SIP: A Carrier's Perspective
We've recently devoted a lot of attention to the rise of the session initiation protocol (SIP) for IP telephony signaling, and, we think, with good reason. The innovation that we've already seen emerge from SIP initiatives is only a taste of what we believe to be the protocol's potential.
Nevertheless, what makes the most sense technologically is not always what wins in the marketplace. We were therefore pleasantly surprised to discover major telecom carriers to be as committed as the vendor community to the development and adoption of SIP.
MCI WorldCom, under the direction of Henry Sinnreich, Distinguished Member of Engineering, is now carrying out one of the most sophisticated implementations of SIP to date. MCI has already developed its own SIP redirect/proxy/location servers, and is working with other vendors in areas like softswitches and IP telephones.
"We chose SIP because it is completely integrated with other Internet and web protocols," notes Sinnreich. "With SIP, everything that has been learned from web services can now be applied to telephony."
SIP's technical elegance alone would not win carrier adoption, of course. "The idea is simple," says Sinnreich. "You invest money in new network infrastructure only if it can bring new revenue. And new revenue comes from services that don't exist today. On the web, we've already seen an explosion of new multimedia services. So if you can apply a set of integrated web protocols that would include telephony, the potential for more new services is almost obvious."
While "new services" is already a mantra in discussions of Internet telecom, some of the real "newness" that convergence promises has been obscured.
In the worst cases, the "next-gen" network starts to look almost identical to the "legacy" network. Sinnreich blames this dilution (and we agree) on carriers' and equipment vendors' desire to protect their traditional sources of revenue. This turf war, he says, is reflected at the protocol level.
"At this point, you basically have three camps. One is H.323, which has basically been pushed by big players in the computer industry who want to enter the communications business. My personal opinion is that H.323 has effectively already failed in the U.S., and is now starting to fail overseas, mainly because it is based on an ISDN architecture. The second camp is SIP, which is the pure Internet play. The third, which I consider to be the most dangerous and potentially negative, is those in the telecom industry who are trying to preserve circuit-switched control and signaling systems, using the Internet as just a cheaper wire. The call agent in the case of MGCP or MEGACO, for example, is essentially there to preserve the signaling and control architecture of SS7 and the Intelligent Network. The software, of course, is all proprietary, so that the vendor who implements the call agents and softswitches in the carrier's network now has control over that carrier's services."
Turf Protection
Confusion surrounds the relation of protocols like the Media Gateway Control Protocol (MGCP) and MEGACO (its likely successor) to SIP, as they are complementary in certain ways and mutually exclusive in others. Sinnreich explains, however, "MGCP and MEGACO are great protocols for internally controlling an IP telephony gateway. But when they are used as control protocols for delivering services across the network, the carrier essentially puts his fate in the hands of the softswitch or call agent vendor. By limiting the user's access to a proprietary group of application servers, the MGCP or MEGACO call agent basically reinvents unequal access of the PSTN, only now it's located at the control level, whereas it used to be at the transport level."
While some try to avoid taking such strong positions on VoIP protocols by claiming "protocol agnosticism," Sinnreich sees this notion as untenable. "The Internet and the web are nothing but a collection of protocols, which have been so well designed that now everybody can communicate with everybody else in an inexpensive and effective way. Executives sometimes ask me, 'Why all this talk about protocols, why should I be interested in protocols?' I have to explain that soon, the core of our business will be based on these protocols."
The New Service Paradigm
Unlike MCI, startup carrier Level 3 entered the market unencumbered by an existing circuit-switched infrastructure. Level 3 also does not provide services directly to end users, but offers its network infrastructure to other service providers. Almost from day one, the carrier was committed to SIP. Matt Johnson, product marketing manager for Level 3's Dynamic Bandwidth Applications and Softswitch-Enabled Services Group, says that by pushing more intelligence out to the network endpoints, SIP can "generally simplify the systems required in the network."
Level 3 also takes a very strategic position on the softswitch's role in network infrastructure. According to Johnson, "The softswitch should behave basically as a web server behaves, providing a kind of 'dumb intelligence.'" In Level 3's network, softswitches are platforms that provide open interfaces to services, but do not themselves contain the service intelligence. SIP, because it facilitates point-to-point connections, is crucial to this model.
Yet Level 3 sees SIP not just as a signaling protocol, but as an enabling technology for a fundamentally different way of delivering telecom services. Level 3's entire business model, in fact, is based on the idea of disaggregated services. "We're focused on carrying out an enabling strategy," Johnson explains. "We won't ever touch the end user directly with our network, but we will enable ASPs or ITSPs to provide innovative applications to the end user. In effect, we're turning the revenue model of traditional networks inside out, by giving customers access to the services they want from any number of different providers."
