Resource Capabilities Discovery
Resource Capabilities Discovery WG
||Resource Capabilities Discovery
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A variety of resource identifiers have been widely deployed on the
Internet as a means of identifying various resources, services, and
destinations. However, a means of attaching a set of attributes or
characteristics to a given resource identifier and subsequently
assessing those attributes or characteristics has not been specified and
A particularly important resolution service of this general type is one
which, when given a mail address identifying a particular mail
recipient, will return a series of attributes describing the
capabilities of that recipient. This differs from a directory service in
that no searching or other advanced query operations are involved.
The primary purpose of this service is to distribute information
about resources or services to the global Internet; as such, it is
not intended for dissemination of private information. However,
the group will also consider whether there is a need for the
query protocol to include authentication, and thus permit
administrators to restrict the capabilities that are returned
according to a locally specified security policy.
The first task of this working group will be to define a general
resolution protocol that will translate resource identifiers to a list
of attributes. At a minimum the service must be capable of returning
mail recipient capabilities as described above, but ideally the service
should also handle more general capability and characteristics
The second task of this working group will be to define an
administrative model and update protocol that can be used to set up and
maintain the information the resolution protocol accesses.
This protocol will obviously require strong authentication. The
working group will also consider whether privacy services are
necessary for the update protocol, and include such services
in the protocol if it finds that they are necessary.
The service resulting from the combination of these two protocols must
meet the following requirements:
(0) The resolution protocol must be highly scalable, as the intent is to
deploy it very widely.
(1) Resolution protocol and server overhead must be very low, as some
applications will make very heavy use of it.
(2) Identifiers input to the resolution service must be formatted as
Uniform Resource Identifiers (URIs) containing one or more DNS
domains. Note that mail addresses can be presented as mailto: URIs
to meet this requirement.
(3) Facilities to support inheritance within the attribute store will be
essential, as the number of identifiers may be very
large. Specifically, mechanisms must be provided by which
administrators can set default values for members of their
(4) Existing protocols will be profiled for use as part of this service
whenever possible rather than developing new protocols. In
(a) The DNS must be used as the first step in the resolution
service, This is because all the URIs under consideration here
contain a DNS domain and the DNS is already properly delegated.
(b) Existing DNS record types such as SRV and NAPTR will be used if
feasible, to ease deployment.
(c) A lightweight resolution protocol may be defined by this working
group if no existing protocol proves to be suitable.
(d) An existing administrative model and maintenance protocol will
be used if feasible. Possible candidates for this include ACAP
The means to register and extend the set of attributes must be
specified. However, specification of actual attributes needed by
various applications of this service is outside of the scope of this
This group will collaborate with the ENUM working group to determine
the degree to which it is appropriate for the two efforts to share
technology or protocols when solving their respective problems.