# Transport-Layer Limitations for NFV Orchestration in Resource-Constrained Aerial Networks
## 2 Background and Related Work  
Improving data rates and lowering communication latencies are some of the main challenges for developing new infrastructures and technologies for the 5 th generation of mobile networks in the near future. However, accomplishing these objectives requires evolving and adapting all current technologies and concepts to produce significant improvements in those areas, by introducing new paradigms with the potential to reshape the next decade of mobile infrastructures. In this fashion, NFV has risen as one of the key enablers of 5G communications, aiming at softwarizing currently deployed physical network functions, i.e., eliminating the usage of specialized equipment to build network functions in favor of using generic hardware. The main guidelines for creating NFV deployments were defined by the NFV Industry Specification group through a reference architectural framework described in [7]. In this document, Virtualized Network Functions (VNFs) are considered the central elements of the architecture, defined as software implementations of network functionalities (e.g., a router, a load balancer or a traffic generator). These elements are deployed in an NFV Infrastructure (NFVI), which has all the required storage, computing and networking resources needed to support the virtualization and execution of network functionalities. Moreover, the NFVI elements (nodes) provide an abstraction layer to separate VNF functionality from the hardware being used underneath, ensuring that no further specialized equipment is necessary unless a VNF specifically demands it. This behavior saves costs in both network deployment and maintenance, as well as simplifying new network functionalities development. However, having isolated VNFs (i.e., network functionalities) is not enough to establish a complex environment for providing end-to-end services such as those present in currently traditional networks. In this case, VNFs interconnect between themselves to generate Network Services (NSes), whose purpose is building more complex behaviors while easing the service chain provisioning for telecommunication operators and Service Providers. To help coordinating operations over the NFV environment, the same NFV Industry Specification group defined a Management and Orchestration (MANO) system. This component is responsible for deploying and managing the lifecycle of VNFs inside the NFV infrastructure. To cover all lifecycle requirements and phases, the MANO system is divided into three different components: (1) the Virtualized Infrastructure Manager (VIM), responsible for controlling and monitoring the resources of an NFV infrastructure (including storage, networking and computing resources); (2) the Virtual Network Function Manager (VNFM), responsible for instantiatiating, configuring, modifying and terminating VNFs; and (3) the NFV Orchestrator (NFVO), in charge of coordinating the deployment of individual VNFs, and their interconnection, to build the requested service graph. On the other hand, SUAVs have been an attractive technology for the research community thanks to their increased mobility support with respect to other technologies, such as terrestrial vehicles. There has been quite an effort to develop new applications using these devices in many engineering fields. Examples of these applications are supporting search and rescue operations [3], forest fire automatic detection [4], precision agriculture [8] or moving cargo from different warehouses along a delimited geographical area [9], just to name a few of them. SUAVs have also been considered to provide networking functionalities and services over geographic areas. The work in [10] presents a solution that uses UAVs for supporting backbone communications to mobile ground stations. In [11], the authors design a solution to enable a broadband network for emergency communications using geolocalization.