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This bottom layer is responsible for activating, maintaining, and deactivating the physical connection for bit transfers between "Data Link Entities." It provides the hardware means of sending and receiving a bit stream (a "bit pipe") through the network at the most basic electrical, mechanical, functional and procedural levels. An example of a physical layer ISO standard is the RS-232 interface. Devices at this level include cables, connectors, hubs, multiplexers, repeaters, receivers, switches, the 802.11 access point and other hardware.
Here is a simple mnemonic phrase to remember the correct order of the layers:
7 Application—All
6 Presentation—People
5 Session —Seem
4 Transport—To
3 Network—Need
2 Data Link—Data
1 Physical—Processing
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