SIP Gives Organizations Plenty of IP Telephony Choices

When it comes to planning for a flexible IP telephony deployment, don’t chug. SIP!

Designed to be extensible and flexible, Session Initiation Protocol, or SIP, is an IETF-developed signaling protocol that works alongside SIP-compliant network devices as well as VoIP for telephony, XML for data tagging, and other established networking standards. SIP initiates, modifies and terminates interactive communications sessions—from voice calls to video to interactive games—among users.

“Organizations considering an IP telephony solution don’t necessarily care about the technicalities behind a signaling protocol, but they do care about the business benefits it provides them,” says Martin Ruddle, senior product manager for platforms at ShoreTel. SIP is now being used to deliver services that benefit customers via SIP trunking and SIP desktop support.

“SIP does the signaling to make sure your media path is directed to the correct point, such as the gateway to the PSTN or to a PC on the network,” Ruddle explains. SIP itself does not prevent packets from being dropped or voice calls from breaking up, but reputable carriers’ quality-of-service measures and/or Service Level Agreements should keep those problems in check.

Gaining Momentum Here and Abroad
For its part, SIP trunking, which numerous carriers in North America and Europe are now rolling out, allows the use of SIP communications instead of the more typical analog, T1 or E1 trunk connections. While established carriers like AT&T and Verizon are making all three available, Ruddle expects SIP trunks to ultimately replace E1 and T1.

“Running a pure IP trunk to the service provider allows for more control from the enterprise’s point of view, as well as more options over the link,” Ruddle says. For example, SIP trunking makes it possible to use virtual numbers. Say a California-based business with a presence in New York wanted to give New York customers the ability to place a local call that’s automatically routed to the California office. “That’s the kind of service you might have seen from a cell phone provider in the past, but it is now available from an enterprise service provider,” Ruddle says.

One important benefit of SIP’s flexibility is that it doesn’t dictate the connectivity used to get to the trunk, Ruddle explains. “If you’ve bought a data T1 connection for your business, you could also purchase SIP signaling from any carrier that would allow you to set up and tear down calls through the network. So in other words, I could have a data connection from AT&T that provides bandwidth for my voice path, but the telephone service I could purchase from another carrier.” That carrier could be one of the new SIP providers that are cropping up as SIP momentum grows.

A new breed of carrier, like Bandwidth.com, with whom ShoreTel is working closely, can either provide customers with just SIP signaling—or, through a partnership with Level 3 Communications, support customers’ media paths as well as connectivity.

Bandwidth.com is among those carriers that have verified their offerings work with ShoreTel SIP trunking in the ShoreTel certification labs. Five others are also completed and ten more are in the process of completing. Both carriers and vendors are testing a range of products—from SIP tie lines to SIP wireless phones to SIP conference-room phones—in ShoreTel’s labs and in their own facilities to certify that they work with ShoreTel offerings.

New Security Considerations Emerge
Ruddle notes that those considering SIP trunking need to pay close attention to network and security matters—more so than they would an old-fashioned Primary Rate Interface (PRI) trunk. “With PRI, the carrier just terminated the trunk and signaling at your site, there were few security concerns. With SIP trunks, due to security concerns over IP connections to enterprise networks, it’s good practice to terminate the carrier connection outside of your firewall. The SIP trunks have to traverse the firewall securely and so you have to think about how you’ll do IP Network Address Port Translation (NAPT).” ShoreTel partners with Ingate Systems to provide a validated enterprise session border controller solution for NAPT which Ingate offers as the SIParator®. The SIParator is proven to solve the NAPT traversal issues, provide access control and normalize SIP between the Internet telephony service provider (ITSP) and ShoreTel. The combination is robust and highly configurable to meet the needs of most organizations.

At the desktop, not all of the current generation of SIP phones can support the same capabilities, such as multi-line appearance or paging. Yet use of the SIP protocol enables users to mix and match among various IP telephones, which is an appealing prospect for companies using different models of phones—such as one with a ruggedized handset for field use or wireless phones (ShoreTel supports wireless SIP phones from Hitachi). “By supporting SIP desktops, ShoreTel allows customers to bring specialized third party SIP devices into their particular environment,” Ruddle says.

The key driver for organizations considering a SIP-based IP telephony deployment is the choices it affords them now and in the years to come. “With SIP trunking, there are more offerings from carriers coming online,” Ruddle adds. “And from the desktop, SIP support will allow customers choice to introduce specialized devices at their own pace.”

ShoreTel 7.5, in controlled release now, offers native support for SIP.