lated as SCTP layer 4 over IP. When these IP packets are the focus of the transport network, we speak of an IP TNL. If these IP packets are further encapsulated in Ethernet layer 2 frames and these are the focus of the transport network, we speak of an Ethernet TNL. For further details on NG-RAN protocols, refer to Section 3.3. As a concrete example, in conventional backhauling, packets from a CU destined for the appropriate UPF, are delivered to the transport network as IP/GTP/UDP/IP/Ethernet. Here, the outer (first) "IP" represents the user's IP datagram including IP header with the UE's address as source address (SA) and the server or peer's address as destination address (DA), while the inner (second) one is the backhaul IP header with CU's source address and UPF's destination address. Note that a single CU may connect to multiple UPFs, and the appro- priate UPF depends on the UE's session. For the gNB-CU/DU split (described in Section 4.2), packets from a DU destined for its CU are delivered to the transport network as PDCP/GTP/UDP/IP/Ethernet where PDCP represents the (encrypted) user traffic with ROHC compressed headers. The IP is the xHaul IP (SA = DU, DA = CU). Note that a single DU may only connect to a single CU. The xHaul network must perform several functions. First and foremost control of for- warding behavior. While the outer IP designates the packet's ultimate destination, unless the network is trivial there will be multiple possible paths and path parameters (priorities, shaping/policing mechanisms, etc.). Most often the xHaul network will employ a transport tunneling mechanism (unrelated to the mobile network's GTP tunnels), such as MPLS or GRE, although more recently an approach utilizing segment routing has been proposed. As for any carrier grade network there must be resilience mechanisms, such as APS (possi- bly with rings) or FRR. Optionally there will be multiple gateways to exit the network. To trigger these mechanisms FM OAM is required, and PM is often needed as well. It is generally ag