US Robotics USR2450 Informações Técnicas descarregar pdf (Página 18)

V 2.2 Copyright SystemExperts 2001,2002,2003

Key Factors in Technology

n Regulation

n Determines who gets what and how

n In US “competition” was king

n Regional Bell’s and one other (1/2 each)

n In Europe “interoperability” was king

n Government owned “Bells”, so no competition, so let’s

interoperate

n Need to exchange billing and accounting information

n Security was designed to protect against fraud

n As opposed to protecting your data

V 2.2 Copyright SystemExperts 2001,2002,2003

Cellular Basics

n Two Connections Types

n Circuit Switched

n Packet Switched

n More efficient (~10x) than circuit switched

n Transmission techniques

n Frequency Division Multiple Access (FDMA)

n Frequency range is divided into channels

n Dedicated channel/frequency per call

n Time Division Multiple Access (TDMA)

n Each call gets a “timeslot” of time on a certain frequency

n Code Division Multiple Access (CDMA)

n Uses spread spectrum techniques (i.e., is spread over the

available frequencies)

n Each call has a unique code

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US Robotics USR2450 Informações Técnicas Página 18