Metropolitan Area Network (MANs) are also referred to as transport networks, or
regional transport networks. They link hubs to headends. MANs typically operate over
shorter distances than core, backbone networks. They carry a mix of voice, data, and
video on demand, as well as television signals.
Older MANs transmit traffic to headends over Synchronous Optical Network
(SONET) rings. Cable operators and traditional telephone companies have transitioned
some of their metropolitan networks to all-IP, Gigabit Ethernet networks or to
a combination of SONET and Gigabit Ethernet. It is complex and costly to upgrade
all of a carrier’s MANs simultaneously. However, carriers have the option of gradually
upgrading a few networks at a time. Unlike large core networks, they don’t involve
the immense upgrades as do core networks. MANs are equipped with either redundant
fiber rings or the simpler Optical Transport Network (OTN) option as backup technologies,
in the event of a fiber cut or equipment failure.
