Virtualized SBCs lower cost of SIP trunking but lack scale

A virtualized session border controller (SBC) for the Avaya Aura platform reduces the costs of SIP trunking and eases management for small to midsized deployments, but large implementations will probably need to stick with dedicated hardware appliances.

Vendors are starting to introduce virtualized session border controllers (SBCs) in order to reduce the costs and management overhead that can make Session Initiation Protocol (SIP) trunking too expensive for smaller enterprises.

The benefits of virtualization are equal across technologies -- reduced hardware footprint, more efficient use of resources, lower heating and cooling costs -- including unified communications (UC) applications. But virtualization has its limits, especially in a real-time communications environment.

Avaya has added a virtualized Acme Packet session border controller to its Aura platform for small to midsized deployments of SIP trunking, but large implementations will probably need to stick with dedicated hardware appliances.

I think an entry-level virtualized session border controller is good to get into [the technology], but I think the scalability is a key factor.
Mark Holloway
Lead VoIP ArchitectRegional U.S. service provider

"There's really no way to guarantee at what point this virtual machine [can no longer] handle call processing," said Mark Holloway, lead voice over IP (VoIP) architect for a regional U.S. service provider, which he declined to have identified.

"It's not an area you want to put at risk [of] calls not completing or having some issue because the performance of the machine is degrading," added Holloway, who writes a technical blog about carrier and enterprise VoIP. "I think an entry-level virtualized session border controller is good to get into [the technology], but I think the scalability is a key factor."

However, virtualized session border controllers will appeal to smaller enterprises that want to embrace SIP trunking as a way to save money on public switch telephone network (PSTN) connectivity. These smaller companies are often frustrated with the large upfront investment for the session border controllers required for SIP trunking, Holloway said. Acme Packet's enterprise SBCs are "designed to run in redundant pairs, so a customer would have to spend $100,000 just on the hardware," he said.

"From people I know, people I've talked to, [the capital expense] was always the showstopper," he said. "[They'd say] 'The cost of getting an SBC is so high, so why would I want to move to SIP trunking?' I think Acme has really broken that wall."

Finding support for session border controllers is also difficult, especially because they usually operate in a multivendor environment where "there's a lot of finger-pointing going on" between vendors during support calls, Holloway said. Enterprises will benefit from a setup like Acme Packet and Avaya's, in which Avaya will be the face of the product, he added.

"The Acmes are not easy boxes to configure -- they're monsters -- and there's not a lot of help out on the Internet … so, short of calling Acme or hiring a consultant, you're really pigeon-holed. There's no way out," Holloway said. "With the Avaya [platform], all of that goes away because it appears to be a single-vendor solution, even if it isn't…. They're the go-to vendor providing all [of the] support."

Avaya Aura embraces virtualized session border controllers

As part of a recent refresh of virtualized UC and collaboration applications for its Aura platform, Avaya announced it has begun reselling Acme Packet's Net-Net OS-E appliance under its Aura brand as a virtualized session border controller. The Aura SBC supports up to 750 concurrent SIP sessions, which translate to about 5,000 users, according to Steve Hardy, director of marketing for Avaya's UC products and solutions.

Avaya's Aura System Platform, the virtualization technology that supports applications such as Aura Session Border Controller, uses Citrix's Xen hypervisor and is designed to run on commercial servers. The Aura SBC, which has been available since June 8, does not replace Avaya's existing reseller agreement with Acme Packet for its physical appliances.

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"For a smaller enterprise -- maybe up to several hundred or even a thousand users -- trying to get UC capabilities to as few servers as possible makes a whole lot of sense," said David Yedwab, founding partner of Market Strategy and Analytics Partners LLC, a New Jersey-based consulting firm. "For a larger, more distributed organization, [it's necessary to have] a dedicated device doing all of the things that the session border controller needs to do to ensure the quality, security and flexibility of communications."

Holloway said redundancy will also be a key for enterprises deciding between physical and virtual session border controllers for their SIP trunking infrastructure.

"A common deployment model would be to have a high-availability pair -- two SBCs that look like one -- and you have two pairs to have them geographically redundant … in the event of an outage in one location," Holloway said. "With a virtualized environment … it probably doesn't scale to that level. You might be limited [in] how much redundancy you can truly provide."

A call center with hundreds or thousands of agents serving a number of clients may not want to take that gamble, he said.

"You can pretty much guarantee the things that can cause issues on servers are pretty much eliminated on a [dedicated] hardware appliance," Holloway said. "You reduce the inherent vulnerability issues."

Dave Michels, an independent telephony consultant based in Boulder, Colo., said that enterprises which have already virtualized other parts of their IT infrastructure will see the most benefit from a virtualized session border controller.

"Virtualization is an economy of scale thing -- the more things you virtualize, the better," Michels said. "The companies that are investing heavily in virtualization want as much [infrastructure] to fit in that strategy as possible. But organizations that don't have the expertise of economies of scale -- don't have a capacity or disaster recovery plan based around virtualization -- will prefer an appliance."

Virtualized session border controllers hold appeal, expected to grow

No other major SBC vendor appears to have developed anything similar -- session border controller software abstracted for deployment in a virtual machine (VM) -- according to Yedwab. Earlier this year, managed service provider Nectar Services Corporation announced its Virtual Session Border Controller service, offered via a software as a service (SaaS) model.

But don't expect it to remain a quiet market for long, Yedwab said.

"The standard server stuff is going broader and broader, as is the virtualization movement, so it doesn't surprise me that key capabilities like those being provided by session border controllers to make SIP-based IP networks work more efficiently [are being offered for virtual machines]," he said. "Virtualization of all or many of the capabilities [in a UC environment] makes a lot of sense."

Let us know what you think about the story; email: Jessica Scarpati, News Writer

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