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Re: [hono-dev] Command and Control / Cloud to Device
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Registered Office: Berlin, Registration Court: Amtsgericht Charlottenburg; HRB
148411 B
Chairman of the Supervisory Board: Dr.-Ing. Thorsten Lücke; Managing Directors:
Dr. Stefan Ferber, Michael Hahn
On Mon, 2018-03-12 at 16:34 +0000, Gordon Sim wrote:
> On 12/03/18 16:21, Marc Pellmann wrote:
> > This means for each device, that connects to an adapter the
> > adapter will create a receiver link with a Hono messaging
> > instance and Hono messaging with the Router network. Also a
> > consumer application instance creates a sender link with the
> > Router network for each device, to which it wants to send a
> > command as soon as this is connected.
> >
> >
> > Just for completeness, if using message routing, the application
> > would need to have a separate link for each device it wishes to send
> > to. It could use a so-called 'anonymous sender', with the address of
> > the device specified in the 'to' field on the message.
> >
> >
> > I am not sure if I understand the implications of using this anonymous
> > sender correct - could you explain it a little bit more (I did not found
> > a further explanation in the QPID documentation)?
>
> Basically you create a link with no target address, and then put the
> address in the message. So you can send a message to 'foo' then 'bar'
> over the same link. Does that help?
>
> > Having a million receivers and senders attached to a router network
> > and communicating using message routing is certainly realistic
> > (tests of that scale have been carried out, though on bare metal
> > only at present). I'm not aware of tests of link routing at that
> > scale, which is not to say it is not realistic, just that it should
> > be investigated further.
> >
> >
> > With the use case of sending commands to the devices, we may could use
> > message based routing. The problem, that we do not have flow control
> > seams not such a problem in this direction. WDYT?
>
> If you send unsettled, then you do get flow control with message-routed
> traffic. The credit is not directly relayed, but messages are not
> silently dropped and back-pressure will be propagated. If there are no
> active recipients (active links with credit granted) then senders will
> not get credit to send messages. You can in fact use the availability of
> credit to send as an imperfect indication that there is a receiver on
> the address (or in the hone case that the device is connected).
My understanding is, though, that we would only know if _any_ device is connected
at all, but not, if a particular one is connected, if we are using an anonymous
sender, right?
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