A proposal for Fast Router Discovery

INTERNET DRAFT                                            JinHyeock Choi
Expires: November 2002                                      DongYun Shin
                                                             Samsung AIT
                                                                May 2002


               Fast Router Discovery with AP Notification
                <draft-jinchoi-l2trigger-fastrd-00.txt>


Status of this Memo

     This document is an Internet-Draft and is in full conformance with
     all provisions of Section 10 of RFC2026.

     Internet Drafts are working documents of the Internet Engineering
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Abstract

     This document presents Fast Router Discovery with AP Notification.
     For seamless handoff, a mobile node MUST quickly discover its new
     access router. In our proposal AP caches Router Advertisement
     message and sends it to a new mobile node as soon as L2 association
     is made.  We present a way for AP to cache necessary RA. By putting
     'RA Caching' and 'AP Notification' functionality on an Access Point, 
     we get the optimized result without IPv6 standard change.



Table of Contents:

     1. Introduction
     2. Terminology
     3. Proposal Overview
     4. Operation Description
       4.1 RA Caching
       4.2 AP Notification
     References




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1. Introduction

     The primary movement detection mechanism for Mobile IPv6 defined in
     [2] uses the facilities of IPv6 Neighbor Discovery [1], including
     Router Discovery and Neighbor Unreachability Detection. Mobile node
     MUST quickly detect when it moves to a link served by a new access
     router, so that it can acquire a new care-of address and send
     Binding Updates quickly. Mobile node MUST receive Router
     Advertisement from a new access router as soon as possible.

     There are several hindrances for sufficiently fast Router
     Discovery. First Neighbor Discovery protocol [1] limits routers to
     a minimum interval of 3 seconds between sending unsolicited
     multicast Router Advertisement messages. Second before a mobile
     node sends an initial Router Solicitation, it SHOULD delay the
     transmission for a random amount of time. Third a router MUST delay
     a response to a Router Solicitation by a random time too. Though
     solutions are proposed by [2], [3], they require IPv6 standard [1]
     change.

     In our proposal AP (Access Point) caches RA (Router Advertisement)
     message and sends it to a new mobile node as soon as L2 association
     is made.  We present a way for AP to cache necessary RA. By putting
     'RA Caching' and 'AP Notification' functionality on an Access Point, 
     we get the optimized result without IPv6 standard change. In our scheme, 
     mobile node receives Router Advertisement just after L2 association is 
     made which is the earliest possible time under current standard.



2. Terminology

     The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
     "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in
     this document are to be interpreted as described in RFC 2119.

          Access Router (AR)
            An Access Network Router residing on the edge of an Access
            Network and offers IP connectivity to mobile nodes

          Access Point (AP)
            An L2 entity that has station functionality and provides
            access to the distribution services, via the wireless
            medium for associated stations.



3. Proposal Overview

     In Wireless LAN technology, when a MN (mobile node)
     arrives at a new link, it should associate with its new AP.





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     In our proposal, AP caches RA message beforehand and sends it to a
     mobile node as soon as L2 association is made.

     We can cache RA in AP manually or use the following scheme. AR
     (Access Router) periodically multicasts unsolicited RAs, which go
     through AP. So AP can scan incoming L2 frames and cache necessary
     RA. AP scans L2 frame either continuously or periodically to update
     stored RA. Moreover if AR and AP are under same network
     administration, they can be configured such that AP caches RA
     efficiently.



4. Operation Description

     Our proposal consists of 'RA Caching' and 'AP Notification', 'RA
     Caching' periodically scans incoming L2 frame for unsolicited RA 
     and stores it. 'AP Notification' sends stored RA to new MN as soon 
     as L2 association is made.



4.1. RA Caching

     AP scans incoming L2 frame for unsolicited RA.

     First it scans L2 frame header to see whether it is a multicast
     frame. If not, AP sends that frame down link and scans next L2
     frame. If so, AP looks IP header to check whether it contains
     unsolicited RA. If incoming L2 frame doesn't contain unsolicited
     RA, AP sends that frame down link and scans next L2 frame. When AP
     finds unsolicited RA, it stores it.

     AP can scan continuously, updating old RA with new RA. Or if it
     costs too much for AP to scan every incoming L2 frame, we can
     control the scanning rate. For example, we can set timer and
     execute scanning every T seconds. Or we can make AP to be able to
     send Router Solicitation message. Periodically AP sends Router
     Solicitation. Then AR will send RA and AP caches it. It is noted
     that AP doesn't need to have IP address since it can use
     unspecified address as its source address.



4.2. AP Notification

     When a new MN arrives at AP, it sends Association Request Message
     with its MAC address. Then AP grants association by sending
     Association Response Message. As soon as association is made, AP
     sends stored RA to a new MN with MAC address in Association Request
     message. MN receives RA just after association is made which is the
     earliest possible time in current standard.




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References


[1]  T. Narten, E. Nordmark and W. Simpson, Neighbor Discovery for IP
     Version 6 (IPv6), RFC 2461, December, 1998.

[2]  D. Johnson, C. Perkins and J. Arkko, Mobility Support in IPv6,
     draft-ietf-mobileip-ipv6-17.txt, May 2002

[3]  J. Kempf, M. M Khalil and B. Pentland, IPv6 Fast Router
     Advertisement, draft-mkhalil-ipv6-fastra-00.txt, April 2002


Author's Addresses

   JinHyeock Choi
   i-Networking Lab, Samsung AIT (SAIT)
   Phone: +82-31-280-9233
   Email: [email protected]

   DongYun Shin
   i-Networking Lab, Samsung AIT (SAIT)
   Phone: +82-31-280-9552
   Email: [email protected]
































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