  Emerging integrated space and terrestrial networks (ISTN) built upon low
earth orbit (LEO) satellite constellations aim at providing planet-wide
Internet services, not only for residential users, but also for mobile users
(e.g., in airplane and cruise scenarios). Efficiently managing global mobility
and keeping connections active for mobile users is critical for ISTN operators.
However, our quantitative analysis identifies that existing mobility management
(MM) schemes suffer from frequent connection interruptions and long latency in
ISTN scenarios. The fundamental challenge stems from a unique characteristic of
ISTNs: not only users are mobile, but also core network infrastructures (i.e.,
LEO satellites) are frequently changing their locations in the network. To
facilitate seamless and low-latency satellite Internet services, this paper
presents SKYCASTLE, a novel network-based global mobility management mechanism.
SKYCASTLE incorporates two key techniques to address frequent connection
interruptions in ISTNs. First, to reduce the interruption time, SKYCASTLE
adopts distributed satellite anchors to track the location changes of mobile
nodes, manage handovers and avoid routing convergence. Second, SKYCASTLE
leverages an anchor manager to schedule MM functionalities at satellites to
reduce deployment costs while guaranteeing low latency. Extensive evaluations
combining real constellation information and mobile user trajectories show
that: SKYCASTLE can improve up to 55.8% uninterrupted time and reduce 47.8%
latency as compared to other existing MM solutions.
