Middle Mile, Fronthaul, Broadband: Good Examples of how Words Change Meaning in Era of Virtualized Networks

Telecom terms change meanings over time. We used to define “broadband” as any data rate at 1.544 Mbps or faster. Now the definition is more flexible, and deliberately changes over time. The U.S. Federal Communications Commission defines “broadband” as a minimum downstream speed of 25 Mbps, with 3 Mbps upstream. 

In a mobile network, “backhaul” used to mean the trunk connection between a cell tower and a mobile switching center. These days, as networks are virtualized, we talk about fronthaul, mid-haul and backhaul. All those deployments occur within a local network, but “fronthaul” applies to the connection between a baseband site and a radio site, for example.

Mid-haul can refer to the connection between a baseband processing site and a controller. Backhaul then refers to the connection with a wide area network access point. 

So it is with “middle mile.” Classic fixed telco networks featured wide area networks for long-haul traffic, connecting tandem offices, for example. Connections from central offices to end users or remote hubs were part of the local trunking network. 

The local access network then ran from central offices or remote hubs to end user locations. We did not use the term “middle mile.”

In the context of  internet traffic, “middle mile” often refers to that portion of the network connecting internet traffic from an ISP’s servers to an internet traffic exchange point or peering location. 

Partly a physical concept and partly a business concept, the middle mile is the segment of a network between an internet peering point or collocation center and central offices, headends, or ISP data centers. 

source: Telegeography

Still, it is a somewhat-murky concept. Facebook, for example, sometimes refers to the middle mile as facilities linking its own data centers at distances of hundreds of miles. That is hard to reconcile with a definition focused on connections between internet peering locations and headends or ISP data centers or telco central offices. 

Others appear to use the term “middle mile” to refer to private networks of almost any distance that move traffic between a wide area network colo location and an ISP’s headend or data center. 

Traditional telco voice networks connecting central offices within a city or region might also be called “middle mile” instead of trunking networks. 

It might be easier to look at “middle mile” as a business concept, representing capacity costs or investments that are made to move traffic between an ISP headend and an internet traffic exchange point.