Subject: [Monami6] Comments on draft-petander-mip6-mbb-00.txt

From: Christian Vogt <[email-masked]>
Date: Tue, 18 Oct 2005 20:13:51 +0200

Hi Henrik, hi Eranga,

I took a good look at draft-petander-mip6-mbb-00.txt.  These are very
valuable considerations indeed.  A few comments below.

You assume that the MN affects the L2 handoff at the time it receives
the (first) Binding Acknowledgement (BA).  Note, however, that
performing the L2 handoff right upon sending the Binding Update (BU)
would mitigate the issue with binding inconsistencies at the MN and the
CN.  All packets that a CN/HA would send/tunnel to the MN prior to
processing the BU would be lost at the old care-of address (CoA).

If the L2 handoff takes a long time, initiating it as early as this
would be ok, since the MN would loose packets during the L2 handoff anyway.

But I agree that deferring the L2 handoff until BA reception has a
higher potential, especially when L2 handoffs become faster than they
are today.

You have to be a bit careful with correspondent registrations, though,
since those require a return-routability procedure.  I noticed that you
are doing research with multiple interfaces, which allows you to check a
new CoA while remaining attached to the old link.  But if the MN has a
single interface only, it will not be able to run a CoA test from the
old link.

You may want to take a look at the following draft, however:

   draft-vogt-mobopts-early-binding-updates-00.txt

This draft---in particular section 4, 7th paragraph and
onwards---defines how a single-interfaced MN can use Early Binding
Updates and Credit-Based Authorization for handoff anticipation and
proactive Mobile IPv6 signaling.  Here is a nutshell view:

(1)  The MN performs proactive HoA tests while communicating at the old
link.

(2)  When it detects that a handoff is imminent, the MN sends an Early
Binding Update (EBU) to each of its CNs.

(3)  The MN continues to communicate through the old CoA, at the old
link, until it receives the first Early Binding Acknowledgement (EBA).

(4)  The MN hands off to the new link.

(5)  The MN resumes communications through the new CoA.

(6)  The MN performs a concurrent care-of-address test with the each of
its CNs and subsequently sends a standard BU to each of them.

Some comments:

(a)  EBUs do not provide reachability confirmation, since no CoA test is
done to protect them, but...

(b)  ...CNs use Credit-Based Authorization to prevent misuse of EBUs and
protect the period until a concurrent CoA test is done and a standard BU
is received.

(c)  Credit-Based Authorization also prevents misuse of Alternate CoA
options, which in this case contain CoAs that differ from the IPv6
source address.

(d)  According to your draft, a CN must keep the old-CoA binding after
receiving an EBU.  A bit different than in your draft, the CN can
release that binding once it receives a standard BU.

(e)  A MN is assumed to learn about the prefixes used on the new link
through external mechanisms.

Best regards,
- Christian

--
Christian Vogt, Institute of Telematics, University of Karlsruhe
www.tm.uka.de/~chvogt/pubkey/
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From: Henrik Petander <[email-masked]>
Date: Wed, 19 Oct 2005 10:01:54 +1000

Hi Christian,

Thanks for reading the draft and commenting it. Replies to your
comments are inline.

On 10/19/05, Christian Vogt <[email-masked]> wrote:
> the (first) Binding Acknowledgement (BA).

Actually we assume only that MN performs MIPv6 handoff at this time.
L2 handoff and IPv6 link attachment can be performed before the MIPv6
handoff, if MN is capable of connecting to both the old and new access
router simultaneously, which is required for make-before-break
handoffs, which our draft focuses on. In successful make-before-break
handoffs the delays of L2 handoff and IPv6 link attachment do not lead
to packet loss. The handoff procedure for a make-before-break handoff
would be:

1) Find a suitable next AR using idle interface A, while using
interface B for active communications via old AR.
2) Perform L2 handoff and IPv6 link attachment on interface A with new AR
3) Perform MIPv6 handoff to switch traffic to new interface.

In the draft we focus only on 3), since 1) and 2) can be done with the
existing protocol specs for IPv6 (in handoffs to foreign networks). I
hope this clarifies the intent of our draft.

> would be ok, since the MN would loose packets during the L2 handoff anyway.

This is true in the case of break-before-make handoffs, in which MN
loses connectivity with its old AR before establishing connectivity
with a new one. However, for make-before-break handoffs L2 handoff
delay does not have a direct connection with packet loss, only on the
probability of being able to finish the handoff before connectivity at
the old CoA ends.

> proactive Mobile IPv6 signaling.

Thanks for the pointer. If your draft is used with make-before-break
handoffs, it will reduce the time required for handoff. Shortened
handoff time increases the probability of a make-before-break handoff
finishing before the connectivity at old CoA ends.

Best regards,
Henrik

---

From: Christian Vogt <[email-masked]>
Date: Wed, 19 Oct 2005 09:00:36 +0200

Hi Henrik,

 > to packet loss. The handoff procedure for a make-before-break handoff

ok, if the MN has multiple interfaces, it can set up the 2nd interface
at any time btw. BU transmission and BA reception.

However, you can do a make-before-break handoff even with a single
interface.  This is actually what we did in
draft-vogt-mobopts-early-binding-updates-00.txt.

Nonetheless, the scope of your draft is two interfaces, I see this.  And
given that you are using two interfaces, you can do a care-of-address
test on the 2nd while communicating with the 1st.

I agree with the rest of your comments.

Take care!

- Christian