## 4 Description of the Proposed Transport System
### Low-Latency Packet Forwarding (LLPF) Scheme
priority of stream-2 is more than the priority of stream-1) arrived at the ingress ports of the bridge. These priorities can be determined based on the information obtained from the global matrix of the proposed LAPC algorithm. It can be observed in Figure 3 that based on the priorities, the frames of high-priority HERS (i.e., stream-3) preempted the frames of low-priority HERS (i.e., stream-2); then frames of low-priority HERS (i.e., stream-2) preempted the frames of LERS (i.e., stream-1). The new and previously preempted frames of the LERS would be transmitted only when there is no high-priority frame left in the queues or a predefined threshold for the preempted frames is reached. As a result of the above procedure, the high-latencyexperiencing streams that were given more priority in the considered scenarios would experience the low queuing delays, and ultimately, the E2E latencies of all the eCPRI streams can be mitigated. The proposed schemes have certain implementation requirements to be deployed in the considered Ethernet-based fronthaul bridged networks. To compute the low-latency paths in the LAPC scheme, the values of link capacities, link distances, and link costs would be known to the algorithm, which can be determined with the IS-IS protocol. The number of connected RRHs, the configured eCPRI line rates on the RRHs, the size of eCPRI bursts, and the placement of the BBU pool in the topology are well determined in the fronthaul network [18]. The low-latency packet forwarding scheme mainly uses the output values of the LAPC scheme (i.e., global matrix) and requires the bridging nodes that can support the frame preemption operations. Both schemes require that the intermediate bridges should be reconfigurable so that the proposed schemes could be programmed. This functionality can be achieved in the fronthaul networks by using the worldwide available OpenFlow switches with the SDN techniques [19]. The proposed frame preemption-based mechanism is easy to implement and less complex as compared to the legacy packet forwarding schemes such as traffic scheduling [23]. The study [26] reported that due to the utilization of the traffic scheduling techniques in the fronthaul networks, the computational time increment exponentially with the increase of incoming traffic streams at the bridges, which makes it impractical for the multiple bridged networks. In the proposed EFBNs systems, the whole procedure of path selection, E2E latency computation, and accordingly enabling the preemption on the different routes is completed before the transmissions. During the transmissions, the controller periodically collects the topology information using the IS-IS protocol, and the above procedure is executed only when the number of connected RRHs, eCPRI line rates, or link capacities are modified. The proposed scheme yields the computation time up to 1.5 minutes for 100 Gbps of eCPRI traffic load in the considered fronthaul scenarios, which reduces with the reduction of traffic load or the number of connected RRHs in the topology. The path reconfiguration is executed only when the physical topology changes, which typically changes infrequently. Thus, the several minutes of computation time before the transmissions is not a problem or an issue of secondary importance as long as the latency parameters are within the limits, which are the main concern of fronthaul networks [18; 36]. Moreover, the computational time can be further minimized by parallelizing the calculation for the proposed schemes.