cal chan- nel, by means of tunneling or pseudowires. In order for a network slice to conform to its QoS criteria, it needs to be defined E2E, that is, on the air interface, the transport network, and in the core. To support slicing in the transport network the packets need to be classified as belonging to a particular slice. 16 Resource isolation aspects are not defined by 3GPP and are left for vendor implementation. 6 Enabling Technologies In the case of fronthaul this may not be possible, both because different slices are mixed together in the air interface, and because there may be no easily recognizable identifier for classification (unless slices are differentiated by RF band). In other cases the GTP headers or UDP ports must provide the necessary classification labels. Furthermore, for the split option 1, different slices may be directed to different UPFs, but at the split option 2 (the DU/CU split) there is only one CU for a given DU, and thus the different slices need all to be delivered upstream to the same CU, but may traverse different paths or incur different forwarding behaviors at intermediate NEs. To support slicing using an Ethernet service, it is necessary to provide a mapping from a 3GPP-defined network slice identifier, that is, network slice selection assistance infor- mation (NSSAI), to some identifying fields in the Ethernet packet, such as 12-bit VLAN identifier (VID) or the 3-bit PCP. Ethernet VPNs would then constitute a form of soft net- work slicing. VPN technologies utilize tunneling, isolation of forwarding tables between different tenants, and overlay topology to provide connectivity between different sites of each virtual network. The VPN overlay and the underlay network resources are loosely coupled, and statistical multiplexing still functions to improve network utilization. Carrier Ethernet supports a palette of isolation types, including (MEF 6.1): E-LINE - point-to-point Ethernet service: - Ethernet private line (EPL) - dedicated bandwidth E-LINE service, further subdivided by 