# Transport-Layer Limitations for NFV Orchestration in Resource-Constrained Aerial Networks
## 3 Orchestration in Intermittently Available Platforms  
As we have described in the previous section, the research community has shown growing interest towards the softwarization of network functions over SUAV platforms: these aircraft may have enough potential to provide a flexible environment to run VNFs on an NFVI infrastructure, allowing development and creation of a wide variety of NSes. Furthermore, this infrastructure can take advantage of its mobility to deploy these NSes in any kind of environment/area where common vehicles might not be able to access or have difficulties to do so, e.g., natural emergencies, or would imply additional costs on deploying and managing a complete infrastructure, e.g., remote rural areas with no easy access. Moreover, some VNFs could also take advantage of the mobility of the aircraft to build NSes that require movement to perform any set of actions (e.g., moving cargo from different warehouses with predefined paths over a delimited geographical area [9] or a road traffic monitoring system [2]). However, a prior work of the authors [6] points out the existence of several challenges that should be taken into account when dealing with NFV in SUAV scenarios, to enable the automatic deployment, configuration, and operation of the aforementioned NSes. In the following, we provide a more comprehensive description of these hurdles, using the reference scenario shown in Figure 1 as an example. As it can be seen in Figure 1, the scenario is composed of several SUAVs with enough computational, storage and networking resources to build an NFV infrastructure, i.e., each one of the aircraft is an NFVI node or serves to onboard an NFVI node as payload. These NFVI nodes are interconnected through wireless communication technologies (e.g., WiFi of line-of-sight radio links), building a Flying Ad-Hoc Network (FANET) that enables multi-hop data communications. The infrastructure is controlled from a Ground Control Station (GCS), where a VIM is located. The NFVO will communicate with the VIM to coordinate the automatic deployment of NSes over the ad-hoc network formed by the NFVI nodes, as well as retrieving information from the status of the compute, storage and network resources, as well as from the VNFs, from each one of the aircraft. Every aircraft can be placed at any location over a delimited geographical area, either remaining its position static the whole time or moving through a scenario, both autonomously or instructed by an operator from the GCS, depending on the situation and the type of aircraft and/or service. Despite all its parallelisms with traditional cloud-based NFV infrastructures, there are some differences that must be pointed out. First, SUAVs have a communication range between aircraft due to the limitations of wireless communications. In consequence, they need an adequate distribution to provide enough coverage for the whole target area, implying that not all SUAVs will be able to reach the GCS directly in most cases and, in consequence, VIM-SUAV communication will be mostly performed through intermediate nodes, forwarding both orchestration traffic (i.e., the traffic needed to manage and monitor the available NFVI resources and/or services) and data traffic (information transmitted and/or received by VNFs as part of their normal operation) through the network. Finally, when mobility is enabled, SUAVs may be constantly breaking links that might disrupt SUAVs communication, as new ones must be dynamically created again with other nodes constantly, which can harm certain types of communications. Moreover, these SUAVs need the aid of a battery to stay afloat in the air during an operation/service, requiring a subsequent replacement when this battery is depleted, disrupting even more this communication. Despite all those differences, in a prior work [5], we presented a functional prototype of an NFV system capable of deploying virtual functions and services over resource-constrained SUAV networks.