Rogers says that potential cost savings aren’t limited to the telecom services bill. “You may have lower capital expenses, because SIP trunking is supported natively on most systems and doesn’t require any special hardware,” he explains. Rather than purchasing equipment to act as a gateway, handling codec translations and signal handoffs from TDM to IP, many new platforms allow for direct connection to SIP services without the need for sometimes costly external appliances.These expenses can add up quickly when hardware must be purchased to support multiple locations or multiple systems.
Many organizations are already using an IP-PBX system. (A PBX, or private branch exchange system, is an internal switchboard for routing and managing calls). For those that are, the gateway that’s currently managing the IP-to-TDM handoff required for communication with the public switched telephone network (PSTN)can be removed. The existing PRI requires this translation, but it’s unnecessary in a SIP environment. The SIP trunk services will plug directly into the IP-PBX, which is able to communicate natively via SIP for a clean, translation-free connection. Many legacy TDM-based PBXs can also utilize SIP services—they’ll need to add a device that manages the SIP-to-TDM handshake.
Long is quick to warn that there are situations where organizations might also want to consider adding a session border controller (SBC) to the mix, such as when several interconnected PBX systems work together to support voice traffic. “In the more complex environments, where a single enterprise may be running multiple PBXs, we do see advantages to deploying a session border controller,” he says. The reasons often include better security—this is a network-connected system, after all—as well as the ability to normalize the various interfaces in a multi-system environment.
Before beginning any SIP migration efforts, Wes Rogers, COO of nexVortex, Inc. in Herndon, Va., encourages organizations to conduct a thorough review of their existing architecture to ensure they know what the network looks like today and what it needs to look like tomorrow. “Where we see most of the challenges is actually at the edge of the enterprise,” he says. Problems are often related to existing firewalls, which may have settings that will conflict with SIP trunking. Much of the legwork required to set up new SIP services is often focused here. “You need to make sure that you understand the firewall technology and that you can open up the correct ports and tunnels to allow the SIP traffic in and out of the enterprise to the public network,” Rogers explains.
In the last decade, the quality and reliability of IP networks has improved tremendously. This evolution makes SIP trunking even more attractive, Studt says, because it now offers “the same if not better quality than the PSTN, because you’re eliminating a lot of the codec translation.” Instead of moving from IP within the enterprise to TDM and then back to IP at the other end of the call, SIP eliminates these transcoding steps. Removing those multiple hops and handoffs also removes many of the quality issues that can arise any time a translation occurs. It may be another force behind SIP’s increasing popularity.