INTERNET DRAFT M. Ohta draft-ohta-smooth-handover-wlan-00.txt Tokyo Institute of Technology June 2002 Smooth Handover over IEEE 802.11 Wireless LAN Status of this Memo This document is an Internet-Draft and is subject to all provisions of Section 10 of RFC2026. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet- Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/1id-abstracts.html The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html Copyright (C) The Internet Society (June/15/2002). All Rights Reserved. Abstract This memo describes, based on the experience of MIS (Mobile Internet Services, Inc.) for commercial mobile IP service over IEEE 802.11b based wireless LAN environment, how smooth handover between access points is implemented. The major obstacle for the smooth handover is time required to scan frequency bands and latency of mobile registration is not so much a problem, both of which is solved with terminals having two transceivers. 1. Introduction MIS (Mobile Internet Services, Inc.) is the first, and currently the only, ISP in the world to commercially provide mobile IP service. M. Ohta Expires on December 15, 2002 [Page 1]
INTERNET DRAFT Smooth Handover over WLAN June 2002 MIS uses IEEE 802.11b based wireless LAN infrastructure and puts a lot of wireless LAN access points to let its subscribers move around with IP mobility. MIS started public field trial in August 2001 and started commercial service in April 2002. During the trial, a possible problem of the wireless LAN became apparent that it takes considerable amount of time, often more than a second, to scan all the possible frequency bands, which is required upon handover to find the next access point better than the current. For some applications such as web browsing, it is not a problem. However, for streaming applications such as Internet telephony, smooth handover with little or no service interruption is strongly desired. The problem is solved by terminals having two wireless transceivers. 2. Smooth Handover with Two Transceivers To prevent the service interruption, it is necessary that a terminal, which is expected to run service-interruption-sensitive applications, should have two wireless LAN transceivers, one for keeping connection to the the current access point and another for scanning frequency bands to search alternative ones. 3. Smoother Handover with Two Transceivers With the elimination of service interruption for frequency band scanning, there still is a smaller amount of service interruption for mobility registration, which can also be eliminated. With two wireless LAN transceivers, just after one transceiver find a new access point better than the current, a new connection to the new access point should be established through the transceiver. Then, mobility registration for the new access point should be initiated. Still, another transceiver should keep connecting to the current access point. A while after the terminal confirms a successful mobility registration, the terminal should terminate the connection to the old access point and, as described in section 2, start scanning newer access points. M. Ohta Expires on December 15, 2002 [Page 2]
INTERNET DRAFT Smooth Handover over WLAN June 2002 During mobile registration, 4. Applications of the Technique The technique described in sections 2 and 3 was deployed in recent PHS (personal handy phone, 32Kbps mobile telephone system available in Japan and other countries) service, only after which, PHS can support stable and smooth handover. In general, the technique requires two sets of transceivers, which increases the cost of terminals, which is welcome to wireless LAN chip vendors, it also reduce the cost of network by eliminating intelligent intermediate entities for half-hearted smooth mobility. Note that a CDMA based wireless transceiver can simultaneously use two access points with different code without additional RF modules. 5. Security Considerations To prevent anonymous and/or unpaid access to the Internet, access points of MIS have packet-wise cryptographical authentication mechanism to disallow unauthorized access to the Internet. To prevent subscribers share a single subscriber ID with single payment, the mechanism disallows multiple terminals with a single subscriber ID simultaneously use access points. As a side effect, the mechanism, basically, disallows a terminal simultaneously use multiple access points. However, to allow for the smooth handover, a terminal is allowed to simultaneously use access points with overlapping service area. 6. Author's Address Masataka Ohta Graduate School of Information Science and Engineering, Tokyo Institute of Technology 2-12-1, O-okayama, Meguro-ku Tokyo 152-8552, JAPAN Phone: +81-3-5734-3299 Fax: +81-3-5734-3299 EMail: mohta@necom830.hpcl.titech.ac.jp M. Ohta Expires on December 15, 2002 [Page 3]
INTERNET DRAFT Smooth Handover over WLAN June 2002 7. Full Copyright Statement "Copyright (C) The Internet Society (June/15/2002). All Rights Reserved. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English. The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns. This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. M. Ohta Expires on December 15, 2002 [Page 4]