What is “Ethernet in the First Mile”?

Ethernet in the First Mile (EFM) is the nickname of IEEE Std 802.3ah-2004, an amendment to the Ethernet standard, specifying “Media Access Control Parameters, Physical Layers, and Management Parameters for Subscriber Access Networks”. The EFM standard was approved by the IEEE Standards Board in June 2004, and officially published on 7 September 2004.

The “Last Mile” is the name traditionally given to the part of a public communication network that links the last provider-owned node (the central office, the street cabinet or pole) with the customer premsises equipment (CPE). The “First Mile” is the exact same thing, viewed from the customer's perspective.

EFM does not improve or replace the existing Ethernet. It is a set of additional specifications, allowing users to run the Ethernet protocol over previously unsupported media, such as single pairs of telephone wiring and single strands of single-mode fiber (SMF). This makes the EFM port types suited for use in subscriber access networks, i.e. the networks that connect subscribers to their service provider.