Minimum delay function placement and resource allocation for Open RAN (O-RAN) 5G networks

Digitalization is a journey that has been started and put ICT industry in a crucial situation to provide required infrastructure for diverse range of data hungry, short tempered applications and services. One of the main technologies that will pave the way towards new digital ecosystem is fifth Generation of mobile technology. To meet 5G network service requirements, innovative architectures, technologies and standards focusing on cloudification are employed. Cloudification of network functions along with the use of virtualized network functions (VNFs) and containerized network functions (CNFs) allows agile and scalable service provisioning. The use of VNFs and CNFs has been started from core and networking middleboxes but then extended to RAN functions. Open radio access network (O-RAN) proposes an interoperable and standard architecture for cloudified RAN. The main idea behind this architecture is to make RAN more flexible. O-RAN allows different layers of RAN to be split and deployed as virtual function and openly communicate with each other for service provisioning. In this paper, we model an End-to-End mobile network operator (MNO) employing O-RAN. We consider a mobile network architecture, with three layer hierarchical data centers (Local, Regional, and Core) to add flexibility in resource allocation, and increase reliability, taking the advantages of O-RAN. MNO receives various service function requests (SFRs) requiring accommodation on the network. We assume RAN and core functions are deployed as CNFs on the data centers. Users of SFRs connects to remote radio heads (RRH) to receive the service. In this paper, we mathematically model the CNF placement and resource allocation of an O-RAN enabled LTE/5G network while trying to minimize the End-to-End delay of the data plane. We study the problem in two different cases First, we assume that the SFR traffic traverse through a single path across the RAN functions and model this problem. This is a mixed integer non-linear programming problem. With some change of variables, we make it a linear mixed integer programming problem but it is still non-trivial to solve. Then, we model the problem for the case where traffic of an SFR can be split and be served via multiple CNFs. We proposed a gradient based scheme to solve the minimum delay problem in this case. Experimental results indicate that by increasing the number of service requests in a network, the proposed GBMD(Gradient-Based Minimum Delay) algorithm serves up to 90% End-to-End Delay decrease. Another improvement on the performance of a network will occur by levering GBMD algorithm for around 72% End-to-End delay reduction in case of limited resources.