The Physical Layer

The physical layer is concerned with creating 1s and 0s on the physical medium with electrical impulses/voltage changes. Common physical layer communication specifications include the following:

• EIA/TIA-232—Electrical Industries Association/Telecommunications Industry Association specification used for communicating between computer devices. You can use different connectors; this interface is often used for connecting computers to modems.

• V.35—International Telecommunication Union Telecommunication Standardization Sector (ITU-T) signaling mechanism that defines signaling rates from 19.2 Kbps to 1.544 Mbps. This physical interface is a 34-pin connector and also is known as a Winchester Block.

• RS-449—Uses 37 pins and is capable of longer runs than RS-232.

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