Subject: [MEXT] draft-wong-mext-simultaneous-ps-00

From: "Dr. Daniel Wong" <[email-masked]>
Date: Wed, 20 Feb 2008 19:21:21 +0800

dear all,

We have submitted an IETF draft on simultaneous mobility, by Wong,
Dutta and Schulzrinne. We believe this is a problem faced by Mobile
IPv6 as well as some other mobility protocols, and would appreciate
comments on it, both in the mailing list and also in IETF 71 in
Philadelphia. The URL is
http://www.ietf.org/internet-drafts/draft-wong-mext-simultaneous-ps-00.txt

thanks!

-- 
Dr. Daniel Wong
Assistant Professor
Malaysia University of Science and Technology
** check out my book on wireless IP at
http://www.must.edu.my/~dwong/book.html **
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From: Rute Sofia <[email-masked]>
Date: Wed, 20 Feb 2008 12:12:10 +0000

Hello Daniel,

some comments to the draft after a quick look and mostly related to MIP .
- Intro,

it would be better to state up front that you the problem you mention 
only applies to active sessions between a MN and a *mobile* CN, 
particularly if there is any form of direct binding registration between 
them.  You mention two devices on the move but only later state that 
they are actually the parties in an active session.

- terminology,
   * define what you mean with "border router"; "backbone router"; "edge 
router", given that later you have a scenario using this terminology but 
never defined it.

4.1 Typo in "Since both home agents are stationary and
    can always be reached through IP routing simultaneous mobility does
    present a problem to MIPv4."; I believe you mean DOES NOT

Concerning MIPv6. Even though the problem is real and may start to 
happen more frequently with the increase of mobile devices and more 
complex mobility patterns, there are some things that are not clear with 
the description you provide:
- while on the move and based upon scenario 3, you state that the BU 
information sent by MN1 to MN2 (CN) does not reach the latter. You need 
to be more explicit. There are two possible cases: a) MN1 performs the 
"correspondent registration" and immediately moves to a new attachment 
point; b) MN1 performed a L2 handover (is already attached to the new 
location) and starts the BU exchange with HA *and* CNs. We have the same 
process for the second MN (CN)

a) could be more problematic than b) given that MN1 sends a BU that 
never reaches the CN. However, what you never explain in detail is the 
ack that is sent by the CN.
  For b), it must be mentioned that the CoAs have different states, 
according to RFC4866 (section 3.5, concurrent CoAs tests; 
verified/unverified addresses).

Specifically for the case of MIPv6, there are some details that need to 
be worked upon to really understand the implications of having two 
participating nodes in a session simultaneously moving...

BR,
Rute

-- 
Rute Sofia, PhD ([email-masked], +351 22 2094263)
http://www.inescporto.pt/utm/~ian/
Area Leader/Responsa'vel de A'rea
IAN: Internet Architectures and Networking
UTM: Telecommunications and Networking Unit
INESC Porto
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---

From: "Kilian Weniger" <[email-masked]>
Date: Wed, 20 Feb 2008 15:57:26 +0100

Hi Daniel,

according to section 6.1 of RFC3775, Mobile IPv6 nodes always send
mobility header messages (e.g., Binding Update, HoTi, and CoTi messages)
without applying Binding Cache/Binding Update List check. Based on this
I suppose BU/HoTi/CoTi messages are sent to the correspondent node's
*home address* and not to the corresponent node's care-of address. This
implies that mobility header messages are always routed over
correspondent node's home agent and that the condition for simultaneous
mobility problem as described in the draft ("Binding updates are sent
directly to the most current known address (known by the sender) of the
intended recipient Mobile Host.") should not be fulfilled. Even though
one or two Binding Updates may get lost during a simultaneous mobility
event, the mobile nodes should always be able to recover from this due
to the routing of retransmitted mobility header messages over the home
agents. 

The relevant text in section 6.1 of RFC3775 is: 
  "Mobility Header messages MUST NOT be sent with a type 2 routing
   header, except as described in Section 9.5.4 for Binding
   Acknowledgement.  Mobility Header messages also MUST NOT be used with
   a Home Address destination option, except as described in Section
   11.7.1 and Section 11.7.2 for Binding Update.  Binding Update List or
   Binding Cache information (when present) for the destination MUST NOT
   be used in sending Mobility Header messages.  That is, Mobility
   Header messages bypass both the Binding Cache check described in
   Section 9.3.2 and the Binding Update List check described in Section
   11.3.1 which are normally performed for all packets.  This applies
   even to messages sent to or from a correspondent node which is itself
   a mobile node. "

BR,

Kilian

> -----Original Message-----
> From: [email-masked] [mailto:[email-masked]] On 
> Behalf Of Dr. Daniel Wong
> Sent: Mittwoch, 20. Februar 2008 12:21
> To: [email-masked]
> Subject: [MEXT] draft-wong-mext-simultaneous-ps-00
> 
> dear all,
> 

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