W3C home > Mailing lists > Public > public-device-apis@w3.org > February 2013

Re: [discovery-api] Consolidated comments and questions

From: Jean-Claude Dufourd <jean-claude.dufourd@telecom-paristech.fr>
Date: Fri, 08 Feb 2013 16:07:53 +0100
Message-ID: <511514C9.2000707@telecom-paristech.fr>
To: public-device-apis@w3.org
Le 8/2/13 15:27 , Rich Tibbett a écrit :
>
>>
>> And also, my question about polling boils down to: what is the practical
>> difference between "available" and "online" ?
>
> 'available' means that the service is present on the local network but 
> not yet shared with any web page.
>
> 'online' means the the service is present on the local network and 
> shared with a web page.
>
> We settled on these terms for lack of a better naming suggestion.
>
>>
>> What is "online" ? A response to ping is characteristic of the device,
>> not of the service.
>> Is there anything standard in Bonjour and UPnP that can be used as a
>> test of online-ness ?
>
> 'online' is a concept specific to this specification when a 
> NetworkService object is provided to a web page. At that point the 
> service is either online or offline for that web page to interact with.
>
>> Should the implementation poll for that ?
>> Should the online attribute and events not be optional (SHOULD or MAY,
>> rather that MUST now) ?
>
> There is some use to receiving these events for a web page. There is 
> the option for the web page to check the online-ness of a shared 
> NetworkService object by querying its .url attribute via an e.g. XHR 
> call. If that fails with a 4XX then they may be able to assume that 
> the service is no longer responding and hence offline.
>
> Since we're aware of general registration/deregitration/expiry of 
> Local-networked Services in the network at the underlying 
> implementation level we provide any status updates we can through the 
> 'online' attribute of the corresponding NetworkService object as a 
> convenience feature.
>
>> If it is too similar to "available", should it not be removed 
>> altogether ?
>
> It seems there's enough of a difference to warrant both events. One is 
> a generic notifier of the state of the network relating the requested 
> service types fired against NetworkServices. The other is a specific 
> notifier of the state of the service fired against its corresponding 
> NetworkService object.
>
JCD: I still do not understand the difference.
You write:
/'available' means that the service is present on the local network but 
not yet shared with any web page. //
////
//'online' means the the service is present on the local network and 
shared with a web page. //

/If "I" see a NetworkService object, then it has been provided to the 
web page "I" am in.
A NetworkService object has no existence (for the purpose of this 
standard) until it is provided to a web page.
So if "I" see it, then online and available must have the same value.
Best regards
JC
//

-- 
JC Dufourd
Directeur d'Etudes/Professor
Groupe Multimedia/Multimedia Group
Traitement du Signal et Images/Signal and Image Processing
Telecom ParisTech, 37-39 rue Dareau, 75014 Paris, France
Tel: +33145817733 - Mob: +33677843843 - Fax: +33145817144
Received on Friday, 8 February 2013 15:08:21 UTC

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