Resolution of URNs and LIFNs

The structure of URNs provides just enough of a toe-hold to facilitate scalable, distributed resolution. Resolution is a process by which a client may access the resource named by a URN. It works as follows:

1. The client queries a well-known registry for information about the namespace identifier. The information returned will either indicate services and locations for all URNs with that identifier, or it will contain instructions, specific to that name space, which indicate the location of the naming authority within the NSS, and where to find the registries for that naming authority.
2. In the latter case, the naming authority is extracted from the URN and one of the registries for that naming authority is queried.
3. Each registry queried returns either (a) referral instructions for further queries (for a narrower portion of the name space) or (b) a list of services, locations of those services, and protocols which may be used when communicating with those services.
4. When the latter is found, the resolution process stops, and the client chooses one of the available services and locations. Among the services provided by RCDS are: URN-to-catalog record mapping and LIFN-to-location mapping.

The resolution process allows for mutiple servers at each registry, so it is both scalable (allowing the load to be split across multiple servers) and fault-tolerant (if a query fails at one server, the same query may be submitted to a different server).

RCDS clients may also be configured to consult ``proxy'' resolution servers (which perform queries on behalf of clients and cache results) as well as ``fallback'' resolution servers (which can be consulted when there are no ``official'' servers for a domain or when the ``official'' servers do not respond.)