Re: [Lsr] Flow Control Discussion for IS-IS Flooding Speed

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Les,

> Then the LSP transmitter is operating without information from the LSP receiver. Additional information from the receiver can help the transmitter maintain a more accurate picture of reality and adapt to it more quickly.
>  
> [Les:] This is your claim – but you have not provided any specifics as to how information sent by the receiver would provide better adaptability than a Tx based flow control which is based on actual performance.



This is not a claim. This is normally how control loops work. See TCP. When the receiver’s window opens, it can tell the transmitter. When the receiver’s window closes, it can tell the transmitter. If it only opens a little bit, it can tell the transmitter.


> Nor have you addressed how the receiver would dynamically calculate the values it would send.


It can look at its input queue and report the current space.  ~”Hi, I’ve got buffers available for 20 packets, totalling 20kB.”~  


> For me how to do this is not at all obvious given common implementation issues such as:
>  
> Sharing of a single punt path queue among many incoming protocols/incoming interfaces


The receiver gets to decide how much window it wants to provide to each transmitter. Some oversubscription is probably a good thing.


> Single interface independent input queue to IS-IS itself, making it difficult to track the contribution of a single interface to the current backlog


It’s not clear that this is problematic.  Again, reporting the window size in this queue is helpful.


> Distributed dataplanes


This should definitely be a non-issue. An implementation should know the data path from the interface to the IS-IS process, for all data planes involved, and measure accordingly.


> If we are to introduce new signaling/protocol extensions there needs to be good reason and it must be practical to implement – especially since we have an alternate solution which is practical to implement, dynamically responds to current state, and does not require any protocol extensions.


If we are to introduce new behaviors, they must be helpful. Estimates that do not utilize the available information may be sufficiently erroneous as to be harmful (see silly window syndrome).

Tony