Is There Really an Enterprise "Middle Mile?"

Terminology changes in the connectivity business, over time. Consider the term “middle mile,” which has come into use over the past decade. 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.