1. In a multi-speed serial bus having a tree topology, a method for establishing an optimal data transmission rate between a first node and a second node comprising the steps of: upon completion of establishing said topology, determining a common ancestor node between said first node and said second node; comparing the data transmission rate of said first node with the data transmission rate of each node between said first and said ancestor node; setting the data transmission rate from said first note to said ancestor node to be equal to the lowest data transmission rate associated with any node between and including said first node and said ancestor node; comparing the data transmission rate of said second node to each node between and including said second node and said ancestor node; and establishing the data transfer rate between said first node and said second node as being the transfer rate associated with any node between said first node and said ancestor node and between and including said second node and said ancestor node, which any node has the lowest data transmission rate amongst said nodes.