The answer to question 01: They can guarantee a certain amount of bandwidth. The answer to question 02: T1s are 1.544 Mbps, whereas E1s are 2.048 Mbps; E-carrier has 30 channels, while T-carrier has 24. The answer to question 03: The 10GbE WAN PHY (10GBASE-SW, -LW, and -EW) and OC-192 are compatible.