Goin' on a SIP trip
Cable is jumping on board with a technology that’s poised to play a
key part in IP-based applications and services
SIP (session initiation protocol), a technology considered more of a hobby in the late 1990s than the start of something great, is quickly coming into its own thanks to small but pioneering companies such as Vonage and its adoption by corporate behemoths like AT&T Corp.
Though SIP has traditionally been tied to voice services, it's designed to do much more than that. Devices based on the technology are also being made to handle more advanced applications, including video telephony.
Network-agnostic, SIP, at its core, opens up communications between two intelligent end points. The end points also keep all of the communication "state" information, including all data about the call and everything that happens during a given session.
There are plenty of SIP devices out there today, many of which run on cable's high-speed networks without the operator's knowledge. But with so much innovation and general activity happening in the SIP arena, what has the cable industry been doing about it?
A lot, it turns out. But a quick look back also reveals that the industry looked into it early on, only to uncover many of the technology's shortcomings. In fact, smart, SIP-like endpoints were considered during the formative days of PacketCable 1.x as operators and vendors began looking at the different protocols and approaches available.
As evaluations progressed in the late 1990s, two options were considered: a network-centric approach and distributed call signaling. At the time, AT&T Broadband was pushing for a distributed approach that leveraged smart, pre-SIP end points that didn't particularly care much about the network on which they were riding.
Others argued that the distributed approach would enable the end points to establish calls without the operator's knowledge, which presents a problem if the operator is thinking about replacing primary line telephony services.
The distributed model also didn't enable the operator to prioritize and re-route calls should the network become congested or overloaded. On top of that, those with enough smarts could hack those end points or flush the buffers to get free service.
Because of those potential problems, the network-based call signaling (NCS) architecture eventually won out and formed what became PacketCable 1.x., a spec that enables MSOs to identify and authorize the clients on the network.
"There's SIP the architecture, and there's SIP the protocol," he says. SIP the architecture, he explains, is what services like Vonage and AT&T's CallVantage do today–connecting a SIP end point to a SIP end point.
"They will always be a best-effort service. They won't have security like PacketCable will and QoS like PacketCable will," Craddock says. "I'll give Vonage a lot of credit. They've done a lot of great stuff on the front-end in terms of features and being able to get in and change your service and do the self-provisioning and so forth. But it's stuff that any of us can and will do, as well."
And how it will be used by cable could look much different than how it's being used today.
SIP, for example, could play a key role in how operators create a converged IP infrastructure, notes Mark Barber, vice president of corporate telephony for Charter Communications.
"In many ways, SIP is the glue that we've been looking for. It allows you to merge all of the different media," Barber says. "It's simple to write applications to and, quite frankly, it works with very little interoperability effort."
Still, because there are some regulatory issues that still need to be sorted out, he doesn't necessarily see SIP as an automatic replacement for primary line service. Instead, it could augment that or give operators the ability to give their voice customers some portability and mobility options. "Both services can co-exist on our network," Barber says.Doing one better
Plus, thanks to recent developments surrounding the PacketCable Multimedia (PCMM) architecture, cable operators should be able to do something that Vonage and AT&T can't do today: provide quality of service.
As operators moved into PCMM, the SIP subject came up again and operators discussed how to take the best of that technology and the best of the PacketCable architecture, which handles provisioning, configuration, management and monitoring of streams with QoS.
It was then decided to add a SIP Proxy to the PacketCable mix. In that scenario, the SIP Proxy talks to the SIP endpoint and translates it to PacketCable on the backend. In addition to the SIP Proxy, operators will also have to add a policy server, a component of the PCMM architecture that pushes policy down to open up the required QoS and bandwidth required for a call.
"Now you can enforce network policy," Craddock explains. "You can do everything you need to do as a network provider, but you can fully interface with a very smart SIP client."
SIP is found in a variety of "smart"
end points, including videophones.
"What's making SIP more useful is PCMM," says Ted Griggs, chairman of Syndeo Corp., maker of the Syion 426 call management server. "You get the QoS of NCS, but you can do it with a standard device. You don't need an MTA (multimedia terminal adapter). The other advantage is that SIP doesn't have to be a device. It can be a soft client on the PC or on your set-top."
But even some MTA suppliers are already thinking about adding SIP extensions. "We have some very preliminary SIP-based MTAs and SIP-based software," says Tim Doiron, senior director of product management for ARRIS. "If [operators] choose to deploy SIP, we certainly want to be a participant in that, and we will."Provisioning issues
Although policy servers eliminate the QoS issue, there are still some other tricky provisioning issues to deal with when it comes to SIP. Hackers, for example, could compromise those SIP end points to filch service or to launch denial of service attacks.
Under PacketCable 1.x, provisioning is well protected when MTAs do their proper handshakes with the provisioning servers. It already assumes that the MTA is in a hostile environment.
SIP, on the other hand, is very similar to the old analog wireless days when cell phone identity numbers and serial numbers were sent in the clear so that anyone with a scanner could use the information to steal service via a different phone, explains Kerbey Altmann, Sigma Systems' voice and multimedia service strategist.
"SIP today has little security in the end points," he says. Someone so inclined could spoof or impersonate the handshake. The cable industry, Kerbey adds, already has some SIP working groups developing security and provisioning specs, but they are still in the draft stage.
Sigma Systems is testing a SIP provisioning platform in the lab presently, and hopes to move into a technical trial with a "big" operator sometime this summer, executives there say.SIP support
Because of the momentum and growing interest in SIP, most PacketCable vendors already support the technology or are in the process of doing so.
Nortel Networks already has a SIP-compliant application manager, the Multimedia Communications Server, that's in trials and deployments. It's able to talk to the manufacturer's line of call management servers.
"We've got the application manager providing the interface to various clients using SIP," says Elaine Smiles, director of cable marketing for Nortel. "We're doing that now and working with some customers on some technical trials this summer."
Telcordia Technologies, which makes a line of call management servers, media gateways and SS7 gateways, has already added a SIP Proxy to its wares, says John Falzon, the company's vice president of call agent operations. The company also makes a policy server–either sold separately or as an integrated product–for the PCMM architecture.
Cedar Point is supporting SIP in its
flagship product, the SAFARI C3
"We have the underpinnings for that functionality to be extended to a SIP policy server," says Rafael Fonseca, Cedar Point's vice president of product evolution and systems engineering. "We already do call routing on NCS end points, so it's a minor extension."
Cedar Point demonstrated video telephony using SIP end points at last month's National Show. "It's in demo-ware right now...but in the third quarter of 2003, we expect to have something that could be trialed," Fonseca says.
"We've supported SIP since day one," says Syndeo's Griggs. Though cable's interest in SIP has been growing in the U.S., support of the technology is well under way in Japan, where 80 percent of the cable telephony subscribers on Syndeo's platform are running SIP.
AudioCodes, which OEMs IP products to customers such as Nortel, Siemens and Alcatel, has already added SIP extensions to its line of gateways and media servers.
"Fundamentally, we're agnostic," says Ben Rabinowitz, vice president of the company's systems group. "We'll keep supporting everything and see where the market takes us, but you can't ignore SIP forever."
Siemens Carrier Networks also supports SIP in its line of gear, including its HiQ 8000 call management server, which is currently supporting Cablevision Systems Corp.'s IP telephony product.
"We've had the design in the product since the beginning. It's been in our product for two years or so," says Mike Clement, Siemens' voice over cable solutions manager.
The emergence of SIP and PacketCable Multimedia has also caused some to call the relevance of PacketCable 1.x into question.
In the April edition of Cable Datacom News, industry analyst Michael Harris wrote that the PacketCable 1.x Network Call Signaling (NCS) that operators are deploying now "seems like an IP telephony antique. But honestly, how can this be a surprise when the initial PacketCable 1.0 specification was completed in December 1999?"
Net2Phone created a SIP-based architecture that complements its
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But, until the regulatory climate for VoIP is completely settled and MSOs still want to tackle the primary line market, 1.x is still very pertinent, despite the other types of IP services that operators might offer, others say.
"The answer today is, yes [1.x is relevant], especially if you want to offer $40 or $50 primary line replacement service," says ARRIS' Doiron, pointing out that PacketCable 1.x covers all of the primary regulatory requirements, including CALEA. "SIP has yet to address all of those issues."
Though SIP "is a simpler model, it has its drawbacks, including tightness of security and QoS," adds John St. Julian, Telcordia's vice president of strategy. "The [PacketCable] NCS specification has gone to great lengths to outline the concerns there and to put those details in those specifications."
"Will SIP obsolete PacketCable? I don't know, which is why I think it's important that we become knowledgeable on both technologies," concludes Barber of Charter Communications. "There are certain things that PacketCable does that SIP may not be able to achieve in the short-term, but, thus far, SIP is proving itself as a very robust technology."