Layer 1. The Physical Layer

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Layer 1. The Physical Layer

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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