Promiscous Mode: In a network, promiscuous mode allows a network device to intercept and read each network packet that arrives in its entirety. This mode of operation is sometimes given to a network snoop server that capture and save all packet for analysis (for e.g. for monitoring network usage)
When a data packet is transmitted in a non-promiscous mode, all the LAN devices "listen to" the data to determine if the network address included in that data packet is theirs. if it is nt that data packet is passed on to the next LAN device until the device with the correct network address is reached. That device then receives and reads the data.
the promiscuous mode is something that needs to be supported by the network card. when the network card is in promiscuous mode, it accepts all packets, even if the destination MAC of the frame doesn't match its own MAC. However, broadcasts are accepted anyway. Without promiscuous mode frames with MACs other than one interface has are ignored (apart from broadcasts again).
A 802.11 LAN is based on a cellular architecture where the system is subdivided in to cells, where each cell (called Base Service Set or BSS, in the 802.11 nomenclature) is controlled by Base station (called Access Point , AP)
Even though a Wireless LAN can be formed by a single call called Access point, normal structure is that it will be formed by multiple cells which are connected with another medium such as a backbone which is called a Distribution System or DS. The backbone could be a LAN cable or wireless LAN itself.
The whole interconnected network cells including multiple cells, their access point and DS is seen to the upper layers of the OSI model as a single network. and is called a standard Extended service set (ESS).
The 802.11 standard also defines a concept called "Portal" which is actually a medium to interconnect between 802.11 and another 802 LAN. This also sometimes called translation bridge.
Very Good link on knowing the inner details of IEEE 802.11
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