[54] LOW COST SEARCHING METHOD AND APPARATUS FOR ASYNCHRONOUS TRANSFER MODE SYSTEMS
[75] Inventors: Rene Glaise, Nice; Jean-Marie Munier, Cagnes sur Mer, both of France
[73] Assignee: International Business Machines Corporation, Armonk, N.Y.
[21] Appl. No.: 09/061,370
[22] Filed: Apr. 16, 1998
[30] Foreign Application Priority Data
Oct. 1, 1997 [EP] European Pat. Off 97480019
[51] Int. C I. II04I. 12 56
[52] U.S. CI 370/395; 370/392; 711/216;
714/781
[58] Field of Search 370/389, 392,
370/397, 399, 471, 395, 393; 711/202, 203, 216; 714/781, 776, 758, 807, 752, 748, 750, 745, 792
[56] References Cited
U.S. PATENT DOCUMENTS
4,588,985 5/1986 Carter et al 340/347
A method and an apparatus for searching a bit field whose significant bits comprise two contiguous bit fields such as the VPI/VCI bit fields of an ATM cell header. The invention uses a hash key based on CRC-n calculated on the bit field to be searched. One m bit field part of the significant bits of the bit field to be searched can be concatenated with the CRC-n to form a double hash key. It appears that, L being the total of the two contiguous bit field lengths, if L=m=n+p, p being greater or equal to 4, the scattering of data to be searched is perfect. The method comprised a first step of pointing to a first address with the hash (or double hash) key and reading a maximum of 2P addresses before reaching the addresses containing the bit field to be searched.
8 Claims, 17 Drawing Sheets
