SIP trunking migration: Enterprise opportunities and challenges

Lower costs come with interoperability problems with legacy systems
End of the PSTN

Source: iStock

Responding to developments in the enterprise communications market, more and more companies are migrating to SIP trunking services.

In fact, one-third of nearly 300 enterprises recently surveyed by Webtorials have deployed SIP trunking, with an average cost savings of 33 percent.

In addition to reduced costs, SIP trunking offers enterprises benefits such as centralization of lines, rapid disaster recovery and a resilient unified communications (UC) platform. However, there are a number of challenges, not the least of which is compatibility with legacy systems.

SIP trunking providers include Acme Packets (NASDAQ: APKT), ADTRAN (NASDAQ: ADTN), AudioCodes (NASDAQ: AUDC), Avaya, Band Tel,, Broad Soft (NASDAQ: BSFT), Broadvox, Ingate Systems, IntelePeer, Mitel Networks (NASDAQ: MITL), Objectworld Communications and Sonus Networks (NASDAQ: SONS).

Despite the difficulties of integration, what developments have fueled this migration to SIP trunking services?

Driving SIP migration is the "move to an IP environment--both wired and wireless," said Michael Finneran, principal at dBrn Associates. "Now, we are seeing SIP trunking on the wired front. But with the move to LTE, the whole idea is to have an all wireless IP network, referred to as the enhanced packet core," he told FierceEnterpriseCommunications.

"In some cases, the operators will push their voice traffic over an MPLS [multi-protocol label switching] where you can guarantee quality of service. But for a number of them, their value claim is you can start up a trial right now if you have any spare internet capacity," Finneran observed.

Another push driving SIP trunking is the overall move to unified communications. "SIP provides you the signaling tools you need to establish the wide variety of connections you are going to need in the UC environment. It is the right solution at the right time," he said.

Show me the money

Finneran, who recently published a white paper called SIP Trunking 101: A Primer, explained that SIP trunking offers attractive pricing for enterprises. "Your raw cost per minute is low and you get flexibility from using SIP trunk versus a traditional PRI [prime rate interface]. You typically pay for a certain number of simultaneous connections--SIMS... You don't have to buy your trunks in bundles," he said. 

SIP trunking is particularly beneficial if the enterprise has multiple sites. "You might have 10 SIMS in three different locations in three different time zones. But if you are not using a SIM in your Los Angeles office, it is available to make calls in your New York office," he explained.

Dave Michels, an independent analyst and creator of the Talking Pointz blog, agreed that price was a benefit that first attracted companies to SIP trunking. "More and more we are seeing other drivers, such as having converged networks," Michaels told FierceEnterpriseCommunications.

With SIP trunking, enterprises can get additional features, such as high-definition voice, and there are operational benefits around disaster recovery and high availability, he said.

"If you have a TDM [time-division multiplexing] trunk coming into a router or phone system, if that phone system fails, you can't easily move those T-1s to a different location… With SIP all you have to do is bring up another server and configure that for the SIP trunk, and the SIP trunk moves dynamically. That is a huge disaster recovery benefit," Michaels noted.

Jon Arnold, principal with J Arnold & Associates, agreed that SIP trunking offers benefits to companies with multiple locations. "In situations that have multi-branch operations, especially ones that are far apart, SIP trunking is attractive. Every time you add a branch location to your LAN [local area network], you just route more bandwidth to that location to add the voice piece," Arnold told FierceEnterpriseCommunications.

"When you move to a full rollout of VoIP across your organization, the more decentralized you are, the more attractive SIP trunking becomes," he added.

VoIP is the entry point

"VoIP is the entry point for SIP trunking," Arnold said. "When enterprises go down the path of IP telephony, they have typically made an upgrade from a PBX to an IP-PBX, and now they are looking to get the benefits of converged networks. If you can shift the voice traffic off of the legacy voice network onto the data network, you get economies from consolidation for merging to a single network environment," he explained.

"Once you start down that path, you get comfortable with the idea of voice as just another application in the data network… When you start getting into that environment, the barriers between voice and data break down. Now I have this network that is handling everything. What else can I do with it?" he said.

"That is where SIP trunking comes into the equation… You need to optimize your network to support voice because voice is real-time, and it has to get priority so it doesn't get compromised when you have a lot of non-time-sensitive traffic going over the network," Arnold observed.

Traditional telecom equipment is expensive and inflexible. So when the enterprise realizes that they can port voice over to IP, they will have less need for the legacy equipment, Arnold noted. 

With SIP trunking, an enterprise can buy only the capacity it needs. "That is a real draw for SIP trunking. You are going to spend less money, and you can right size to what you need," Arnold said.

"When the business starts to look at how it optimizes its spend on telephony, it sees that SIP trunking offers some real benefits," Arnold explained. "You get the full end-to-end IP experience and quality. VoIP quality can be better than TDM when it is optimized to the network. The only way to get that is if you have end-to-end IP," he added.

Delays, jitter and packet loss

In a February 2011 survey of more than 400 industry professionals conducted by the SIP School, companies identified a number of problems with the SIP trunking provider, including codec mismatch, one-way audio, trunks dropping intermittently and poor quality from delay, jitter and packet loss.

The top problems with the edge devices include SIP registration failure, one-way audio, quality of service issues due to misconfiguration and firmware updates required to fix issues. For the PBX, the top problems are PBX firmware upgrades needed to fix issues, codec issues, SIP trunk dropping and SIP registration failures.

Arnold admitted that voice quality can still be an issue with VoIP over SIP trunks and legacy systems. "Every time you convert a packet to circuit, you lose some integrity," he said. "If the network can't handle it, that is where you get dropped packets, compromised packets, that's when you get the crappy voice experience."

Arnold said that since SIP is not standardized, there are challenges involved with getting it to work across all platforms and systems. Carriers are reluctant to offer SIP trunking because they cannot guarantee interoperability and it cannibalizes their legacy business, he noted.

Finneran agreed that a chief challenge for SIP migration is compatibility with legacy systems. "The new world will work fine. Getting the new world to work with the old world is the challenge," he quipped.

Interoperability is a challenge that the SIP Forum is tackling head on. The forum was formed by IP communications companies to advance the adoption and interoperability of IP communications products and services based on SIP. It recently established the SIPconnect-Interoperability Certification Task Group to develop appropriate test plans and conformance tools for SIPconnect 1.1, to identify interoperability challenges and to develop a process for resolving industry disputes.

Michaels explained that SIP requires IT managers to have a different skill set from traditional telecom equipment. There is also more security risk with SIP trunking than with legacy equipment, he added.

End of the PSTN?

The enterprise communications future will see the "end of the public telephone network--the entire legacy of circuit switching and TDM access, and all that stuff that grew out of the old Bell system. It is going to be an all-IP environment," Finneran predicted.

SIP trunking will be part of this IP environment, the business-to-business and business-to-consumer calling paths, he added. In the shorter term, SIP trunking migration will continue because of cost and flexibility benefits, he predicted. He said he believes that in five years 80 percent of business network access will be through SIP trunking.

Arnold and Michaels were less bold in their predictions about the end of the public telephone network, but they agreed that the SIP trunking migration in the enterprise will continue as barriers, such as capability and interoperability, are addressed.

"For enterprises, the next step is to prove SIP trunking on a large scale… We know it works for a couple hundred lines. But can it support 5,000 lines? That is what they are going to want to know," Arnold concluded.