Papers published by the Institute of Electrical and Electronics Engineers, Inc. (IEEE) are Copyright © 2005-2008 by IEEE. Personal use of this material is permitted. However, permission to reprint/ republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE.

Papers published by the Association for Computing Machinery, Inc. (ACM) are Copyright © 2005-2008 by ACM. Permission to make digital/ hard copy of part or all of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage, the copyright notice, the title of publication and its date appear, and notice is given that copying is by permission of ACM, Inc. To copy otherwise, to republish, to post on servers, or to redistribute to lists, requires prior specific permission and/or a fee.