  SDN and NFV have recently changed the way we operate networks. By decoupling
control and data plane operations and virtualising their components, they have
opened up new frontiers towards reducing network ownership costs and improving
usability and efficiency. Recently, their applicability has moved towards
public telecommunications networks, with concepts such as the cloud-CO that
have pioneered its use in access and metro networks: an idea that has quickly
attracted the interest of network operators. By merging mobile, residential and
enterprise services into a common framework, built around commoditised data
centre types of architectures, future embodiments of this CO virtualisation
concept could achieve significant capital and operational cost savings, while
providing customised network experience to high-capacity and low-latency future
applications.
  This tutorial provides an overview of the various frameworks and
architectures outlining current network disaggregation trends that are leading
to the virtualisation/cloudification of central offices. It also provides
insight on the virtualisation of the access-metro network, showcasing new
software functionalities like the virtual \ac{DBA} mechanisms for \acp{PON}. In
addition, we explore how it can bring together different network technologies
to enable convergence of mobile and optical access networks and pave the way
for the integration of disaggregated ROADM networks. Finally, this paper
discusses some of the open challenges towards the realisation of networks
capable of delivering guaranteed performance, while sharing resources across
multiple operators and services.
