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The widespread deployments of Wireless LANs are underpinned by two most popular variants of IEEE 802.11 standards, 802.11b and 802.11g. The 802.11g extends 802.11b to support higher data rate via new OFDM-based physical layer, but both of them operate at 2.4GHz band and perform medium access with the same MAC protocol. When the 802.11b and 802.11g devices co-exist in the overlapping coverage area, the interoperability between them needs to be dealt with. The 802.11g defines a protection mechanism to avoid frame collisions between 802.11b and 802.11g devices. Since the legacy 802.11b devices cannot notice a busy channel by sensing the OFDM-modulated 802.11g frames, extra frames (e.g., CTS-to-self frames) are introduced for channel reservation in the protection mechanism.
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