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May 13, 2004
Imagine a telecom network where optical connections could be set up and torn down in an instant by edge equipment, without human intervention. Fantastic, or frightening?
A protocol aimed at achieving this feat has been under development for some time. Called the "Just in Time" protocol, or JIT, it provisions lightpaths in as little as 10 microseconds. And just recently, scientists from the North Carolina State University and MCNC Research & Development Institute demonstrated to the Federal Communications Commission (FCC) that JIT isn't science fiction (see MCNC Touts JIT Optical Protocol).
The researchers make unflattering comparisons with Generalized Multiprotocol Label Switching (MPLS), which takes between several seconds and several minutes to set up or tear down an optical connection.
JIT "is better than GMPLS," says Dan Stevenson, VP of advanced networking and IT at MCNC-RDI. "GMPLS is too complex, and it doesn't get you anywhere near the performance level you need for interactive capabilities."
Applications like grid networking and research networks like the recently announced National Lambda Rail could be first in line to benefit from JIT's faster provisioning. High-energy particle physics experiments generate huge amounts of data in bursts, which need to be sent between different computers without tying up bandwidth for long periods. The U.S. government is also interested in JIT, for reasons it won't specify.
"JIT addresses some very challenging problems in high-performance computing," Dr. Hank Dardy, chief scientist for advanced computing at the Naval Research Laboratory (NRL)’s Center for Computational Science wrote in a statement. "It can take weeks to establish an optical connection through a carrier network, and minutes to do so with generalized multi-protocol label switching, the current industry standard. With JIT, we can provision optical connections between sites in a few milliseconds through our microelectromechanical switches, and in a few microseconds when we deploy faster photonic switches."
NRL has just completed the third JIT demonstration, sending uncompressed, high-definition TV signals between host computers at various Department of Defense locations using commercial ROADMs (reconfigurable add/drop multiplexers) from Lambda Optical Systems Corp. Earlier demonstrations of HDTV transmission at 1.5 Gbit/s and IP data took place, respectively, in November 2002 and September 2003.
It's early days for JIT, which is not a standardized protocol, but things look promising.
"He [Dardy] is the guy that everyone goes to when they want a new technology adopted by the U.S. government," says Geoff Bennett, chief technologist with Heavy Reading, Light Reading's paid research division. "If they're testing with him, they're definitely on the right track."
However, Bennett has some reservations about JIT and the scientists' claims. "I don't think it's as simple as saying that JIT could be a competitor to GMPLS," he says. "GMPLS can use different signaling protocols to set up connections, and, in the future, one of those signaling protocols could be JIT."
Bennett goes on to say that the whole idea of edge equipment automatically setting up and tearing down optical connections on demand "would give the transmission guys the willies" in conventional carriers. It would mean they'd lost control of capacity planning.
Kiss and tellSo how does JIT configure networks in an instant?
Most control plane protocols, including Asynchronous Transfer Mode (ATM) and GMPLS, require handshaking: At each stage of the configuration, the network resources must send back a confirmation message to say that they are ready. Stevenson calls this "tell and wait".
JIT, in contrast is "tell and go": It sends out a network setup message that nails up the connections as it goes, thereby avoiding all the latency associated with handshaking.
Another advantage, says Stevenson, is that an application, as opposed to a user, can make a connection request, which allows provisioning to be truly automated.
All this works fine when the network is lightly used, but what happens if there's congestion? Simple answer: Data gets dropped. And that isn't acceptable to most users.
"JIT was rejected in the past," notes Heavy Reading's Bennett. "The big problem everyone had was that you could never know for sure that a connection has been set. What's changed?"
MCNC-RDI's Stevenson says that blocking probability -- the chance that a connection can't be routed -- has been reduced to an acceptable level. "Quality of service can still be maintained on a network with 60 percent loading in the access and 40 percent in the core," he claims. "That compares favorably to IP networks where utilization is typically 10 to 15 percent."
But there is a catch. To be really efficient, the network must have enough wavelengths, where "enough" is in the range of 16 to 32 wavelengths on a fiber, he adds.
Various techniques are used to reduce the blocking probability. MCNC-RDI has assumed in its calculations that wavelength conversion is a readily available technology -- a questionable assumption, since there aren't any wavelength converters on the market today. Another available technique is called "deflection routing": If the requested port is busy, the switch sends the data out along another random path.
A hardware-based protocol, JIT is built into a prototype rackmounted 3U enclosure that Stevenson calls a JITPAC. "If you have an existing system of OADMs, you acquire some JITPACs, one per OADM. All you need to do is figure out which channel to use for signaling, and you're off to the races."
The JITPAC is capable of interfacing to all existing commercial off-the-shelf switches via a customizable TL1, SNMP, or proprietary interfaces for the purpose of controlling the switches. MNCN-RDI is working towards standardizing the control interface. To that end, the organization is in talks with equipment vendors -- including Cisco Systems Inc. (Nasdaq: CSCO), Calient Networks Inc., and Glimmerglass Networks. In the meantime, says Stevenson, they'll keep kicking the tires.
— Pauline Rigby, Senior Editor, Light Reading
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