One document matched: draft-ohta-smooth-handover-wlan-00.txt

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
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   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
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   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
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   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.




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   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.



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   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








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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
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   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
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   developing Internet standards in which case the procedures for
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   followed, or as required to translate it into languages other than
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   The limited permissions granted above are perpetual and will not be
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   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
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