Charles J. Alpert Milos Hrkic Jiang Hu Andrew B. Kahng John Lillis Bao Liu Stephen T. Quay Sachin S. Sapatnekar A. J. Sullivan Paul Villarrubia Buffered Steiner trees for difficult instances. 4-9 2001 ISPD http://doi.acm.org/10.1145/369691.369699 db/conf/ispd/ispd2001.html#AlpertHHKLLQSSV01