Re: [Roll] MRHOF ETX

"Reddy, Joseph" <jreddy@ti.com> Fri, 08 June 2012 17:24 UTC

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From: "Reddy, Joseph" <jreddy@ti.com>
To: "roll@ietf.org" <roll@ietf.org>
Thread-Topic: [Roll] MRHOF ETX
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Date: Fri, 8 Jun 2012 17:24:09 +0000
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Subject: Re: [Roll] MRHOF ETX
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Hi Om,

I don't think it is accurate to say (ETX*128) should be used everywhere. The draft uses the term ETX with different meanings at different places in the spec. 

Specifically, consider this situation:

A node computes its "path cost for a neighbor" by adding that parent's advertised Rank with the link ETX to that parent node. 

The advertised Rank of the parent is a 16-bit value that has integer and fractional parts. The MinHopRankIncrease parameter determines the length of the Integer/Fraction parts. 

Now when the draft says to add the Rank and link ETX parameters, clearly this cannot be a simple addition of the Rank with either ETX or (ETX*128). Instead, the ETX value must be converted to the same Integer/Fraction representation as the Rank ( i.e., using MinHopRankIncrease ) before being added. 
	
Do you agree ?

-Regards, Joseph


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Message: 6
Date: Thu, 7 Jun 2012 18:45:11 -0500
From: Omprakash Gnawali <gnawali@cs.uh.edu>;
To: Dario Tedeschi <dat@exegin.com>;
Cc: ROLL WG <roll@ietf.org>;
Subject: Re: [Roll] MRHOF ETX
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	<CAErDfUSgw4rxnRefuH=fYnSVVWZeJc4P-ZWvvoZ1uEx5TMUJ9w@mail.gmail.com>;
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On Thu, Jun 7, 2012 at 6:34 PM, Dario Tedeschi <dat@exegin.com>; wrote:
> Hi Philip
>
> When MRHOF refers to ETX, is it the ETX value as defined in RFC6551 (i.e.
> ETX * 128) or some ETX value defined by implementation?
>
> Could this be made more clear in the spec, because we are currently 
> having a discussion in ZigBee-IP as to what this value should be?

ETX * 128 as in 6551.

The suggested value for parent switch threshold with ETX is given in
6551 format in -10. But I just noticed that I forgot to convert it to
6551 format for max link and max path values. They should all be ETX * 128.

- om_p


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