The procedures in this subclause form an optional part of this Recommendation, but are a mandatory requirement for the provision of certain teleservices. Provision of these procedures between the originating user and the originating network, and also between the destination network and the destination user is thus subject to bilateral agreement, e.g. a subscription arrangement for the provision of that teleservice to each user.
These procedures shall apply only in the case where the call, or call request, as currently routed, is entirely within the ISDN. It will not apply to situations involving interworking with non-ISDNs.