[net2-wg] Packet interface

[Henri DF]

> > Second question: seems like there is no way of setting per-packet
> > urgent/reliable/destination metadata.  I must be missing something
> > here; could you clarify?
> 
> Correct. The issue is that for some data link layers, these bits can  
> affect scheduling decisions. For example, under a low-power-listening  
> CSMA layer, urgent can mean "send a long preamble." If we allow per- 
> packet metadata, then there are all kinds of scheduling issues that  
> arise (e.g., an urgent packet in a queue sitting behind un-urgent  
> packets).

I don't quite understand this. Even if each SendPoolEntry has a fixed 
un/urgent bit, the component that provides the SendPoolEntry's can still get an 
un-urgent packet from one SendPoolEntry user, followed by an urgent one 
from another. 

Whether or not this is less difficult to deal with than if we allow 
per-packet changes on the same SendPoolEntry really depends on the 
data structure that is used to queue packets, but it doesn't seem obvious 
that per-packet metadata adds complexity to the provider of SendPoolEntry.


> For example, whether or not you have ACKs enabled on 15.4 greatly  
> changes packet times, due to the two RX/TX transitions you need to  
> make. A time-based RTS/CTS would have issues if you could change  
> reliability.
> 
> If, for example, you want high-priority control traffic and normal- 
> priority data traffic, then you can allocate two pool entries.

What about destination, does a routing protocol have to allocate one pool 
entry per possible destination?

Henri