The Network Cost Transfer Protocol enables an IEEE 802.11 access point (AP) to communicate the network cost and information about the AP type to clients. It defines two vendor-specific information elements (IEs), Network Cost and Tethering Identifier, within the 802.11 Beacon and Probe Response to relay this information to the client. Tethering allows a Windows device to share Internet connectivity from one interface over a Wi-Fi adapter, acting as a network to which other devices can connect.
Network Cost IE is used by clients to determine whether data transferred on that specific connection is metered (section 2.2.1). The Tethering Identifier IE is used to differentiate tethering (device-based) networks from stand-alone APs (section 2.2.2). The difference can then be used to vary the experience in implementation-defined ways.