HVAC Control in the New Millennium.pdf - HVAC.Amickracing

HVAC Control in the New Millenniumbered, they can be resent quickly, even out of order and correctly reassembledby the receiving modem without warming the throughput.The Intel Wireless Modem uses firmware that allows the modem touse standard AT modem commands. Other wireless modems may requirespecial software to operate since the data packets are assembledand disassembled by the computer. AT-type RF modems can be used byany popular communications package since the packet assembly/disassembly(PAD) hardware is right in the modem.Circuit-switched Cellular TechnologyVoice-band cellular or circuit-switched cellular systems use cellulartelephone networks, their land lines and microwave technology to makethe connection. Cellular phones are part of the mobile radio-telephonesystem that transmits data over a range of geographic sites, called cellswhich use low-power transmitters and receivers. The cellular phone cantransmit data instead of voice using the audio signals produced by amodem. It is similar to a connection with two land-line-based modems.But, you can remotely access your LAN or call other mobile computers.You substitute a cellular phone for its land-line-based version.The equipment needed for cellular data transmission is a specialtype of modem. The cellular modem connects to a cellular phone. Thereare also cellular adapters, which connect to both the modem and thecellular phone.Most cellular modems can also use land lines to transmit data andto send and receive fax images. These eliminate the need for a separateland-line-based modem.Not all cellular phones, modems, and adapters are compatible. Acellular modem or adapter must be able to control the bus of the cellularphone. Some companies such as NEC and Mitsubishi use open specificationswhich are widely supported by various cellular modem andadapter vendors. Others are not quite as open, and their modems andcellular phones must be used together.Cellular ProblemsCellular channels can have problems with signal quality. Landbasedtelephone lines offer more consistent quality with minimal noise.©2001 by The Fairmont Press, Inc. All rights reserved.