Congestion Avoidance and Control Van jacobson Lawrence Berkeley Laboratory Michael J Karels+ University of California at Berkeley November 1988 Introduction Computer networks have experienced an explosive growth over the past few years and with that growth have come severe congestion problems. For example, it is now common to see internet gateways drop 10% of the incoming packets because of local buffer overflows Our investigation of some of these problems has shown that much of the cause lies in transport protocol implementations(not in the protocols themselves ): The obvious' way to implement a window-based transport protocol can result in exactly the wrong behavior in response to network congestion. We give examples of wrong behavior and describe some simple algorithms that can be used to make right things happen. The algorithms are rooted in the idea of achieving network stability by forcing the transport connection to obey a packet conservation principle. We show how the algorithms derive from this principle and what effect they have on traffic over congested networks In October of 86. the internet had the first of what became a series of ' congestion col- lapses. During this period, the data throughput from LBL to UC Berkeley(sites separated by 400 yards and two IMP hops)dropped from 32 Kbps to 40 bps. We were fascinated by this sudden factor-of-thousand drop in bandwidth and embarked on an investigation of why things had gotten so bad. In particular, we wondered if the 4.3BSD(Berkeley UNIX) TCP was mis-behaving or if it could be tuned to work better under abysmal network conditions The answer to both of these questions was yes Note: This is a very slightly revised version of a paper originally presented at SIGCOMM88 [12 eY RThis work was supported in part by the U.S. Department of Energy under Contract Number DE-ACO3- vish to reference this work, please cite [12] 76sF00098 *This work was supported by the U.S. Department of Commerce, National Bureau of Standards, under Grant Number 60NANB8D0830Congestion Avoidance and Control∗ Van Jacobson† Lawrence Berkeley Laboratory Michael J. Karels‡ University of California at Berkeley November, 1988 Introduction Computer networks have experienced an explosive growth over the past few years and with that growth have come severe congestion problems. For example, it is now common to see internet gateways drop 10% of the incoming packets because of local buffer overflows. Our investigation of some of these problems has shown that much of the cause lies in transport protocol implementations (not in the protocols themselves): The ‘obvious’ ways to implement a window-based transport protocol can result in exactly the wrong behavior in response to network congestion. We give examples of ‘wrong’ behavior and describe some simple algorithms that can be used to make right things happen. The algorithms are rooted in the idea of achieving network stability by forcing the transport connection to obey a ‘packet conservation’ principle. We show how the algorithms derive from this principle and what effect they have on traffic over congested networks. In October of ’86, the Internet had the first of what became a series of ‘congestion col￾lapses’. During this period, the data throughput from LBL to UC Berkeley (sites separated by 400 yards and two IMP hops) dropped from 32 Kbps to 40 bps. We were fascinated by this sudden factor-of-thousand drop in bandwidth and embarked on an investigation of why things had gotten so bad. In particular, we wondered if the 4.3BSD (Berkeley UNIX) TCP was mis-behaving or if it could be tuned to work better under abysmal network conditions. The answer to both of these questions was “yes”. ∗Note: This is a very slightly revised version of a paper originally presented at SIGCOMM ’88 [12]. If you wish to reference this work, please cite [12]. †This work was supported in part by the U.S. Department of Energy under Contract Number DE-AC03- 76SF00098. ‡This work was supported by the U.S. Department of Commerce, National Bureau of Standards, under Grant Number 60NANB8D0830. 1