Network Slicing by definition is carving out network resources for one or more particular type of traffic and/or service , or in other words, logical partitioning of network resources such as links, nodes, networking plane etc is called Network Slicing.
Some form of logical partitioning is already been used for years such as L3VPN , VRF-Lite or even Vlan and Qos , but these mechanisms does not differentiate in terms of treatment to different traffic types. This is not a true form of Network Slicing.
Network Slicing is gaining more traction in the context of 5G . 5G related services requires different treatment to different traffic types per flow basis because few services are bandwidth hungry , others are latency sensitive . Now, to cater to this unique requirement of differential treatment , traditional way of slicing or resource partitioning may not help.
Segment Routing with the help of SR traffic engineering (SRTE) and Flex-algo (Flexible algorithm) provides excellent solution to accomplish the requirement. Using Flex-algo , IGP custom algorithms can be created with user defined metric such as delay, TE-Metric etc instead of default metic of cost. (Cost is the default metric used by IGP such as OSPF/ISIS in best path calculation).
Depending upon the requirement, different traffic types can be steered into different paths and leverage custom algorithms (Flex-algo).
For example, 3GPP defines three types of 5G services eMBB, uRLLC and mmTC. Out of three, uRLLC is delay sensitive service, so this can be easily steered to path or portion of the network which can provide minimum end-to-end latency calculated with the help of Flex-algo with metric as delay, and rest of traffic can be sent across path calculated based on default metric.
Also, there are underlay performance monitoring probes like PM (performance monitoring), Y.1731 are required to measure real time latency , link losses , bandwidth etc so that IGP can calculate best path basis custom defined metric.
Business motivation behind Network Slicing is to provide differential Enterprise SLA , premium business VPN , flow-aware services like SD-WAN and 5G services (eMBB, uRLLC, mmTC).