packet 60 byte + 8 byte udp + 20 byte ip + 36 byte mac+llc
 = 124 byte = 992 bit

1Mbps
    144us preamble + 48us plcp header = 192us phy
    992 bit data == 992us
  = 1184us data frame
  = 10us sifs
    192us phy
    112 bit data = 112us
  = 304us
  sum 1498us
    

6Mbps
    16us preamble + 4 us plcp = 20 us phy
    16 bit service + 6 bit tail + 992 bit data = 1014 bits == 43 symb. == 172us
  = 192us data frame
    + 6 us extension time + 10 us sifs
  = 16 us ifs
    20 us phy
    16 bit service + 6 bit tail + 112 bit data = 134 bits == 6 symb. == 24 us
  = 44 us
