# On the Rollout of Network Slicing in Carrier Networks: A Technology Radar
## 7 TN Domain
### Transport Technologies
Apart from the rich built-in features (e.g., highly scalable, responsive, programmability) [68], what makes SR [69] an ideal technology option for the IP underlay is that it can be used with both the MPLS forwarding plane (SR-MPLS) and the IPv6 forwarding plane (SRv6). Examples of realization of slicing in SR networks can be found in [70; 71]. The basis of this realization lies in the ability of SR to encapsulate additional information for discriminating traffic associated with different slices [72]. The solutions explained so far, belonging to the as-is and deploy rings in the technology radar, are part of the soft slicing category presented in Section 2. In the medium term (the testing ring in the radar), as novel B2B offerings come into service portfolio and the slicing requirements get burdened, the capabilities offered by soft slicing solutions are not enough. In this regard, operators have started to evaluate new technologies, working on three main directions:  
* **Hard slicing**. In this workstream, the operators are focused on trialing technologies like Flexible Ethernet (Flex-E), Flex-O and DWDM. These technologies are used to realize the concept of isolated traffic flows operating on common links that avoid negatively influencing the performance of each other in case of congestion. In particular, **Flex-E**[35] bets on the principle of calendar-based channelization, which consists of bundling or dividing physical Ethernet interfaces into multiple Ethernet hard pipes based on timeslot scheduling. The work in [73] gives further details on how Flex-E technology might be used to implement hard slicing. **Flex-O**, described in the ITU-T G.709.1/Y.1331.1 recommendation [74], provides Optical Transport Network (OTN) interfaces with comparable functionality to that of Flex-E based Ethernet interfaces. Finally, **DWDM** can be used for physical resource separation at wavelength level. Adaptive transponders over Wavelength Division Multiplexing (WDM), spectrum fragmentation and Optical Cross-Connect (OXC), and Reconfigurable Optical Add-Drop Multiplexer (ROADM) are optical network virtualization techniques that can be exploited for network slicing, so that wavelengths can be right-sized for the specific requirements of every slice. * **Deterministic techniques**. Flex-O, Flex-E and DWDM are ideal for providing guarantees for throughput and delay, which will be a common pattern across most of the uRLLC scenarios. Apart from these hard slicing technologies, in order to enable deterministic real-time performance in transport networks, novel full-stack approaches are also proposed in the underlay, with techniques such as those outlined by the IEEE TSN Project Group (layer 2 aspects) and the IETF DetNet Working Group (layer 3 aspects). On the one hand, **TSN** is a set of IEEE 802.1 amendments that enable determinism of time-critical traffic flows, even in cases where traffic flows with different statistical characteristics are multiplexed. The use of slicing in TSN-based networks is discussed in [75]. On the other hand, **DetNet** defines a set of techniques to extend deterministic behavior to in-slice layer 3 paths. These techniques span from explicit routes, packet replication and elimination, to congestion protection with E2E synchronization [76]. * **SD-WAN**. It is not uncommon that B2B customers contracting 5 GC slices will request QoS-assured connectivity across their enterprise sites. This setup may result in a multi-site B2B slice, typical in PNI-NPN scenarios. In this case, Software Defined WAN (SD-WAN) [77] is a good candidate solution for the DN segment. Some operators have started to execute PoCs in this direction, e.g., [78]. Finally, the focus in the longer term is on making **O-RAN fronthaul interface slicing-aware**[59]. Unlike the midhaul and backhaul segment (3 GPP interfaces), where slicing information is injected with the the EP_Transport IOC (see Figure 7B), the fronthaul segment (O-RAN interface) does not currently support slicing features.