[Tinyos-devel] Feedback on TEP 124

Martin Haenggi mhaenggi at nd.edu
Sat Feb 7 16:40:35 PST 2009


Looks good to me.

Best,
Martin

On Feb 7, 2009, at 5:58 PM, Omprakash Gnawali wrote:

> Thanks Martin for your comments. I think we are down to one final item
> in our discussion.
>
> ...
>> Section 2.3:
>>
>>>> One popular way to define the
>>>> bi-directional link quality between a node pair (A,B) as the
>>>> probability that a packet transmitted by A will be successfully
>>>> received and acknowledged by B.
>>
>> Rewrite: Either insert "is" after "way" or replace "as" by "is" or
>> something.
>>
>>>> This approach computes the
>>>> bi-directional link quality of a node pair (A,B) as the product  
>>>> of the
>>>> link quality of (A,B) and (B,A).
>>
>> Suggest to rewrite as: "According to this definition, the link  
>> quality is
>> computed as ..."
>> However, the step from the definition of link quality as the  
>> "roundtrip"
>> success
>> probability to the product of the link qualities is not correct.
>> As I said earlier, this would only hold if the successes of the two
>> transmissions were independent, and in most cases they are not. So  
>> the
>> product
>> is a pessimistic metric, and I'd prefer to use the minimum of the two
>> probabilities.
>> At least a remark should be included that taking the product is  
>> only valid
>> assuming
>> independence (and does not follow directly from the definition  
>> above); and
>> perhaps a scenario can be included where independence would be  
>> justified
>> (I can't think if any except some far-fetched ones such as high  
>> mobility).
>
> I have shortened the text:
> "
> One popular way to define the
> bi-directional link quality between a node pair (A,B) as the
> probability that a packet transmitted by A will be successfully
> received and acknowledged by B. This approach computes the
> bi-directional link quality of a node pair (A,B) as the product of the
> link quality of (A,B) and (B,A).
> "
>
> to
>
> "Routing protocols often
> compute the bi-directional link quality of a node pair (A,B) as a
> function (product, min, etc.) of the link quality of (A,B) and (B,A).
> "
>
> so that we limit ourselves to observations on how routing protocols
> use the information that is exchanged using this protocol. What do you
> think?
>
> - om_p



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