Method and apparatus for a token bucket metering or policing system with a delayed filling scheme

Abstract

Methods and apparatus are disclosed for a token bucket metering or policing system with a delayed filing scheme which may be used, inter alia, in a computer or communications system, such as a packet switching system, router, or other device. The token bucket scheme updates the number of tokens in a particular bucket in response to an expiration of a timer or a receipt of a packet corresponding to a packet stream being metered or policed based on the particular bucket. One implementation determines whether a difference between a current time value with a last bucket update time value equals or exceeds a predetermined time interval. If the difference between the current time value with the last bucket update time value equals or exceeds the predetermined time interval, then a predetermined number of tokens is added to a bucket, and the last bucket update time value is incremented by approximately the predetermined time interval. In one implementation, the predetermined number of tokens corresponds to the number of tokens required to send a maximum sized packet and the predetermined time interval corresponds to the time required to accumulate the number of tokens required to send a maximum sized packet at the corresponding token generation rate. In this manner, a simple addition operation may be used to update the number of tokens in a token bucket to ensure that a maximum sized packet may be sent. Also, by updating the last bucket update time value by approximately the predetermined time interval, and not merely setting it to the current time, tokens which should be added to the token bucket are not lost, but rather added at a later time.