Spec: 4.3.4 SERVICE IDENTIFIER: HS_SERV

Any DO-IRP service can be defined in terms of one or more HS_SITE elements. These HS_SITE elements may be assigned directly to the relevant prefix identifier, or an additional level of indirection may be introduced through the use of an HS_SERV element in the prefix identifier record. The value of the HS_SERV element contains the service identifier, meaning an identifier whose record contains the HS_SITE elements defining the DO-IRP service. This way, the HS_SITE elements can be maintained in a separate record

Use of service identifiers allows sharing of service information among multiple prefixes. It also allows changes to service configuration (e.g., adding a new site) to be made in one place rather than in every prefix identifier involved.

Although not typical, a prefix identifier may have multiple HS_SITE and multiple HS_SERV elements. In such a case the service information for the prefix should be considered as the concatenation of the HS_SITE elements in the prefix identifier record, together with the service information from all of the HS_SERV elements.

The use of service identifiers raises several special considerations. Multiple levels of service identifier redirection should be avoided due to their lack of efficiency, but are not signaled as an error. Looped reference of service identifiers or HS_SERV elements that refer to non-existent service identifiers should be caught and error conditions passed back to the user.

4.3.5 SERVICE IDENTIFIER: HS_SERV.PREFIX

HS_SERV.PREFIX serves the same role with respect to HS_SITE.PREFIX as HS_SERV serves with respect to HS_SITE. If a prefix identifier has an HS_SERV.PREFIX element, the data of that element is an identifier, whose corresponding record describes, via one or more HS_SITE.PREFIX elements and/or recursively via HS_SERV.PREFIX elements, the service information at which clients may be able to resolve derived prefixes of the original prefix.