[Nsi-wg] Message Delivery Layer

[Inder Monga]

Reliable transport means that there are retries and acknowledgements. If
the message cannot be delivered because the other NSA has issues or the
intervening network is partitioned for some reason, so the NSA is
unreachable, then MTL will pass that failure up to the NSA layer to manage.

This failure event is handled within the MDL rather than by the NSI state
machine, thats all what the MDL does. Yes, it is simple. MDL can choose to
retry again, or have a timeout, before pushing the failure event upto the
state machine. An implementors MDL layer can be non-existant and can just
forward the MTL error as a delivery error to the state machine.

Why call it a different layer? This was what Tomohiro proposed and the
group agreed. I do not have special preferences here.

Inder



On Wed, Dec 12, 2012 at 2:06 AM, Jeroen van der Ham <vdham at uva.nl> wrote:

> Hi,
>
> On 7 Dec 2012, at 13:41, Jeroen van der Ham <vdham at uva.nl> wrote:
> > On 6 Dec 2012, at 16:26, Inder Monga <imonga at es.net> wrote:
> >> The MDL layer essentially handles the case when MTL fails to deliver a
> >> message. The scenario being, whichever reliable message transport layer
> or
> >> multiple of them below, tries to deliver the message end to end. In case
> >> the message does not reach after multiple retries, the error is handed
> to
> >> MDL layer (and yes it is logical). The MDL layer can have a different
> >> timeout, choose to deliver the message again or try a differnet
> mechanism.
> >> That is upto the implementor. This prevents the NSI state machine
> having to
> >> deal with message timeouts and retries at the application layer. It
> >> simplifies the state machine .
> >>
> >> If there is more confusion lets have a skype call.
>
>
> I want to follow up on this further. You state that if the MTL layer fails
> to deliver a message somehow. We have stated that the MTL should be a
> reliable transport mechanism, so a delivery failure means something more
> complicated is going on.
> You're stating that you want to leave it to the implementor to figure out
> how to deal with this.
>
> That's all fine with me, but why do we have to call this another layer,
> instead of just stating the above?
>
> Jeroen.
>
>
>
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