Randy Young, the vice president of network engineering for managed facility-based VoIP provider Cypress Communications, says that switching to a VoIP network from a TDM network often results in problems such as echo and latency unless the VoIP vendor takes certain steps to ensure that they will have high service quality.
"When you route calls to a SIP provider, you want to peer directly with their network rather than go directly across the Internet and hop across two or three different networks," he says. "Personally speaking, we prefer peering to going through an open Internet."
Looking forward, says Brandt, service providers have strong incentives to provide strong TDM-to-VoIP transition services because they want to develop enough trust with businesses so that businesses will eventually let them manage enterprise voice platforms. And while there may be bumps such as latency and echo along the way, Brandt says service providers will only be successful if they can prove trustworthy to enterprise users.
"The smooth transition to VoIP is going to be slow, but they're starting to gain some ground," he says. "At the beginning stages of VoIP, it was kind of an unknown quantity. But now that greater understanding of VoIP is out there, some enterprises are releasing control of their platforms again to the carriers."
Besides providing a smooth transition from TDM- to SIP-based VoIP, what other advantages does SIP trunking have?
The biggest one is simply cost savings. As Lazar puts it, "If you've got a small office and you're paying $800 a month for a dedicated T-1 line and a gateway, you can use SIP trunking to move that into the cloud for less money."
But it isn't just about the money -- SIP trunking can greatly simplify your network architecture as well. As Network World blogger ddonahue outlined last year, SIP trunks provide the same links for both intra-office calls sent over the WAN and outside office calls sent over the PSTN or even the Internet.
"The main advantage of SIP trunking is that you don't have to run additional lines into your main site," says Tolbert. "By allowing you to trunk into whoever you want to use who has capacity at the other end, it gives you a kind of Vonage-type connection for a business-class customer."
Brandt expresses a similar view, and notes that SIP trunking shrinks the footprint of technologies that enterprises need to use to the point where IT departments need only a single or dual Ethernet connection instead of the multiple cables and pieces of hardware they'd need for a traditional TDM system. And in addition to being good for users, Brandt says that it's a boon for carriers as well.
"Just like with enterprises, SIP trunking lets carriers decrease the overall number of hardware components in their data centers," says Brandt, whose company relies on Avaya media gateways to support SIP trunking capabilities.
On top of all this, Lazar notes that SIP trunking gives companies strong call-routing capabilities to send incoming calls to outsourced call centers. Thus, he says, a retail chain can automatically send calls from one of its stores into a call center, and thus cut down on the amount of labor it uses to answer phones within the store. If the call center doesn't have the answer to customers' question, they can be easily transferred back to the store for an on-site employee to answer. Tolbert also says that SIP trunks provide a simple and quick way to handle calls coming in through PSTN and through SIP systems.
"When I converted my VoIP system from my traditional system, it took me about 15 minutes," says Tolbert, who uses VoIP vendor Syspine's small-business phone system with Microsoft's Response Point System installed. "And support-wise, I don't have to do squat with it. I helped train one of the secretaries to manage the entire system, which is something I couldn't have done with a traditional TDM phone system."