August 14, 2017

SIP Trunking: What Is It? Why Do I Need It? How Do I Deploy It?

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 A SIP trunk is a direct connection between your organization and an Internet telephony service provider (ITSP). It enables you to extend voice over IP (VoIP) telephony beyond your organization’s firewall without the need for an IP-PSTN gateway. This simpler configuration is easier and less expensive to design, operate, maintain, and upgrade. And because ITSPs deliver services (notably long distance) at substantial savings, your investment in SIP trunking can give a quick and substantial return on investment.

In addition to VoIP calls, SIP trunks can also carry instant messages, multimedia conferences, user presence information, Enhanced 9-1-1 (E9-1-1) emergency calls, and other SIP-based, real-time communications services. Microsoft Office Communications Server 2007 R2 users can place local and long distance calls with caller ID and call hold over SIP trunks. As SIP-based communication technologies advance and SIP trunking becomes commonplace, additional services are likely to become available.

With all of the benefits that SIP trunking provides (especially the substantial cost savings), it’s no wonder that SIP trunking is a hot topic in unified communications. This article gives an overview of this popular new technology and its benefits, information about how it’s deployed, and answers to questions about SIP trunking that people frequently ask Microsoft product managers and engineers.

This paper uses SIP trunking to describe using the Session Initiation Protocol (SIP) and Real-Time Protocol (RTP) to connect Office Communications Server 2007 R2 directly to an ITSP over an Internet Protocol (IP) connection for the purpose of originating and terminating telephone calls.

SIP is used to create and control the communications sessions that are the basis of VoIP telephony. SIP is also used for instant messaging, presence updates, multimedia, conferencing, and other real-time services that can traverse a SIP trunk. RTP manages the actual voice data in a VoIP calls.

The “trunk” in SIP trunking is a term from circuit-switched telecommunications. It refers to a dedicated physical line that connects switching equipment. A SIP trunk is similar to its circuit-switched predecessor in that it is a connection between telecommunications systems, but it is different because the connection it describes is a virtual connection. This connection can be made over a line that is used only for SIP trunking, over a dedicated line that carries SIP trunking with other IP traffic, or over the Internet on a virtual private network (VPN).

Deploying SIP trunking can be a big step towards simplifying your organization’s telecommunications and towards preparing for the latest real-time communications enhancements, but the biggest motivation for most organizations is immediate and substantial cost savings.

  • Save money on long distance serviceLong distance service typically costs significantly less with a SIP trunk connection.
  • Eliminate IP-PSTN gateways (or even your entire PBX)Because SIP trunks connect directly to your ITSP without traversing the publicly switched telephone network, you can get rid of IP-PSTN gateways and their attendant cost and complexity. Some ITSPs will even host a PBX for you, taking over both the PBX hardware and user administration if you choose, with substantial cost savings from reduced complexity, maintenance, and administration.
  • Eliminate a redundant networkDeploying SIP trunking is a logical step towards the goal of having a single, IP-based network, rather than redundant telephone and data networks.
  • Eliminate BRI and PRI subscription feesWith a SIP trunk connected directly to an Internet telephony service provider, you can dispense with costly BRIs and PRIs, replacing them with service that can cost significantly less. Furthermore, with SIP trunking you don’t need to buy lines in blocks of 24 or 32. Instead, you can buy the bandwidth you need, in smaller increments, and at better prices.
  • Extend the capabilities of Office Communications Server with new services from ITSPsWith a SIP trunk in place, you can extend existing capabilities with additional services, such as E9-1-1 emergency calling. In the future, we expect ITSPs will to new services, such as greater integration with mobile phones and presence information on devices that are not running Office Communicator.