A space- and time-efficient hash table hierarchically indexed by Bloom filters

Abstract

Hash tables (HTs) are poorly designed for multiple memory accesses during IP lookup and this design flow critically affects their throughput in high-speed routers. Thus, a high capacity HT with a predictable lookup throughput is desirable. A recently proposed fast HT (FHT) [20] has drawbacks like low on-chip memory utilization for a high-speed router and substantial memory overheads due to off-chip duplicate keys and pointers. Similarly, a Bloomier filter-based HT (BFHT) [13], generating an index to a key table, suffers from setup failures and static membership testing for keys. In this paper, we propose a novel hash architecture which addresses these issues by using pipelined Bloom filters. The proposed scheme, a hierarchically indexed HT (HIHT), generates indexes to a key table for the given key, so that the on-chip memory size is reduced and the overhead of pointers in a linked list is removed. Secondly, an HIHT demonstrates approximately 5.1 and 2.3 times improvement in on- chip space efficiency with at most one off-chip memory access, compared to an FHT and a BFHT, respectively. In addition to our analyses on access time and memory space, our simulation for IP lookup with 6 BGP tables shows that an HIHT exhibits 4.5 and 2.0 times on-chip memory efficiencies for 160 Gbps router than an FHT and a BFHT, respectively.