Level 3 Communications will provide a national fiber backbone to support DirecTV’s ambitious high-definition television expansion plans.

Financial terms were not disclosed, but Level 3 will supply bandwidth and data center services and upgrade DirecTV’s backbone to support and aggregate HDTV signals from local markets for rebroadcast to the DBS provider’s customers. Going back to a deal first agreed to in 1999, Level 3 already provides a “substantial portion” of DirecTV’s existing private line backbone for standard-definition video services.

Initially, DirecTV has tapped Level 3 to provide HD support in Atlanta, Boston, Chicago, Dallas, Denver, Los Angeles, New York, and San Francisco. It’s expected that DirecTV will use Level 3’s network and colocation services in 15 additional cities.

DirecTV, which has already tapped Tandberg Television to supply encoders for the early phases of its hi-def expansion, announced plans last year to tap an array of new satellites to offer hundreds of local HD channels and about 150 national HD channels.