  Enabling users to move to different geographical locations within a network
and still be able to maintain their connectivity and most essentially,
continuity of service, is what makes any wireless network ubiquitous. Whilst
challenging, modern day wireless networks, such as 3GPP-LTE, provision
satisfactory mobility management (MM) performance. However, it is estimated
that the number of mobile subscriptions will approximately touch 9 billion and
the amount of data traffic will expand by 5 times in 2024 as compared to 2018.
Further, it is expected that this trend of exponential growth will be
maintained well into the future. To cope with such an exponential increase in
cellular traffic and users alongside a burgeoning demand for higher Quality of
Service (QoS), the future networks are expected to be highly dense and
heterogeneous. This will severely challenge the existing MM solutions and
ultimately render them ineffective as they will not be able to provide the
required reliability, flexibility, and scalability. Consequently, to serve the
5G and beyond 5G networks, a new perspective to MM is required. Hence, in this
article we present a novel discussion of the functional requirements from MM
strategies for these networks. We present a novel qualitative assessment of the
state-of-the-art mechanisms based on their ability to satisfy the reliability,
flexibility and scalability criteria for future MM strategies. We then present
a study detailing the research challenges that exist in the design and
implementation of MM strategies for 5G and beyond networks. Further, we chart
out the potential MM solutions and the associated capabilities they offer to
tackle the persistent challenges. We conclude this paper with a vision for the
5G and beyond MM mechanisms.
