Subject: RE: [Mip4] WG adoption call on draft-kulkarni-mobileip-dynamic-as signment-02.txt

From: Tsirtsis George <[email-masked]>
Date: Fri, 12 Dec 2003 09:12:49 -0500

The discussion was, however, about redirection to an HA that does not
necessarily share any state with the current HA. The question is whether
such redirection should only be optional or whether optional and compulsory
redirection should be allowed....(I prefer the latter).

Non of this seems to me to be affecting your draft as you describe below but
I will wait for it to come out so I can get the full picture of what is
being proposed.

Thanks
George

-----Original Message-----
From: Henrik Levkowetz [mailto:[email-masked]]
Sent: Friday, December 12, 2003 2:01 PM
To: Tsirtsis George
Cc: 'Kent Leung'; [email-masked]
Subject: Re: [Mip4] WG adoption call on
draft-kulkarni-mobileip-dynamic-as signment-02.txt

On Friday, 12 Dec 2003, Tsirtsis wrote:

> I think the point of my suggestion below is to make sure that session
> disruption does not take place in the normal case:
> - MN sends ALL-AERO-ONE-ADDR when idle or 
> - HA sends an HA-Redirect in a positive RREP, in which case MN initiates
> redirect as soon as idle). 

Ok so far,

> I think, however, that it is worth letting the HA redirect a mobile in a
> compulsory way (HA sends HA redirect in negative RREP) if that is what
needs
> to be done from network perspective (e.g.: topology reasons, overloading
> etc).

Yes, but I'm not sure whether it belongs in this draft or in the other.

> Note that MIP already allows session disruptions since an HA can always
> reject a RREQ in which case sessions will be dropped. HA redirection
> improves on that by allowing an HA to redirect an MN to another HA rather
> than dropping it altogether.

Right, but see below.

> P.S: So, does your draft compete with this one? or it solves a different

The intention is to _not_ compete. The charter says:

  Home agent assignment at the time of mobile-ip registration, rather
  than preconfigured for the mobile node, has been proposed in
  draft-kulkarni-mobileip-dynamic-assignment-01.txt. The WG will
  take on the task of completing this. The ability to switch the home
  agent assigned to a mobile node while registered will also be
  considered as part of this task. 

So the draft I'm working on will propose a message which can be originated
by the HA, saying in essence "from now on, the registration you had with
HA so-and-so will insead be handled by me"; the intention being to support
failover, overload etc.  One prerequisite for this mechanism is that the
two HA's have some way to share state - the most straightforward way being
to forward registration request and reply messages from the active HA to
the standby HA.

So I guess the dividing line would be whether the circumstances were such
that you could continue a session, or whether you anyhow would need to
break and re-establish. In the latter case, it seems reasonable to make
it part of dyn-assignment, in the other case it seems to belong with
the upcoming draft (reg-reassignment? failover? xxxx?).

	Henrik

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---

From: Henrik Levkowetz <[email-masked]>
Date: Fri, 12 Dec 2003 16:40:45 +0100

On Friday, 12 Dec 2003, George Tsirtsis wrote:

> necessarily share any state with the current HA. 

<chair hat off>
  Ok. It wasn't clear to me at first that this was what you desired,
  rather than what you thought you at best could get...
</chair hat off>

> The question is whether

<chair hat on>
  From the viewpoint of the problem the dyn-assignment draft originally
  aimed to solve, only dynamic assignment at the start of a session was
  considered and seemed to make sense.
  
  If we are now talking about extending this to a mechanism which will
  break off a session, but include a next-ha in the RRP refusal, I think
  we need to make sure we have a constituency which needs such a thing,
  and we have to weigh the benefits against the drawbacks of having 
  a re-assignment mechanism which breaks off the current session.
</chair hat on>

<chair hat off>
  If we're going to have a mechanism to refuse a re-registration with
  a pointer to another HA, I'd prefer to be able to have it both
  optional and compulsory, as you seem to prefer too. But I'm not
  quite sure if the benefits in reduced round-trips of such a solution
  outweigh the simplicity of the HA simply refusing a registration, and
  the MN subsequently trying to register a new session and at that time
  be assigned a new HA, according to the mechanism of the current draft.
  Possibly it does.
</chair hat off>

> I will wait for it to come out so I can get the full picture of what is

<chair hat off>
  Fair enough.
</chair hat off>

	Henrik

---

From: Kent Leung <[email-masked]>
Date: Fri, 12 Dec 2003 07:57:09 -0800

Right, the solution provided in this draft is for dynamically assigning
an HA for initial registration.  The mechanism allows the network to
choose an HA when MN request with AZOA or notify the MN the assigned
HA when MN request an administratively prohibited HA in RRQ.

Kent