Telephone Number Mapping (ENUM) Service Registration for Presence Services
updated by
- rfc-6118 — Update of Legacy IANA Registrations of Enumservices
Extracted elements (15)
ENUM is used to bridge telephone-number-based systems and URI-based presence systems, enabling, for example, a cellular telephone's address book to subscribe to presence for stored E.164 numbers and display availability to the user.
The 'pres' URI scheme was chosen over protocol-specific URIs (e.g., SIP URIs) because it provides a protocol-agnostic identifier for presence services, ensuring greater compatibility across different presence protocol implementations.
SIP (RFC 3261) is one protocol that can convey presence information and manage subscriptions/notifications via pres URIs, but the 'pres' URI scheme is protocol-agnostic and the mechanism in RFC 3861 is used to discover mutually supported presence protocols.
Other URI schemes appropriate to presence services MAY be used in the regexp field of an NAPTR record using the 'E2U+pres' enumservice, in addition to the preferred 'pres' URI scheme.
The URI scheme appearing in the regexp field of an NAPTR record using the 'E2U+pres' enumservice SHOULD be the 'pres' URI scheme, as it ensures greater interoperability than URI schemes specific to a particular presence protocol.
Revealing a pres URI may expose the full name or employer of the target depending on the URI structure. The use of anonymous URIs mitigates this risk. More serious risks involve unauthorized distribution of presence information.
An NAPTR record for the 'E2U+pres' enumservice has the form: IN NAPTR 100 10 "u" "E2U+pres" "!^.*$!pres:[email protected]!" under the e164.arpa origin, as shown in the example for +441296783880.
Presence architecture participants are watchers and presentities (per RFC 2778). Watchers subscribe to and are notified of changes in presentity presence; ENUM enables discovery of presence services for E.164 numbers.
Presence Information Data Format (PIDF, RFC 3863) defines the baseline presence data format with two states: OPEN (resource can accept communication) and CLOSED (resource cannot). PIDF is extensible for service-specific statuses.
The 'E2U+pres' enumservice is defined for advertising presence information associated with an E.164 number. It appears in the services field of an NAPTR record, composed of the 'E2U' resolution service subfield and 'pres' protocol subfield.
The 'pres' URI scheme provides a generic way to locate a presence service without identifying any particular presence protocol. Techniques for dereferencing the pres URI to locate a presence service are defined in RFC 3861.
This document registers the 'E2U+pres' enumservice under the IANA enumservice registry described in RFC 3761. The service name is 'E2U+pres', the URI scheme is 'pres:', and the intended usage is COMMON.
All DNS records, including ENUM records, must be considered publicly available to all inquirers. Information in an ENUM record set is open to the public, raising privacy concerns about exposure of presence URIs that may reveal the full name or employer of a target.
Any presence protocol used with the 'pres' URI scheme is required to meet the security requirements of RFC 2779, including authentication of watchers, integrity, and confidentiality, to prevent unauthorized distribution of presence information.
Unlike traditional telephone numbers, a pres URI may require callers to provide cryptographic credentials for authentication and authorization before presence information is returned, potentially providing greater protection from unwanted callers than the PSTN.