[CAP] Presidential CAP questiion

Mon Oct 15 13:38:49 PDT 2007

Agreed, you point out very well why preemption doesn't really apply in a 
packet-switched network, but the destination systems are still very 
likely to have that need, correct? TV and radio broadcasts are just as 
single-channeled as they ever were.  So a Presidential message, while 
not needing to preempt other messages at the router level, would have 
enough priority to be handled differently at the broadcast level 
(potentially pre-empting other broadcasts, if the current model is 
followed) as well as being treated favorably at the server level, using 
priority queuing techniques as you mention.

So, from the network perspective, we can say "high-priority" instead of 
"pre-empting", but from the broadcasters' point of view, "pre-empting" 
still applies.
The original poster, if I read him correctly, was asking whether there 
was a source of messages that were of that highest priority that would 
cause broadcasters to interrupt current broadcasts, as per the various 
Executive Orders.  The details of how the message gets from the source 
to the destination needn't apply.

Rex Buddenberg wrote:
> I think the question really has to do with the nature of packet
> switching and the archaic circuit switched notion of pre-emption.  (With
> Presidential as just one instantiation)????
>
> In circuit-switched networks, a channel can carry only one application
> at a time.  Which translates to user terms of 'gotta hang up on one
> conversation to pick up another'.  Pre-emption is a means of forcing the
> first conversation to close so one can barge in with the second.  In the
> interior of the network, pre-emption is represented by a parallel 'grab
> the circuit'.  In abstract terms, circuit switched networks are
> connection-oriented.  
>     
> But in packet switched systems things change.  Packets arrive at routers
> from multiple applications in no particular order or organization.
> Layer 3 plumbing in the internet is expressly connectionless and
> stateless.  Therefore, pre-empting' a connection makes no sense -- there
> aren't any.  (*more below)
>
> This doesn't translate quite as intuitively to end system applications.
> It may make sense to interrupt one human conversation to get a
> converser's attention.  But this has nothing to do with the underlying
> plumbing any more. 
>
> There was a working group in IETF a few years ago thrashing emergency
> services issues.  Great amounts of flame and heat trying to get some of
> the members to understand that 'pre-empt' belonged in places like SIP
> servers, not routers.  
>
>
>
>
> *in most of the internet infrastructure, there's enough overprovisioning
> that fiddling with packet priorities within a router makes no sense
> either -- there's nothing you can do to 'improve' service if there's no
> congestion.  The place where this does become important is at the parts
> of the internet where we reach to mobile platforms -- the radio-WANs.
> But that's a different conversation, so I won't chase it here unless
> somebody rings back (it's my research area).  Here the issue is not
> pre-emption in the customary sense, but a packet prioritization sense
> where 'the most important packets get handled first'.  The definition of
> 'most important' is always disputed along with the means of marking
> packets with appropriate labeling.  
>
>
>
> On Mon, 2007-10-15 at 14:16 -0400, matt hoffman wrote:
>   
>> Art is certainly the authority on this, but I'll second that impresson. 
>> I've worked on IPAWS-related prototypes implementing CAP interfaces, but 
>> I have never heard mention of any system that disseminated Presidential 
>> messages via anything other than the existing EAS framework.
>>
>> Matt
>>
>>
>> Art Botterell wrote:
>>     
>>> Jim -
>>>
>>> I can't speak for FEMA, but I would expect that presidential messages will go from WACA to FEMA for distribution through the IPAWS framework to EAS, cellular and other dissemination media.  Of course, presidential alerts have been, to date, vanishingly rare.
>>>
>>> - Art
>>>
>>>
>>> Art Botterell, Manager
>>> Community Warning System
>>> Contra Costa County Office of the Sheriff
>>> 50 Glacier Drive
>>> Martinez, California 94553
>>> (925) 313-9603
>>> fax (925) 646-1120
>>>
>>>   
>>>       
>>>>>> "Jim Trawick" <JimTrawick at viaRadio.com> 10/15/2007 7:45 AM >>>
>>>>>>         
>>>>>>             
>>> Although there's been a lot of talk about the Presidential messaging
>>> possibilities in DEAS and at least three different versions of what that
>>> might be (PBS, NOAA and DHS variations, that I'm aware of), is anyone aware
>>> of a specific, currently available Presidential source (i.e., pre-empting
>>> all others, even those in progress, per various Executive Orders), which is
>>> available in CAP format (or any other digital, text-oriented format), and if
>>> so, what that current source might be, and through whom it might be
>>> currently available? Surely one must have been employed in the DMIS EAN test
>>> back in June.
>>>
>>>  
>>> Jim Trawick
>>> Senior Software Engineer
>>> viaRadio Logo Scaleable smaller no tag no background
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