Slice A Slice A-> AC-A Slice A - VPN A Slice B Slice B-> AC-B Slice B - VPN B Slice C-> AC-C Slice C - VPN C Slice C Figure 9.10 Network slicing in transport example. AC stands for attachment circuit; each AC is associated with a VRF (virtual private network routing and forwarding) instance and customer A's (Slice A's) routes are dis- tributed only for sites of VPN-A. On top of the logical separation (different VPNs) for slices, further services may be configured when needed, like guaranteed capacity (e.g. with MPLS Traffic Engineering), specific connectivity service to a local UPF or Mobile Edge Computing (MEC) function, higher availability, and SO forth. SDN can help greatly in provisioning the transport services needed for the slices, especially if there are many slices and slice-specific configurations are needed over a heterogeneous transport network. 9.5.2 URLLC Transport Ultra-reliability and low latency introduce a new level of performance requirements for transport, but only for a specific, limited area. Since the environment and the use cases for the URLLC services vary, transport design alternatives are also very much case spe- cific. 9.5.2.1 Latency For the low-latency service, server and content are implemented physically close to the cell site, implying a local UPF function and possibly collapsing radio and core elements to the same site. The resulting transport network architecture is very different from the traditional macro 5G network. In order to guarantee 1-2 ms latency, deterministic behavior is needed from the trans- port network. The related IEEE task groups are the TSN and Deterministic Networking (DetNet) in IETF [22, 23]. 9.5.2.2 Reliability For ultra-reliability (5 nines to even 8 nines), any transport leg from the terminal via cell site up to the core network and to the server or other peer needs to be taken into account. In 3GPP 22.261, reliability is defined as the "percentage value of the amount of sent network layer packets successfully delivered to a given system entity within the 