## 1 Introduction  
The fifth-generation mobile networks (5G) support the realization of various wireless communication services with diversified throughput and latency requirements, such as eMBB, URLLC, and massive machine-type communications (mMTC). The deployment of these services is facilitated by the 5G RAN architecture defined by the 3 GPP organization in technical specifications [1, 2] and developed in parallel within the Open RAN (O-RAN) Alliance activities [3]. In 5G RANs, radio baseband processing functions, traditionally realized in a Baseband Unit (BBU) in 4G networks, are split between radio (RU), distributed (DU), and central (CU) units. The specification [1] defines several functional split options. Whereas the RU replaces the remote radio head (RRH) in 4G and is associated with the antenna, the DU and CU are separate components that can be located in different areas of the network. The DU and CU functions can be virtualized and executed on general-purpose processes available at processing pool (PP) facilities, or in small Data Centers (DCs) [4]. The flexibility in placing the DU and CU entities supports realizing 5G services. Namely, the DUs responsible for performing time-critical radio frequency functions are located near the RUs, which limits the RU-DU latencies and, simultaneously, the bandwidth required for DU-CU links. In addition, multi-access (mobile) edge computing (MEC) has been proposed to reduce traffic load and support latency-sensitive services by extending computation, communication, and storage facilities into the RAN [5]. The radio data between the RU, DU, CU, and a central hub, where the traffic is aggregated and the 5G Core (5 GC) functions typically reside, is transported over the so-called Xhaul network [6]. Standard IEEE 1914.1 [7] defines the next-generation fronthaulinterface (NGFI) architecture implementing Xhaul based on a packet-switched transport network. The NGFI allows for the concurrent transport of fronthaul (FH), midhaul (MH), and backhaul (BH) data flows, respectively, between the RU-DU, DU-CU, and CU-5 GC over a shared packet network. The enabling technology for NGFI is Ethernet, which has been adapted for fronthaul networks in standard IEEE 802.1 CM [8]. The mapping and encapsulation of 5G radio data into Ethernet frames is defined by the enhanced Common Public Radio Interface (eCPRI) protocol [9] and the Radio over Ethernet (RoE) specification presented in standard IEEE 1914.3 [10]. Eventually, Time-Sensitive Networking (TSN) mechanisms that prioritize the latency-sensitive traffic in the Ethernet-based fronthaul are proposed in [8]. Fifth-generation transport networks are expected to provide optimized support for different types of services (such as eMBB, URLLC, mMTC, 4G), following their specific requirements, among others, in terms of throughput, latency, mobility, reliability, and availability [11; 12]. To achieve this, the concept of network slicing has been identified by 3 GPP as one of the key components of 5G networks [13]. Network slicing allows the network operator to deploy several instances of virtual connectivity service tailored to specific service needs over the same shared physical network infrastructure, where services are strictly separated between different slices [11; 14]. Two concepts of implementing network slicing in the transport network are discerned: hard and soft [15; 16]. Hard slicing typically assumes the physical separation of transmission resources (such as time slots or wavelengths in optical networks) assigned to network slices, which are dedicated and not shared with other slices. Alternatively, in soft slicing, the resources can be shared between slices while maintaining the expected levels of service quality in particular slices. The packet-switched Xhaul transport network architectures specified in NGFI [7] and O-RAN [16] assume network slicing implementation. These networks generally use the soft slicing approach as they allow the sharing of transmission resources, such as switches and links.