Data Flow Examples
Case 1: Packet from a station under one AP to another in same AP’s coverage area.
Case 2: Packet between stations in an IBSS.
Case 3: Packet from an 802.11 station to a wired server on the Internet.
Case 4: Packet from an Internet server to an 802.11 station.
Case 1: Communication Inside BSS
AP knows which stations are registered with it so it knows when it can send frame directly to the destination.
Case 2: Ad Hoc
Direct transmit only in IBSS (Independent BSS), i.e., without AP.
Note:
in infrastructure mode (i.e., when AP is present), even if B can hear A, A sends the frame to the AP, and AP relays it to B.
Case 3: To the Internet
MAC A determines IP address of the server (using DNS).
From the IP address, it determines that server is in a different subnet.
Hence it sets MAC R as DA.
Address 1: BSSID Address 2: MAC A Address 3: DA
AP will look at the DA address and send it on the ethernet.
AP is an 802.11 to ethernet bridge.
Router R will relay it to server.
Case 4: From Internet to Station
Packet arrives at router R – uses ARP to resolve destination IP address.
AP knows nothing about IP addresses, so it will simply broadcast ARP on its wireless link.
DA = all ones – broadcast address on the ARP.
MAC A host replies with its MAC address (ARP reply)
AP passes on reply to router.
Router sends data packet, which the AP simply forwards because it knows that MAC A is registered.
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