Subject: Sub-optimal Terminology (was Re: [nemo] Re: I-D ACTION:draft-ietf-nemo-ro-problem-statement-01.txt)

From: Chan-Wah Ng <[email-masked]>
Date: Fri, 04 Nov 2005 19:41:43 +0800

On Mon, 2005-10-31 at 19:19 +0100, Alexandru Petrescu wrote:
> Suggestions I have,
> 
> > With current Network Mobility (NEMO) Basic Support, all 
> > communications to and from Mobile Network Nodes must go through the 
> > bi-directional tunnel established between the Mobile Router and Home 
> > Agent when the mobile network is away.  This results in various 
> > inefficiencies associated with packet delivery.  This document 
> > investigates such inefficiencies, and provides for the motivation 
> > behind Route Optimization (RO) for NEMO.
> 
> So either call the draft "inefficiencies of NEMO", or alternatively do
> the following.  Resume the problems of NEMO basic protocol that relate
> to RO in a few lines.  Put these lines in the abstract.  For example:
> 
> "With NEMO Basic Support protocol, IP paths for application-layer data
>  are artificially including the fixed HA of every Mobile Router, even
>  when nested.  This leads to multi-angular routing, while shorter IP
>  paths would avoid the Home Agents.  Additionally, the number of tunnel
>  encapsulation layers when using nested moving networks may grow to a
>  point that fragmentation becomes too heavy load.  Finally, there exist
>  at least one simple mobility configuration ("mobile" HA, MH at home
>  below MR) that is not supported by the NEMO Basic Support protocol.
>  This document formulates the above problems."
> 
> Or something along these lines, I mean concentrate the document into the
> abstract and clearly articulate one of the problems that really breaks
> something, or that shows NEMO Basic Support is useless in that case.
> And shortly :-)

OK.

> 
> > 2.  NEMO Route Optimization Problem Statement
> > 
> >    In essence, the goal of Route Optimization in NEMO is to reduce
> >    limitations and sub-optimalities introduced by the bi-directional
> >    tunnel between a Mobile Router and its Home Agent (also known as the
> >    MRHA tunnel).
> 
> Compare to this:
> 
> > 2. NEMO RO problem statement
> >
> >    Given the NEMO Basic Support protocol all IP paths for application
> >    data is forced through the Home Agent, although shorter paths exist
> >    between LFN and CN (application runs between LFN and CN).
> >    Additionally, with multiple MRs and nested moving networks several
> >    levels of encapsulation are used for that application data, whereas
> >    it is be possible to use none.
> >
> >    Multi-angular routing through HAs and multiple encapsulation lead
> >    to the following inneficiencies: ...
> 
> So a problem statement is a problem statement, not a list of
> inefficiencies that are addressed by the goals of some RO solutions.
> 

OK.

> Overall I like the document, it's short and easy to grasp for me, thanks
> for maintaining it.

Thanks for the suggestions.  However, I do have a concern over the
choice of words.  It might suggest that perhaps a terminology is needed
for the phenomenon where the routing path is anchored at the home
agent(s).

In MIPv6, I recall it used to be called "triangular
routing" (traditionally though, I doubt it is used in RFC3775).

You seems to favour the generalization of this term into "multi-angular
routing".  Logical, since with multiple HAs, there would be more than
three vertexes.

In some of the NEMO-related individual drafts (eg.
draft-thubert-nemo-ro-taxonomy), there have been instances on the use of
"dog-leg routing" and "pinball routing".

In draft-ietf-nemo-ro-problem-statement, however, we have sticked to the
very general term "sub-optimal routing".

What do the rest of the WG think?  Is there a need to have a more
specific term?  Or is sub-optimal routing good enough?

/rgds
/cwng

---

From: "T.J. Kniveton" <[email-masked]>
Date: Fri, 4 Nov 2005 14:10:12 -0800

> routing".  Logical, since with multiple HAs, there would be more than

Multi-angular makes less sense to me than triangular.
> "dog-leg routing" and "pinball routing".
dog-leg routing is sometimes used to be roughly synonymous to  
triangular routing. Pinball routing is a term which describes the  
route getting bounced back and forth like a pinball. I don't know  
whether it's used in other places in routing literature; I hadn't  
heard it before.

> very general term "sub-optimal routing".

Sub-optimal routing, as you mentioned, is very general. In fact,  
whereas pinball, triangular and dog-leg routing describe routing  
phenomena in certain circumstances, sub-optimal routing describes a  
general quality, not a specific scenario. It could mean almost  
anything other than shortest / cheapest path.

> specific term?  Or is sub-optimal routing good enough?

I'd like to use a different term, though I'm not sure the best one  
has been suggested yet.

TJ

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From: Masafumi Watari <[email-masked]>
Date: Mon, 07 Nov 2005 06:47:32 +0900

Hi,

Alex, thanks for your comments.  Overall, I agree about making it
clear on what the problem is.

Some comments about the terminology below.

On 2005/11/05 7:10, T.J. Kniveton wrote:
>> You seems to favour the generalization of this term into "multi- angular

I agree.

> triangular routing. Pinball routing is a term which describes the  route 
> getting bounced back and forth like a pinball. I don't know  whether 
> it's used in other places in routing literature; I hadn't  heard it before.
> 
>>
> general quality, not a specific scenario. It could mean almost  anything 
> other than shortest / cheapest path.

In keeping the document at a generic level, I don't see any problem
using sub-optimal routing.  I mean with nested-NEMO, you could draw
lines that look like a star for example...

> I'd like to use a different term, though I'm not sure the best one  has 
> been suggested yet.

watari

---

From: Alexandru Petrescu <[email-masked]>
Date: Mon, 07 Nov 2005 18:14:47 -0800

> I'd like to use a different term, though I'm not sure the best one  has

Maybe something along the lines of through-HA-enforced routing, or
through-the-HA TTH routing...

Alex

---

From: Alexandru Petrescu <[email-masked]>
Date: Mon, 07 Nov 2005 18:17:16 -0800

> lines that look like a star for example...

A star pictured as a hexagon is "multi-angular" still :-)

I agree with you.  I could live with "sub-optimal" too.

Alex