  The Next Generation 5G Networks can greatly benefit from the synergy between
virtualization paradigms, such as the Network Function Virtualization (NFV),
and service provisioning platforms such as the IP Multimedia Subsystem (IMS).
The NFV concept is evolving towards a lightweight solution based on containers
that, by contrast to classic virtual machines, do not carry a whole operating
system and result in more efficient and scalable deployments. On the other
hand, IMS has become an integral part of the 5G core network, for instance, to
provide advanced services like Voice over LTE (VoLTE). In this paper we combine
these virtualization and service provisioning concepts, deriving a
containerized IMS infrastructure, dubbed cIMS, providing its assessment through
statistical characterization and experimental measurements. Specifically, we:
i) model cIMS through the queueing networks methodology to characterize the
utilization of virtual resources under constrained conditions; ii) draw an
extended version of the Pollaczek-Khinchin formula, which is useful to deal
with bulk arrivals; iii) afford an optimization problem focused at maximizing
the whole cIMS performance in the presence of capacity constraints, thus
providing new means for the service provider to manage service level agreements
(SLAs); $iv)$ evaluate a range of cIMS scenarios, considering different queuing
disciplines including also multiple job classes. An experimental testbed based
on the open source platform Clearwater has been deployed to derive some
realistic values of key parameters (e.g. arrival and service times).
