rnet traditionally a NMS configured switch forwarding tables. In MPLS-TE a path computation element (PCE) (RFC 4655) was later added to optimize centralized path computation, and still later SDN advocated centralized control of IP and consequent simplification of the forwarding elements to become so-called whitebox switches. Use of SDN for 5G transport networks is described in ITU-T G.7702. One advantage of the PCE approach over the related SDN one is that the PCE did not instruct the NEs, leaving the steering function to the source node, while the SDN controller needs to reach out and maintain state with every whitebox switch. Because of this, SDN controllers are single points of failure, suffer from scalability issues, and even minor pro- gramming bugs in SDN controller code can impact unrelated flows. Recently an alternative called segment routing has gained popularity for MPLS and IPv6. Segment routing, similar to source routing, dictates forwarding by a list of path stations in the packet. Unlike source routing, this list of intermediate addresses is inserted by the ingress router, not by a source host, avoiding the negative security implications of source routing. In MPLS segment routing, the list of intermediate nodes is implemented as a stan- dard MPLS stack, with each label switch router (LSR) popping the top of stack label, rather than swapping it. 6.6.5.4.4 Support for Slicing A network slice is defined (3GPP TS 23.501, TS 28.530) as a logical network that provides specific network capabilities and network characteristics. Hard isolation slicing refers to the dedicating of resources to a slice instance (such as the assignment of a wavelength on a fiber), while soft isolation slicing refers to isolation of slice instances using shared resources. 16 Slice instances can't exchange packets or directly observe each other, but still may dynamically interact (e.g. due to resource contention), if soft slicing isolation is used. Soft slicing is achieved through logically multiplexing the data plane over a physi