Time and Freshness (velocity) criterion refers to how important is the data delivery between things and fog/cloud, hence this is according to the requirements of the
IoT system on how recent is the data, whether it should be in real-time, near realtime or at anytime. The delay that results from withholding/processing data at the thing, fog and cloud levels until its transfer to the end-user. This may also include the delay for holding data at the thing level in preparation for transferring the collected data (i.e., real-time vs batch processing) to either fog, cloud, or fog/cloud nodes.
Volume criterion refers to the amount of data that things produce and send to fog/cloud nodes. For instance, if the fog can handle up-to a set image size in pixels, so when an image with a bigger size is captured, this might be directed to the cloud to take care of it; otherwise, the image can be partitioned into sub-graphs, in which case the fog can work in a collaborative mode to perform the processing.
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