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[discovery-api]possible problem with using _services._dns-sd._udp. query

From: Jean-Claude Dufourd <jean-claude.dufourd@telecom-paristech.fr>
Date: Wed, 23 Jan 2013 14:15:11 +0100
Message-ID: <50FFE25F.2090609@telecom-paristech.fr>
To: public-device-apis@w3.org
Dear all

I have found this text in an Apple FAQ:
"Queries for "_services._dns-sd._udp.local." behave somewhat differently 
than standard mDNS queries. Normal mDNS long-lived queries will return 
ADD/REMOVE events as records are registered and deregistered, however, a 
service type enumeration meta-query will not be told about REMOVE events 
when a service is deregistered. Otherwise, the meta-query behaves 
identically to a standard mDNS query. It will receive REMOVE events when 
a network interface is disabled or if the PTR record expires from the 
cache naturally."

The text later admits it is a non-standard behaviour, but claims it 
optimizes the network resources.

If this behaviour is widespread, then the serviceAvailable part of NSD 
cannot be implemented when using this type of meta-query.
Is it not better then to only use standard queries ?
Best regards

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 Wednesday, 23 January 2013 13:15:39 UTC

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