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Voice Trunking in an IP World:Charting a Practical Path for PRI and SIPMichael HarrisKinetic Strategies

01Time Warner Cable Business ClassWhite Paper: Voice Trunking in an IP World: Charting a Practical Path for PRI and SIPVoice Trunking in an IP World:Charting a Practical Path for PRIand SIPInformation technology (IT) leaders understand that a converged InternetProtocol (IP) network is the endgame for innovative organizations. However,the real-world road to All-IP means leveraging existing technologyinvestments as well as intelligently integrating leading-edge IP capabilities.Utilizing Session Initiation Protocol (SIP) trunking for IP PBX telephonesystems is a practical step in the evolution of business networks that currentlyrely on Primary Rate Interface (PRI) connections.The IP PBX EdgeThree out of four U.S. companies have adopted IP PBX solutions to reducetelephone system operating costs and complexity while enabling features thatdrive productivity¹. IP PBXs use SIP—a signaling communications protocolfor IP networks—to route voice, video and messaging traffic through anorganization’s data network. With feature-rich SIP enabled IP phones thatconnect to the company LAN via Ethernet or Wi-Fi, office telephoneextensions become virtual rather than physical. SIP phones are also offeredas software clients for computers, laptops, smartphones and tablets, allowingworkers to receive calls and messages anytime, anywhere across a range ofwireline and wireless services.“More than 80 percent ofcompanies with more than 100employees say SIP is veryimportant to their business.”According to a recent survey, 40 percent of companies are leveraging SIP tosupport unified messaging, presence management or softphone clients onPCs or mobile devices². Rather than guessing whether a colleague is readyto communicate, presence offers real-time information about individualavailability and how best to reach that person—via office phone, mobilephone, instant messaging, videoconference or other means. With SIP, voicecalls and messaging can also be linked with customer relationshipmanagement (CRM) applications. For example, as incoming call numbers arerecognized, the customer service associate sees a pop-up window withinformation about the caller. Likewise, click-to-call features within CRMapplications speed outbound dialing. Not surprisingly, more than 80 percent ofcompanies with more than 100 employees report that SIP is very important totheir business3.Figure 1Top Factors for Deploying IP VoiceCost savingsFoundation for UCFeature functionalityCustomer service/support integrationCollaboration application integrationImprove productivityEase of managementSource: IDC10% 20% 30% 40% 50%In a recent survey by IDC, businesses reported the following top factors fordeploying IP voice: cost savings, building a foundation for unifiedcommunications (UC), adding feature functionality, integrating with customerservice and collaboration applications, improving productivity and ease ofmanagement for IT staff4. (See Figure 1.)

Time Warner Cable Business ClassWhite Paper: Voice Trunking in an IP World: Charting a Practical Path for PRI and SIP02Debunking TrunkingBy using TDM-IP voice gateways that link their IP PBX to the Public SwitchedTelephone Network (PSTN), businesses have been able to realize many of thebenefits of SIP without having to replace existing connections with telecomcarriers. These carrier connections, called trunks in telecom speak, aretraditionally offered as PRI services. PRI trunks deliver voice traffic as part ofIntegrated Services for Digital Network (ISDN) specifications that interfacewith the PSTN.PRI trunks are usually offered in blocks of 24 channels (23 for voice and 1 forsignaling) through T1 or DS3 circuits. This fixed-channel allocation has longbeen a source of frustration for IT managers. When it needs extra callcapacity, a growing organization is often forced to buy a block of 24 channels,even when far fewer are actually required. Fortunately, some innovativecarriers now offer fractional PRI services, enabling organizations to purchasedigital voice channels in smaller increments, such as 8, 12 or 16.SIP trunking offers even more flexibility and granularity, enabling organizationsto purchase the exact number of call paths needed. Better yet, there is noneed for TDM-IP gateways that support the conversion of IP packets to PSTNtraffic over an ISDN PRI circuit. With SIP trunking, organizations cansupplement or bypass PRI infrastructure, extending the benefits of IP and SIPbeyond the internal IP PBX edge.Five Key Benefits of SIP TrunkingAs well as a future-proof network evolution path, SIP trunking offerscost-savings on telephone service charges and legacy equipment upgrades,flexibility in scaling call capacity, enhanced business continuity capabilities,unified communications and efficiencies through All-IP convergednetworking. Let’s look at the five key advantages of SIP trunking in more detail.1. Cost Savings: SIP trunking helps organizations reduce costs by supportingthe convergence of separate voice and data networks, consolidatingoperational support staff, reducing equipment needs and enabling thepurchasing of only the required calling capacity.Ovum, a leading telecomresearch firm, finds that businesses normally realize network and usage costsavings within the first few months of transitioning to SIP trunking, and mostorganizations achieve “more than 60 percent cost savings over existinginfrastructures and trunking services.”5“SIP trunking can generally resultin more than 60% cost savingsover existing infrastructures andtrunking services.”2. Scalability: Rather than buying PRI trunks in fixed blocks of 24 channels, SIPtrunking capacity can be scaled more flexibly. As it adds PRI channel blocks,the organization may also need to add capacity to the legacy voice-gatewayhardware interconnecting its IP PBX with PRI circuits—an approach that canbe more costly and cumbersome. SIP trunking provides a native SIP interfacebetween the customer IP PBX and the service provider IP network and allowsgranular scaling of call capacity over IP data connections. Additonally, SIPtrunking eliminates the need for on-site installation and offers rapid softwarebased provisioning of additional capacity in as little as one call path at a time.As a result, your organization will be more nimble and able to respond quicklyto system and application growth needs.3. Alternate Routing and Business Continuity: The enhanced failovercapabilities of SIP trunking benefits business continuity and disaster recoverystrategies.

Time Warner Cable Business Class“SIP trunking is more flexible andefficient, and thus can provide partof the hard savings needed tosupport a UC business case.”03White Paper: Voice Trunking in an IP World: Charting a Practical Path for PRI and SIPFigure 2SIP Trunking Alternate Routing & Business TN2:45 O8PQRSHOLDDEFJKLSEND2:45 UTEMSG2ABC5JKL8TUV0OPERSPEAKERSERVICE PROVIDERLINE4Customer PortalCLEAR3DEF6MNO9WXYZAlternate Routing Table#SENDFailover SiteSIP TrunkLAN SwitchIP PBXEquipment failure214-555-00002:45 quartersSIP trunks can be programmed to support automatically triggered alternate routes by phone numberparameters in the event of a system, PBX or network failure. Many providers offer customer administrationportals for ease of setup and management.For example, SIP trunking can be configured to automatically route calls toanother telephone number or trunk group during a connection failure and,following restoration, return call traffic to the primary destination. (SeeFigure 2.)“North American businesses areusing a combination of services;there isn’t going to be a 100%cutover [from PRI] to SIP.”4. Unified Communications: Businesses are embracing UC to enhancecollaboration and responsiveness. SIP is an essential element in many UCapplications, such as instant messaging and presence, unified messagingand audio/video/web conferencing, as well as mobile softphone apps. SIPtrunking helps keep UC applications on the IP network, avoiding chargesassociated with PSTN termination and interconnection. As StrategicNetworks Group explains, “SIP trunk services act as the glue to supportmulti-location VOIP, IM, web or IP videoconferencing applications. Comparedto many legacy carrier access lines and trunks, SIP trunks are more flexibleand efficient, and thus can provide part of the hard savings needed tosupport a UC business case.”65. All-IP Networking: SIP trunking may serve as an essential building block formigrating to a flexible All-IP network that delivers voice, data and videotraffic. By handling SIP voice calls as IP data, SIP trunking provides anext-generation solution for supporting your network evolution needs.The Hybrid PathAll-IP network idealists can learn lessons from the energy-efficient vehiclemarket. While all-electric vehicles are the ultimate approach, they accountfor less than 15 percent of electric-capable vehicle sales. Hybrids dominatethe industry.Likewise, while 75 percent of U.S. companies have adopted IP PBXs, only 13percent of organizations exclusively employ SIP trunking to link their IP PBXwith telecom service providers7.

Time Warner Cable Business ClassWhite Paper: Voice Trunking in an IP World: Charting a Practical Path for PRI and SIP04Figure 3Business Use of SIP and PRI Trunks 2013-201580%60%SIP TrunksPRI Trunks40%20%Source: Infonetics Research20132015To leverage their legacy voice investments, organizations often pursue ahybrid path that includes both PRI and SIP trunking solutions as part of aphased migration of their network to IP services. That said, SIP trunks arepoised to overtake PRI services as organizations steadily evolve towardconverged IP networks. Currently, 38 percent of businesses use SIP trunks.That total is expected to reach 58 percent in 2015. Over the same period theuse of PRI trunks is forecast to decline from 71 percent to 55 percent ofbusinesses. (See Figure 3.)“The WAN configuration decisionwill depend on the number of officelocations, as well as the mix ofusers, devices and applications ateach location.”According to Infonetics Research, “North American businesses are using acombination of services; there isn’t going to be a 100% cutover [from PRI] toSIP.” Therefore, service providers that can aid in this evolution by offeringboth PRI and SIP trunking solutions may prove to be preferred partners.Loading SIP TrunksSome carriers bundle bandwidth and quality of service (QoS) with SIP trunkingto simplify network cost and capacity planning. Other service providersrequire the customer to handle SIP trunking traffic engineering and QoSconsiderations. For those organizations that must do their own trafficengineering for SIP trunking, the required bandwidth is calculated based onthe projected number of concurrent voice calls. One simple formula for thiscalculation can be expressed as:SIP Trunk Peak Bandwidth Maximum Simultaneous Calls 100 kbps9With this formula SIP trunk capacity for 10 concurrent calls equates to1 Mbps of bandwidth.Trunks and BranchesA key decision for organizations with multiple operating locations is whetherto centralize or distribute SIP trunking. This choice is driven by several factors,including the current and planned PBX architecture, the use of unifiedcommunications, the geographic distribution of branch office locations,branch office bandwidth utilization and redundancy needs.