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IntroductionChapter 4: Taking a Peek at SIPTrunking ConsiderationsIn Chapter 4, you find out the questions to ask and the thingsto consider before you commit to a SIP trunking deploymentand when you choose an Internet Telephony Service Provider(ITSP) to provide your SIP trunking service. You also see theimportant considerations to keep in mind when selecting aSession Border Controller (SBC).Chapter 5: Ten Reasons to ChooseSonus SBCs for SIP TrunkingIf you read Chapters 1 through 4, I hope you’re sold on SIPtrunking and also have a good idea about what makes a goodSIP trunking solution. But even if you haven’t, Chapter 5 iswhere you look at some of the attributes of the SBCs offeredby Sonus and understand how Sonus SBCs may match up wellwith your SIP trunking needs.Icons Used in This BookThis book calls out important bits of information with iconson the left margins of the page. You’ll find three such icons inthe book.The Tip icon points out bits of information that aid in yourunderstanding of SIP trunking or provides a trick of the tradeto help save you time, money, and much more.The Remember icon points out textual tidbits that you shouldlock away in your memory for future use.I try to keep the technical jargon and discussion to a minimum.You won’t need to know these factoids to get the most out ofthe book, but you may find them interesting.These materials are the copyright of John Wiley & Sons, Inc. and anydissemination, distribution, or unauthorized use is strictly prohibited.3

4SIP Trunking For Dummies, Sonus Special EditionThese materials are the copyright of John Wiley & Sons, Inc. and anydissemination, distribution, or unauthorized use is strictly prohibited.

Chapter 1Getting Acquainted withSIP TrunkingIn This Chapter Saying hello to PBX trunking Digging deeper into enterprise PBX trunks Discovering how SIP trunking works Learning the components of SIP trunkingEnterprises of all kinds are dealing with two big trendswhen it comes to their real-time communicationsneeds. First, they’re trying to save money in an era when justabout every business is tightening its belt. Second, they’retrying to figure out how to support a host of new unifiedcommunications applications in an era where new devices,mobile connections, and more sophisticated users aredemanding change right now.In this chapter, you learn about a technology being consideredby many enterprises that meets both of those goals: SessionInitiation Protocol (SIP) Trunking. First, I discuss enterprisePrivate Branch Exchange (PBX) Trunking in general and thenthe difference between circuit-switched and SIP trunking.I follow that by then digging deeper into SIP trunking andlooking at the components required. By the end of thischapter, you should have a pretty good idea what SIP trunkingis all about.These materials are the copyright of John Wiley & Sons, Inc. and anydissemination, distribution, or unauthorized use is strictly prohibited.

6SIP Trunking For Dummies, Sonus Special EditionIntroducing EnterprisePBX TrunkingMany enterprises — in fact, I’d say most medium and largeenterprises — use a PBX telephone system to provide voiceand other communications services to their employees. Youknow what I’m talking about if you dial “9” first to get anoutside line or if you can dial a coworker with just a few of thedigits of her phone number.The telecommunications network connections that connectthe PBX to a telephone service provider are known as trunks.The name implies a tree analogy that explains what a trunk is:all of the individual lines (phones on peoples’ desks) are thebranches of the tree, connected to a bigger line (the trunk),which connects back to the network. Trunking is a big dealbecause it lets an enterprise pay for fewer phone “lines” thanit has users with phones — the PBX lets a larger number ofusers and stations effectively share a smaller number ofconnections to the outside world — it’s sort of the time shareof the phone world, but you get to use it more than two weeksa year.The thing to remember about enterprise voice trunking isthat it’s an efficient and cost-effective alternative to buyingan individual phone line for every person in the enterprise.Imagine both the cost and the management hassle of thatapproach.Understanding the Types ofEnterprise PBX TrunkingFor many decades, PBX trunks were traditional analog circuitswitched voice lines just like the ones you may buy from yourlocal phone company for your home. For example, a smallbusiness may purchase three lines from the phone company,connect them to a small business phone system (essentiallya mini-PBX, sometimes called a key system) and then sharethose lines among the six or seven people (extensions) in theoffice.These materials are the copyright of John Wiley & Sons, Inc. and anydissemination, distribution, or unauthorized use is strictly prohibited.

Chapter 1: Getting Acquainted with SIP TrunkingGoing Digital with PRIAnother option for connecting a PBX to a telephone carrieris known as a Primary Rate Interface (PRI) line. PRI is a TimeDivision Multiplexing (TDM) interface, provided over standardtelecommunications copper or fiber lines. PRI uses a T1interface in North America or an E1 interface in other parts ofthe world.T1 and E1 lines are carved into 23 or 30 individual voice lines,respectively. Essentially, a T1 or E1 is a souped-up phone linethat can carry multiple voice lines over a single pair (or pairof pairs, in some cases) of copper phone lines, by using somedigital trickery to divide the voice signals up by time slots. Allthe extensions in the office connect to the PBX, which thenconnects to one or more PRIs and on to the phone companynetwork.Entering the SIP worldThe PRI system worked well for a long time, but a moreefficient (in terms of both bandwidth utilization and cost) andmodern system has begun to replace circuit switched voice:SIP trunks, which utilize Voice over IP (VoIP) and the SIP.SIP trunking uses a data connection — the same connectionthat a business uses for Internet access, for connecting tocloud services, or for hosting its e-commerce site — to carryvoice signals as VoIP to a service provider who can handlethat kind of voice signal.A carrier who can offer VoIP services is called an InternetTelephony Service Provider (ITSP). An ITSP could do justthat, or it could be your familiar local and long distancecarrier who offers VoIP services in addition to moretraditional circuit-switched voice services.Understanding How SIPTrunking WorksSIP trunking relies on Internet protocols and Internet servicesinstead of old-fashioned circuit-switched voice protocolsThese materials are the copyright of John Wiley & Sons, Inc. and anydissemination, distribution, or unauthorized use is strictly prohibited.7

8SIP Trunking For Dummies, Sonus Special Editionand services. With SIP trunking, voice communications canbe merged with the data services an enterprise uses. In fact,many smaller enterprises merge their voice and data onto asingle “Internet” data connection while larger enterprises maykeep them separate but save significant amounts of money byusing cheaper data services for voice instead of TDM trunking.In other words, voice (and related communications servicessuch as video, which I discuss in Chapter 2, when I talk aboutUnified Communications, or UC) is just another data servicebeing delivered over an enterprise’s data network.A good way to understand this concept is to think about thephone functionality on your Android, Windows, or iPhonesmartphone. It’s just another one of the apps on the phone,instead of a dedicated hardware device. When you want tocheck Facebook comments, you click the Facebook app, andwhen you want to make a call, you click the Phone app (or theSkype app, for that matter).The key protocol that supports VoIP connections is SIP andis basically the controller of calls (and other UC sessions).Here’s a way of understanding SIP: Think of your voice as adata connection, and your language (like English) is theprotocol that lets other people understand your voice. SIPisn’t the only language (there are others such as H.323), butit’s the most common. SIP relies on clients and servers in thenetwork to exchange information about the following: Who’s connected to the network? Where are they located? What resources are available to them (in other words,what applications can they access and use, and whatkind of phone or device are they using)? Who’s inviting people to begin a session, if they accept,and when are they done?A SIP trunk is a virtual connection between an InternetProtocol Private Branch Exchange (IP PBX) and a telephoneservice provider providing SIP-based voice and UC services,connected over an enterprise’s data network connections.These materials are the copyright of John Wiley & Sons, Inc. and anydissemination, distribution, or unauthorized use is strictly prohibited.

Chapter 1: Getting Acquainted with SIP TrunkingIntroducing the Componentsof SIP TrunkingSome of the components needed to implement SIP trunkingare hardware devices that you need installed on your network,while another component is the service itself, provided by athird-party service provider. I cover those components inthis section, but Figure 1-1 shows some of the necessarycomponents in a typical deployment.Figure 1-1: SIP trunking components.IP PBXThe key element to SIP trunking is a phone system that canconvert voice calls into VoIP calls for transmission across theSIP trunk. While there are other devices out there that can dothis job — various VoIP gateway type devices, for example —the most common and cost-effective mechanism is an IP PBX.Session border controllersA key element of a SIP trunking solution — and I do meankey — is the Session Border Controller (SBC). The SBC is theThese materials are the copyright of John Wiley & Sons, Inc. and anydissemination, distribution, or unauthorized use is strictly prohibited.9

10SIP Trunking For Dummies, Sonus Special Editiondevice that sits on the border between an enterprise’sprivate network and the public network provided by data andtelephony service providers. The SBC plays a few very vitalroles in managing SIP traffic for voice and other UC servicesand applications, including the following: Security: SBCs protect the network against threats by Protecting against Denial of Service and DistributedDenial of Service “flood” attacks, which attempt tooverload network components and prevent voiceservices Preventing unwanted ingress into the network(SBCs “hide” the topology and network addressesof devices “inside” the enterprise network) — youdon’t want everyone coming in and making callsfrom your IP PBX Providing encryption for sessions traveling acrossthe network, especially if you care about peopleeavesdropping on you Protecting against toll fraud from malicious outsideusers accessing the network Routing: The SBC provides inter-network connectivity toallow remote workers to make phone calls and also allowolder IP devices to be used on your network. Quality of Service: The SBC keeps an eye on overallnetwork utilization and on the policy-based prioritiesfor different applications and users. It also determines ifand when sessions should occur and what priority andamount of bandwidth they should be assigned — all onthe fly. SIP translation: Different vendors have slightly differentdialects of SIP — an SBC can “speak” these differentdialects and allow uninterrupted connectivity betweendifferent network segments. Transcoding and transrating: The SBC can actuallymodify the “payload” or content of SIP sessions tochange codecs (coder and decoders) and change bitrates to make sure both ends of a SIP session cancommunicate, regardless of what kind of client or networkis in use.These materials are the copyright of John Wiley & Sons, Inc. and anydissemination, distribution, or unauthorized use is strictly prohibited.

Chapter 1: Getting Acquainted with SIP Trunking11Session Management SystemAn optional but often very useful addition to a SIP trunkingimplementation is a Session Management System. Withoutsession management, many or even most UC applicationswill have their own servers, their own management systems,their own policy enforcement, and their own policy databasesystems — each of these elements individually controlledand managed. Session management brings all these elementsunder a single system’s control, saving time and money.Session management has an additional benefit: It providesintermediation and federation (in the computing sense, notthe political one) between different platforms, different networks, and different geographies. So a session managementsystem makes it easy for a UC application to be deployed onetime and then provided to users (based on policies) no matterwhere they are, what device they are using, what kind of IPPBX is installed in their office, and so on. This ability tocentrally and quickly deploy new applications is a big deal forenterprises with heterogeneous network infrastructures —like companies who’ve merged or with subsidiaries who “didtheir own thing” when they built their networks.Session management isn’t a “must have” for SIP trunking, butit’s a problem solver for complex UC deployments. Sessionmanagement is something you definitely should consider asyou move from a simple voice-centric UC deployment andstart adding new multimedia apps.ITSP/SIP service providerYour SIP sessions — whether they’re voice calls, videoconferences, multimedia sessions, or whatever (the sky’sthe limit) — need a public network provider to get to wherethey’re going if they’re not internal calls handled on your ownenterprise network. That’s the role of a service provider —just as it was with traditional circuit-switched voice.A service provider that provides transport and terminationof SIP calls is the ITSP — sometimes also called a SIP serviceprovider. You can really think of an ITSP as just a “phoneThese materials are the copyright of John Wiley & Sons, Inc. and anydissemination, distribution, or unauthorized use is strictly prohibited.

12SIP Trunking For Dummies, Sonus Special Editioncompany,” with the difference being their interface with yournetwork (through your SBC and onto your IP PBXs) is adata connection using SIP to control the flow and routing ofsessions.In fact, many traditional phone companies are beginning tooffer SIP trunking services to their enterprise customers —after all, if someone is going to cannibalize your legacycircuit-switched voice services, it may as well be your owncompany, right?In its doorman role, the SBC first and foremost determineswhich sessions should even be allowed on and off theprivate portion of the network. So “spam” calls or calls fromblacklisted users (like telemarketers) can just be stopped atthe door and not allowed in, while other sessions can alwaysbe connected (whitelisted) or connected when certainconditions are met (greylisted). Additionally, the doormanpart of the SBC also determines what UC applications asession can access, based on policy, availability, and thecapabilities of the clients on either end of the connection.Seeing the role of an SBCin SIP trunkingThe SBC is essentially the trafficcop and doorman of SIP trunking.In its first role (traffic cop), the SBClooks at each individual sessioncrossing between the internalenterprise network and the externalITSP network and determines whereand when that session shouldgo — in other words, where thesession should be routed and whatpriority the session will be assignedwhen the network is busy. The SBCalso determines how many lanes(how much bandwidth) should beassigned to a session, based onnetwork utilization and the policiesestablished for the network.Finally — and perhaps mostimportantly — the SBC performs SIPinterworking, which allows devicesthat use subtly different variants ofSIP to communicate with each othereffe

SIP Trunking For Dummies, Sonus Special Edition, is not written as a technical manual for telecom engineers looking for deep techie knowledge or tips for planning SIP trunking deployment — there are plenty of 600-page technical books for those purposes. Instead, you'll find that this book is designed