Subject: [manet] Is minimizing the wire length in Mesh USEFUL?

From: "RuiZhe Wu" <[email-masked]>
Date: Sat, 01 Apr 2006 00:00:27 +0800

Dear All:

I have read Qiu's paper "Optimizing the Placement of Integration Points in
Multi-hop Wireless Networks". The main goal is minimize the total number of APs
that a Mesh network needed. I don't know whether the main layouts was spent in
just purchasing APs or deploying connecting wire in Mesh Networks ? So I wonder
whether minimizing the total length of wire is useful while designing a mesh
networks. Maybe there is some papers about this have published?

Thanks a lot!

WU R.Z

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From: Fred Baker <[email-masked]>
Date: Fri, 31 Mar 2006 09:18:56 -0800

On Mar 31, 2006, at 8:00 AM, RuiZhe Wu wrote:
> I have read Qiu's paper "Optimizing the Placement of Integration  
> Points in Multi-hop Wireless Networks". The main goal is minimize  
> the total number of APs that a Mesh network needed. I don't know  
> whether the main layouts was spent in just purchasing APs or  
> deploying connecting wire in Mesh Networks? So I wonder whether  
> minimizing the total length of wire is useful while designing a  
> mesh networks. Maybe there is some papers about this have published?

I would guess he was minimizing money spent.

I think this is an Operations Theory problem. At the end of the day,  
you want to have "enough" bandwidth on your most heavily loaded  
links, and you want a cut-set of two (at least) in your routing, so  
that when (not if) you have a temporary outage traffic still has a  
path. You also want to minimize your outlay of capital. When you  
gratuitously add a link, which is to say that you provide additional  
service to someone who already has adequate service and has a  
protection path to cover failures, your bang/buck valuation for the  
action is dangerously close to zero. It doesn't make business sense,  
whatever the routing research might tell you.

Wire length, in the end, is propagation delay, and it might be cost.  
I would suggest that minimizing propagation delay is a good thing if  
it is a big change - for example, if you have a choice of a 630 ms  
RTT and a 150ms RTT, guess which one you pick. But trying to pick  
between 110 and 120 ms, or between 10 and 12, is a fool's errand.  
When the difference is only marginally noticeable to the application  
or the user, there are much more important things to think about.  
Gamers will tell you differently - they buy high-end NIC cards to  
shave off half a millisecond. They also don't run their games across  
the Internet. They go to LAN parties. Concern yourself with the  
issues of your market. As to costs, suppose you have a choice between  
adding a lambda to a fiber that already exists and goes *almost*  
where you want it to but is twice the length you would like, or  
laying a new fiber to exactly where you want it. From a cost  
perspective, the difference is the cost of putting a lambda on a  
fiber or laying a fiber AND putting a lambda on it. The latter is  
more, a lot more. So wire length doesn't tell you much about cost in  
the general case.

You might read
http://www.ietf.org/rfc/rfc3439.txt
3439 Some Internet Architectural Guidelines and Philosophy. R. Bush,
      D. Meyer. December 2002. (Format: TXT=70333 bytes) (Updates  
RFC1958)
      (Status: INFORMATIONAL)

This is a note written by operational folks about the behavior of  
real operational networks, giving guidelines for networks that work.  
They note that giving a network a lot of routing options sometimes  
works against routing convergence - the network winds up taking time  
to think about them all and may have a hard time deciding, due to  
various characteristics of the routing protocols we use. There is  
also a lot of other good thought there.