An edge is the edge or transition between two networks or subnetworks, for example between a high-speed network and an access network.
Edge routers are used only at network transitions and perform the switching function between the core network and the access area, thus providing subscribers with broadband access over the last mile. These are edge devices that are connected to the core routers in the core network and switch data from the bundled DSL lines.
In addition to simple edge routing, which is based on the network layer, there is also encapsulated edge routing. In this case, the core network, for example an ATM network, is used only as a fast transport network. The data is packaged as LLC data packets in ATM cells, transmitted over the ATM network and unpacked again on the receiving side. The procedure is described in RFC 1483.