This section of IEC 1334-4 covers the services required of, or by, the DCP Logical Link Control (LLC) sublayer entity at the logical interfaces with the application layer and the MAC sublayer. In general, the services of a layer (or a sublayer) are the capabilities which it offers to a user in the next layer. In order to provide its service, a layer (or a sublayer) builds its functions on the services which it requires from the next lower layer or sublayer. Services are specified by describing the information flow between the application layer and the MAC-sublayer. That is by describing the service primitives and parameters which characterize each service. These primitives are associated with the connectionless transmission. NOTES 1 This section refers to the three-layer reference model described in IEC 1334-4-1 but provisions are made for future extensions of this model to more than three layers. 2 Provisions are also made in this section for future extensions to connection oriented transmission. In this clause, reference is made to the OSI reference model ISO 7498.