Reference document

Aggregation Services
The Aggregation Services provide the aggregation of traffic over parallel converging transmission paths, and involves Packet-, Frame- and Circuit-based Transport Services, where each of the services uses the same Transmission Service to converge into a given network node (often referred to as concentrator). They are only concerned with a selective “fan-out” and do not involve broadcast. Aggregation Services apply within and at the edge of the core. Aggregation Services within the core provide the aggregation of transport flows from multiple edge-points that connect to the aggregation node (e.g. concentrator) over transmission lines not involving switching or routing. Aggregation Services at the edge provide the aggregation of access flows from multiple end-nodes that connect to the aggregation node over transmission lines. Like Communications Access Services, Edge Transport Services and Transit Services, Aggregation Services can be closely mapped to the OSI stack lower layers.
Transport Services