Subject: [Mip6] draft-deng-mip6-ha-loadbalance-01.txt comments

From: Brian Haley <[email-masked]>
Date: Thu, 01 Apr 2004 18:14:41 -0500

Hi Hui, Rong, Xiaolong and Kai,

 > Title	: Load Balance for Distributed Home Agents in Mobile IPv6
 >
 >http://www.ietf.org/internet-drafts/draft-deng-mip6-ha-loadbalance-01.txt

I have a few comments on your draft.

First, I think this might be useful, for example, when someone wants to 
take a home agent offline for maintenance, etc., being able to 
proactively notify MNs to switch HAs would be a good thing.

I do have some technical questions though.

 > 6.  Modified Router Advertisement message
 > ...
>      L              1-bit "Load Balance" flag.  When set, Load Balance
>                      information will be broadcasted based on Router
>                      Advertisement message, Load Balance information 
>                      option will be included in the options.

Is this bit just specifying that a Load Balance Information Option is 
present?  If that's the case then you don't need it, you can just 
include the option in the RA (similar to the Advertisement Interval 
option in MIPv6).  The length field in the RA signifies whether there's 
options present or not.

> 7 New Load Balance Information Option Format
 > ...
>    Queue Size (2 byte):          
>            
>       A coarse parameter for the Queue Size in the router's TLT

Not all systems can determine the depth of their pending Binding Update 
queue (if that's what queue this is).  And what does TLT mean?

>    Registered MN Number (2 byte):        
>   
>       Registered MN number. If more than 256 MN could register a HA, 
>       the field should be a coarse paramter for the MN number in the
>       router's TLT

256 MNs seems like a really small number, I would assume a HA would have 
tens of thousands at a minimum (most requests I have seen are at least 
100,000).  I also find it hard to quantify this value into something 
meaningful between HAs.  For example, 10,000 might be a lot of bindings 
for one HA, but not for another - it's pretty subjective.

Why can't you just use HA preference from the Home Agent Information 
Option?  That allows 65535 different values, which seems like more than 
enough to me to order HAs on a link.  When a HA falls below some preset 
preference, asuming it re-calculates it dynamically, it can try and 
handoff future MNs to it's peers.

> 8.  Home Agent Reassignments
 > ...
>    The home agent may select a new home agent in the Home Agents List 
>    for the timeout mobile node according to our home agent reassignment 
>    algorithm. If a new home agent is assigned to the timeout mobile 
>    node, the home agent actively sends out an ICMP Reply message to the 
>    mobile node without the reception of any ICMP Request message. 
>    Different from the standard ICMP reply packet, the ICMP here should 
>    only contain one home agent in the home agent list, which is the 
>    newly selected home agent, other than contains a list home agent.

It's not clear which ICMP reply you're sending to the MN, a DHAAD reply?
I'm not sure a MN would process an unsolicited DHAAD reply since it 
can't match the id with a corresponding request.

Would it be easier to define a new message - Home Agent Handoff Message, 
that the HA could send to the MN to tell it to either use another 
specific HA (by explicitly including an address), or any other HA (by 
not including an address).  If the MN knows of no other HAs, then it can 
do DHAAD to see who's available.

The Home Agent Handoff (HAH) message is used by the home agent to signal 
the mobile node it should use another Home Agent for subsequent Binding 
Updates.

0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |     Type      |    Length     |           Reserved            |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       +                                                               +
       |                                                               |
       +                      Home Agent Address                       +
       |                                                               |
       +                                                               +
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Home Agent Address

    The address of the preferred Home Agent.  If set to the unspecified
    address, the mobile node should do DHAAD to find another Home Agent.

Of course the HA shouldn't be trying to handoff the MN if it doesn't 
know of any other HAs.

-Brian

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---

From: "DENG, HUI -HCHIBJ" <[email-masked]>
Date: Sat, 3 Apr 2004 22:12:12 +0800

Hi, Brian

>proactively notify MNs to switch HAs would be a good thing.

We really appreciate your comments.
Some new ideas have been explained by you

>option in MIPv6).  The length field in the RA signifies whether there's 

What you said is totally right, we know that the length field in the RA will 
indicate this option is present or not, why you put this flag here is for 
other future potential load balance usage.

>queue (if that's what queue this is).  And what does TLT mean?

Here the queue size means the buffer size of Home Agents.
which not only include their pending binding udpate queue, 
but also some tentative triangle traffice like encapsulated packet.
Here TLT stands for traffic load table in the version 00, we forget to modify
it to Home Agent List in the version 01.

>handoff future MNs to it's peers.
Here maybe what we describe is not clear, because we use coarse number,
not exactly 256 MN, for example, 100 means 1 MN, so 25600 means 
256 MN. anyway, we totally agree with you about quantify value might not 
be suitable, it will be a subjective topic.
As far as the preference, another author Kai , he has the same idea with you
maybe he will explain how is his comments.

>    address, the mobile node should do DHAAD to find another Home Agent.

Until now, we have not yet working on whether MN can handle the 
unsoliciated DHAAD reply message, what we expect is how to reduce 
the definition of new message in this draft. 

>Of course the HA shouldn't be trying to handoff the MN if it doesn't 
such unspecified HA address case must be considered in documents.

>-Brian

Really thanks for your so many valueable and kindful suggestions.

B.R.

Hui

---

From: "Kai Zhang" <[email-masked]>
Date: Tue, 6 Apr 2004 00:07:03 +0800

----- Original Message ----- 
From: "DENG, HUI -HCHIBJ" <[email-masked]>
To: <[email-masked]>; <[email-masked]>
Sent: Sunday, April 04, 2004 4:53 PM
Subject: FW: [Mip6] draft-deng-mip6-ha-loadbalance-01.txt comments

>-----Original Message-----
>From: DENG, HUI -HCHIBJ 
>Sent: 2004?4?3? 22:12
>To: Brian Haley; [email-masked]
>Subject: RE: [Mip6] draft-deng-mip6-ha-loadbalance-01.txt comments

Hi Brian,

Thank you for your comments. It help us to improve our draft.

>other future potential load balance usage.

For instance, some HAs probably  not allow the MNs from other HAs to
switch to itself. Thus the L flag bit is useful in this case. Also some future 
functions will use this flag.

>but also some tentative triangle traffice like encapsulated packet. Here TLT stands for traffic load table in the version 00, we forget to modify it to Home Agent >List in the version 01.

>Here maybe what we describe is not clear, because we use coarse number, not exactly 256 MN, for example, 100 means 1 MN, so 25600 means 
>As far as the preference, another author Kai , he has the same idea with you maybe he will explain how is his comments.

The load balance scheme proposed in our draft can balance not only the traffic
load but also the number of the register MN in different HAs. That's the reason
why we do not just use HA preference as defined in the Home Agent Information
Option. However, I agree with your comments, using the exact value of buffer or
number of MNs is not proper in real world. Maybe we will modify the value to a
kind of preference to order the HAs in the home link. 

Best Reguads,
KaiŠž¦j)bž	b²Ó"§¨žµú+‚m¦ÏÿÃ"z×è®æj)fjåŠËbú?š*z