# Transport-Layer Limitations for NFV Orchestration in Resource-Constrained Aerial Networks
## 1 Introduction  
The future introduction of 5G technologies into the market is expected to completely change the telecommunications industry for the next decade to come: increased data rates, improved wireless transmission latency, and cost optimization will bring new and exciting opportunities to develop novel functionalities and applications for both consumers and the industry itself [1]. However, these objectives can only be reached with an appropriate evolution of our contemporary technologies, since current mechanisms may not provide a viable and cost-effective solution to meet the ever-increasing data demands. In this context, we can see why the Network Functions Virtualization (NFV) paradigm has been perceived by many researchers and operators as one of the key enablers for 5G, since the softwarization of network services and functions can reduce both deployment and maintenance costs, as well as easing its development and maintenance. Another technology that has received significant attention in recent years has been Small Unmanned Aerial Vehicles (SUAV). Due to their limitless mobility and their capacity to onboard diverse hardware equipment as their payload, they provide a powerful tool that enables a wide range of new and appealing applications and services, such as road traffic monitoring using SUAVs [2], providing support for search and rescue missions [3] and natural disasters [4]. Moreover, given that they maybe used to transport computing, networking and storage resources (e.g., by onboarding single-board computers), the research community has taken the first steps to build NFV infrastructures based on these SUAVs to support the cost-effective deployment of network services with data communications over delimited geographic areas [5]. However, despite the existing research efforts, there still are important challenges and hurdles that need to be addressed to effectively support NFV operations over resource-constrained platforms, such as those that can be onboarded on SUAVs. In an exploratory research work [6], we succinctly identified these hurdles. In this paper, we continue this research line, presenting a more detailed analysis of these challenges from a theoretical perspective. Following this analysis, the paper focuses on a specific but relevant aspect: studying how the intermittent availability of the aerial communications affect the dissemination of NFV orchestration information, i.e., the information that has to be exchanged to coordinate the computing, networking and storage resources onboarded on SUAV units. In particular, the paper presents the results of several simulation scenarios, using both TCP (the transport protocol commonly used to disseminate orchestration information in traditional cloud computing environments) and UDP, in order to measure the performance of orchestration traffic in an aerial network composed of several SUAVs. Moreover, we analyze the behavior of both transport protocols in idle scenarios (i.e., no presence of background traffic sharing the wireless medium with the orchestration traffic) and in scenarios with congested wireless links. Our simulation results suggest that the use of TCP to disseminate orchestration information across an aerial network of SUAVs presents some limitations. Considering these results, the paper anticipates a set of research directions for contributing to a future view of an effective integration of NFV technologies into SUAV platforms. The rest of this paper is structured as follows: in Section 2, we look at NFV concepts, including NFV orchestration and its main principles, and we review the existing literature regarding SUAVs and some of their applications. In Section 3, we introduce NFV orchestration in aerial ad-hoc networks, analyzing the potential challenges and hurdles of the use of NFV technologies in this new environment, and pointing out potential approaches that could be followed to address those challenges.