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CCIE Security Exam Certification Guide by Henry Benjamin

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Asynchronous Communications and Access Devices

An asynchronous (async) communication is a digital signal that is transmitted without precise clocking. The RS-232 session between a router and PC through the console connection is an example of async communications. Such signals generally have different frequencies and phase relationships. Asynchronous transmissions usually encapsulate individual characters in control bits (called start and stop bits) that designate the beginning and the end of each character.

For example, the auxiliary port on Cisco routers can be used to connect a modem and allow out of band (not via the network) management.

The Cisco AS5300 is an example of a device that supports both synchronous and async communication, such ...

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