Avoiding collisions (more) idea:allow sender to "reserve"channel rather than random access of data frames:avoid collisions of long data frames sender first transmits small request-to-send(RTS)packets to BS using CSMA o RTSs may still collide with each other(but they're short) BS broadcasts clear-to-send CTS in response to RTS ▣RTS heard by all nodes o sender transmits data frame o other stations defer transmissions Avoid data frame collisions completely using small reservation packets! 6:Wireless and Mobile Networks 6-21 6: Wireless and Mobile Networks 6-21 Avoiding collisions (more) idea: allow sender to “reserve” channel rather than random access of data frames: avoid collisions of long data frames  sender first transmits small request-to-send (RTS) packets to BS using CSMA  RTSs may still collide with each other (but they’re short)  BS broadcasts clear-to-send CTS in response to RTS  RTS heard by all nodes  sender transmits data frame  other stations defer transmissions Avoid data frame collisions completely using small reservation packets!