The recently published [IEEE802154e] standard formalizes the concept of link-layer resources in LLNs. Nodes are synchronized and follow a schedule. A cell in that schedule corresponds to an atomic link- layer resource, and can be allocated to any pair of neighbors in the network. This allows the schedule to be built to tightly match each node's bandwidth, latency and energy constraints. The [IEEE802154e] standard does not, however, present a mechanism to do so, as building and managing the schedule is out of scope of the standard. This document describes the 6TiSCH Operation Sublayer (6top) and the commands it provides to upper network layers such as RPL or GMPLS. The set of functionalities includes feedback metrics from cell states so network layers can take routing decisions, TSCH configuration and control procedures, and the support for decentralized, centralized or hybrid scheduling. In addition, 6top can be configured to enable packet switching at layer 2.5, analogous to GMPLS.