International Journal of Wireless Information Networks, Vol. 5, No. 1, 1998 1068-9605 / 98 / 0100-0043$15.00 / 0 Ó 1998 Plenum Publishing Corporation 43 A Survey of Handover Techniques for Wireless ATM Networks C.-K. Toh 1,3 and Bora Akyol 2 This paper provides a review and comprehensive comparison of existing handover schemes proposed for wireless ATM networks. Existing schemes include those proposed by NEC, Olivetti, Bell Labs, Cambridge, Stanford, CMU, Berkeley, Michigan, VTT, and Columbia. We highlight the methodologies employed by the various schemes and reveal their differences. We discuss is- sues related to the effect of ATM switch architectures on mobility implementation and on future handover paradigms. KEY WORDS: Wireless ATM; mobile handover protocols. 1. INTRODUCTION Several local- and wide-area wireless ATM archi- tectures have evolved over the past few years. The rea- sons for their evolution are diverse. Some architectures aim at providing seamless integration with broadband ISDN, while others aim to support mobile multimedia. Nonetheless, the fundamental aim of wireless ATM is to provide mobility support for mobile ATM users as they roam from one location to another. The term `mobility support’ in a wireless ATM en- vironment refers to the ability to establish and tear down mobile connections and to provide a mechanism for mobile handovers, location tracking, and queries. Sev- eral handover mechanisms have been proposed and stud- ied, and some have been implemented. Depending on the handover strategy employed, the amount of traf®c disruption, cell loss, cell delay variation, and signaling traf®c generated can vary considerably. Since wireless ATM aims to provide multimedia services to mobile hosts (MHs), the performance of the handover proto- col thus has a signi®cant impact on the traf®c char- 1 Hughes Research Laboratories, Malibu, California 90265; e-mail: cktoh@isl.hrl.hac.c om [formerly with Cambridge University]. 2 BBN Systems and Technologies, Cambridge, Massachusetts 02140; e-mail: bakyol@bbn.com [formerly with Stanford University]. 3 To whom correspondence should be addressed. acteristics and hence the user-perceived quality of ser- vice (QoS). Existing handover schemes can be classi®ed in accor- dance with the path rebuild strategy employed. They include the following handover schemes: (a) connec- tion extension [31], (b) full reestablishment [16], (c) incremental / partial re-restablishment [16], (d) multicast join [16], and (e) multicast group [16, 8, 7]. In the connection extension scheme, a mobile connection is extended from the previous base station (BS) to the new BS. In the full reestablishment scheme, a new connec- tion has to be established from the new BS to the remote end host. In the incremental reestablishment approach, a partial connection is established from the new BS to a node residing on the connection path prior to handover. In the multicast-join scheme, a partial path is established from an intermediate switch to the new BS, using the feature of ATM multicast. This is quite similar to the problem of handling dynamic host membership in multi- casting [30]. Finally, in the multicast-group scheme, mul- tiple connections are always established to multiple wire- less cells surrounding the wireless cell where the MH is currently residing. Hence, this scheme is sometimes referred to as the `torch’ or `footprint’ approach. Instead of reserving communication resources to all neighbor- ing cells, an alternative approach is to allow only