On the Impact of Caching for High Performance Packet Classifiers

Hash functions have a space complexity of O(n) and a possible time complexity of O(1). Thus, packet classifiers exploit hashing to achieve packet classification in wire speed. Especially evolvable hash functions can adapt to a changing classification data base. But hash functions do have an important flaw. Some of the hashed keys may result in a large number of collisions. If those keys occur frequently, overall performance of a hash based packet classifier suffers. Although there is only limited or no existing locality in the data to be computed by a packet classifier, utilizing a cache can solve this problem. Unlike classical caches known from microprocessors, which are not adequate for packet classification and lookup algorithms, the proposed cache bases on a different strategy. It caches only the keys producing the most collisions instead of the ones that occur most often. That way, a cache improves the worst case performance of a hash function-based classifier. Based on simulatio...

• Type: Conference
• Year: 2008
• Where: GLOBECOM
• Authors: Harald Widiger, Andreas Tockhorn, Dirk Timmermann
• Keywords: Communications, GLOBECOM 2008, Hash Functions, Packet Classification, Packet Classifier