No More Scrambled Internet Video or Garbled Audio
Source Newsroom: University of Arizona
Newswise — Internet service providers may soon be able to guarantee quality of service thanks to software being developed by Marwan Krunz, an associate professor in the University of Arizona's Electrical and Computer Engineering department.
Krunz and his students are developing Internet routing software that supports video conferencing, voice transmission, and other real-time applications on a mass scale, at reasonable cost.
Computer engineers refer to this kind of software as "architecture for the Internet." The new architecture is being developed under a 3-year, $350,000 NSF Information Technology Research (ITR) grant.
Currently, information (video, audio, graphics, text) is broken down into small data packets. These packets are sent from the source computer to one or more destination computers through a series of intermediate computers called routers. Some routers, such as those found on university campuses, are privately owned and shared on a reciprocal service basis with other users. Other routers are fee-supported, and operated by Internet providers such as AOL or Earthlink.
Packets might go through only one or two routers when traveling within a city. But on a cross-country jaunt, packets might hit a dozen or more, Krunz says.
While this is happening, one router might temporarily go down or may become overloaded, slowing the transmission rate. This can interrupt continuous reception at the destination computer, scrambling the video or garbling the audio.
With the system now used to route traffic, Internet providers can only make best-effort attempts and can't offer ironclad guarantees of service.
"Quality-of-service addresses this issue by guaranteeing that digital packets will travel end-to-end in a certain number of milliseconds," Krunz explains. "Other types of guarantees are related to reliability — that none of the packets will be dropped due to overflows or conditions inside the network." This is what happens when one of your e-mails seems to evaporate in hyperspace.
The beauty of the Internet, and also its curse, is that it's probably the largest distributed system ever created, Krunz says. There is no centralized control. If one router goes down, packets are simply routed through another. It's like a gigantic road system. If one of the roads is closed, traffic finds an alternate route.
Past efforts to develop routing schemes with guaranteed service have involved complex systems that fail under a crush of data because each router needs to maintain a huge amount of information, such as the identity of every packet, its destination, which routers it has been through, and many other details.
Krunz and his graduate students are developing a "stateless" system, which means that routers or gateways (where data jumps on and off the Internet) don't have to maintain a lot of information. Their system uses simple instructions that are contained in the packets themselves. Among other things, these instructions include the packet's delay requirement (how long it can take to travel from source to destination) and how much time remains before it must be delivered. Those with the shortest delay times — the ones that have guaranteed service — are given priority, while "best-effort" data flows when it can.
Part of the system involves probe packets that move out in advance of a connection to find the fastest path. Repair algorithms are another feature. If data is flowing along a path and a server goes down or traffic suddenly increases dramatically clogging a router, the repair algorithm explores nearby routers, chooses an alternate path, and re-routes the data.
All of this is done with software at the machine level. "We're actually redefining the software down to the kernel in the operating system of the router itself," Krunz explains. This software needs to be installed on thousands of routers for the system to work, but it is backward compatible, allowing data to flow through routers with older software.
"The overall advantage here is to be able to deploy real-time services, such as video teleconferencing, over the Internet at a large scale and reasonable cost," Krunz says. "So ultimately, as an end user, you will get guaranteed public-telephone-quality voice or video, but over the Internet."
Related Web sites
UA Broadband Networking Lab
Marwan Krunz's homepage
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