Study: Differentiated Networks More Efficient

A new study by researchers at Rensselaer Polytechnic Institute, AT&T Labs, and the University of Nevada, Reno suggests that an Internet where all traffic is treated identically would require significantly more capacity than one in which differentiated services are offered.

Findings from the study were presented June 22 at the 15th IEEE International Workshop on Quality of Service (IWQoS 2007) in Evanston, Ill. IWQoS is a premier workshop on quality of service research, featuring rigorously reviewed technical sessions and papers.

As the Internet becomes more crowded with high-bandwidth applications and content, a wide-ranging debate is taking place about the issue of “network neutrality,” which involves both economic and technical aspects. One aspect of the debate involves whether application traffic that requires performance assurances (e.g., VoIP) could be serviced differently, or what the impact would be if all traffic were to be treated in an undifferentiated manner.

“We wanted to take one piece of the overall debate and approach it quantitatively,” says principal investigator Shivkumar Kalyanaraman, professor of electrical, computer, and systems engineering at Rensselaer. “The study makes clear that there are substantial additional costs for the extra capacity required to operate networks in which all traffic is treated alike, and carrying traffic that needs to still be assured performance as specified in service level agreements (SLAs).”

Using computer models, the researchers compared the current “best-effort” approach with a tiered model that separates information into two simple classes — one for most types of information and another for applications requiring service level assurance for high-bandwidth content like video games, telemedicine, and Voice over Internet Protocol (VoIP).

The study was meant to answer one basic question, according to Kalyanaraman: “If I want to meet the needs of applications that require service level assurances, how much more capacity do I need"”

The additional capacity needed for an undifferentiated network compared to a differentiated network is referred to as the Required Extra Capacity. The study estimates that the Required Extra Capacity in even modestly loaded networks could approach 60 percent. At times of heavy demand on the network, the Required Extra Capacity in an undifferentiated network could amount to an additional 100 percent or more of the total capacity required when differentiation is permitted.

“Clearly, an undifferentiated network in this context is less efficient and more expensive,” says coauthor K.K. Ramakrishnan of AT&T Labs. “We believe understanding the real impacts of the alternative strategies is important as the debate about network architecture unfolds.”

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The Next Great Earthquake

The 2004 Sumatra-Andaman earthquake and resulting tsunami are now infamous for the damage they caused, but at the time many scientists believed this area was unlikely tocreate a quake of such magnitude.

In the March 23 issue of the journal Science, a geophysicist from Rensselaer Polytechnic Institute urges the public and policy makers to consider all subduction-type tectonic boundaries to be "locked, loaded, and dangerous."

"Seismologists have long tried to determine which subduction boundaries are more likely than others to break," says Robert McCaffrey, professor ofearth and environmental sciences at Rensselaer. "Yet, the great earthquake of 2004 ruptured a segment that was thought to be among the least likely to go."

On Dec. 26, 2004, the earth beneath the Indian Ocean buckled and ruptured, unleashing one of the largest earthquakes in recorded history. Shockwaves from the magnitude 9.2 (M9) quake created a wall of rushing water that devastated communities up to 1,000 miles away.

M9 earthquakes typically occur at a specific type of tectonic boundary called a subduction zone, where one plate is gently slipping underneath another plate, which causes friction, cracking, and lifting of the plates. An M9 earthquake can be created by only 20 meters of slip between two converging plates -- less then the length of an 18-wheeler truck -- but its effects can be global in their impact.

Slips of this length only occur every 200 to 1,000 years or more at aparticular boundary, leaving no reliable historic records to track their frequency, McCaffrey notes. Complete records are only available going back 100 years. Scientists had widely accepted that the age and speed of the subducting plate is important in creating M9 earthquakes, based primarily on support from this 100-year historical record.

But this narrow understanding put the Sumatran subduction zone in avery low risk category. McCaffrey suggests that such limited records are incapable of mapping a trend in geological events that could be several centuries or more apart.

Geologists also focused on the temperature of subduction zones, indicating that temperature at the plate convergence region plays a strong role in the strength of a resulting earthquake. These thermal considerations place the Andaman subduction zone in the high-magnitude class, but one pitfall with this type of classification is that it characterizes some subduction zones as being incapable of producing an M9.

"[The day of the quake], Earth gave us a stark reminder of the important difference between improbability and impossibility," McCaffrey says. "Our understanding of where and when the next great earthquake will happen is in its infancy at best. We have not had enough time to decipher M9 behavior."

In creating new public policy, McCaffrey urges officials to consider all subduction zones as lethal. "Several are near densely populated landareas, and the potential impacts of shaking and tsunamis cannot be overstated," he says.

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New Coating Is Virtual Black Hole for Reflections

Researchers have created an anti-reflective coating that allows light to travel through it, but lets almost none bounce off its surface. At least 10 times more effective than the coating on sunglasses or computer monitors, the material, which is made of silica nanorods, may be used to channel light into solar cells or allow more photons to surge through the surface of a light-emitting diode (LED).

Publishing in the March 1, Nature Photonics, lead author Jong Kyu Kim and a team from Rensselaer Polytechnic Institute in Troy, N.Y., reveal how they crafted the coating, which reflects almost as little light as do molecules of air.

Guided by National Science Foundation-supported electrical engineer Fred Schubert, the researchers developed a process based on an already common method for depositing layers of silica, the building block of quartz, onto computer chips and other surfaces.

The method grows ranks of nanoscale rods that lie at the same angle. That degree of the angle is determined by temperature. Under a microscope, the films look like tiny slices of shag carpet.
By laying down multiple layers, each at a different angle, the researchers created thin films that are uniquely capable of controlling light. With the right layers in the right configuration, the researchers believe they can even create a film that will reflect no light at all.

One critical application for the material is in the development of next-generation solar cells. By preventing reflections, the coating would allow more light, and more wavelengths of light, to transmit through the protective finish on a solar cell surface and into the cell itself. Engineers may be able to use such a technique to boost the amount of energy a cell can collect, bypassing current efficiency limits.

Another application would involve coating LEDs to eliminate reflections that cut down the amount of light the LED can emit. The researchers hope the efficiency gains could allow the light sources to compete more effectively with fluorescent and incandescent bulbs. So, they will next focus their attention on solid state lighting.

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