SIP gets serious

SIP for Business enhances enterprise features and boosts interoperability.

For John Haltom, network director for Erlanger Health systems, communications software based on Session Initiation Protocol is literally a lifesaver.

Erlanger, a large Tennessee hospital management group, is developing software that will soon let nurses receive SIP-based instant messages from machines such as IV pumps, heart monitors or other medical devices. Erlanger uses SIP-based servers, handsets and software from Nortel, Research in Motion (RIM) and Microsoft.

But with all of SIP's promise, one problem has been a killer for Haltom's IT staff.

"Everyone has their own interpretation of the standard," Haltom says. "And technically, they all adhere to the standard, but in a way that is just different enough so that different vendors' products can't talk to each other."

The cure for this, some vendors and industry observers say, might be SIP for Business (SIP-B). While not an IETF standard, SIP-B is a multi-vendor effort to outline a set of advanced features for business telephony networks. Because vendors could deploy features that are similar in different ways, as defined by the IETF standard, SIP-B would spell out specifics on how advanced SIP-based features - multi-line appearances, conference call bridging - would work across multi-vendor products.

The calling features, such as hold, transfer and multiple-line appearances, are based on standard IETF-defined call flows - collections of complex back-and-forth handshakes and acknowledgement messages between SIP servers and endpoints. Proponents of SIP-B say that the 40 or so call flows outlined by the IETF are not enough to satisfy customers used to the more than 800 features on old IP PBX systems.

"We tend to get carried away by the latest and greatest technology," says John Weald, CTO of Sylantro Systems, a maker of SIP-based IP gear for carriers. "But sometimes we don't think about the small business around the corner with an old key phone system. If SIP products can't do the features in those old Toshiba or Nortel systems, then SIP-based IP PBXs or hosted services won't be competitive there."

Sylantro is one of the main vendors behind SIP-B, along with partners Siemens, Polycom and Citel, and several others. These firms have agreed upon a set of 18 additional SIP features that IP phones must support, including old PBX features such as call park, multi-line appearances on phones, distinctive phone rings, and advanced conferencing and bridging features.

Some vendors, such as Avaya, Siemens and Nortel, use a mix of SIP and proprietary extensions to mimic these PBX features. "We have to guard against putting in too many proprietary solutions just to meet market demand, because that defeats the purpose of SIP," says Scott Augerson, director of SIP business development for Siemens.

SIP-B skeptics

Others in the industry are more skeptical of the SIP-B effort, saying that SIP already meets most business feature requirements.

"For most of the call flows outlined in SIP-B ... we do that already," says Scott Wharton, vice president of marketing for BroadSoft, a SIP softswitch maker that competes with Sylantro and Siemens. He says the idea behind SIP-B is a non-issue in the industry, and adds that the IETF's definition of SIP offers more than enough capabilities for business phones.

"This idea that SIP is not ready and not able to be supported is a myth," he says. He adds that vendors such as Siemens, Avaya, Cisco and Nortel don't want commoditization of IP phones through the broader adoption of standards such as SIP.

"The reason they have not implemented SIP is because they make a lot of money on their existing phone sets," Wharton says.

Talking the talk

Erlanger's Haltom isn't interested in all the vendor wrangling. He just wants to get simple third-party SIP-based IP phones to work on a network with mixed SIP and proprietary. "There are lots of companies with SIP-based phones that are supposed to just be plug and play, but they just won't talk," he says.

As for the state of SIP-B, Sylantro's Weald says the RFC Sylantro submitted to the IETF has since expired. But his firm and other SIP-B supporters are looking to still promote the idea of SIP-B through the SIP Forum, a multi-vendor consortium for promoting the development and adoption of SIP software and hardware.

"There is still strong support among our group [of SIP-B proponents] and the SIP Forum looks to be the best place to promote this, as opposed to the IETF," Weald says.

Whether more vendors latch on to the idea of SIP-B through the SIP Forum remains to be seen. One vendor of SIP-based enterprise IP PBX gear, Zultys, is moving toward SIP-B compliance. This is being spurred by the convergence of carrier-based VoIP services with enterprise-focused IP PBX and phone gear, says Patrick Ferriter, Zultys' marketing vice president.

He says Zultys is beginning to sell its SIP-based IP PBXs with SIP services from carriers that use Sylantro and BroadSoft equipment.

Ferriter likens the state of SIP to the early days of ISDN. "Back many years ago, you had one standard for ISDN, but a bunch of different variants for depending on what region you were in," he says.

"With the IETF's definition of SIP, you do have a very solid base," Ferriter says. He anticipates more vendor cooperation on SIP, with elements of SIP-B, over time.

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Copyright © 2005 IDG Communications, Inc.

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