From the SIP Trunking Experts

December 05, 2008

SIP Trunking: Now Ready for Prime Time

By Seamus Hourihan Vice President of Marketing and Product Management, Acme Packet

For the debut of Border Crossings, a recurring TMCnet feature in which I’ll explore deployment issues around voice over IP (VoIP) and Unified Communications (UC) in enterprises and contact centers, I felt Ihad to address the elephant in the room: the free-falling economy. The coming twelve months will find each of us seeking ways to justify our very existence to our employers, let alone any new IT projects that entail significant capital and operating expense. If your project can’t help your company generate new revenue or save money, you might as well not get out of bed.

But the early returns from deployment of SIP trunking services — those IP-based offerings pitched as low-cost replacements for ISDN-PRI trunks and other TDM-based services for connecting IP-PBXs and ACDs to the PSTN — might just give you a reason to be chipper on your commute to the job that you may just continue to hold down. The dramatic cost savings that SIP trunks offer are compelling enough of a reason to look at them, but that’s just the beginning. And whether you’re enthusiastic about SIP trunks or not, don’t be surprised if your service providers start hawking them to you aggressively. Here’s why:
  • The cost savings from SIP trunks can be eye-popping. One Acme Packet enterprise customer recently began migrating its entire network from PRIs to SIP trunks. The key driver? Savings of $200,000 a month on recurring costs alone. That kind of ROI makes it easier to embrace the new hardware they’ll need to safely and effectively take advantage of those SIP trunks (in this case, Acme Packet session border controllers). Those costs will be further offset by the customer’s ability to retire its voice gateways, as the VoIP-to-TDM conversion (and the associated infrastructure and management overhead) will now reside in the service provider network.
  • SIP trunks can yield business continuity benefits like the ability to fail over from your primary data center to a remote disaster recovery site over geo-redundant SIP trunks to one or more providers. Geo-redundancy also lets you route traffic to a secondary provider if your primary provider suffers an outage.
  • Geo-redundant SIP trunks can be deployed with more intelligent routing, for example, using a session border controller to load-balance VoIP and UC traffic and selectively route sessions to the most appropriate provider, e.g., whichever one offers the best rates for the time of day, the highest historical session quality to the call destination, the codecs that the VoIP or UC endpoint prefers, etc.
  • Service providers will use SIP trunks to compete for your business. Competitive service providers see SIP trunking as a way to get their foot in your door and to siphon off voice dollars from your incumbent provider. Take advantage of this: invite your incumbent’s biggest competitor to pitch their SIP trunking services, and consider calling in some smaller providers, too, the kind that lead with SIP trunking services. Before long, you’ll be able to invite your local cable MSO to the table as well. Having multiple hungry providers vying for your business isn’t the worst hand to play. (Maybe there’s some upside to the downturn after all.)
  • SIP trunking lays the foundation for Unified Communications between enterprises. Some of Acme Packet’s largest enterprise customers are already planning on federating their presence, instant messaging, and other UC applications with those of their business partners, suppliers, and key customers, aiming to reduce human latency in their supply chain and customer service operations. SIP trunks will provide the necessary flexibility and low cost needed for such multi-enterprise connections.
  • SIP trunks reduce power consumption by as much as 80% over PRIs, according to the estimate of one Acme Packet service provider customer. That not only bolsters the business case for SIP trunks, but also supports your organization’s green IT initiatives.
So what’s the catch? Well, SIP trunking services carry a little bit of baggage with them, and at a minimum you’re going to have to rent the $3 cart. Here are a few issues to think about before you take the plunge:
  • Interworking. Acme Packet has already helped the vast majority of VoIP service providers to work out the kinks of peering with other providers, so we can tell you that little incompatibilities can add up to big headaches when deploying SIP trunks. SIP is not a rigorously codified standard: it supports numerous options for transport protocols, encryption protocols, codecs and DTMF transport. Slight variations in how your IP-PBX vendor implemented SIP versus how your service provider’s softswitch did it can be confounding. Similar issues pertain if you still use H.323 instead of SIP, or TCP where your provider uses UDP, or IPv6 while your provider is still on IPv4. How will you prevent these issues from stretching out your deployment and thereby your time to ROI?
  • Security. Deploying SIP trunks means connecting your data center or contact center to another IP network whose level of security you won’t have a great handle on. A malicious or profit-driven insider at your service provider wouldn’t have a terribly difficult time mounting a denial of service attack that could bring down your IP-PBX and crush your voice services. Thus it’s probably wise to hide your VoIP/UC infrastructure’s address topology, making directed attacks a little harder. What measures are you taking to defend against these and other security threats that are specific to VoIP and UC?
  • Session quality. One problem TDM trunks don’t exhibit is call quality issues associated with trunk saturation — when TDM trunk capacity is reached, callers get a busy signal. By contrast, VoIP calls can still be admitted past the point where link bandwidth can sustain acceptable call quality. Further, sudden spikes in incoming call loads, whether naturally occurring or the result of a deliberate denial-of-service attack, can overwhelm your IP-PBXs or ACDs. How will you manage these conditions, and how else can you make your inbound and outbound SIP sessions play nice with any existing quality-of-service schemes you have in place to maintain voice quality?
  • Regulatory compliance. No doubt your PRI trunks today mesh neatly with existing measures you’ve taken to meet regulatory requirements like E9-1-1 call prioritization, domain separation and call recording. How will you bring those functions forward into the world of SIP trunking?
The good news is that enterprises and contact centers already have some excellent examples to emulate on how to address these issues.  Service providers started worrying about cross-IP-border issues with VoIP when they first began peering with their fellow service providers years ago. In future columns, I’ll explore some of these questions in detail. In the meantime, hang onto your shorts: 2009 could be a bumpy ride.

James Slaby oversees Acme Packet's efforts to market its session border control solutions to the large enterprise and contact center markets. To read more of James’ articles, please visit his columnist page.

Edited by Greg Galitzine