[Sis-ams] a design question for us to think about

[Krupiarz, Christopher]

Scott,

Thanks that helps.  Are messages that are published instead of announced
handled in a different fashion between continuia?  Are published
messages not put in the envelope data structure?  I guess I'm confused
about the differences of how messages which arrive from a remote
continuum to a node depended on how they are sent (either published or
announced).

Chris 

-----Original Message-----
From: sis-ams-bounces at mailman.ccsds.org
[mailto:sis-ams-bounces at mailman.ccsds.org] On Behalf Of Scott Burleigh
Sent: Wednesday, February 07, 2007 9:06 PM
To: sis-ams at mailman.ccsds.org
Subject: Re: [Sis-ams] a design question for us to think about

Krupiarz, Christopher wrote:
> Scott,
>
> To keep processing and traffic down, I'd vote for option 1.  One point

> I'm not clear on:  are the messages on subject X sent to the the nodes

> in the remote continuum even if there are no nodes in that continuum 
> subscribed to that message or is it that if there is at least one node

> registered to receive that message then all nodes in that continuum 
> received that message?
>   
Good question, Chris.  Message *publication* really isn't at issue here:

a message published in one continuum will result in delivery of that
message to all subscribers -- and nobody else -- in all continua.  The
question only comes up when a message is *announced* in one continuum
and destined for (say) all nodes in all continua.

The purpose of announcement (as opposed to publication) is to get the
message to a set of nodes selected explicitly by the sender rather than
to a set of nodes self-selected implicitly by the receivers, by virtue
of their subscriptions.

But it's impossible to get a message to a node that hasn't advertised
some mechanism by which it is prepared to accept that message (e.g., an
open socket) -- either by subscription or by invitation.  The tricky
part is that messages on subject X that are announced locally can't be
delivered to a node that has neither invited nor subscribed to messages
on subject X -- but messages on X that were announced remotely *can* be
delivered to such a node.  This is because remotely announced messages
are sent privately by the RAMS gateway as the *contents* of "envelope" 
messages whose subject is 0 (zero) rather than X (and all nodes
automatically invite messages on subject 0 at registration time,
precisely so that the RAMS gateway can send remotely sourced messages to
them).

Scott

> -----Original Message-----
> From: sis-ams-bounces at mailman.ccsds.org 
> [mailto:sis-ams-bounces at mailman.ccsds.org] On Behalf Of Scott Burleigh
> Sent: Monday, February 05, 2007 1:10 PM
> To: sis-ams at mailman.ccsds.org
> Subject: [Sis-ams] a design question for us to think about
>
> Hi, AMS fans.  A small design issue has come up (a couple of times,
> actually) that I would like to hear opinions on from the WG.
>
> In a nutshell: because messages that cross continuum boundaries are 
> sent by the destination continuum's RAMS gateway as enclosures within 
> private messages on subject zero -- which every node automatically, 
> invisibly invites at registration time -- it's possible for remotely 
> announced messages on subject X to be delivered to a node that has 
> never invited or subscribed to messages on subject X.  That is, the 
> absence of an invitation or a subscription to messages on a given 
> subject doesn't prevent reception of messages on that subject sent by 
> nodes in other continua -- though it *does* prevent reception of 
> messages on that subject sent by nodes in the local continuum.
>
> This hasn't seemed like a high-priority problem, but it eventually 
> needs to be resolved somehow: message reception behavior should be 
> consistent, one way or the other, regardless of whether the 
> sender/announcer is in the local continuum or a remote continuum.
>
> There are two ways we can go here:
>
> 1.	Provide a way for nodes to exclude reception of uninvited
> messages
> from remote continua that is as effective as the absence of an 
> invitation is in excluding reception of uninvited messages from within

> the local continuum. [Note that the delivery of *unauthorized* 
> messages (e.g., a denial-of-service attack) can be prevented already, 
> using standard AMS mechanisms: there can be a constrained list of 
> authorized issuers of messages on a given subject, and node 
> authentication at registration time can be used to assure that a given

> node is an authorized issuer.]
>
> 2.	Just say that AMS provides ways to receive messages but no way
> to
> prevent reception of a message, and provide some sort of automatic 
> default invitation (issued at registration time) so that locally 
> sent/announced messages are received even in the absence of an 
> explicit invitation, just as remotely sent/announced messages are.
>
> We really don't have any requirements from anybody one way or the 
> other that I can recall.  Is it important to be able to exclude 
> uninvited (as opposed to unauthorized) messages, or is it important to

> enable delivery
> -- announcement, say -- of messages that haven't been specifically 
> invited?
>
> Any strong opinions on either side?
>
> Scott
>
>
>
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>   



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