Re: [Anima-signaling] GRASP and unicast UDP

[Toerless Eckert <[e-mail]>]

Thanks, Brian

I think your self-experience with UDP should help to rule that out.
Not sure how much of that experience summary could go for example
into explanatory draft text. I am always a fan of that, but most people
on the IETF seemingly not.

Wrt to CoAP: I would hope that similar to bootstrap, we could define
CoAP as an extension, so that we can continue to keep the main GRASP
draft on a fast track to WGLC.

Cheers
    Toerless

On Thu, Aug 18, 2016 at 08:10:23AM +1200, Brian E Carpenter wrote:
> On 17/08/2016 18:23, Toerless Eckert wrote:
> > Thanks a lot for the insight. How about trying CoAP ?
> 
> Two comments on that.
> 
> 1) I woke up before the alarm went off this morning, and had exactly that
> thought. But I'd have to study CoAP in detail to understand whether it
> helps. Maybe Carsten can advise on this.
> 
> (In GRASP, you may get multiple simultaneous requests or multiple simultaneous
> discovery responses. The problem in a nutshell is that with TCP you have
> accept(), which fires up a new socket for each incoming transaction, but with
> UDP you have to manage sharing the socket yourself.)
> 
> 2) I also realised that we can't leave it open in GRASP whether discovery
> uses TCP or UDP for the discovery response. Otherwise discovery might not work
> between two random implementations.
> 
>    Brian
> 
> > 
> > On Wed, Aug 17, 2016 at 04:42:40PM +1200, Brian E Carpenter wrote:
> >> To entertain myself while waiting for comments on other matters, I spent
> >> quite some time (and swear words) on hacking the prototype GRASP to use
> >> UDP instead of TCP for unicast operations (i.e. discovery responses,
> >> synchronization responses, and negotiation).
> >>
> >> My conclusion is that it's a fairly silly thing to do, except possibly
> >> for discovery, which only involved a normal amount of debugging. I'm sure
> >> this is something that DNS server developers are very familiar with:
> >> writing a robust server handling things over UDP is a great deal harder
> >> than doing it with TCP. In fact I gave up when I realised that for
> >> the negotiation case (where there are an unpredictable number of messages
> >> in both directions) I was basically going to have to rewrite half of TCP,
> >> and still not have a robust solution. Without a lot more work, the UDP
> >> solution is riddled with timing-dependent issues. (At one point, adding
> >> a print statement for debugging fixed the bug, so that I simply couldn't
> >> debug it...)
> >>
> >> Of course, all this could be solved with more work, but I'm really not
> >> sure we should recommend UDP at all, except for discovery responses.
> >> I can't really imagine a real autonomic node that doesn't have TCP code.
> >>
> >> Comments?
> >>
> >>     Brian
> >>
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> > 

-- 
---
Toerless Eckert, [e-mail]