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The end-to-end network heterogeneity involves the three aspects listed here, and all of them would influence the performance of the other nonfunctional requirements.

 Device-to-fog (D2F). Represents the radio network and the communication protocol used between the fog server and the end-device. In general, D2F has a broad range of networking options and hence, increase the complexity from the perspective of both fog server provider and the tenant. For instance, radio network options encompass IEEE 802.11 series, IEEE 802.15.4, Bluetooth, 3G/4G cellular Internet, LoRa, SigFox, NB-IoT, LTE-M, 5G New Radio (5G NR), and so forth, which indicates that the provider may need to support multiple radio networks in order to fulfill multitenancy. On the other hand, tenants also need to consider the available radio network provided by the fog server in order to optimize their applications.

 Fog-to-fog (F2F). Represents the communication network between fog nodes in both horizontal and vertical manner. For example, Figure 1.7 illustrates the vertical communication between two LV-Fog nodes, while both LV-Fog nodes also rely on an iFog node to interconnect them to the cloud. Explicitly, the F2F network would highly influence the performance of the tenant-side application, especially when the application requires a certain process or decision making from the cloud.Figure 1.7 The three types of end-to-end networking.

 Fog-to-cloud (F2C). Represents the communication network between the fog node and the cloud, which has a similar influence as F2F to the tenant-side applications. In particular, depending on the underlying infrastructure, geo-location of the cloud and the intercontinental routing path between the fog node and the cloud, the latency between the end-device and the cloud can be very different. Therefore, besides the D2F and F2F, the tenant also needs to consider the F2C network, especially when the application is unable to operate fully in a self-managed manner.