Vol.:(0123456789) 1 3 Photonic Network Communications (2020) 40:245–255 https://doi.org/10.1007/s11107-020-00896-7 ORIGINAL PAPER Dedicated and shared solutions for reliable function splitting in 5G X‑haul Bahare Masood Khorsandi 1  · Didier Colle 2  · Wouter Tavernier 2  · Carla Raffaelli 1 Received: 1 November 2019 / Accepted: 17 June 2020 / Published online: 6 July 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020 Abstract Functional splitting, referred as X-haul, is introduced in the 5G networks to support flexibility and meet service requirements. Each split option has a different impact on latency and bandwidth characteristics. Depending on the split, a certain amount of redundant resources is required to provide resiliency against outages or failures, as in the case of the uRLLC service. This paper proposes novel reliable function placement algorithms for functional splitting to guarantee service continuity in case of single CU/DU or link failure, namely based on dedicated and shared path protection principles. The proposed techniques not only provide a scalable approach to design full protection against single failure but also exhibit significant savings in terms of network resources, by suitably sharing redundant backup resources. The obtained results show significant improve- ment in terms of bandwidth saving and multiplexing gain with respect to conventional C-RAN fronthaul, depending on the distance constraints, thus suggesting design criteria for 5G aggregation networks. Keywords 5G · X-haul · Function chain · Resiliency · Location algorithm 1 Introduction The fifth generation of mobile technology (5G) is positioned to address the demand and business contexts of 2020 and beyond. It is expected to enable a fully mobile and connected society and to empower economic transformations in count- less ways coming from novel services. Applications intro- duced along with 5G require massive machine-type com- munications (mMTC), enhanced mobile broadband (eMB), ultra-reliable low latency communications (uRLLC) to be supported by a single infrastructure. [1]. Despite the appealing design aspects of centralized radio access network (C-RAN), one key obstacle in its adoption is the excessive capacity requirements on the fronthaul links to provide baseband units (BBUs) and remote radio units (RRUs) connections [2]. Shifting all baseband processing to the remote BBU hotel implies the adoption of a high number of optical channels with strict latency constraints. To relax the excessive fronthaul requirements, the concept of C-RAN is being revisited, and more flexible distribution of baseband functionalities between the RRU and BBU hotel is consid- ered. Rather than offloading all baseband processing to a sin- gle entity like the BBU hotel, it is possible to divide it into several blocks throughout the network which leads to the significant reduction of the bandwidth needed on the trans- port links [3]. This concept is known as “functional split” and was firstly introduced in the new architecture design for the 5G access network named “X-haul” or “crosshaul” [4]. X-haul (front/mid/backhaul), defined as the common flexible transport solution for future 5G networks, aims at integrating the fronthaul and backhaul networks with all their wired and wireless technologies in a common packet-based transport network under an SDN-based and NFV-enabled common control [5]. This solution will hence enable a flexible and software-defined reconfiguration of all networking elements in a multi-tenant and service-oriented unified management framework. * Carla Raffaelli carla.raffaelli@unibo.it Bahare Masood Khorsandi bahare.masood@unibo.it Didier Colle didier.colle@ugent.be Wouter Tavernier wouter.tavernier@ugent.be 1 DEI, University of Bologna, Bologna, Italy 2 IMEC, Ghent University, Ghent, Belgium