SB 3100 = DOCSIS 1.0 max of 3.0 Gbps down 512kbps up SB 4100 = DOCSIS 1.1 max of 15 Gbps down 1.5Mbps up SB 5100/5120 = DOCSIS 2.0 max of 30 Gbps down 3.0Mbps up SB XXXX = DOCSIS 3.0 max of 150 Gbps down 15.0 up due out in 2007 according to Motorola. WAY ahead of comcast! The whitepaper did not address caps or burst speeds.