TimeFlip: Using Timestamp-Based TCAM Ranges to Accurately Schedule Network Updates

摘要

Network configuration and policy updates occur frequently, and must be performed in a way that minimizes transient effects caused by intermediate states of the network. It has been shown that accurate time can be used for coordinating network-wide updates, thereby reducing temporary inconsistencies. However, this approach presents a great challenge; even if network devices have perfectly synchronized clocks, how can we guarantee that updates are performed at the exact time for which they were scheduled? In this paper, we present a practical method for implementing accurate time-based updates, using TimeFlips. A TimeFlip is a time-based update that is implemented using a timestamp field in a ternary content addressable memory (TCAM) entry. TimeFlips can be used to implement atomic bundle updates, and to coordinate network updates with high accuracy. We analyze the amount of TCAM resources required to encode a TimeFlip, and show that if there is enough flexibility in determining the scheduled time, a TimeFlip can be encoded by a single TCAM entry, using a single bit to represent the timestamp, while allowing a very high degree of accuracy.