SIP for Dummies

SIP Communications

FOR

DUMmIES

AVAYA 2ND CUSTOM EDITION

by Lawrence Miller, CISSP, andPeter H. Gregory, CISA, CISSP

Foreword by Alan B. Johnston

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SIP Communications For Dummies, Avaya 2nd Custom EditionPublished byWiley Publishing, Inc.111 River StreetHoboken, NJ 07030-5774

Copyright 2009 by Wiley Publishing, Inc., Indianapolis, Indiana

Published by Wiley Publishing, Inc., Indianapolis, Indiana

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Contents at a GlanceForeword............................................................v

Introduction.......................................................1

Chapter 1: SIP at a Glance .................................5

Chapter 2: The Case for SIP ..............................15

Chapter 3: How SIP Transforms Communications.............................................21

Chapter 4: SIP Interoperability .........................39

Chapter 5: SIP in the Contact Center .................47

Chapter 6: SIP and Intelligent Communications.............................................55

Chapter 7: Ten Reasons to Use SIP-Enabled Solutions by Avaya......................61

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Foreword

These days, in communications circles, Session InitiationProtocol, or SIP for short, is seemingly everywhere.SIP is supported by practically every manufacturer of IPPhone, Gateway, Call Manager, and IP PBX. It is part of the IPMultimedia Subsystem (IMS). It is powering the fastest grow-ing VoIP (Voice over IP) residential and enterprise providers.It is a part of PC operating systems and has been enthusiasti-cally adopted by the open source movement. It is a key part offixed mobile convergence (FMC) and Unified communications.

Years ago, someone proposed a usage of SIP that was dubbedSIP for Light Bulbs! Dont laugh, it may happen yet.

So what is SIP and why is the industry buzzing about it? Thisbook will tell you. What can you use SIP for? This book will tellyou that too. Why is SIP so important? Youll find that here, too.

Before I leave you in the competent hands of the authors, I will add a few of my own answers here. SIP can be called arendezvous protocol. That is, it allows endpoints on theInternet to discover, locate, negotiate, and establish sessions.What kind of sessions? Any kind of sessions. SIP is used toestablish VoIP (of course), video, gaming, text, call control,and others Im sure Ive left out. Recent extensions to SIP addin instant messaging and presence capability. What is pres-ence? This book will tell you, but presence stands ready torevolutionize enterprise communications the same way publicInstant Messenger networks have revolutionized consumercommunications.

Besides all these applications and uses, SIP is also generatingits own ecosystem. In the same way that the Internet openedup networking by displacing closed, proprietary networkingprotocols, SIP has opened up communications and displacedclosed and proprietary signaling protocols. It has created anentire ecosystem of interoperable and configurable devicesand services that is revolutionizing the way communicationsis done.

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Not bad for a little protocol developed in academia back inthe mid-1990s by such thinkers as Henning Schulzrinne andJonathan Rosenberg.

The authors have done an excellent job of explaining thewhat, why, and how of SIP in an understandable way. Enjoyyour read of SIP Communications For Dummies, Avaya 2ndCustom Edition!

Alan B. Johnston

September 2008

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Introduction

Youve probably heard a lot about voice over IP (VoIP)or IP telephony in recent years. Theres a lot of industry

buzz and excitement about it, but you may be at a loss toexplain some of the benefits of VoIP for your business. Thereal advantage of VoIP and, more broadly, real-time IP commu-nications, is in the way it can transform your business com-munications architecture into an intelligent communicationssystem using a simple but powerful protocol, known as theSession Initiation Protocol, or SIP.

SIP makes it possible to easily connect the various compo-nents of an overall communications system, rapidly deployapplications, reduce costs, and improve customer service andemployee productivity by simplifying or SIP-fying yourorganizations communications architecture.

Vendors are increasingly incorporating SIP into their variousIP communications products, including:

Phones, gateways, proxies, and servers

Softphones software applications that provide voicecommunication capabilities on PCs, PDAs, and othermobile devices

PBX (Private Branch Exchange) systems

Instant messaging (IM) programs

Videoconferencing systems

Collaboration systems

SIP is an open protocol standard, with an active working groupon the Internet Engineering Task Force (IETF). Avaya and othermajor companies are active in the IETF SIP working group andin other industry groups, working to ensure that SIP-enabledsolutions work across businesses and enterprises with a variety of legacy, new, and evolving networking and telecommu-nications infrastructures and products to enhance and revolu-tionize the world of real-time business communications.

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SIP Communications For Dummies, Avaya 2nd Custom Edition 2

About This BookThis book explains SIP from both a business and a technicalperspective. You not only learn what SIP is and how it worksbut, more importantly, how SIP can benefit your entire organi-zation by transforming your real-time business communica-tions to gain a real competitive advantage.

Foolish AssumptionsWe assume that you have a keen interest in ensuring that yourcompanys networking and telecommunications systems areup to the challenges of intelligent communications today andinto the foreseeable future. Regardless of your role withinyour organization, this book will help you quickly get up tospeed on how SIP can revolutionize real-time electronic com-munications for your business or enterprise.

How This Book Is OrganizedEach chapter of this book covers a different aspect of SIP. Youmay want to read the book cover to cover to gain a more com-plete understanding of SIP, or you may prefer to skip aroundto find out what you need, when you need it. But be fore-warned, we didnt just save the best for last. This book ischock full of good information throughout!

Chapter 1: SIP at a Glance provides a brief overview ofthe SIP protocol including some history about its develop-ment as an industry standard and its basic components.

Chapter 2: The Case for SIP describes some of the keyfeatures of a SIP-enhanced IP communications infrastruc-ture and its potential benefits and advantages for busi-nesses and enterprises.

Chapter 3: How SIP Transforms Communicationsexplains how SIP enhances customer service andemployee productivity, and how SIP scales from the

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smallest businesses to the largest enterprises. We covertopics such as presence, AORs, peer-to-peer SIP, SIPtrunking, the IP Multimedia Subsystem (IMS), and theservice-oriented architecture (SOA).

Chapter 4: SIP Interoperability explains what vendorsare doing to make multi-vendor integration with SIP asstraightforward as possible. We also cover topics such ashybrid infrastructures, connection points, platforms andapplications, endpoints, the communications ecosys-tem, survivability, security, and federated presence.

Chapter 5: SIP in the Contact Center describes how SIPtransforms your call center into a full-service contactcenter to help your business better serve its customers.

Chapter 6: SIP and Intelligent Communications looks athow SIP continues to evolve and improve, incorporatingmore communications technologies and supporting moreenhanced communications capabilities.

Chapter 7: Ten Reasons to Use SIP-Enhanced Solutionsby Avaya cuts straight to the chase why your busi-ness needs SIP-enhanced communications and howAvaya can help!

Icons Used in This BookThroughout this book, we occasionally use icons to call atten-tion to material especially worth noting. Here is a descriptionof the icons youll encounter:

Some points bear repeating, and others bear remembering.When you see this icon, take special note of what youreabout to read.

This icon highlights technical information that will eithermake your pocket protector curl or help you fall asleep!

If you see a tip icon, perk up youre about to find out howto save yourself some aggravation.

Introduction 3

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Where to Go from HereWhether youre just hearing about SIP for the first time, con-sidering a SIP project, neck-deep in it, or looking to take yourexisting telecommunications infrastructure to another level,always keep your eye on the big picture. Avaya has keenvision and a strong commitment to SIP and unified communi-cations. Turn the page and discover for yourself why Avaya isa leader in intelligent communications.


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Chapter 1

SIP at a GlanceIn This Chapter Defining SIP

Playing nice with others . . . through standards

Sketching out a simple SIP architecture

People have more options today for communicating witheach other than ever, yet we often have a harder time getting through to anyone. We now have a dizzying array oftechnologies and communication devices, literally at our fin-gertips, that can deliver voice, text, and even video, in real-time. It seems everyone has too many devices, too manynumbers, and too little time.

Yet with more people more connected than ever before, anunintended and unexpected communications paradox hasemerged in our quest to make it convenient for anyone toreach us anywhere, anytime, and any way, it has actuallybecome more difficult to simply communicate with eachother. Determining the best way to get in touch with your cus-tomers, clients, and partners at any given time can be a daunt-ing task, and letting people know how to get in touch with youat any given time is no easy feat, either. Simply put, communi-cation has become device-centric, not user-centric.

This chapter introduces SIP, a widely adopted industry stan-dard protocol that is helping businesses and enterprises of all sizes solve these issues and enhance communicationscapabilities.

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What Is SIP?Session Initiation Protocol (SIP, as in sipping from a fire hose ona hot day) is an open signaling protocol standard developedby the Internet Engineering Task Force (IETF) in cooperationwith many industry leaders, including Avaya, for establishing,managing, and terminating real-time communications overlarge IP-based networks, such as the Internet. Communicationsvia voice, video, or text (instant messaging), may take placeusing any combination of SIP-enabled devices, such as a soft-phone on a laptop computer, a wireless handheld device orPDA, a mobile phone, an instant messaging client on a desktopPC, or an IP phone with videoconferencing capabilities.

SIP is an application layer peer-to-peer communication pro-tocol for establishing, manipulating, and tearing down com-munication sessions. But, you can do a lot more with SIP thanjust setting up telephone calls. The protocol is extensible meaning developers can easily write custom applications forSIP to accommodate video, instant messaging, and otheremerging communications media and features, using tools andprogramming languages, like Java, that are already familiar toInternet developers. Using SIP, simple-to-develop and quick-to-deploy custom applications can be easily integrated into yourcommunications sessions.

SIP is used to identify, locate, and enjoin parties who want tocommunicate using any peer-to-peer media type. However, SIPdoes not transport the media itself: That is handled by codecswithin the communications programs or devices.

SIP builds on a number of existing communications protocolsand has rapidly become the standard for service integration(how new services and applications are created and com-bined) within most large fixed and wireless carrier networks.Thus, SIP is positioned as a single unifying protocol that willtransform not only communications within an enterprise, butcommunications between an enterprise and its ecosystem ofcustomers, clients, partners, and suppliers. For businessesthat need to sort out and reconnect their current tangle of dis-parate communications protocols and programs, SIP is arefreshing solution that can simplify and enhance your com-munications capabilities.

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Setting the StandardAlthough you may not be familiar with SIP by name, its actu-ally based on many protocols that are widely used across theInternet and in many enterprise applications today. And, justas common standards and interoperability have been key tothe success of the Internet and IP networks, SIP is a widelyadopted standard that promotes interoperability and drivesdown costs in communications networks.

Youre probably already familiar with a protocol very similarto SIP HTTP (HyperText Transfer Protocol) yep, we affec-tionately refer to that bit before the www as H-T-T-P, colon,slash, slash when browsing to an Internet Web site. In effect,SIP is to intelligent, unified communications, as HTTP is to

Chapter 1: SIP at a Glance 7

What does SIP have to do with music?Absolutely nothing! But the originalIETF draft of the SIP protocol, pub-lished in February 1996, was titleddraft-ietf-mmusic-sip-00 notquite as catchy as, say . . . SIP Com-munications For Dummies! Thosewild and crazy guys at the IETF gaveus mmusic instead an acronymfor Multiparty MUltimedia SessIonControl.

Although SIP was originally the brain-child of the telephony industry, whichenvisioned a better way to set up andmanage telephone calls, the computerindustry saw the potential to revolu-tionize all real-time communicationswith SIP. Initially, SIP was developedas a means to invite people to largemultimedia broadcasts on theInternets multicast backbone, knownas Mbone. Mbone was used to

facilitate the distribution of streamingmultimedia content including educa-tional seminars, broadcasts of spaceshuttle launches, and riveting IETFmeetings.

Today, SIP enables a wide array ofservices and applications thatenhance real-time communicationsfor businesses and enterprises. Youcan find the latest core SIP specifi-cation in IETF RFC (Request forComments) 3261 (now simply titledSIP: Session Initiation Protocol),and its not just a one-hit wonder:Currently, some 289 RFCs related toSIP have been published, showingjust how much of a factor SIP is in thecommunications industry today and will continue to be for tomorrowand beyond.

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information exchange on the World Wide Web (WWW) itmakes the communications infrastructure transparent to end-users and enables ready access to many modes of communi-cation. Just as pointing your browser to an HTTP Web siteenables you to play a video, download a picture, or read text,SIP has been designed to support multimedia communica-tions in real-time.

SIP is modeled after HTTP, and in fact uses much of HTTPssemantics and syntax. Both SIP and HTTP use a plain text-based language. What does this mean for your business? SIPsmessages are easy to program and interpret, making it easierto achieve interoperability between disparate networks anddifferent vendor solutions, saving you money and enablingyou to rapidly deploy new applications to support your busi-ness and customer needs. SIP is also very modular and exten-sible (like XML, or the Extensible Markup Language), allowingfor integration with legacy systems and new and evolvingtechnologies. These properties make SIP an ideal protocol for implementing a standards-based unified communicationsnetwork.

Although the protocols are similar in their simplicity, SIP goeswell beyond the capabilities of HTTP, for example, by embed-ding intelligence in a communications session to sense themedia capabilities of an end device and the availability of auser to communicate.

The SIP standard is defined in RFC 3261 by the InternetEngineering Task Force (IETF). For anyone familiar with thebattle between Blu-Ray and HD DVD formats, the importanceof industry standards cannot be overstated. SIP has been awidely adopted industry standard for more than ten years.Additionally, several neutral consortiums, including SIP Forumand SIP Center, arrange meetings and events, such as SIPit,where companies with SIP-based hardware and software prod-ucts can test interoperability with other SIP-based products.This testing helps to promote smoother integration of SIP-based products in carrier and enterprise networks.

The IETF is a large, open, international community of networkdesigners, operators, vendors, and researchers concerned withthe evolution of the Internet architecture and its operation.


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Some vendors have gone above and beyond these efforts withactive SIP interoperability and ecosystem programs. In a well-run SIP ecosystem, devices and services obviously need towork together seamlessly, and the only way to absolutelyensure that they do is for vendors to test their SIP-based prod-ucts together. For example, Avaya has made a long-standingcommitment to establishing openness and interoperability for SIP through its Developer Connection program, which sup-ports software developers, systems integrators, and serviceproviders in testing interoperability and developing SIP-basedsolutions in conjunction with Avaya products and services.You can find more information about interoperability effortsin Chapter 4.

The potential impact of SIP goes beyond internal communica-tions within a business or enterprise. SIP has become a signal-ing standard for carrier networks. Service providers nowprovide SIP-based trunk services that can reduce costs andextend an enterprises SIP environment into the public net-work. The adoption of SIP for external connectivity will lead toa transformation in communications between an enterpriseand its ecosystem of partners, suppliers, and customers. SIPmay eventually become the unifying protocol for all real-timeIP-based communications. You can learn more about SIPtrunks, PSTN (Public Switched Telephone Network) and PBX(Private Branch Exchange) connectivity, and connecting dis-parate enterprise islands in Chapter 3.

SIP goes well beyond traditional telephony by facilitating anytype of peer-to-peer communication session, including instantmessaging, video gaming, voice and video conferencing, andcollaboration.

SIP is not designed to be a one-stop shop for all your protocolneeds. SIP is used to set up, manage, and tear down media ses-sions (for example, voice, text, and video). SIP works withother network protocols as well as application-layer technolo-gies to provide complete end-to-end functionality. One suchprotocol is the Session Description Protocol (SDP), which car-ries within it information about the session that youre settingup (namely, the type of media, the codec to use, and the pro-tocol for actually transporting the media).


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Basic SIP ComponentsWhen you are ready to enhance your enterprise communica-tions with SIP, youll need to understand the basic buildingblocks that form the foundation of your new SIP-enabledenterprise.

User agentsUser agents (UAs) are applications installed on SIP endpoints,such as an IP phone, mobile phone, wireless device or PDA, ora laptop or desktop PC (see Figure 1-1), that interface betweenthe user and the SIP network. A UA can act as either a clientor a server. When sending SIP requests, the UA acts as a useragent client (UAC), and when servicing a request, it acts as auser agent server (UAS). A back-to-back user agent (B2BUA) isan application that acts as an intermediary between two par-ties, but appears as an endpoint to both parties like a mid-dleman. It serves as both UAS and UAC simultaneously toprocess session requests.

Figure 1-1: Some typical SIP user agents.

[email protected]

Softphone

PDA

SIP Phone

Dual-ModeMobile Phone

Instant Messaging


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SIP devices can communicate directly if they know eachothers URI (Uniform Resource Identifier) or IP address, butmore commonly, SIP servers are used in an enterprise net-work to provide an infrastructure for routing, registration, andauthentication and authorization services.

IP-based devices can identify and communicate with oneanother using IP addressing alone. However, in most cases,your network uses the Domain Name System (DNS) to estab-lish sessions with device names, which DNS translates into IPaddresses. Similarly, SIP devices frequently consult directoryservers (often by name), which provide endpoint addressesthat the devices then contact to set up a call.

SIP serversSIP servers provide centralized information and enablementservices in a SIP ecosystem. The core SIP servers and anoverview of their basic functions are described here.

Registrar Server. When users come online, they need tomake sure that others are aware theyre available to takeand make calls. The Registrar authenticates and registersusers when they come online, and stores information onthe users logical identities and the communicationsdevices or physical entities (IP address) of the communi-cation devices they can use. The devices are identifiedby their URIs.

Location Service. As users roam, the network needs tobe continually aware of their locations. The locationservice is a database that keeps track of users and theirlocations. The location service gets its input from theregistrar server and provides key information to theproxy and redirect servers. A SIP proxy or redirect serveruses this information to obtain the mapping from logicalSIP addresses to physical SIP addresses, so that commu-nication sessions can be properly established and maintained.

Redirect Server. If users are not in their home domains,sessions need to be redirected to them. The redirectserver maps a SIP request destined for a user to the URI ofthe device closest to the user. For example, if a call isdestined for [email protected] and the user is


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on the road, the companys redirect server may reply tothe callers UA (or to the requesting proxy server) with thecontact address of the users mobile phone, so that theincoming call can be redirected to the mobile phone.

Proxy Server. A proxy server takes SIP requests,processes them, and passes them downstream whilesending responses upstream to other SIP servers ordevices. A proxy server may act as both a server and aclient, and may modify certain parts of a SIP requestbefore passing it along. A proxy is involved only in thesetup and teardown of a communication session. Afteruser agents establish a session, communications occurdirectly between the parties.

Presence Server. Presence servers accept, store, anddistribute presence information that allows users to seethe availability of people they want to contact. The pres-ence server has two distinct sets of clients:

Presentities (producers of information) providepresence information about themselves to theserver to be stored and distributed.

Watchers (consumers of information) receive pres-ence information from the server. Watchers cansubscribe to certain users, much like instant mes-saging users choose which buddies to add totheir list.

Presence is a key feature in SIP-enabled communications net-works. Dont worry if you dont yet understand the concept:You can read more about it in Chapter 2.

Now, you may be saying to yourself, whew, thats a lot ofservers! However, these functions can often be provided by asingle appliance, such as Avayas SIP Enablement Servicesplatform or the development environment provided by theAvaya SIP Application Server.

A Basic SIP Call ExampleThis section walks you through a basic SIP communicationsession how it works, and how SIP supports it. Figure 1-2illustrates the session.


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In Figure 2-2, two people [email protected] [email protected] use SIP user agents (UAs) tomake a point-to-point call through a proxy server. Examples ofUAs could be an Avaya SIP Phone, a SIP softphone, or a PDAphone. The proxy server works to connect the two UAs. Thecommunication then follows these steps:

Figure 1-2: A typical SIP sessions ladder diagram.

1. [email protected] (the UAC) initiates a session by inviting [email protected] andsending this request to the proxy server at smallcompany.com.

Michelles UA generates an INVITE request, which issent to the proxy at smallcompany.com. The INVITEmessage contains Session Description Protocol (SDP)parameters that define the types of media she is capable of accepting and where she wants the mediato be sent.

2. The proxy at smallcompany.com performs a DNS SRVrecord lookup for SIP services at bigcompany.comsince bigcompany.com is a foreign domain. This

Michaels softphone

Proxy server

Johns SIP phone

INVITE F1

100 Trying F3

200 OK F8

INVITE F2

100 Trying F4

180 Ringing F5

200 OK F7

ACK F9

180 Ringing F6

200 OK F11

BYE F10

Media Session

Dashboard

Profile:

Communications

Username:

Password:

Set Up:

Default

[email protected]

*****

Login

HistoryContacts


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record lookup returns proxy.bigcompany.com,which is then resolved to a physical IP address by DNS.Michelles INVITE request is then forwarded to theproxy server at bigcompany.com.

3. The bigcompany.com proxy server receives andprocesses the invitation, and looks up Tonys contactin the location database of the Registrar (physical IPaddress of the UA).

4. The location database of the Registrar returns [email protected] where Tony is currently located.

5. The bigcompany.com proxy server forwards theINVITE request to Tonys UA at [email protected].

6. The UAS at [email protected] asks Tony whetherhe wants to accept the call. Tony may hear a ring, seea text message, or see a blinking LED.

7. Tonys acceptance is sent back through the bigcompany.com proxy, which forwards it to the smallcompany.com proxy, which forwards it to MichellesUA. The body of Tonys acceptance includes SDPparameters defining the selected media chosen fromwhat Michelle had originally offered and where Tonywants the media to be sent.

8. Michelles UA responds to the acceptance with an ACK(acknowledgement) directly to Tonys UA, which tellsTonys UA that Michelle is ready to start the call.

9. At the end of the conversation, Tony hangs up hisphone. His UAC sends a BYE message directly toMichelles UA.

10. Michelles UAC responds with a 200-OK messagedirectly to Tonys UA, which ends the session.

Though this call flow describes the initiation of a basic phonecall, that simple call flow would be the same for establishingvideo conferencing or other media sessions using SIP.


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Chapter 2

The Case for SIPIn This Chapter Connecting people anywhere, anytime, on any device

Introducing AORs one convenient address for everything!

Using voice, video, text, and more!

Simplifying communications architectures for businesses large andsmall

Preparing for a bold new future with SIP

What business initiatives are driving your organizationstechnology strategy? Perhaps its improving your cus-tomers experience? Or, increasing the productivity of youremployees? Or, minimizing your operating costs? Gee, thoseall sound good! How about all of the above!

SIP is one solution that can help your business achieve thesegoals. For example:

Presence allows your employees and customers to com-municate more efficiently.

User-centricity gives your users more flexibility andoptions while improving control of technology andgreatly simplifying device (and communications) management.

Multi-modal capabilities provide a richer communicationsexperience and empower your business to better serveyour customers.

Simplified architectures promote interoperability whilesimultaneously allowing your business to reduce costs,rapidly deploy new applications and solutions, and growwith your business.

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SIP Communications For Dummies, Avaya 2nd Custom Edition 16To illustrate the potential of SIP for your business or enter-prise, we examine some of these key features and advantagesand show you how SIP can help you address this myriad ofbusiness challenges!

The Presence Is Now!SIP supports a new model for communications through its useof the Extensible Messaging and Presence Protocol (XMPP, whichcan also be used for presence) and SIP for Instant Messagingand Presence Leveraging Extensions (or more simply, SIMPLE).Both are widely adopted open protocol standards defined bythe IETF.

In an intelligent communications network, people can specifytheir communications preferences and availability. This fea-ture is known as presence an intelligent network overlaythat makes it easier for a calling party to reach an availableand willing-to-be-called party. Presence enables people toinform others of their status, their availability, and how theycan be contacted before a communication session evenbegins, thereby increasing productivity by making it easier toreach people more efficiently. Many devices can provide pres-ence information, which is particularly powerful when inte-grated across all of a persons communication devices, suchas IP phones, mobile phones, softphones, wireless devices,and PDAs.

Presence is not limited to a single person; it can also apply toa group of people (for example, Finance) or a device (forexample, Phone Status = Off-hook or On-hook).

Even more exciting, both people and applications can accesspresence information, providing the opportunity to createnext-generation converged communication applications. Forexample, your network can deliver new capabilities such aspolite calling (calls that are less disruptive for the party beingcalled) based on information from her calendar applica-tion, calls to an executive can automatically be routed to anassistant if the executive is busy. This can eliminate the needfor the caller to leave a voice mail and allows the executive tostay focused on her current meeting.

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Making the World Revolvearound You with User-CentricCommunications

Over the last few years, business communications havebecome largely device-centric. The more devices you use, themore numbers and addresses others need to know in order toreach you. And without presence, as described in the previ-ous section, communication has become a guessing gamewhen trying to connect with people, wherever they may beand whatever they are doing.

Chapter 2: The Case for SIP 17

Is it a business card or a phone book?Like many busy people, you proba-bly have a number of ways forothers to get in touch with you andyou want a convenient way for themto know how to reach you withoutyour business card starting to lookmore like a phone directory! Forexample, you probably have somecombination of the following:

At least four phone numbersincluding home, office (main anddirect), and mobile

An SMS address for text mes-saging on your mobile phone

Various instant messaging (IM)screen names or aliases

A fax number

Numerous corporate and per-sonal e-mail addresses andaliases (such as [email protected],[email protected], [email protected], [email protected])

Contacting you may have become aguessing game for your customers,clients, and partners. It shouldnt bethis hard! The user now controlshow people communicate with you,and SIP can help by providing asingle address for all your communi-cation devices.

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With SIP, your business communication becomes user-centric,once again making it easier for you to reach your customersand for your customers to reach you. A SIP address of record(AOR) provides one unifying identifier that can be mappedacross multiple devices and media types. No more tracking ofmultiple phone numbers, e-mail addresses, and IM contactnames. You can think of an AOR as your public address.

One Protocol, Many Modes of Communication

New SIP-enabled converged communications solutions enableusers to interact with each other or with an application, in avariety of ways. Input can be via speech, keyboard, telephonekeypad, or mouse. Various modes of output may include syn-thesized speech, audio, plain text, motion video, and/or graph-ics. And best of all you control how people reach you. Hereare some examples that SIP-enabled solutions can facilitate:

Voice/IM/video: A common interface provides access toinstant messaging, voice, and video services, tiedtogether with presence. Initiating communications is thesame for all modalities, and users can switch from onecommunication method to another on the fly to bestmeet their needs.

Inline translation services: A SIP request, originatingwith an English-speaking user, might contain a Web serv-ices request to translate a message into another languagefor a non-English-speaking recipient.

Multimodal messaging: A SIP-enabled voice messagingsystem could provide features such as:

Voice-mail headers to the end-user via text

Display-enhanced voice-mail by delivering text orgraphics menus instead of voice-based menus

Virtual business cards with every voice call so thatthe user can have the callers contact informationavailable

Playback, skip, rewind, pause, slowdown, andspeedup buttons using a graphical user interface(GUI) in a screen phone


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Speech-to-text translation: In situations where the calleronly has a phone and the called party only has a textdevice (PC, laptop, wireless device), a SIP-enabled trans-lation service could provide text-to-speech and speech-to-text translation.

Web-based Interactive Voice Response (IVR): Usersmay surf the Web as opposed to working their waythrough IVRs. Such systems could be used from a hotelroom to order services, for example.

Because SIP uses the Session Description Protocol (SDP) todetermine what type of media stream the answering UA cansupport, SIP can make intelligent choices for modality.

SIP can also support multiple media types within a single com-munication session. This broad support creates a naturalsolution for providing communications that adapt to the userbased on the situation and the communication device beingused.

The term multimodality refers to the ability for a user (or deviceor application) to communicate through more than one mecha-nism. For example, a user may be able to input text via voice ortyping on a keyboard. An application such as the Avaya SIPsoftphone can deliver either a text or voice message.

Streamlining CommunicationsArchitecture

Communications networks today are complex and costly tooperate and maintain. By comparison, a SIP communicationsarchitecture consists primarily of SIP endpoints and SIPservers. This means that your business can simplify its commu-nications network and reduce associated costs. Endpoints arealso called user agents the programs and devices that actu-ally perform the communications between end-users. In smallerbusinesses, the user agents can be smart enough to communi-cate with one another without servers. In larger enterprises, SIP servers such as proxies, registrars, and presence servers,facilitate user agent communications.

Chapter 2: The Case for SIP 19

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SIP scales well for even the smallest businesses, where SIP-enabled endpoints can be established in the absence of cen-tralized proxies and registrars. We discuss SIP for small officesin Chapter 3.

SIP offers a single unifying protocol for all real-time communi-cations. For example:

With SIP being widely deployed in both service providerand enterprise networks, the need for gateways thattranslate one protocol to another (for example, IP toTDM, or Time Division Multiplexing) is minimized.

Proprietary signaling protocols give way to a single stan-dard interface for all connectivity whether for addingendpoints, deploying contact center adjunct services, oreven connecting to trunk services for external communi-cations.

In addition to its forward-looking innovative uses, SIPsupports the legacy public switched telephone network(PSTN) and Private Branch Exchange (PBX) systems,which will be around for some time to come.

See Chapter 3 for more on SIP trunking.

An equally important foundation of SIP is the concept of dis-tributed intelligence. This concept, evident in peer-to-peer(P2P) architectures such as Avaya Quick Edition, creates anew paradigm in communications, requiring no PBX or com-munication server, only intelligent phones and other endpointdevices as the mechanism for establishing a working commu-nications system.

The Future Is Now!SIP, an extensible and versatile open protocol, has wide adop-tion throughout the industry. New solutions that will empoweryour business and employees to better serve your customersnow make intelligent communications routing and other deci-sions based upon interaction with users, such as a person'sknown physical location linked to presence.


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Chapter 3

How SIP TransformsCommunications

In This Chapter Enhancing end-user communications with presence, preference,

user-centric communications, and mobile devices

Understanding peer-to-peer SIP for small offices

Taking a look at SIP trunking, federation, IMS, and SOA for the enterprise

SIP can revolutionize real-time IP communications in anyorganization, large or small. This chapter takes a look athow SIP-enabled features like presence and addresses ofrecord can enhance the productivity and quality of communi-cations for end users. We also examine SIP for small andmedium businesses and discuss some of the unique challengesfor small and distributed business environments. Finally, wesee how SIP scales to even the largest enterprises and serviceprovider networks, providing the framework for new andevolving architectures such as IMS and SOA, and making SIP atruly universal solution for intelligent communications.

How SIP Transforms End-UserCommunications

Are you spending more time managing your communicationsdevices and looking up phone numbers or addresses thanactually communicating with others? If so, SIP is about to sim-plify your life and let you control your communicationsdevices, rather than having them control you.

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To Be or Not To Be . . . Available with PresenceWhen a user activates a communications device (user agent,or UA), the device registers its presence on the network, indi-cating its ability to communicate. The concept of presence issomewhat analogous to the telephone networks busy signal,signaling to a caller that you are unable to talk right nowbecause youre already talking with someone else. But, SIPtakes presence a step further.

Presence distributes the following information:

User status (that is, online or offline)

User availability (such as Available, Away, In aMeeting, On the Phone, and Busy)

Users desired contact method (such as instant messag-ing, desk phone, mobile phone, pager, and so on)

SIPs presence states also permit predictable rules-based rout-ing decisions to be made. These decisions are based on ausers specific presence state, and on customizable prefer-ences that include any information the user wants to share.

Presence doesnt just apply to people and need not only applyto a single entity; presence can also be associated with adevice or group. For example, a presence status might capturethe status of a device (Phone Status = Off-Hook) or thestatus of a user (User Status = Online). Presence forcomposite entities like contact center groups or shared docu-ments can be similarly represented.

Using presence to route communicationsSIP can make call-routing decisions based on presence infor-mation by enabling users to inform others of their status,availability, and how they can be contacted before a com-munication session even begins. A user can communicatestatus and availability to others through multiple devices

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such as IP phones, mobile phones, softphones, instant mes-saging, pagers, video conferencing, e-mail, wireless devices,and even TDM phones connected to an intelligent IP PBX.

Presence can span a number of different communication chan-nels and provide an aggregate view of a users presence (thatis, availability across all of an individuals SIP-enableddevices). Possibilities include:

Setting the users status to Away when his phone andkeyboard are inactive for some time

Making inferences about a users presence throughmobile device location information

Checking a users calendar to see whether he is in ameeting or on vacation

Checking a users e-mail to see whether he is reading orsending e-mail, or whether he has an Out of Officesetting

SIP uses presence to make routing decisions for a variety ofincoming communications including:

Routing incoming calls from a desk phone to a mobilephone if the user has indicated that he is roaming andprefers calls routed as such

Classifying non-urgent incoming communications aspolite calls that the user can choose to answer, forward,or ignore

Routing urgent incoming calls and e-mail to others if theuser is on vacation or in an extended meeting

When a SIP proxy (a server that processes and forwards SIPrequests between calling and called parties) receives anINVITE (request to communicate), it uses the called partyspresence to make a routing decision, sometimes called forking. The forking decision may be to a specific party (an intelligent fork), or it may send several INVITEs to differ-ent addresses (parallel forking).

Forking is an old UNIX term where a process clones itselfinto two or more new processes. In the SIP context, forkingrefers to sending multiple simultaneous INVITEs to other par-ties to initiate a communication session.

Chapter 3: How SIP Transforms Communications 23

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AORs 0ne address to rule them allAnother key feature of SIP is its ability to use an end-usersaddress of record (AOR) as a single unifying public address forall communications. With SIP-enhanced communications, ausers AOR becomes her single address that links the user toall of the communication devices or services that she uses. Forexample, Eileen Dovers AOR might be sip:[email protected]. Using this AOR, you can reach Eileen on any of her multiple communication devices (her UAs) withouthaving to know each of her unique device addresses or phonenumbers.


Presence means being there for your customers

Every successful company strives toprovide superior customer service,with call centers or contact centers(you can read more about contactcenters in Chapter 5), which are oftenthe first contact an upset customermay have with your company whendealing with a particular issue. Buthow can your customer serviceagents get to all the information theyneed to provide quick, accurateresponses for your customers?

A credit card company that providesongoing support for its customersthrough a contact center offers oneexample of how SIP presence canhelp you deliver superior customersupport. The names, places, andevents are fictitious, but the possibil-ities are real:

A customer planning an overseas tripcalls with a question about monetary

conversion rate policies. The cus-tomer service agent checks herfinance expert presence tab andsees that an internal resident expertis off the phone and available for con-sultation. The agent clicks the IM taband is automatically routed to theavailable expert. The agent then gets,and quickly relays, the expertsanswer to the customer. The cus-tomer then asks about a disputedtransaction with a merchant. Theagent brings up the merchant infor-mation, which displays the presenceand availability of the merchantscustomer service agents for phonecalls or IM, and contacts an availableagent who can look up details of thetransaction and send it back via aWeb-page push. Complete customerservice with a smile (or maybe just asmiley face icon)!

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To complement AORs, SIP supports Uniform Resource Identifiers(URIs) that establish a common addressing scheme for all of anindividuals user agents. A URI address follows the same basicformat as a Web or e-mail address: contact-address@domain. Using this format, SIP can map the unique addressesof a users multiple devices and services to a communicationdomain, and then link all the user agents to a users single AORfor that domain. Some examples of how a URI might be appliedinclude:

A phone: sip:[email protected];user= phone

A fax: sip: [email protected];user=fax

An IM user: sip:[email protected]

A user typically has just one SIP AOR, such as sip:eileendover@domain. Each of the users devices then hasits own URI, such as sip:[email protected];user=fax.

Because a SIP URI supports both numeric (phone numbers)and alphanumeric (Internet-style addresses) formatted con-tact addressing, the public switched telephone network (PSTN)and the Internet can be seamlessly linked together. With SIP,users can potentially contact any user, whether they are onthe PSTN or the Internet.

As with e-mail addresses, users probably wont memorizeother users SIP AORs. Instead, theyll use address books andbuddy lists, just like they do on their e-mail systems, mobilephones, and IM clients today. A SIP AOR will be just anotherdata field associated with each person or group. When usedby a SIP device, the URI will be retrieved and used to commu-nicate with another party.

Better mobility with SIP and IMSBecause an AOR can be associated with any number ofdevices and/or applications, SIP can leverage all kinds ofmobile communications devices as part of a SIP-enabledenterprise. By applying intelligent forking , SIP can direct com-munications to any number of mobile UACs (user agent clientdevices) including mobile phones, wireless devices, and soft-phones or other applications installed on a laptop computer.


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Initial efforts to develop SIP-enabled mobility solutionsfocused on voice calls within wireless networks to lowerusage charges and require fewer phones. For example, Avayaand its partners pioneered the development of multimode SIPphones with both mobile and WiFi capability. These develop-ments served as an important step towards next-generationSIP-enabled communications applications.

Consider a business communications solution where SIP isthe common interface providing integration between enter-prise networks and service provider networks. While roamingin a service provider network, users can stay in touch withtheir virtual enterprise anywhere, anytime, any place asthough they had never left the premises.

Users can instantly receive enterprise voice messagenotifications while out of the office.

Users working across multiple locations dont have tocarry yet another phone, pager, or PDA.

Services support improves because managers canquickly locate field technicians within a customer area toprovide better responsiveness.

SIP-enabled user devices can respond to a phone call byresponding with a short text message that lets the callerknow the persons availability.

SIP is well suited for mobile environments. SIPs registrationfunction is similar to that in GSM and 3GPP networks. When auser turns on a SIP device, it registers the user and sends thedevices URI to the registrar server, which routes calls to andfrom the user. This system ties together multiple communica-tion silos (for example, e-mail, IM, desk phone, and mobilephone) using a single address that can reach the user regard-less of location.

What about customized options such as address lists, buddylists, and speed dials? SIP preference features can make thesecustomizations mobile. For example, Avayas Personal ProfileManager provides a centralized service that communicateswith SIP endpoints to receive, store, and distribute contactlists, access control lists for user presence, and device param-eters such as speed dials and feature button mappings to


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the SIP endpoint currently in use. A Web-based interface, theSIP Personal Information Manager, allows users to securelymanage and view their profile and device information usingany standard Web browser. The user simply authenticatesthrough the endpoint and his stored data is securely down-loaded to create a customized user environment.

Native mobility is one of the reasons the Third-GenerationPartnership Project (3GPP) has adopted SIP as its primary sig-naling protocol for the IP Multimedia Subsystem (IMS). Otherreasons for using SIP as a core underlying technology for sup-porting IMS include simplicity, flexibility, extensibility, andfamiliarity recall that SIP is a plain-text, open protocol stan-dard similar to HTTP that simply establishes, manages, andterminates real-time IP communications sessions over a widearray of mediums including voice, video, and text (refer toChapter 1).

IMS provides a framework for innovation within a serviceprovider network, enabling rapid development of new andinnovative multimedia applications and content over a mobilenetwork. SIP is the key to delivery of these innovations fromIMS to mobile networks and users.


Keeping up with mobile usersSIP enables seamless mobile com-munications anytime, anywhere.For example, suppose a bank execu-tive adds a new contact to her per-sonal profile and assigns it a hotbutton or speed-dial. She initiates aSIP call through the internal networkusing her dual-mode mobile phone tocheck voice mail. While still listeningto messages, she walks out of theoffice to her car and the callswitches on the fly to her mobileservice provider network. She thenarrives at the main office still on hermobile phone. The intelligent networkusing SIP detects her presence and

switches the call back to the com-panys wireless network automati-cally. The executive finds a mobileuser cubicle with a PC and softphoneapplication; upon authentication, herentire contact list and phone featuresare downloaded. She then checksher buddy list, sees via presence thather new contact is online and avail-able for a phone call, and she initi-ates a connection. Her contact is outin the operations center, so the net-work intelligently forks the connec-tion over to his PDA (which containsa SIP telephony client), and the callbegins.

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How SIP Transforms SmallOffice Communications

Small offices including small or mid-sized businesses andsmall branches of large enterprises are becoming moredynamic in form and function and are becoming increasinglydistributed. These work environments must address chal-lenges that although not unique, can be nonetheless dauntingfor small offices, including:

Capital costs: As small offices seek to maintain a moredynamic form that focuses on the localized needs of theirmarkets, they often find themselves balancing the needfor adaptability with the upfront capital costs of commu-nications solutions.

Operating and administrative costs: Communicationssolutions often require on-site technical installation andmaintenance services. Additional costs are incurredwhen local support is required to fix problems, addcapacity, or perform basic administrative tasks.

Speed: For many small offices, competitive advantage isall about speed time to deployment drives time tomarket. Developing new applications that integrate withcomplex communications architectures through openbut proprietary APIs (application programming interfaces)can be a time-consuming event requiring detailed plan-ning, staging, testing, and debugging.

Business continuity: Small businesses are often moresensitive to disruptive events than larger businesses. Thesurvivability of a small business may be threatened byeven a relatively minor or short-term event lasting only afew days.

Peer-to-peer (P2P) SIP is one solution for small- and mid-sizedbusinesses. P2PSIP collapses some of the more complex serverfunctions into the phones (or other endpoints) themselves.P2PSIP relies on the core SIP philosophy that intelligence incommunications solutions should reside in the endpoint (referto Chapter 1 for more about the variety of available SIP end-points, or user agents). Contrast this approach with that ofold-fashioned analog telephones that do little more thanamplify voice signals and rely upon complex and fixed-costPBX switches to provide communications functionality.


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Peer-to-peer SIP communicationsoverviewIn large enterprises, SIP is most often implemented using cen-tralized services such as proxy servers, presence servers, gate-ways, and location servers yet with redundant edge devicesthat understand multiple home-proxies. But, SIP endpoints canalso function without all of these central services in small-officesettings bringing the advantages of SIP to small and mediumbusinesses, such as cost reduction, converged voice/video/data over SIP trunking, presence, and UC applications.

Avaya is an active member of the IETF P2PSIP working groupthat is working to define a P2PSIP protocol standard and toaddress issues such as security and privacy in a peer- to-peercommunications network.

P2PSIP effectively replaces the registration, location, andlookup steps of SIP. It handles three functions:

Registering a phone or a user with the peer-to-peer over-lay network (when the phone or user joins the network)

Looking up a phone or a user in the peer-to-peer overlaynetwork (when a call to the phone or user is made)

Dynamically sharing information when peers join andleave, so that the load is balanced across peers, and sothat the sudden loss of one or more peers doesnt causethe peer-to-peer network to lose track of its current registrants


Avaya IP OfficeIP Office is a highly modular IP tele-phone system designed to meet theneeds of home offices, standalonebusinesses, and networked branchand head offices for small and mid-size businesses. The award-winningIP Office gives growing companies a

complete solution for telephony, mes-saging, networking, conferencing,customer management, and unifiedcommunications, thereby helpingbusinesses reduce costs, increaseproductivity, and improve customerservice.

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With P2PSIP technology, you can drastically simplify tele-phone system setup and installation. Plug an IP telephone intoyour local area network, and it configures itself. In minutes, allusers have access to the most commonly used features,including voice mail, conferencing, and auto-attendant. Asimple PSTN gateway also acts as a peer to the phones andcan provide access to the PSTN. And a peer-to-peer solutioneasily grows with your business. As you add employees,simply add telephones.

How SIP Transforms EnterpriseCommunications

SIP fundamentally improves the efficiency of communicationsbetween enterprises and their partners, suppliers, and cus-tomers. The initial benefit of IP communications has been primarily limited to intra-enterprise communications.Communications between enterprises, even those that areVoIP-enabled, still largely require a circuit-switched handoffthat impacts voice quality, adds complexity, and introducesadditional expense through intermediate carriers. SIP changesall of that by interconnecting SIP communications architec-tures and the PSTN, and with SIP trunking and federation services.

Enterprises can benefit from the simplification of enterprisenetworks through SIP standardization for both internal andexternal communications. As SIP becomes ubiquitous in bothservice provider and enterprise networks, a single standardinterface for all connectivity is available for adding endpoints,deploying contact center adjunct services, or even connectingtrunk services for external communications. Proprietary sig-naling protocols, including variants of voice-centric T1 and E1standards, and hardware-intensive digital/analog interfacesgive way to a simple, logical SIP interface that connects appli-cation servers residing on industry-standard platforms. WithSIP as a unifying protocol, you can dramatically reduce theneed for dedicated hardware gateways and devices.


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Working together: SIP and the PSTNClearly, the telecommunications industrys system of countrycodes, area codes, city codes, and telephone numbers willcontinue to serve many people around the world for sometime to come. So, how do you call SIP users with URIs from aplain old telephone system (POTS) using a dial-up telephone,and vice versa?

Fortunately, the mapping between SIP and telephony proto-cols has already been defined. Gateways that link the Internetwith the PSTN are widely deployed and used by VoIP usersevery day. SIP URIs can also be used to carry telephone num-bers. For example, sip:[email protected];user=phone contains the phone number for directory assis-tance in New York, New York.

By porting a PSTN telephone number to a SIP/PSTN gateway,incoming telephone calls can be routed to SIP phones, callmanagers, and PBXs.

Many service providers have already adopted SIP for theirinternal PSTN telephone call routing. With SIP-to-PSTN inter-working (providing connectivity between these two systemsthrough a defined interface standard) in place, carriersthroughout the world are working with SIP vendors like Avayato offer exciting new SIP trunk services to the enterprisemarket.

Trunking with SIPTrunking refers to the means used to transport inbound andoutbound calls between the enterprise and external entities(including branch offices and other remotely located partiessuch as business partners, customers, and suppliers). In thissection, we describe the differences between traditionaltrunks and SIP trunks, as well as some of the characteristics ofSIP trunks that are attractive to businesses.


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Before SIP and VoIP, enterprises connected their internal PBX-based telephone systems to carriers via dedicated TDM(Time Division Multiplexing) trunks. Companies paid for themwhether they were idle or busy, and incurred toll and tariffcharges, particularly expensive for long-distance calls.

Today, many companies integrate voice and data over IP net-works and link their sites using wide area networks to reducecommunications costs within the enterprise. However, tradi-tional PSTN circuits are still used to communicate with theircustomers and suppliers, partners, and the outside world.

SIP trunks enable enterprises to carry their voice data over apure IP connection to carrier clouds, rather than through sep-arate voice-only circuits. An enterprise SIP proxy peers witha carrier SIP proxy, with the appropriate federations and secu-rity protections established between them. The IP circuit con-tinues to carry e-mail, Web, data, and other corporate trafficas it does today, and voice is simply added to the mix asanother IP application. SIP sets up and tears down voice callsto and from the enterprise over this IP circuit.


How SIP trunking can help you improve customer service

SIP can improve the way a retail busi-ness services its customers. Supposea retailer with several store locationswants to offload the task of handlingphone calls from its store employeesso they can focus on in-store cus-tomers, but the retailer has no directconnectivity between its customerservice center and each store.

SIP-based trunking enables a recon-figuration of communications toaddress the problem. Through SIP-based DID (Direct Inward Dialing)mobility inbound service, the serviceprovider transports local calls to each

store over the SIP network directly tothe customer service center.

Without making any changes to thelocal stores, the retailer is now ableto free up store employees to servein-store customers, improve cus-tomer service over the phone byreducing hold times and busy signals,and still retain a local presence to itscustomers through a local accessnumber. And with SIP trunking, thecustomer service center can replacedozens of traditional TDM (Time-Division Multiplexing) trunk lines witha single SIP link!

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On-net calls traverse the carriers VoIP backbone (which istypically dedicated to voice so that voice quality can be guar-anteed). Off-net calls ride the carrier IP network until the lastmile where a gateway converts VoIP to TDM for calls to PSTNparties (see Figure 3-1).

Figure 3-1: SIP trunks change how you make connections to carriers.

SIP trunks offer a number of advantages, including:

PSTN origination/termination and cost savings: ManySIP service providers support origination/terminationservices directly to the PSTN from their SIP networks.This allows the enterprise to reduce monthly recurringcosts associated with multiple TDM circuits by deployinga single IP pipe to the provider network.

DID and Toll-free Number Mobility: These features takeadvantage of the fact that SIP is geographically agnostic.Calls destined to local or toll-free numbers can be auto-matically rerouted over the service provider SIP networkto another enterprise location. For enterprises, thissystem offers great flexibility in providing a local pres-ence in all their markets while routing calls to a central-ized call center for more efficient service.

Session Border Controllers (SBCs for short) are edge securitydevices that sit at the edge of a SIP enterprise network and acarrier or ISP network cloud. Among the multiple functions

Phones

SIP Proxy

Router

IP Data/Telephony

All Communications

ServiceProvider

SIP Network

PSTN LongDistance

PSTN LocalAccess

LAN


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these devices can provide, some SBCs have been designed tosupport both inward and outward translation of URIs to E.164(phone number addressing).

In a converged network, voice becomes an IP application,sharing the common network infrastructure and services.

Where no one has gone before connecting enterprises to federated servicesA common concern for companies contemplating the switchto SIP is how quickly all these nifty advances are going tocome together in a truly comprehensive way. In particular,how can isolated enterprises exchange directory information?Sure, each step toward SIP is a step in the right direction, buthow do you get everyone marching in step? The answer: federation.

In recent years, businesses have enthusiastically adopted IPfor their internal communications. For example, today farmore IP PBXs are sold than TDM PBXs. However, most ofthese IP communication infrastructures stop at the enterpriseboundary. IP PBXs fall back to TDM and revert to phonecalls for communication outside of the enterprise. As a result,IP communications islands are growing, but they are notinterconnected. With SIP, interconnection of these islandsover the Internet is accomplished. The benefits of intercon-nection are enormous. For example, you can

Extend SIP-enhanced services beyond the enterpriseboundary

Make additional modes of communication available,including multimedia and instant messaging

Establish higher-quality connections

Reduce costs by bypassing TDM network interconnections

If two enterprises both use SIP, they can interconnect andenable SIP-to-SIP calling, interact via multimedia sessions andinstant messaging, and exchange presence information.


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What are the obstacles to interconnection? To enjoy the fullbenefits of SIP, you need to overcome three main barriers:

Enabling SIP islands to discover the existence of oneanother

Ensuring that the two islands interoperate

Managing and controlling interconnections so that spamand abuse do not become rampant

One solution to these issues is federation. Federation builds anetwork of open communications within the ecosystem of SIPcommunications. Accomplishing this interconnectivity mayrequire one or more of the following:

A federation service that provides discovery servicesenabling other SIP islands to be discovered from just atelephone number or address. A number of databasesand directories are available. One such database isENUM, described in the next section.

A federation service built on top of SIP that providesinteroperability over a wide range of services and fea-tures such as voice, video, presence, and IM. A federationservice may also provide gateways for interoperabilitywith non-SIP devices.

A federation service that authenticates users and setspolicies for acceptable use. A SIP equivalent of caller ID ispossible in this model, enabling users to trust a callingparty. This helps avoid the anarchy of e-mail in whichanyone can claim to be anyone else (spoofing).

An alternative to federation is direct peering. In this mode, twoenterprises get together, exchange directory and routing infor-mation between them, and set up policies and procedures forcommunication. Although this system may work among ahandful of enterprises, direct peering is cumbersome whenconnecting multiple enterprises and obviously does not scalelike a federation.

Mapping phone numbers to URIsTo interconnect SIP islands, your network needs a method ofdiscovering a SIP URI from a telephone number. The ENUMprotocol has been developed by the IETF Telephone Number


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Mapping working group for this purpose. ENUM has a DNS-based architecture and protocol by which standard telephonenumbers can be expressed as a Fully Qualified Domain Name(FQDN) in a specific Internet domain (e164.arpa). The resultof the ENUM query is a series of records (defined in RFC 3402)that gateways, proxy servers, and even SIP endpoints can useto contact one or more resources associated with that number.

As SIP continues to be adopted by service providers, ENUMwill become part of the suite of services that a serviceprovider connecting to a SIP enterprise network can deliverthrough the PSTN. On your SIP phone, youll be able to punchin a URI for your friends TDM landline or mobile phone, andthe carriers ENUM server will seamlessly connect you.

An alternative to ENUM is LDAP (Lightweight Directory AccessProtocol), which can store both a users URI and all associatedphone numbers (E.164 addresses). SIP applications can thenreference entries stored in LDAP to resolve and translatephone numbers to URIs. Many applications already supportLDAP interconnectivity. For example, Avaya CommunicationManager with either Avaya SIP Enablement Services or AvayaSIP Application Server development environment can inter-face with LDAP to send calls bound for SIP URIs to standardtelephones on the enterprises IP PBX.

Enterprise SOA and intelligentcommunications Service Oriented Architecture (SOA) is a methodology thatfocuses on three major objectives:

Designing IT infrastructures that allow different applica-tions to interoperate and exchange data via a commoncommunications protocol

Leveraging existing applications by exposing their capa-bilities as services that can be easily used by other applications

Using these services to automate business operations


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SOA is possible in an advanced, intelligent communicationsinfrastructure based on a value proposition of strategic valueversus economic efficiency. At the heart of the strategic valueproposition is the promise that communications capabilities,when closely integrated with business processes and applica-tions, can greatly enhance the speed and ability of enterprisesto respond to changes in customer and market demands.

SIP-enabled communication services extend and simplify com-munications within enterprise processes with a portfolio oftelephony, messaging, speech, and contact center solutions.

SIP integrates easily with the Web service environments being developed for many business critical applications. Forenterprises, this means the introduction of powerful multi-modal communications, embedded as a service within theirbusiness applications. It also means that information on userpresence can be incorporated into application business logic.Communication becomes a tool not just for users, but also forthe enterprises critical business applications.


Avaya Unified CommunicationsAvaya Unified Communications com-bines SOA and SIP, along with busi-ness-intelligent technologies thatintegrate business-context knowl-edge and user communication con-text knowledge. The end vision is acomprehensive, multi-channel com-munication access architecture thathelps increase business agilitythrough rapid, intelligent responses to

business events that can find andconnect the right people, at the righttime, with the right devices. UnifiedCommunications has intelligent inte-gration that enables businesses tokeep their decision-making processesmoving towards resolution, whetherfor application-to-application, human-to-application, or application-to-human communications related tasks.

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Chapter 4

SIP InteroperabilityIn This Chapter Getting acquainted with industry and vendor interoperability

initiatives

Examining interoperability within the enterprise

Looking at interoperability beyond the enterprise

Appreciating SIP security and survivability

As previously discussed, SIP is an open and extensibleIETF protocol standard that has gained widespread support and acceptance among a growing community of hardware and software vendors. In this chapter, we discussinteroperability within enterprises and among enterprises,including topics such as hybrid infrastructures, the communi-cations ecosystem, survivability, federated presence andsecurity.

Proving That We Can All Just Get Along!

SIP is an open protocol standard developed to help facilitatereal-time IP communications and other forms of peer-to-peerand group communications. Communications hardware andsoftware vendors have recognized the universal appeal of theSIP protocol and are adding SIP capabilities to a rapidly grow-ing number of products. Various interoperability initiativescurrently under way include:

Development of a reference architecture of commonnetwork elements

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SIP Communications For Dummies, Avaya 2nd Custom Edition 40 Specification of the basic protocols (and protocol exten-

sions) that must be supported by each element of the reference architecture

Specification of the exact standards associated withthese protocols

Specification of standard methods for negotiating proto-cols, protocol extensions, and exchanging capabilityinformation between endpoints

Definition of authentication methods to ensure usersecurity and accurate billing

Several organized groups and communities are actively work-ing to promote SIP interoperability, including:

Developer Connection is Avayas program to promoteinteroperability between Avaya products and others inthe market. Go to http://devconnectprogram.com.

SipCenter promotes the development of SIP-based products and interoperability. Go to http://www.sipcenter.com.

SIP Forum promotes industry interoperability by hostinglive testing events, defining and creating compliancetests, and developing industry-wide technical recommen-dations. More information is available at http://www.sipforum.com.

SIPconnect is a standards-based initiative of the SIPForum to promote direct peering between SIP-enabled IPPBX systems and VoIP service provider networks byensuring interoperability between SIP trunks and legacyTDM environments. Go to http://www.sipforum.com/sipconnect.

SIPit (SIP Interoperability Tests) is a week-long semi-annual test event held at locations around the world forthe purpose of promoting global SIP interoperability. Moreinformation is available at http://www.sipit.net.

SPEERMINT is an IETF working group established toaddress peering and operational issues in real-time IPcommunications sessions. Learn more at http://www.ietf.org/html.charters/speermint-charter.html.

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These are just a few examples of the interoperability initia-tives that are accelerating the already rapidly growing adop-tion and reliability of multi-vendor SIP environments.

Multi-Vendor IntegrationOne challenge many enterprises face is multi-vendor PBX net-working. Traditionally, interconnection has required the useof Q-interface Signaling protocol (QSIG) to enable support ofsupplementary services between systems. This does providelimited interoperability between systems, but it doesntaddress the management issues caused by the duplication offeatures and systems, or the training complexity arising fromdifferent user experiences with each system.

Although SIP isnt a silver bullet, it does provide enterpriseswith more options for multi-vendor integration within an IPtelephony environment based on open standards. For exam-ple, a variety of user agents (such as a softphone) can be con-nected to the PBX using SIP. And, with federated services(refer to Chapter 3), you can support basic connectivitybetween different vendors systems, devices, and applicationsusing SIP. Soon, SIP will enable enterprises to combine multi-ple PBXs into a single system, which reduces complexity forboth users and administrators. Interoperability within the SIPecosystem, which spans a wide range of telecommunicationsand networking technologies and services, is key to SIPswidespread adoption and rapid growth.

Avaya is committed to fostering SIP interoperability, reflectedboth in its extensive portfolio of SIP products and applica-tions and its interoperability testing and certification pro-grams such as DevConnect, the SIP Ecosystem Partnerprogram, and the BusinessPartners program.

Avaya is clearly committed to SIP interoperability among vari-ous vendor products. At a recent industry interoperabilityevent (Interop 2007), Avaya was the only major telecommuni-cations vendor to successfully demonstrate basic SRTP inter-operability for both PBXs and phones. We discuss SRTP inmore detail later in this chapter.

Chapter 4: SIP Interoperability 41

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SIP is designed to simply set up, manage, and tear down callsand sessions. Although the SIP protocol is expanding, otherprotocols are still necessary to address interoperability withsystems and applications such as:

Interactive Voice Response (IVR) systems

Firewalls

Conferencing bridges

Instant messaging platforms

In essence, these systems must rely on much more than SIP towork together today.

Internal to the EnterpriseEnterprise telecommunications infrastructures can often beclassified in one of three distinct phases in their evolution.

In the first, or traditional phase, enterprises have separateinfrastructures for voice and data networks. Time divisionmultiplexing (TDM) is used for voice, and Internet protocol (IP)is used for data.

This paradigm is sooo twentieth century (literally)! Prior to2000, ISDN and TDM voice networks used the Signaling System#7 (SS7) set of protocols to set up and tear down telephonecalls on the PSTN. Applications were developed to interfacedirectly with connection-management protocols, which inter-faced directly with ISDN- and TDM-based access protocols.


Avaya Intelligent Presence ServerWith the introduction of AvayaIntelligent Presence Server in early2008, Avaya became one of the firstSIP vendors to crack the code onfederated presence, providing a scal-able, high performance presenceaggregation service that collects anddisseminates rich presence from

Avaya and other third-party sources.Using rich presence, users gain theability to more effectively reach thepeople they need, leveraging the mul-tiple channels of communicationsavailable to them, no matter whatvendor applications, platforms, orend-devices they are using.

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In this phase, interoperability between voice and data sys-tems is largely non-existent. Your telecommunications circuitsand data circuits are separate and unable to share excesscapacity or offload excess traffic. Thus, your network may becrawling while your phones sit idle, or your Internet connec-tion may be blazing fast but your increasingly frustrated cus-tomers get continuous busy signals when trying to call you.And, you get to pay the same circuit rates whether they arebusy or idle!

This also means that your various devices and applicationsdont interoperate. Your office phone is just your office phoneand your mobile phone is just your mobile phone two sepa-rate phone numbers to reach one person, and two separatevoicemail systems. And e-mail, instant messaging, video con-ferencing, and on and on!

In the second, or converged networks phase, enterprisesbuild out their IP networks to leverage a common infrastruc-ture that flattens, consolidates, and extends their voice and data networks. This enhances the IP network to meetenterprise-class criteria: improving quality of service (QoS)and increasing the reliability of real-time, mission-critical business and communication applications. Applications, builton the Computer Telephony Integration (CTI) overlay, interfacedirectly with connection management protocols, which inter-face with H.323 and IP-based access protocols.

Ripping and replacing everything in one step is often tooexpensive for organizations, particularly given their large cap-ital investments in legacy PBX equipment. Still, organizationscan attain significant cost savings now by implementing coreSIP routing (using a gateway if needed) and trunking, bydeploying selected SIP applications such as conferencing,mobility, and Unified Communications, and by taking advan-tage of SIP features such as centralized management of dial-plans and on-net calling.

Finally, in the third phase, enterprise communications capabil-ities are closely linked to business processes and applicationsto deliver real business advantage, allowing an organization to quickly adapt to changing customer needs and market situations.

Chapter 4: SIP Interoperability 43

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In this phase, interoperability of systems and applications isthe key to success. Peering and loose coupling promotesrapid development and deployment of applications with SIPas the unifying protocol between applications, connectionmanagement, and access-layer protocols. In this model, inno-vative uses of SIP include intelligent customer routing in contact centers (discussed in Chapter 5) and voice portals at the edge providing customers with self-service options.

External from the EnterpriseInteroperability with the PSTN is achieved through gateways,SIP trunking (explained in Chapter 3), and through SIP-T, aprotocol used mostly by service providers to carry ISDN sig-naling within SIP messages.

Many enterprise communications vendors, including Avaya,actively promote interoperability programs with carrier net-works. Avaya co-founded SIPconnect (now part of SIP Forum)to define interoperability specifications for the carrier-to-enterprise interface. Through its SIP certification program forservice providers, Avaya has tested and certified interoper-ability with a number of service providers.

SIP Security and SurvivabilityBecause SIP relies heavily on an IP-based network and utilizesa plain-text language similar to HTTP, SIP-enabled applicationsare potentially vulnerable to many of the same security threatsthat plague corporate networks and the Internet today. Theseinclude authentication, authorization, and privacy issues,denial of service and buffer overflow attacks, and SPIT (SPAMover Internet Telephony).

Fortunately, many of the same solutions to these problems areeffective for securing SIP implementations as well. These mayinclude:

HTTP Digest Authentication using MD5 for challenge/response user authentication

Signaling channel encryption using Transport LayerSecurity (TLS) for end-to-end session security


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Certificate Authorities (CA) for authentication in networksusing SRTP and TLS

Secure Real-Time Transport Protocol (SRTP) or IP Security(IPSEC) using Advanced Encryption Standard (AES)encryption to provide authentication, confidentiality, andintegrity for protection of the media (to prevent eaves-dropping, for example)

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