Of all of the network terms that have vague or even inconsistent definitions, “metro network” ranks high on that long list.
The problem with nailing down the purpose of metro networks is that shifting missions for the public network have created almost whipsaw changes in the way service providers should optimally connect network equipment.
Changing regulatory requirements and competitive forces are also having a major effect. These changes are forcing constant revisions to the optimal infrastructure for the metro network, and that’s likely to continue and even accelerate in the near future.
In the beginning, a local voice call mission for metro networks. In the age of voice calls over the public switched telephone network (PSTN), most calls were local, so switching offices were arranged in a hierarchy to minimize the number of switches needed to complete a given call.
This aggregated local exchanges into “metro areas” within which users could make local calls. Each metro area had one or more interexchange POPs that provided inter-metro calling. In this era, a metro in the US was called a “LATA” for “local access and transport area.”
Stage 2: Metro networks morph into broadband Internet aggregators. As broadband Internet grew, new demand brought changes in the way traffic flowed. Nearly all broadband traffic moved through the access and metro infrastructure to an Internet Service Provider’s POP, which meant the role of lower-tier sites or offices in connecting calls was replaced by a role of aggregating traffic for the efficient use of optical transport resources.