CAP on mobility control for 4G LTE networks

The CAP theorem [1] exposes the fundamental tradeoffs among three key properties of strong consistency, availability and partition tolerance in distributed networked systems. In this position paper, we take the CAP perspective on 4G mobility control. We view the control-plane management for mobility support as a distributed signaling system. We show that the impossibility result of the CAP theorem also holds for mobility control: It is impossible for any mobility control to guarantee sequential consistency, high service availability, and partition tolerance simultaneously. Unfortunately, the current 4G system adopts its mobility scheme with the notion of sequential consistency. Our empirical study further confirms that, the incurred data unavailability (i.e., data service suspension) time is comparable to that induced by wireless connectivity setup. We argue that the desirable mobility control for the upcoming 5G networks should take a paradigm shift. We discuss our early effort on re-examining the consistency notion for higher availability and fault tolerance.