"Middle Mile" Sometimes is "Muddled Mile"

Some seemingly define middle mile too loosely. In fact, some projects talked about as middle mile might not have anything to do with middle mile infrastructure. In fact, local access often is what is meant, not middle mile infrastructure.  

Terminology changes in the connectivity business, over time. The term refers to the part of the network segment between the core network backbone (the wide area network) and the local access network.

Think of this as what we used to refer to as the trunking network, or perhaps the distribution network. If the core network terminates at a class 4 switch or a colocation facility, then the “middle mile” is the transport network connecting the colo to the local access network (a central office or headent, for example).

 

Some illustrations tend to distort the network architecture, even when subject matter experts correctly understand the concept. In this illustration, which shows the way an enterprise user might see matters, the entire WAN is considered “middle mile,” not simply the connections between a colo site and the WAN. 

source: Telegeography

That is understandable if we conceive of the network the way an enterprise might: that “everything not part of my own network” (“my local area network”) is “in the cloud,” an abstraction. 

Even viewed that way, the middle mile is an abstraction. It is part of the network “cloud,” in the sense network architects have depicted it: all the network that is not owned by the enterprise. 

The point is that there is a difference between network terms such as “middle mile” as a description of network facilities and the use of the term (perhaps even incorrectly) as a matter of networking architecture. 

“WAN transport” is not “middle mile,” in terms of network function. But everything other than the enterprise LAN is “cloud” or “not owned by me” in terms of data architecture. But in that sense the term middle mile is unnecessary.

Of course, such terms are more important for service providers than end users and customers. Even if WAN and “network core” refer to specific parts of a network; access to a different part;  and middle mile, distribution, backhaul or trunking network being a third part, none of that matters to most enterprises or consumers buying connectivity. 

The term arguably matters most to retail internet service providers needing to reach internet points of presence. It matters most when ISPs need to buy capacity on such networks to reach an internet PoP. 

Still, usage does change, 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. 

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.