Terminology and Definitions Acronyms and Abbreviations Acknowledgement

Transcription

1 Contents Foreword Terminology and Definitions Acronyms and Abbreviations Acknowledgement xiii xv xvii xxi 1 Introduction General Introduction On Voice over IP and Telephony over IP Context Proliferation of Middleboxes IP Exhaustion Problem Migration to IPv Lightweightness and Optimisation of CAPEX and OPEX Avoid the Overspecification Phenomenon Interconnection Issues Enhancement Strategies to Solve SIP Issues IAX: Towards Lightweight Telephony Architectures IAX and Standardisation Rationale What This Book is Not Structure of the Book Part One: IAX Protocol Specification Part Two: Discussion and Analysis Part Three: Deployment Scenarios in SIP-Based Environments 9 References 10 Further Reading 10 2 The IAX Protocol at a Glance What Does IAX Stand For? Is IAX Specific to the Asterisk Platform? What is the Difference between IAX2 and IAX? Why another New VoIP Protocol? 11

2 vi Contents 2.5 How Does IAX Solve VoIP Pains? How is Calls Multiplexing Achieved? And What About Demultiplexing? What Port Number Does IAX Use? What Transport Protocol Does IAX Use? Is IAX a Reliable Protocol? How Does IAX Ensure Reliability? Is there an IAX Registration Procedure? Does IAX Registration Differ from SIP Registration? How Are Media Streams Transported in IAX? Is CODEC Negotiation Supported by IAX? Is On-Fly CODEC Change Possible During a Call? IAX: a Path-Coupled or Decoupled Protocol? Can IAX be Aware of the Status of the Network Load? What About Security? Could IAX Devices Be Managed? Is Firmware Version Updating Supported by IAX? Can IAX Be Extended to Offer New Features? How is an IAX Resource Identified? What Does an IAX URI Look Like? Is it Possible to Set a Call Involving Several IAX Servers? Is it Possible to Discover the Location of an IAX Resource? What Is DUNDi? What Is TRIP? What Is ENUM? 15 References 16 Further Reading 16 Part One: IAX Protocol Specifications 3 IAX Uniform Resource Identifier Introduction Format of IAX Uniform Resource Identifiers Examples of IAX Uniform Resource Identifiers Comparing IAX Uniform Resource Identifiers IAX Uniform Resource Identifiers and ENUM ENUM Architecture: Overview ENUM Validation Rules Call Routing in an ENUM-Enabled Telephony Domain ENUM Service Registration IAX ENUM Service Registration Examples of IAX ENUM Service Registration 29 References 32 Further Reading 33

3 Contents vii 4 IAX Frames Introduction Full Frames Structure Trace Example Mini Frames Structure Trace Example Meta Frames Meta Video Frames Meta Trunk Frames Encrypted Frames Conclusion 46 References 46 Further Reading 46 5 IAX Information Elements Introduction List of IAX Information Elements Example of IAX Information Element Traces 66 References 66 Further Reading 66 6 IAX Messages Introduction Taxonomy of IAX Messages IAX Requests/Responses IAX Requests IAX Responses Information Elements and IAX Messages IAX Functional Categories IAX Media Frames IAX Reliable/Unreliable Messages 77 References 78 Further Reading 78 7 IAX Connectivity Considerations Introduction IAX Transport Protocol IAX Port Number IAX Call Multiplexing and Demultiplexing IAX Reliability Mechanism IAX Timers Registration Retransmission Connectivity 84

4 viii Contents 7.6 Authentication and Encryption Conclusion 87 References 87 Further Reading 87 8 IAX Operations Introduction Provisioning and Firmware Download Context Provisioning Examples Firmware Update Registration Procedure Call Flow Examples Call Setup Procedure Successful Call Setup Flows Unsuccessful Call Setup Flow Call Setup with a Server Call Tear-Down Call Monitoring Call Optimisation Context Examples of a Call Transfer Call Flow Conclusion 101 References 101 Further Reading 101 Part Two: Discussion and Analysis 9 IAX and Advanced Services Introduction CODEC Negotiation Video Sessions Negotiation of Several Media Types in the Same IAX Session Presence Services Instant Messaging Topology Hiding Mobility Personal Mobility IP Mobility Miscellaneous Conclusion 115 References 116 Further Reading 116

5 Contents ix 10 Multi-IAX Servers Environment Introduction Focus Discovery of IAX Resources Static Configuration DUNDi TRIP Setting End-to-End Calls Load Balancing Objective Implementation Alternatives Path-Coupled and Path-Decoupled Discussion Service Provider Requirements SIP: a Path-Decoupled Protocol IAX: a Path-Coupled Signalling Protocol Discussion Forking Route Symmetry Conclusion 131 References IAX and NAT Traversal Introduction Structure NAT Types Overview Examples of NAT Types IAX and NAT Traversal Discussion Reference Architecture Discussion Operational Considerations Deployment Scenarios The IP Exhaustion Problem IAX, NAT and P2P Considerations Conclusion 152 References 152 Further Reading IAX and Peer-to-Peer Deployment Scenarios Introduction Scope A P2P Solution for Corporate Customers MEVA Architecture MEVA-Related IAX Frames MEVA Information Elements How to Subscribe to a MEVA Service 160

6 x Contents Contact Table Session Establishment Leaving the MEVA Service Optimisation Issues MEVA Architecture with a Point-de-Rendezvous Conclusion 167 References 167 Further Reading IAX and IPv Introduction Context and Assumptions Service Migration to IPv Structure The IP Address Exhaustion Problem IPv6: a Long-Term Solution Overview Between IPv4 and IPv6: Where Is IPv5? IPv6 at a Glance Why IPv6 May Be Problematic for Telephony Signalling Protocols: the SIP Example Overview Additional SIP Tags including IP-Related Information IPv6-Embedded SIP Examples IAX: an IP Version-Agnostic Protocol? Deployment of IAX Services in a Pure IPv6 Environment Heterogeneous Environment Context and Reference Architecture Analysis of Registration-Based Operations Call Setup and Call Optimisation Conclusion 189 References 189 Further Reading IAX: Towards a Lightweight SBC? Introduction IP Telephony Administrative Domain Deployment Scenarios Access Segment Interconnection Segment Deployment Contexts Legal Requirements Technical Considerations Service Limitations Caused by SBCs Functional Decomposition Taxonomy of SBC Functions in an SIP Environment 198

7 Contents xi Topology Hiding Media Traffic Shaping Fixing Capability Mismatches NAT Traversal Access Control Protocol Repair Media Encryption Validity of these Functions in an IAX Architecture Topology Hiding Media Traffic Shaping Fixing Capability Mismatches NAT Traversal Access Control Protocol Repair Media Encryption Lightweight SBC Conclusion 204 References 204 Further Reading 204 Part Three: Deployment Scenarios in SIP-Based Environments 15 Scenarios for the Deployment of IAX-Based Conversational Services SIP Complications Structure Beyond the SIP-Centric Era Methodology Overall Context SIP is Adopted as De Facto Signalling Protocol Heavy Border Equipment Routing Confusion NAT Traversal Issues The Need to Take into Account the IP Exhaustion Problem and Migration to IPv6: Easing IPv4 IPv6 Interworking Fixed Mobile Convergence Investment Implementation Availability Conclusion Architectural Requirements Brief Comparison Signalling Message Length Media Stream Length Security NAT Traversal Peer-to-Peer Firewall Traversal 217

8 xii Contents Routing Considerations IPv6 IPv4 Interworking Keep-Alive Feature Forking Routing Taxonomy Access Segment Core Segment Border Segment Introducing IAX into Operational Networks Rationale Alternatives Conclusion 220 References IAX in the Access Segment of SIP-Based Service Architectures Introduction A High-Level Description of the Interworking Function Examples of Call Flows Reference Architecture Provisioning and Firmware Update of End Devices Registration without Authentication Registration with Authentication Call Setup Call Tear-Down Aliveness of Registered Users Registration Release without Authentication Registration Release with Authentication Bandwidth Optimisation: An Extension to SIP Conclusion 237 References Validation Scenario Overview Configuring Asterisk Servers Configuration Operations Configuration Files Configuring the SIP Express Router (SER) Overview Configuration File User Agent Configuration Conclusion 244 Further Reading 247 Index 249