Subject: [mobile-ip] newest version of move detection addressing Erik's latest feedback

From: "Ed Remmell" <[email-masked]>
Date: Fri, 9 May 2003 17:50:00 -0700

Jari -

This newest version addresses Erik's latest feedback (except for MN rate
limiting of RS's when L2 up/down indications occur):

Definitions added to Section 3.2:

    L2 handover - process by which the mobile node changes from one
    link-layer connection to another. For example, a change of wireless
    access point is an L2 handover.

    L3 handover - subsequent to an L2 handover, a mobile node detects
    a change in an on-link subnet prefix that would require a
    change in primary care-of address. For example, a change of access
    router subsequent to a change of wireless access point typically
    results in an L3 handover.

11.5.1 Movement Detection

    The primary goal of movement detection is to detect L3 handovers.
    This section does not attempt to specify a fast movement detection
    algorithm which will function optimally for all types of
    applications, link-layers and deployment scenarios; instead, it
    describes a generic method that uses the facilities of IPv6 Neighbor
    Discovery, including Router Discovery and Neighbor Unreachability
    Detection. At the time of this writing, this method is considered
    well enough understood to recommend for standardization, however it
    is expected that future versions of this specification or other
    specifications may contain updated versions of the movement
    detection algorithm that have better performance.

    Generic movement detection uses Neighbor Unreachability Detection
    to detect when the default router is no longer bi-directionally
    reachable, in which case the mobile node must discover a new default
    router (usually on a new link). However, this detection only occurs
    when the mobile node has packets to send, and in the absence of
    frequent Router Advertisements or indications from the link-layer,
    the mobile node might become unaware of an L3 handover that
    occurred. Therefore, the mobile node should supplement this method
    with other information whenever it is available to the mobile node
    (e.g., from lower protocol layers).

    When the mobile node detects an L3 handover, it performs Duplicate
    Address Detection [13] on its link-local address, selects a new
    default router as a consequence of Router Discovery, and then
    performs Prefix Discovery with that new router to form new care-of
    address(es) as described in Section 11.5.2. It then registers its
    new primary care-of address with its home agent as described in
    Section 11.7.1. After updating its home registration, the mobile
    node then updates associated mobility bindings in correspondent
    nodes that it is performing route optimization with as specified in
    Section 11.7.2.

    Due to the temporary packet flow disruption and signaling overhead
    involved in updating mobility bindings, the mobile node should avoid
    performing an L3 handover until it is strictly necessary.
    Specifically, when the mobile node receives a Router Advertisement
    from a new router that contains a different set of on-link
    prefixes, if the mobile node detects that the currently selected
    default router on the old link is still bi-directionally reachable,
    it should generally continue to use the old router on the old link
    rather than switch away from it to use a new default router.

    Mobile nodes can use the information in received Router
    Advertisements to detect L3 handovers. In doing so the mobile node
    needs to consider the following issues:

    o  There might be multiple routers on the same link, thus hearing a
       new router does not necessarily constitute an L3 handover.

    o  When there are multiple routers on the same link they might
       advertise different prefixes.  Thus even hearing a new router
       with a new prefix might not be a reliable indication of an L3
       handover.

    o  The link-local addresses of routers are not globally unique,
       hence after completing an L3 handover the mobile node might
       continue to receive Router Advertisements with the same
       link-local source address.  This might be common if routers use
       the same link-local address on multiple interfaces.  This issue
       can be avoided when routers use the Router Address (R) bit, since
       that provides a global address of the router.

    In addition, the mobile node should consider the following events
    as indications that an L3 handover may have occurred:

    o  With some types of networks, notification that an L2 handover has
       occurred might be obtained from lower layer protocols or device
       driver software within the mobile node.  However, for some
       wireless technologies and deployment scenarios, an L2 handover
       may not always require an L3 handover, for example, if both the
       old link and the new link share the same access router and thus
       the same on-link prefixes. Therefore, link-layer indications do
       not guarantee that an L3 handover has occurred.

    o  If Router Advertisements that the mobile node receives include
       an Advertisement Interval option, the mobile node may use its
       Advertisement Interval field as an indication of the frequency
       with which it should expect to continue to receive future
       Advertisements from that router.  This field specifies the
       minimum rate (the maximum amount of time between successive
       Advertisements) that the mobile node should expect.  If this
       amount of time elapses without the mobile node receiving any
       Advertisement from this router, the mobile node can be sure that
       at least one Advertisement sent by the router has been lost.
       The mobile node can then implement its own policy to determine
       how many lost Advertisements from its current default router
       constitute an L3 handover indication.

    o  Neighbor Unreachability Detection determines that the default
       router is no longer reachable.

    Upon receiving such indications, the mobile needs to send Router
    Solicitations to discover routers and prefixes on the new link.

Thanks.
- Ed Remmell
Elmic Systems USA, Inc.

Best of Show Winner, ESC 2003
Click on the link and take a look!
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---

From: Brett Pentland <[email-masked]>
Date: Mon, 12 May 2003 15:11:36 +1000

Oops, I responded to the "Current movement detection process" thread
without noticing the bunch of emails on the same topic in this new
thread.  The sentence I commented on regarding rate limiting RSs is not
in this version of the text, as you noted.

The text looks very good.

Cheers,
Brett.

-- 
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 Brett Pentland                         [email-masked]
 CTIE - Centre for Telecommunications and Information Engineering
 Department  of  Electrical  and   Computer  Systems  Engineering
 Monash University, VIC, 3800,                          Australia
 Phone : +61 3 9905-5245                    Fax : +61 3 9905-5358
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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From: Erik Nordmark <[email-masked]>
Date: Mon, 12 May 2003 16:40:47 +0200 (CEST)

>        may not always require an L3 handover, for example, if both the

s/require/imply/ ??

>        an Advertisement Interval option, the mobile node may use its

Even if the advertisement interval isn't present a MN
would presumably assume movement when its current default router
times out from the default router list. I don't know if it is worth adding
this to the document.

  Erik

---

From: "Ed Remmell" <[email-masked]>
Date: Mon, 12 May 2003 10:32:04 -0700

> times out from the default router list. I don't know if it is worth adding

Erik -

This is already there, I believe:

"  In addition, the mobile node should consider the following events as
   indications that an L3 handover may have occurred.  Upon receiving
   such indications, the mobile node needs to send Router Solicitations
   to discover routers and prefixes on the new link.

<snip>
   o  Neighbor Unreachability Detection determines that the default
      router is no longer reachable."

Thanks.
- Ed

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From: "JinHyeock Choi" <[email-masked]>
Date: Tue, 13 May 2003 08:10:58 +0900

Dear Erik 

> times out from the default router list. I don't know if it is worth adding
 
I doubt that the default router will time out without MN's movement. 
If the default router is still reachable, before time out, MN will perform 
RS/ RA exchange or NUD to extend its lifetime. Hence, IMHO,
we don't have to worry about time out in Movement Detection.

---

From: Erik Nordmark <[email-masked]>
Date: Wed, 14 May 2003 18:46:13 +0200 (CEST)

>       router is no longer reachable."

What isn't there is:
 o The current default router times out from the default router list.
(i.e., when the router lifetime in the RAs expire.)

I might be useful to add that for completeness.
 
But Raj has declared this topic closed which I think is goodness. Time to
move on.

  Erik