# On the Rollout of Network Slicing in Carrier Networks: A Technology Radar
## 3 Impact of Network Slicing
### TN Slicing
#### 3.3.1 On the Mapping of 3 GPP Slice Information into TN Nodes  
To configure the TN slicing behaviour in the WAN resources, the TN management domain needs the following information:  
* Network slice topology. The TN management domain needs to know the application endpoints of the slice to determine the needed WAN resources, which are either physical or virtual nodes. NSMF/NSSMFs provide the application endpoints [32] of 3 GPP network functions taking part in the RAN and CN slice subnets and, if applicable, further information such as the next-hop router IP address configured in these network slice subnets. For example, the CU-UP application endpoints are the IP addresses/VLAN IDs associated with the F1 and N3 interfaces. The TN management  
Figure 6: RRM procedures for slicing. domain correlates this information with the transport network topology and derives the (cell site or border) routers connecting to network functions. * Traffic segregation and mapping to S-NSSAIs. As 3 GPP network functions can be shared by multiple network slices, it is necessary to segregate traffic belonging to specific slices on transport interfaces. One option for traffic segregation is to assign application endpoints to a specific set of S-NSSAI values. This solution is rather simple, as the TN can map packets to connectivity services based on application endpoints, provided that (i) the allocation of S-NSSAI to endpoints is known, and (ii) the application endpoints are visible on the transport layer. While this is the simplest solution in many cases, it is not a universal solution, as the application endpoint addresses are not always visible to the site router, e.g., when there is encryption using IPSec. An alternative solution is the concept of logical transport interfaces, as shown in Figure 7A. A logical transport interface is a virtual interface separated from application endpoints. It can be, for example, a specific IP address/VLAN combination corresponding to an IPSec termination point, or an identifier (e.g., MPLS label, segment ID) that the TN recognizes, or it can be just a logical interface defined on top of a physical transport interface. As long as the interface identity can be derived from packet headers, the TN nodes can perform the mapping to transport connectivity services. * Reachability information. Each logical transport interface carries the traffic associated with some application endpoints that may be using IP addresses separate from the transport interface. These IP addresses must be reachable, hence they need to be advertised to populate forwarding tables. A 3 GPP network function can advertise such reachability information by running a dynamic routing protocol towards the next hop router. * QoS requirements. To satisfy the service requirements captured in ServiceProfile and SliceProfile, each logical transport interface needs to be bound to a QoS profile that includes the applicability and use of DiffServ Code Points (DSCP) [33] and QoS related properties on that interface. To allow the TN management domain to receive this information from the 3 GPP management system, the EP_Transport IOC [15] is defined. Part of the Network Slice NRM fragment (see Figure 1), this class allows the capture of the information that shall be exchanged between the 3 GPP management system (E2E management domain, RAN management domain and CN management domain) and the TN management domain. This information is used to configure WAN resources in such a way that the requirements captured in ServiceProfile and SliceProfile can be fulfilled. Figure 7B shows the construction of the EP_Transport IOC, and how it maps the logical transport interface to application endpoints. Notice that one EP_Transport (representing a logical transport interface) can be associated with more than one multiple EP_Application (representing an application endpoint of a 3 GPP network function), but also the other way around. While the first case captures the typical situation, the second case can be used for the sake of resilience or load balance in the TN.