The era of the Internet of Things brings complexity and deployment costs in smart cities, particularly in Wireless Sensor Networks (WSNs). Utilities such as gas or water providers are keen on delegating the management of the communications to specialized firms, namely WSN Operators, that will share the WSN resource among their various clients. WSN operators will use a functional architecture to manage the Service Level Agreements (SLAs), i.e. the Quality of Service (QoS) clauses they contract with their clients. WSN operators will need a robust and reliable technology in order to guarantee QoS constraints in a wireless environment, as in the industrial world. IEEE 802.15.4e Time Slotted Channel Hopping (TSCH) [1] is one good candidate. Moreover, the IETF experience in IP networks management is an important input for monitoring and QoS control over WSNs. This article gives formal guidelines for the implementation of a SLA architecture for operated WSNs. It distinguishes the various formal algorithms that are necessary to operate a WSN according to SLAs, and determines which functional entities are necessarily technology-dependent. Detailed examples of such entities are developed in an IPv6 over IEEE 802.15.4e TSCH context, such as advocated in the IETF 6TiSCH Working Group [2].