engagement process, which supports the method in which the IS team provides Nortel product feedback to the business units. Gwyneth has twelve years IT experience at Nortel, specifically within the areas of strategy and communication. She has a B.S.M.E. and an M.B.A.

Shane Fernandes is a Network Engineer in the Information Services global WAN engineering group at Nortel, where he is responsible for all aspects of the network including the global corporate backbone and Internet. He has architected networks at various companies for the last fourteen years. Shane has a B.S. from McMaster University.

Shardul Joshi is a Network Engineer at Nortel with seven years experience in the Telecommunications Industry. His primary areas of expertise are Data Communications and Voice over IP, for which he has been slated an SME (Subject Matter Expert). Shardul has passed several expert level certifications in the Data Communications areas and is highly regarded among the Network Engineering community and external customer base. His primary duties involve pre-sales consulting and external customer trials to ensure proper cost-effective solutions are created. In addition to those activities, he works with new product teams to evaluate and ensure that these products provide positive customer experience. Shardul graduated from Angelo State University with a B.S. in Biology and minor in Chemistry in 1996.

Sinchai Kamolphiwong received a Ph.D. degree from the University of NSW, Australia, where his thesis concerned flow control in ATM networks. He is now an Associate Professor in the Department of Computer Engineering, Prince of Songkla University, Thailand. He is a director of Centre for Network Research (CNR). He has published fifty technical papers. His main research interest areas are: ATM networks, IPv6, VoIP, and performance evaluation. He is a committee member of ComSoc (Thailand section) and a member of IEEE Computer Society.Copyright 2004 Nortel Networks Essentials of Real-Time Networking

xii Author BiographiesPeter Kealy has over twenty years experience in the telecommunications industry. He is an RF and Telecom graduate from the Dublin Institute of Technology, Dublin, Ireland. Peter spent seven years working in London, UK, with BT working on varied telephony-based systems as a Field Engineer. Peter joined Nortel in 1996 as a Technical Support Engineer for Optical products and for the past four years has been an Optical Network Engineer specializing in customized engineering procedures including RPR & Optical Ethernet networks.

Joseph King is Director of Network Engineering for North America. Joseph leads the network engineering teams responsible for planning, designing and engineering next generation VoIP networks. He has over 22 years experience in the Telecommunications fieldthe last 17 with Nortel, where he has held various roles in the operations and engineering organizations, supporting both Enterprise and Carrier customers.

Ed Koehler is a Solutions Architect for Nortel Portfolio Engineering Group. He provides advanced consultation and design support for multicast and multimedia-based solutions to the field engineering staff as well as product development direction to the various product groups within Nortel. Ed began his career at Eastman Kodak and was involved in one of the first pilot projects for what was to become the IEEE 802.3 10BaseT specification during the 1986-88 timeframe.

Ali Labed is a Subject Matter Expert in Performance Modeling and Traffic Engineering. He currently works in the Solutions Ready Group in Nortels Ottawa Lab. Ali consults with product line management teams on traffic engineering, MPLS, and LSP resiliency strategies. Ali holds a B.S.C.S, an M.S. in applied mathematics, and a Ph.D. in Computer Science.

Anthony Lugo is an Optical Network Engineer and a Subject Matter Expert in the optical arena. He currently develops and implements complex network reconfigurations for Nortel customers. Anthony served in the United States Navy Submarine Division and received an A.A.S. in Electrical Engineering Technology and a B.S. in Telecommunication Engineering.

Timothy A. Mendonca is Team Leader of Succession Network Design and has thirty years of data, voice, multimedia and security infrastructure solutions design based on disparate technologies for private and public sector organizations. Extensive customer interaction has positioned him with a clear view and vision of the convergence issues. He is currently working on his dissertation for a Ph.D. in Information Systems. His dissertation topic is Knowledge Acquisition Using Multiple Domain Experts in the Design and Development of an Expert System for Implementing VoIP and Multimedia in a Secure Environment.Essentials of Real-Time Networking Copyright 2004 Nortel Networks

Author Biographies xiiiRobert D. Miller has 23 years of experience in designing and engineering networks at Nortel. Rob was the Lead Architect of both the internal voice ESN network and the private ATM network, and has the distinction of making the first voice call over a private ATM network. More recently, he was the Team Leader for the internal VoIP and QoS architectures.

Ralph Santitoro, Director of Network Architecture at Nortel, provides strategic direction and best practice design guidelines for multiservice network convergence. He defined the Network Service Classes (NSCs) and DiffServ mapping discussed in this book, which are being standardized in the IETF. Ralph also founded and chairs Nortel's QoS Core Team, which defines the QoS technology requirements and strategy for Nortels Enterprise and Carrier product portfolios.

Leigh Thorpe is a Senior Advisor with the Solutions Ready Group in Nortel under the CTO. She is responsible for evaluating QoE and developing specifications based on QoE results. Her background includes a B.S. in Physics and a Ph.D. in Experimental Psychology (Perceptual Development). Leigh has directed many selection and characterization tests for codec standards with ITU-T, TIA, and other standards groups. In 1997, she was awarded Nortel Networks Wireless Presidents Award for Quality.Copyright 2004 Nortel Networks Essentials of Real-Time Networking

xiv AcknowledgmentsAcknowledgmentsThe writing, editing, and assembly of a large textbook is a formidable task. We are fortunate that the corporate culture at Nortel encourages collaboration and teamwork. Many people contributed to the successful completion of this project, whether by direct contributions to the text, by supporting the steering committee or individual authors, by removing obstacles, or by championing this project to the senior executives. Thank you to everyone who helped us move forward.

We would like to acknowledge some specific contributions. David Downing, Leader of Wireline Deployment (Americas) for Nortel Networks Global Operations group, was the main sponsor of this work. Account Architect John Gibson was instrumental in initiating the project. Lorelea Moore coordinated the Steering Committee. Michelle Bigham prepared the cover graphics and assisted with internal communications. Ann Marie Bishop tracked actions, published minutes, and tried to keep us on schedule (sorry, Ann Marie!). Mark Bernstein provided valuable input on how effectively we conveyed the main messages and on the integration of ideas across chapters. Rod Wallace, Director under the CTO, and Bill McFarlane, Director, Nortel Networks Global Certification Program, promoted the initiative to Senior Executives across the company.

A big thank you to our many reviewers. Whether they read one chapter or many, whether they focused on technical accuracy or clarity and readability, their feedback and suggestions have greatly improved the quality of the published version.

Finally, we are extremely grateful to the authors, many of whom worked considerable overtime to complete their chapters. Thank you all for your perseverance through the successive drafts, revisions, and detail checking.

Shardul Joshi, Leigh Thorpe, Steve Dudley, and Tim Mendonca, EditorsEssentials of Real-Time Networking Copyright 2004 Nortel Networks

Acknowledgments xvSteering Committee:Lorelea Moore CertificationLeigh Thorpe Editor, CTO's OfficeShardul Joshi Editor, Wireline EngineeringStephen Dudley Editor, Wireline EngineeringTim Mendonca Editor, Enterprise EngineeringCarelyn Monroe Wireline EngineeringJoe King Wireline EngineeringMichelle Bigham Marketing communicationsAnn-Marie Bishop Project Manager

Contributors:The following made significant contributions to the contents of this book:

Mark ArmstrongBenedict BauerRoger BrittPeter BuiJames ChancoPaul CoverdaleSteve ElliottMatt MichelsMustapha MoussaTom TaylorAndrew TimmsCopyright 2004 Nortel Networks Essentials of Real-Time Networking

xvi AcknowledgmentsEssentials of Real-Time Networking Copyright 2004 Nortel Networks

1Chapter 1Introduction

Joseph King

You have an emergency. You know you can dial three digits from any phone, anywhere, any time and within milliseconds you have help. Most people don't understand how it happens, and frankly they don't care. They just count on it to work. The network design engineer both knows and cares how it works. Would you have the same confidence dialing that number if it was being routed across an IP core today? Not if that IP network is the Internet or one of about 85% of the IP networks out there today. Consumer and engineers alike have heard the technology hype: convergence, VoIP, triple play, interactive applications. Voice, data, and video networks are finally becoming one. Why? Because consumers demand it, want it and need it. It is becoming a way of life. Technology is a driving force for the way people communicate. The paradigm has shifted. Consumers are driving this change in technology to support the way they want to work and live. Convergence is occurring between real-time and nonreal-time data networks. Voice over IP is being deployed on networks that were originally designed with a router architecture and best-effort delivery philosophy. Many of these networks are not capable of meeting the performance quality requirements of real-time services such as voice. Voice services are critical. As convergence proceeds and networks begin to carry voice and other real-time services, these networks must adapt to the mission critical nature of those services. The people who design and operate these networks must meet a new set of constraints. Best-effort cannot guarantee the performance of mission critical real-time applications. Throwing more bandwidth at the problem is not sufficient. What is needed is proper network planning and design, which in turn requires a thorough understanding of the operation and constraints of real-time networking and how that interacts with the operation and constraints of IP networking.Because convergence of real-time applications with data networking is new ground for so many people, a group of Nortel subject matter experts have created a real-time networking manual to serve as a shared foundation for engineers and other professional from various areas of the industry. As part of this effort, Nortel has also developed a certification that is focused purely on real-time networking: Nortel Certified Technology Specialist (NCTS)Real-Time Networking. It is a baseline certification in real-time networking, intended to be as applicable to the managers of engineers as it Copyright 2004 Nortel Networks Essentials of Real-Time Networking

2 Chapter 1 Introductionis to the engineers themselves. It provides a foundation for future certifications that will cover specific topics in more detail. This book covers the basics of real-time networking. It addresses the technology, performance requirements, and basic best practices for engineering and implementation. It is not intended to provide detailed treatment of all possible solutions, but rather to bring the reader to a level of competence where he or she will be able to approach specific solutions, to understand the technical documentation, to ask questions, and to understand and use the answers. As stated, it does not touch all possible aspects. For example, security is essential in a world of converged networks. Security is touched on in parts of the book, but not in great detail as this book is focused on the basics of real-time networking. The topic of security in converged networks can easily fill a volume of its own. This book is technology-and standards-focused rather than product-focused. Given that, nowhere in this book are we recommending any single architecture. Each chapter was written by one or more Subject Matter Experts, and contains the fundamentals you need to sit for the associated certification exam. More importantly, it will supply you with the necessary background and guidelines for understanding the networks of tomorrow and making informed decisions about network components, network setup, and network operations. The NCTS Real-Time Networking certification encompasses real-time traffic engineering issues such as guaranteed Service Quality, high availability networking, and the fundamental science of voice transmission. Who better than Nortel to tell you how to deliver high quality, high availability services? Nortel is the world leader in voice, with over 100 years experience in telecommunications. Nortels optical and multiservice switching carry telecom services on an international scale where reliability must meet standards of 99.999%. But this book was not written to discuss Nortel. Instead, we've chosen to focus on standards-based, open networking. At last, a certification that can be applied to any vendor that supports open standards! Convergence is not only about running real-time and nonreal-time services on a single network, but also about assembling many different vendors' products into a single, cohesive standards-based network. Networking is often taught as separate threads. For instance, the OSI model separates the network into layers representing different functions and protocols. Breaking the material down this way helps structure learning. Rather than expose the student to the full complexity of the topic, it is more efficient to expose them to the individual parts. What often happens, however, is that the parts are never reintegrated. Students become designers and engineers, keeping the narrow focus and become experts in individual protocols, boxes, or topic areas. Relatively few expand their focus to see the network as one seamless system.Essentials of Real-Time Networking Copyright 2004 Nortel Networks

Chapter 1 Introduction 3In converged networks, technologies and protocols all interact and should not be treated in isolation as separate threads. To create a single converged network, the threads must be brought together into a single fabric. While the understanding of the individual threads is important, it is the knowledge of how to weave the threads together to create the seamless fabric of converged communications that is key. This book and the accompanying certification focus on the fabric rather than on the individual threads. To this end, the chapter authors are all networking experts with many years of real world experience designing, analyzing, and integrating multiservice real-time networks. The book focuses sharply on real world issues, emphasizing the knowledge, strategies and techniques that are needed to design, deploy, and operate real-time networks in today's world and how to migrate from your existing system to the network of the future.

Section I: Real Time Applications and ServicesThe most critical slice of the convergence pie is real time. All networks can pass best-effort data but not all networks can support real-time services such as voice. Convergence demands real-time capability, but first real time needs to be definedFor our purposes, real time depends on more than just throughput rate. Nor is real time simply another way of saying time-sensitive. For example, broadcast or streaming media are not considered real time even where the signal is live. Viewers often watch a live event several seconds or even minutes after it occurs, without any major impact on their experience. On the other hand, when streaming media are combined with an interactive control, such as a channel changer, it exhibits the responsiveness requirements characteristic of real time. When the user enters a command or sends interactive data, the adaptation of the user's perception and thought processes to the real world put strict constraints on the network response times. If response time is longer, the user experience is degraded. The important factor, then, is not whether streaming media has delay, but rather how delay affects the user experience. Real-time networking is bidirectional and interactive: the user experience depends on a response from another user, or from a device at the other end of the network. It is the ability to engage on simultaneous tasks or applications at once and control the quality of experience across the entire network. Real-time networking is so rapid it creates the illusion that there is no network in between, a kind of virtual reality.Beyond that, the delay starts to become noticeable and unacceptable. Achieving real-time transmission speeds is quite a challenge when it is considered that light traveling through fiber takes an eighth of a second to travel half way around the world. The problem is that sampling, compressing, framing, and synchronizing are time consuming. The early chapters address these issues.Copyright 2004 Nortel Networks Essentials of Real-Time Networking

4 Chapter 1 IntroductionThe first step will be to introduce the concepts of convergence and real time. Network, service, and application convergence are discussed. Examples of real-time services are presented, and the constraints around operating real-time services in a packet environment are discussed. The concept of Quality of Experience is introduced as the fundamental performance requirement for all services and applications. To design a real-time network and assure your customers excellent Quality of Experience, you need to understand the concepts of real-time applications. As discussed earlier, real-time challenges network performance. What are the performance requirements for the major real-time applications and services, and what are the protocols and mechanisms we use to control network behavior?Most all will agree that if the video freezes for seconds while watching the news but the audio continues, the interruption is a mere annoyance. However, if the reverse occurs, and the audio is lost for seconds while the video continues, your comprehension of the news will be severely degraded. For other content, such as sporting events, loss of audio may be tolerable, while video loss is not. That said, interactive voice is one of the most demanding communications services. Consequently, a significant portion of Section I is focused on the quality of voice services and voice codecs.For conversational voice services on a converged network, there are many contributing factors to the final quality. You, as a convergence engineer, need to understand the contributions of various parameters such as delay, packet loss, and echo. Network planning for voice is essential, and tools like the E-Model and its associated quality metric R are invaluable in designing and provisioning a network. Other metrics such as MOS are also used to quantify voice performance.As with voice, there are aspects of video signals that need to be understood. Understanding the concepts of video is critical to a convergence engineer. Impairments such as noise (luminance and chrominance), loss of synchronization signals, co-channel interference, and RF interference are all critical factors for video.Real-time applications are often concerned with the transmission of signals originating in analog mode. Sound signals because of their wave nature necessarily begin as analog signals. An NTSC (ordinary TV) video signal captures the information needed to reconstruct the visual display as an analog stream. To be transported across a digital network, analog signals must be converted to digital information by means of a codec. We discuss the basic characteristics of codecs used for telephony (speech), those for general audio signals, and codecs used for video signals. Also covered are the parameters that underlie the performance of the codec from both a human and technical perspective, common coding standards defined for Essentials of Real-Time Networking Copyright 2004 Nortel Networks

Chapter 1 Introduction 5each of these areas, and the boundary conditions for the effective use of compression codecs in Real-time communications systems.

Section II: Legacy NetworksBefore jumping into packet transmission, protocols, and the technologies involved, let's take a look at Time Division Multiplexing (TDM). Understanding TDM is very helpful to appreciating real time. How does TDM technology support real-time networking? What makes it so reliable? TDM is a declining technology, but much has been accomplished with it and learned from it. Most importantly, TDM will be the benchmark against which users compare packet voice services. Fiber optics was the first example of convergence. Today, almost all networks, applications and protocols converge on a fiber optic cable running SONET. Working with the real-time converged network of tomorrow will require an understanding of SONET and the advancements that have taken place in optical networking.

Section III: Protocols for Real-time ApplicationsMany real-time applications are associated with a stream of data such as voice or video. For real-time applications, there is no time to resend lost or corrupted data. The Real-Time Protocol was created to control the data flow for those applications. RTP does not guarantee that the packets are delivered in a timely manner, but it provides information to the application regarding whether all packets have been delivered and whether packets are in sequence so the application can make the correct decisions about playing out the content of the packets. IP allows packets to make their way from one side of the global network to the other. IP has true universal global access and can reach nearly any business, home, or hotel on the planet. This global reach is a key factor in IP becoming the new focal point of communications convergence. IP can bring about end-to-end connections to more places than any other packet technology.Now that you have an IP infrastructure, you want to have some real-time applications to run on it. To make this happen, you're going to need some control mechanisms for locating other endpoints, call setup, capability negotiation, and so forth. This is where the call control protocols (SIP* and H.323) and the gateway control protocols (H.248/Megaco) come in. These protocols take care of all the housekeeping tasks needed for setting up communication paths optimized for real time. SIP, H.323 and H.248 are critical to a successful user experience. They determine how a session is established between users. These protocols automate provisioning of communications parameters from mapping of the destination IP address against the telephone number, to authenticating the Copyright 2004 Nortel Networks Essentials of Real-Time Networking

6 Chapter 1 Introductioncaller as a real network subscriber, to choice of codec, to determination of IP addresses and ports for running the media, to tracking of usage for every call! As well as session control, you're going to need more control over the network traffic behavior. Most IP networks treat all traffic the same and are referred to as best-effort networks. Best effort means that the network delivers the traffic on a first-come, first-served basis, without regard for the urgency of the content. The speed and completeness of delivery depend on the amount of traffic sharing the nodes and links. Best-effort networks are engineered for connectivity, not for performance: all sessions are admitted, without regard for the effect on overall packet movement through the network. Best-effort makes no bandwidth or performance assurances, so packets may be discarded or delayed under network congestion. Because of this, traffic may experience different amounts of packet delay, loss, or jitter at any given time. As Service Providers and Enterprises alike consider converging network operations to leverage their existing infrastructures, real-time services will join nonreal-time applications riding on IP networks. For real-time services and applications, performance is paramount. The shift from connectivity to performance puts different demands on the network. Can your network handle this? Well, if it has some way of policing the packet flows, it might. This type of policing is typically done with Quality of Service (QoS) mechanisms. QoS mechanisms and protocols are essential to converting the connectivity-based network to the performance-based network. QoS provides ways to streamline packet movement, prevent congestion, and prioritize performance needs for different types of traffic. Spending some time discussing these mechanisms and how they work with various technologies is high on our list of priorities.

Section IV: Packet Network TechnologiesAs an IP certified engineer, your area of expertise may not include ATM and SONET. You design your LAN, are handed a cable from your Service Provider, and off you go. But what is happening in the carrier network? Is it important how the Service Provider is treating your packets? Your packet goes from your office in New York and arrives in London after a bit of delay, but it makes it. Well, it turns out that a lot of things can happen in the network core that can be detrimental to your real-time communications. What you don't know can bite you. As an Enterprise LAN engineer, do you know what questions you should ask your Service Provider? To do more than best effort, you'll want to know the questions and the answers. To get the most out of talking to Service Providers, you'll need some basic understanding of the technologies they use.Essentials of Real-Time Networking Copyright 2004 Nortel Networks

Chapter 1 Introduction 7From the other side of the street, Service Providers need to understand what their Enterprise customers are working with if they are going to serve them well. Frame relay continues to be used extensively in Enterprise networks. Packets crossing the Enterprise boundary encounter NAT. How are these things going to affect your SLA and the final user quality? Both Service Provider and Enterprise networks today are quite complex. Designing a real-time network to work across the combined domain is doubly complex. IP was designed to be a simple protocol. A few entries in a routing table, connect your cables, and you're up and running. It's a great concept, but the complexities of convergence will not allow us to maintain that simplicity. In Section IV, access, WAN, and core technologies are discussed. What are the drivers to move to an MPLS network? What QoS mechanisms are available in ATM and how are they invoked? What are the important things to know about ATM, frame relay, MPLS, SONET, and Optical Ethernet with respect to real-time networking? A convergence engineer needs to understand these network technologies, to be able to comprehend the concepts, and to understand their influence on real-time operation.Convergence is happening in many places. It's already happened at Layer 1. We are now seeing convergence at Layers 2 and 3, and VoIP is just one of the driving factors. The characteristics of the LAN, the WAN, and of course, the access network will come into play in the determination of the final network performance.

Section V: Network Design and ImplementationYou know it's going to happen. It's Friday afternoon, a three-day weekend is coming up, and you want to leave early. But then the call comes in, THE NETWORK IS DOWN. Why does it always happen on Friday? Convergence will make these calls even more heart-stopping. It's not just about the data network anymore. It's about a real-time network carrying voice calls and billing applications. As important as your data may be, these applications are mission-critical. Your CEO/CIO or your customer will be calling to find out when these applications are going to be back up.The network of yesterday was about reliability. Convergence has ratcheted that up a notch. Now it's called survivability. Survivability means your network can continue to provide service in the face of network faults. Fast recovery from failures and strategies for rerouting traffic around a problem are key aspects to survivability. Survivability techniques can be applied at different levels: at the node and link levels, as well as at the network level. They address software as well as hardware failures. In the past, reliability was thought of in terms of hardware. It was provided by redundant processors and dual power supplies. Most vendors offer redundancy at the Copyright 2004 Nortel Networks Essentials of Real-Time Networking

8 Chapter 1 Introductionhardware level, but how can you carry this through to the logical layer? You need to know, or suffer the consequences. Chapters 17 and 18 cover survivability at the network level. Together, let's explore the concepts of Network Reconvergence and MPLS Recovery. In other words, how can you build in survivability at the logical layer. This is a key factor to successful network convergence.The previous sections have discussed the relationship of applications, protocols, and technologies to real-time networking. Once you get to this point, you will have been introduced to some basic real-time services, how packet transport affects them, and some techniques for controlling and enhancing the performance of the packet network to meet the demands of these real-time services. You will understand the concepts of core network technologies and how they need to work on your existing LAN. In Chapters 19 and 20, the concepts are all brought together. Now is the time for the Converged Network Engineer to shine. Managing the complexity of the converged network takes planning. This section of the book helps consolidate the concepts you've learned, and shows how network planning can polish real time over IP to a brilliant shine. These chapters consider network planning for real-time voice and data, and how to translate Quality of Service settings from one network technology to another. In these chapters, potential issues related to real-time networking will be described along with mitigations and best-practice engineering guidelines.

Section VI: ExamplesUp to this point, the authors have maintained a vendor agnostic perspective. The concepts discussed are applicable to any vendor's products. This is consistent with Nortels commitment to open standards. In the next few chapters, however, we want to offer a few examples of what Nortel solutions look like in both the Service Provider and Enterprise environments.The first example illustrates a global-scale Enterprise network, and one that we are particularly proud of. Nortel runs one of the largest real-time Enterprise networks in the world, equivalent in breadth and scope to a Tier 2 Service Provider. In a typical month, more than 1,500 terabytes of routed traffic runs across the network. We will explore the business drivers of deploying QoS in our own network, and how it was implemented. The next two examples highlight Nortels carrier-grade portfolio by providing examples of real-time network solutions. Each example includes descriptions of business and technical challenges faced by Enterprises and Service Providers alike, and it presents the Nortel solution including specific product and service descriptions and network architectures. Note that these are not specific customer networks, but are examples of how a Essentials of Real-Time Networking Copyright 2004 Nortel Networks

Chapter 1 Introduction 9Nortel solution can help both Enterprise and Carrier customers move to the converged network of tomorrow.

Lets Get StartedWhen we first got the idea for this book, we wanted to address a specific issue. Voice and data services are converging onto a single network. Unfortunately, the histories of the two domains, the networks themselves, and the knowledge required for working in these environments are quite different. We wanted to do something to bridge the gap and create a way for the integrated knowledge to be disseminated cost effectively across both the Enterprise and Carrier spaces.While we hope for a broad readership, it was necessary to make some assumptions about the background of the nominal reader. Familiarity with basic IP data networking, the OSI reference model, and the corresponding terminology will be needed to follow much of the explanation, discussion, and examples.One of the goals of the book was to present the material in enough depth to provide a useful ongoing reference but still compact enough that the breadth of issues that confront implementing a converged network could be addressed. There is a lot of material in this book. More material, in fact than any one user of the book might need. Depending on your objectives in reading the book, following are a few suggestions for navigating the material. As mentioned earlier, this book is being produced in conjunction with the NCTS Real-Time Networking certification, there is more depth to the material in the chapters than is needed to prepare for the certification. Those who read this book as preparation for the certification exam should be aware that the exam will address definitions of terminology concerning Real-Time networking, and the associated technologies and concepts. It will also assess your understanding of the issues that Real-Time applications face in IP networks. No exam questions are drawn specifically from Section VI (Examples) or the Appendices, although reading those sections will help you consolidate what you have learned from the earlier chapters.For the reader looking to pass the certification, we advise focusing on how the pieces fit together into the larger picture, rather than memorizing details of individual technical solutions. The exam questions will concentrate more on knowledge of issues and terminology than on solutions to those issues. Aim for a general understanding of the technologies, paying special attention to issues that are highlighted in the text. Identify and digest the key terminology and acronyms. Depending on your professional background, you may find that some terms are used differently than you may be used to.Copyright 2004 Nortel Networks Essentials of Real-Time Networking

10 Chapter 1 IntroductionMany readers will come to this book with strong expertise in one or more of the areas covered, but may have little or no familiarity with other areas. While we assume that readers will have basic knowledge of data networking and TCP/IP, we cover a range of topics associated with convergence and real time. The reader can pick and choose sections and chapters, and does not necessarily need to read the various parts in order.If you're not planning to take the certification, it is our hope that you can use this as a guide as you embark on the journey to convergence. It is our hope that everyone will be able to get something out of this book, regardless of their background or the environment they work in today.

Reading the Transport Path DiagramsThis book employs a set of diagrams to provide a frame of reference for the material in the individual chapters. A diagram will be presented at the beginning of each chapter indicating the network components and functions addressed in that chapter. These transport path diagrams are intended to help the reader appreciate the relationships within the transport path for different network implementations. Because these diagrams are

Figure 1-1: Transport path diagramEssentials of Real-Time Networking Copyright 2004 Nortel Networks

Chapter 1 Introduction 11intended to give a high-level overview rather than a comprehensive summary, they are simplified in some ways for ease of presentation and comprehension. There is no 1:1 mapping between protocol functions and the seven-layer OSI model even though we do mention some of the same elements. This diagram is not intended to convey OSI stack information. We hope that these diagrams will help the reader locate the threads of the individual technologies within the fabric of the overall network.

The arrows used on the diagram are not meant to indicate that a process is strictly one-way, but to illustrate the perspective of application-level data or decision-making looking into the network. In general, the arrows point down to indicate that the real-time application looks towards the Wide Area Network through these layers. In many cases, there are different ways that a real-time application could reach the Wide Area Network. Some technologies, such as Cable and xDSL, have special Layer 2 relationships between the Local Area Network and the Wide Area Network. Not shown on the diagram are the encapsulation mechanisms used by these types of applications to bridge Local Area Network level traffic through Cable or xDSL transport and back into the core IP/ATM networks.The diagram highlights some of the different aspects of real-time issues that are addressed in the book, including transport protocols, session control protocols, Quality of Service (QoS) protocols, and reliability-related protocols. The latter have been included because real-time applications can significantly increase the requirements for network reliability. The braces on the right side illustrate where in the transport path the QoS and reliability features are applied.

ConclusionIt is no longer enough to be solely a data or voice engineer. The networks of today carry essential applications. These applications are not just data anymore. It is about a real-time interactive world. To support convergence, the underlying network must support real-time applications and service with delays less than 250 ms. Convergence demands One Network that brings together all the threads into one fabric. It is no longer about pieces of knowledge; convergence is all about how to weave all the pieces together. It is all about building your engineering toolkit. The NCTS Real-Time Networking certification is part of that kit.The Nortel Certified Technology Specialist (NCTS) Real-Time Networking is just the first step of becoming a Convergence Engineer. This certification was created to not only assist you, the IP certified engineer, but also to help us at Nortel. Convergence is part of our culture and our everyday life. Nortel has built real-time capability into our converged networks. There are advantages of the converged and real-time world, and you as a certified engineer, will be ready to embrace them. Copyright 2004 Nortel Networks Essentials of Real-Time Networking

12 Chapter 1 IntroductionI know you will find value in this study guide as you get ready for your certification. The subject matter experts who created this book hope you enjoy reading this guide as much as we enjoyed creating it. Thank you and best of luck in building your tool kit. Essentials of Real-Time Networking Copyright 2004 Nortel Networks

13Section IReal-Time Applications and Services

Let's begin by looking at the applications that run on real-time networks. Section I examines the characteristics of real-time applications and the issues that arise when we run them over IP. This section looks at the applications as the user sees them, and the implications of IP transport performance on the quality the user experiences. These chapters will give you a detailed view of how network design and implementation decisions can affect the user's experience. Chapter 2, The Real-Time Paradigm Shift, defines what we mean by Real-Time networking. Real time is defined, along with convergence in general and some specific types of convergence. Familiar applications are sorted into real-time and nonreal-time categories, and some potentially distinguishing features of real-time packet traffic are described. Quality of Experience (QoE) is introduced, and its relationship to network and application performance is discussed in detail. The chapter concludes with a discussion of the difference between QoE and QoS (Quality of Service).Chapters 3 and 4 take a look at issues around quality in two popular applications, voice and video. Voice Telephony continues to be the Killer Application of telecommunications. Examining voice impairments provides a good reference point for us to understand both the implications of IP network behavior on real-time applications, and how to interface IP networks with the existing TDM network. Chapter 4 looks at video and the impairments to the image that can result from IP transport.Chapter 5, Codecs for Voice and Other Applications, introduces digitization and encoding, which make it possible to put analog signals over digital networks. The discussion here provides some background on (1) voice and video analog signals and how characteristics of those signals translate into digital mode, (2) codecs that are used to remove redundancy to reduce the amount of data needed to carry the signal information, and (3) how various errors and disturbances of the compressed digital signal affect the reconstituted analog output. Common coding standards for telephony, audio streaming, and video streaming and conferencing are summarized, and guidelines for selecting a codec for VoIP are provided. Copyright 2004 Nortel Networks Essentials of Real-Time Networking

14 Essentials of Real-Time Networking Copyright 2004 Nortel Networks

15Chapter 2The Real-Time Paradigm Shift

Concepts Coveredz Telecommunications convergence z Types of convergence: network convergence, service convergence,

and application convergence. z Convergence removes constraints for users but adds constraints

for network operators z Real-time telecommunications z How to separate real-time and nonreal-time applications and

services z Service quality and performance z Quality of Experience (QoE) z Measuring QoE z Quality of Service (QoS)

IntroductionFor more than a decade, telecom scholars have been publicizing the advantages of convergence to multiservice networks; anticipated benefits range from cost savings from operating a single network infrastructure to productivity gains and/or new revenue from advanced services. Depending on who you talk to, next generation networks are expected to reduce capital expenditures, reduce operating expenses, increase revenues, decrease user cost of telecom services, improve quality, reduce quality, increase the reliability and survivability of the network, increase competition among carriers, and reduce churn in the customer base. Only time will tell which of these predictions are correct, but one thing is certain: meeting user requirements and expectations on converged packet networks is an enormous challenge. The crucial component of this challenge is making real-time services operate over a packet infrastructure. This chapter introduces the concepts of convergence, real-time operation, and Quality of Experience (QoE). No matter what network they run on, real-time services like voice telephony1 and video conferencing require careful engineering to deliver acceptable performance. Convergence of applications and services means that real-time and nonreal-time functions must share a common network environment and/or run side-by-side within the same application. Mixed traffic types from services and applications

1. Hereafter referred to variously as interactive voice or simply voice.Copyright 2004 Nortel Networks Essentials of Real-Time Networking

16 Section I: Real-Time Applications and Serviceswith differing requirements, can end up bumping heads as the traffic moves across the network. Successful deployment of converged networks depends on careful planning and engineering. The building blocks of this success include an appreciation of the characteristics and constraints of the services and applications the network will support, as well as a solid understanding of the network environment. A solid understanding includes knowledge of the transport technologies, the protocols, the available choices for implementation, and issues around interconnection with other networks. The details of network implementation will affect network performance and resiliency. The balance of this book reviews these building blocks, the choices and options available around network architecture, deployment of services on IP infrastructure, and design guidelines for achieving the performance and reliability users and network operators need from real-time services.The criteria for successful performance are based on user QoE. It doesnt matter how smoothly packets move through your network, if the users find that services and applications dont meet expectations. Planning must address the factors that underlie QoE for each service that runs on the network, as well as any interactions or inconsistencies between them. This book introduces real-time networking and many of the real-time concepts.

What is convergence?Narrowly defined, the term convergence, refers to the merging of traffic from two or more separate networks, onto a single network. At present, we are witnessing the convergence of traditional voice traffic (consisting mostly of standard voice telephony) and LAN-based data traffic (consisting mostly computer communications such as e-mail and file transfer) onto a common packet-based infrastructure. More broadly, convergence is used to describe the fusion of function across all aspects of communications. Three main kinds of convergence have been defined:

z Network convergenceCombining network traffic from different services (for example, voice, video, data) on one infrastructure

z Service convergenceCombining previously distinct services (for example, wireline and wireless voice; wireless voice and short message service) into a single service

z Application convergenceMerging of previously distinct applications into a coordinated suite (for example, multimedia, collaboration, and the integrated desktop)

Although convergence has recently gained prominence and notoriety, it is not a recent phenomenon. The telecommunications industry recognized Essentials of Real-Time Networking Copyright 2004 Nortel Networks

Chapter 2 The Real-Time Paradigm Shift 17over thirty years ago that the hierarchical network architecture of the voice network could not continue to grow indefinitely. The introduction of digital networking in the 1970s made it possible for the network to carry non-voice data along with digitized voice. This trend continued in the 1980s with frame relay and ATM. On the data side, private and then public multiprotocol best-effort networks followed, and forerunners to the IP protocols emerged. On the voice side, FAX and voice-band data services ran on a common infrastructure with traditional voice. More recently, convergence continues with the introduction of Storage Area Networking (SAN) and IP telephony; these bring with them the more stringent requirements of real-time operation and business-critical reliability.

Convergence increases optionsFor the user, convergence can increase the number of things one can do and the ways they can be done. Convergence brings down the boundaries between data and voice, between wired and wireless, between public and private, between the central site and the remote si