Unjamming the Information Superhighway and saving the Internet

In the early days of the Internet, Berkeley Lab's Van Jacobson's algorithms kept the network from collapsing.

December 5, 2018

In 1986, the burgeoning Internet was nearly two decades old and had 10,000 users. It was also facing imminent collapse due to network congestion. Van Jacobson, a network researcher at Lawrence Berkeley National Laboratory, dove into the problem and co-authored the solution that is still in use today. At that time, ESnet was in its infancy and Berkeley Lab staff were among those helping to shape networking protocols and infrastructure.

In the late 1980s, the Internet was heralded as the “Information Superhighway” as it carried streams of data at an unprecedented 56 kilobits per second. Then in October 1986, the stream slowed to a trickle and the transmission rate between Berkeley Lab and the University of California at Berkeley, only a quarter-mile away, slowed to 320 bits per second. Mail that had gone through in minutes before soon took an entire day and the whole concept of network communication was threatened and many were saying the Internet couldn’t scale.

Unraveling the data traffic jams
Internet users all over the country puzzled over how to revive it. Jacobson, who headed the lab’s Network Research Group, was among those who became involved. Working with Mike Karels of the Berkeley Unix development group at UC Berkeley, Jacobson spent six months asking themselves why the Internet was failing, “beating our heads against a brick wall,” Jacobson later recalled. Then one night in a Berkeley coffee house, they was a moment of enlightenment. “We turned the question around. The real question was, `How had the Internet ever worked?' “

At the time, workstations would send data at 10 megabits per second to routers, which then fed the data onto the Internet, which had a capacity of 56 kilobits per second. At each onramp, traffic was already backing up. Multiply this by the thousands of people using the network simultaneously and a traffic jam on the Internet was inevitable.

As the traffic had increased on the Internet, the system's many users had relied on what amounted to self-destructive behavior in their attempts to break through the network gridlock. Packets of information would be transmitted to the network by a computer and subsequently returned to the sender because of the congestion. Computers had been programmed to deal with this by immediately trying again, repeatedly resending the message until it went through. Jacobson likened the situation to pouring gasoline on a fire.

A protocol for better online behavior
The solution was to make the network users more polite. Jacobson and Karels wrote what they called “polite protocols” that required a slight wait before a packet was retransmitted. The protocols were integrated into the Transmission Control Protocols (TCP), the suite of communication protocols used to interconnect network devices on the internet.

Jacobson and Karels' protocols were called "Slow Start" and avoided congestion by monitoring the network and, when congestion appeared imminent, delayed the transmission of packets anywhere from milliseconds to a second. Slow Start delays transmission rates based on factors that include the current available capacity of the network as well as a multiple of the round-trip transmission time (essentially, distance) between the sender and the chosen destination. More than 30 years after it was introduced, Slow Start continues to avoid network congestion even though both the speed of the network is now measured at billions of bits per second (gigabits) and the number of users has topped 3.5 billion.

Jacobson and Karels outlined the work in their landmark 1988 paper "Congestion avoidance and control." In it, the authors described and analyzed five algorithms for the TCP that shed light on the flow of data packets and helped solve the problem of congestion. TCP remains the most dominant protocol for moving data on the Internet and Jacobson is widely credited with enabling the Internet to expand in size and support increasing speed demands.

In 2012, Jacobson was honored as an “Innovator” when he was elected as a member of the first class of inductees to the Internet Hall of Fame.

A little back story
From the outset, Lawrence Berkeley National Laboratory was one of the principal architects of network computing, helping to grow the network since 1972. In May 1974, Berkeley Lab connected a Control Data Corp. 6600 computer to ARPANET, establishing the first networked supercomputer and becoming one of a handful of institutions connected to the network.

With the move of ESnet to Berkeley Lab in 1996, this culture of networking innovation has continued apace.


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