Let us begin by looking at a general picture of a common serviced network. The service itself is a starting point and may be broadcast video, Internet, data, etc. that is transported to the last mile through the core network. This core transport may be the metropolitan, national, or international backbone carried over different kinds of network technologies. The last mile or the subscriber network starts at the central office (CO) in the telephone-company case or at the head end in the cable multiple system operator (MSO) case. In the satellite case, the ground dishes pointed to the satellite may be considered the beginning of the last mile. For terrestrial wireless, such as LMDS, the last mile starts at the feeding point to the base stations. To generalize the last-mile architecture, it must be divided into the primary and secondary access networks. The primary access network starts at the CO or the head end and runs to the neighborhood or building. According to modern architectures such as HFC in cable or fiber-in-the-loop (FITL), a fiber runs across the primary access network, feeding a remote node such as digital loop carrier (DLC) in a street cabinet or an optical network unit (ONU) in cable. In the case of a full-copper last mile, the remote node might be the street intermediate distribution frame (IDF). The secondary access network is where the distribution takes place. Distribution takes place in the coax wiring in the case of cable and in the copper wire in the case of the telephone system. The last drop is beyond the point of demarcation that brings the service wire into the customer premises. Figure 1 describes the last-mile topography:

Figure 1. The Last-Mile Picture

Figure 2 generalizes the picture and locates the IRB.

The IRB resides at the last drop, starting at the point of demarcation and terminating at the customers’ premises. Getting access to the IRB requires a complementary fat uplink pipe from the core network through the primary and secondary access networks. In many cases, a single feeder from the core network to the last drop may be used.

The following sections will cover implementation examples with different infrastructures.