A computer network (100, 400, 500, 600, 601, 700) comprising: a first lower level switch (110a, 410a, 510a, 610, 705d, 705e, 705f) having a first port and a second port; a second lower level switch (110b, 410b, 510b, 610, 705d, 705e, 705f) having a first port and a second port; an upper level switch (105, 405, 505, 605, 705a, 705b, 705c) having a first port directly coupled to the first port of the first lower level switch and a second port directly coupled to the first port of the second lower level switch; a first passive optical splitter (115, 415, 515, 615, 715) having a first port coupled to a third port of the upper level switch, a second port coupled to the second port of the first lower level switch, and a third port coupled to the second port of the second lower level switch, the first passive optical splitter configured to transmit signals received at its first port as output signals on both of its second and third ports; and a controller coupled to the first lower level switch, the second lower level switch, and the upper level switch, the controller configured to control transmission of data by the first lower level switch, the second lower level switch, and the upper level switch, wherein the controller is further configured to control the first lower level switch and the second lower level switch to transmit data packets through the first passive optical splitter to the upper level switch by alternately allocating respective transmission time slots to the first lower level switch and the second lower level switch based on relative bandwidth demands of the first lower level switch and the second lower level switch. a first lower level switch (110a, 410a, 510a, 610, 705d, 705e, 705f) having a first port and a second port; a second lower level switch (110b, 410b, 510b, 610, 705d, 705e, 705f) having a first port and a second port; an upper level switch (105, 405, 505, 605, 705a, 705b, 705c) having a first port directly coupled to the first port of the first lower level switch and a second port directly coupled to the first port of the second lower level switch; a first passive optical splitter (115, 415, 515, 615, 715) having a first port coupled to a third port of the upper level switch, a second port coupled to the second port of the first lower level switch, and a third port coupled to the second port of the second lower level switch, the first passive optical splitter configured to transmit signals received at its first port as output signals on both of its second and third ports; and a controller coupled to the first lower level switch, the second lower level switch, and the upper level switch, the controller configured to control transmission of data by the first lower level switch, the second lower level switch, and the upper level switch, wherein the controller is further configured to control the first lower level switch and the second lower level switch to transmit data packets through the first passive optical splitter to the upper level switch by alternately allocating respective transmission time slots to the first lower level switch and the second lower level switch based on relative bandwidth demands of the first lower level switch and the second lower level switch.