The CPBT: A Method for Searching the Prefixes Using Coded Prefixes in B-Tree

Due to the increasing size of IP routing table and the growing rate of their lookups, many algorithms are introduced to achieve the required speed in table search and update or optimizing the required memory size. Many of these algorithms are suitable for IPv4 but cannot be used for IPv6. Nevertheless new efforts are going on to fit the available algorithms and techniques to the IPv6 128 bits addresses and prefixes. The challenging issues in the design of these prefix search structures are minimizing the worst case memory access, processing and pre-processing time for search and update procedures, e.g. Binary Tries have a worst case performance of O(32) memory accesses for IPv4 and O(128) for IPv6. Other compressed Tries have better worst case lookup performance however their update performance is degraded. One of the proposed schemes to make the lookup algorithm independent of IP address length is to use a binary search tree and keep the prefix endpoints within its nodes. Some new methods are introduced based on this idea such as "Prefixes in B-Tree", PIBT. But, they need up to 2n nodes for n prefixes. This paper proposes "Coded Prefixes in B-Tree", the CPBT. In which, prefixes are coded to make them scalar and therefore suitable as ordinary B-tree keys, without the need for additional node complexity which PIBT requires. We will finally compare the CPBT method with the recent PIBT method and show that although both of them have the same search complexity; this scheme has much better storage requirements and about half of the memory accesses during the update procedures.