  In the framework of Network Function Virtualization (NFV), the reliability of
Service Function Chain (SFC), -- an end-to-end service is presented by a chain
of virtual network functions (VNFs), is a complex function of placement,
configuration and deployment requirements, both in hardware and software.
Previous reliability analysis models cannot be directly applied to SFC because
they do not consider aspects of system component sharing, heterogeneity of
system components and their interdependency in case of failures. In this paper,
we analyze service reliability of complex SFC configurations, including serial
and parallel VNF chaining, as well as their related backup protection
components. Our analysis is based on combinatorial analysis and a reduced
binomial theorem, and this simple approach can be utilized to analyzing rather
complex SFC configurations. We consider, for the first time, failure
dependences among VNF components placed in data centers, racks, and servers. We
show that our analysis can easily consider different VNF placement strategies
in data center networks in arbitrary configurations and, thus, be effectively
used for optimizations of the reliable SFC placement.
