| Summary: | 碩士 === 國立中興大學 === 資訊科學與工程學系 === 104 === TCAM is a memory widely used in network devices to store the rules for the packet classifications. It can search all entries simultaneously to report the highest-priority matching entry from all matching entries, where the priority of an entry is defined by its address in TCAM. Because the correctness of TCAM searches is tied to the precise order of TCAM entries, TCAM update procedure may involve the movements of multiple TCAM entries. The search procedure could be interrupted during the time period of updating TCAM. Therefore, an efficient TCAM update procedure is important to sustain the TCAM throughput.
TCAM Update Using Substitute Chains (TUUSC) is an efficient approach for TCAM updates. It reduces TCAM entry movements by additionally considering TCAM entries corresponding to none overlapping rules. In this work, we further reduce the TCAM entry movements by reordering rules. To begin with, each rule is categorized into a chain, which consists of rules that there are no other rules between two consecutive rules in a chain. The maximum update cost of a rule is equal to its sub-chain length, i.e. the number of rules below the chain of the rule. Our scheme starts from sorting the rules according to their sub-chain lengths. Then, the rules with short sub-chain lengths are moved to the positions behind the rules with long sub-chain lengths. As a result, TUUSC can use the moved rules to keep the number of TCAM entry movements in each update below a predefined threshold value if there is at least one rule whose sub-chain length is smaller than the threshold value behind the rules whose sub-chain lengths are larger than the threshold value. Our scheme also maximizes the number of rule insertions whose TCAM entry movements can benefit from the reordered rules. The experimental results show that our scheme can effectively reduce the number of TCAM entry movements for TUUSC.
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