The procedures in this subclause form an optional part of this Recommendation, but are a mandatory requirement for the provision of certain bearer services or 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 bearer service or teleservice to each user.
The support of such basic services may require the ability to support transmission and reception of either two or three bearer capability information elements.
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.
Note - The use of the Low layer compatibility information element in conjunction with these procedures requires further study and the interpretation of any received Low layer compatibility information element is not defined.