MIT Scientists Develop Congestion Control System for Reducing Delays in Wireless Networks

MIT scientists have developed a novel congestion-control wireless network scheme that could decrease lag times while improving quality in video streaming, chat, gaming, and other web services. The researchers have called their new scheme “Accel-Brake Control” (ABC) and say that it achieves about 50% higher throughput and about half the network delays.

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Novel algorithm

The scheme works with a novel algorithm. This algorithm allows routers to communicate how many data packets should flow through a network to avoid congestion while fully utilizing the network.

“In cellular networks, your fraction of data capacity changes rapidly, causing lags in your service. Traditional schemes are too slow to adapt to those shifts,” said first author Prateesh Goyal, a graduate student in CSAIL. “ABC provides detailed feedback about those shifts, whether it’s gone up or down, using a single data bit.”

Conventional congestion-control schemes depend on packet losses to infer congestion and slow down. A router will alert a sender that its sent data packets are in congestion. The sender will then respond by sending fewer packets.

In order to provide greater information, researchers have, in the past, proposed “explicit” schemes that include multiple bits in packets. However, deploying such an approach would require a complete revamp of the way the internet sends data.

“It’s a tall task,” Mohammad Alizadeh, an associate professor in MIT’s Department of Electrical Engineering (EECS) and CSAIL and co-author of the study, said. “You’d have to make invasive changes to the standard Internet Protocol (IP) for sending data packets. You’d have to convince all Internet parties, mobile network operators, ISPs, and cell towers to change the way they send and receive data packets. That’s not going to happen.”

ABC to the rescue

This is where ABC comes to the rescue. ABC still relies on the available single bit in each data packet but does so in such a way that the bits can provide the real-time rate information to senders that they need.

“You’d think one bit wouldn’t carry enough information,” Alizadeh explained. “But, by aggregating single-bit feedback across a stream of packets, we can get the same effect as that of a multibit signal.”

The researchers are now in talks with mobile network operators to test their new scheme and are trying to see if ABC can also be used for apps and web services.