X = 0,x = 6,y = 2。
Take x = 3 for the uplink and y = 2 for the downlink, (3,2)
Take y = 0 for uplink and x = 0 for downlink, (0,0).
Take y = 0 for uplink and x = 6, (6,0) for downlink.
Take y = 4 for uplink and x = 0 for downlink, (0,4).
Take y = 4 for uplink and x = 6 for downlink, (6,4)
*** 5 groups.