[net2-wg] Packet interface

[Philip Levis]

On Dec 1, 2005, at 1:26 AM, Omprakash Gnawali wrote:

>
>
> Is the expected usage pattern of SendPoolEntry a set of communication
> state/handles that might be active concurrently and can be reused for
> differnt destinations at different times ? In that case, if an
> application wants to communicate to N+1 sources, but not at the same
> time, then we can have the application reuse a SendPoolEntry depending
> on the time, protocol etc. So, practically, declaring a handful of
> entries will take care of most cases if you keep track of which
> Entries are no longer in use much like message pool management.
>
> But as Kyle said, it is not obvious how an application would increase
> the number of entries on the fly (if N is a large number). If this
> feature is necessary, some sort of allocation / deallocation of
> Entries ? Sounds like an overkill though.

Let's take a step back here.

If you look at how communication works today in TinyOS, you can only  
have a single outstanding packet for a single destination address. A  
queue is a queue, after all.
This abstraction allows you to have N outstanding packets for K  
destination addresses. It is much more flexible.

On one hand, it may turn out that this is not flexible enough, and  
that experience shows that having a dynamic allocation pool of send  
pool entries is needed. But I don't think that we can answer this  
question without a good deal of experience.

That is, I wouldn't argue that this abstraction is perfect. But I  
would argue it's an improvement. The first question is, based on  
network protocols we have implemented, or data link layers we've  
worked with, are there key pieces of functionality that this  
interface is missing? The second question is, does this interface  
include functionality that you think is unnecessary and so should be  
cut for simplicity? The third and final question is, would you want  
to write code against this interface, if doing so could greatly  
improve protocol efficiency, or would you prefer something different?

Phil

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"We shall not cease from exploration
And the end of all our exploring
Will be to arrive where we started
And know the place for the first time."

- T. S. Eliot,  'Little Gidding'