The bandwidth of content being contributed to network users by service providers of metro and core networks is increasing rapidly. A main factor in this increase is new video services, especially High-Definition TV (HDTV). With modern compression techniques (such as MPEG-4, H.264 and VC-1), HDTV can be transmitted at 8-9 Mbps, and a Standard-Definition TV (SDTV) channel at 2-1.5 Mbps.
The metro and core networks that provide connections between the head ends and the central offices are typically based on optical fiber infrastructures, so they are usually able to cope with this increase in bandwidth. The end-user access network, however, is typically based on twisted-pair copper wires over which Digital Subscriber Line (xDSL) technology is used to provide communication rates of up to 10 Mbps with Asymmetric Digital Subscriber Line 2 Plus (ADSL2+, also known as International Telecommunication Union standard G.992.5), which allows for a single HDTV channel.
The network is represented in hierarchical fashion, with the following layers:                Core Layer        Aggregation Layer (also referred to as the “Metro Layer”)        Access Layer        
The end-user is in the Access Layer. The term “access edge” herein denotes the boundary between the Aggregation Layer and the Access Layer of a network. As a non-limiting example, a Digital Subscriber Line Access Multiplexer (DSLAM) with ADSL2 output to a copper twisted pair medium, as described above, exists in the Access layer on the access edge. Other devices besides a DSLAM may be used to accomplish the processing necessary for delivering data to end-users; in the descriptions and drawings herein, a DSLAM is used only as a non-limiting example of such equipment, for purposes of illustration, and is not intended to restrict the present invention to any specific configuration or use.
Currently, the average number of television sets per household is between 2 and 3, often requiring multiple different HDTV channels simultaneously. As a result, video over xDSL may not have sufficient bandwidth to compete with cable and satellite offerings.
One solution is to bring optical fiber into the end-user's premises (or very close to it), but the capital investment required for such a solution is still very high.