Madge Networks 802.11b Manuel d'utilisateur télécharger pdf (Page 30)

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!

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Madge Networks 802.11b Manuel d'utilisateur Page 30