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

Building Automation, Wireless Technology and the InternetWhen noise is encountered it is usually due to a faulty connection.This noise can result in a lower-than-usual transmission rate. Cellularchannels are vulnerable to noise and interference which can changein intensity and frequency. Throughput can drop off quickly and theerror correction and speed-setting techniques used for land-line telephoneswill not help.The throughput may be cut in half when a large number of dataerrors are corrected. Compared to the faster modems the throughputseems slow and more costly, especially when sending and receivinglarge files.Cell ProtocolSeveral companies have developed special cellular protocols.Microcom created an extension to its MNP-10 protocol. Unlike modems,which try the highest speeds first and then settle for lower ones until areliable connection is achieved, MNP-10 starts at the low end and worksits way up to the highest reliable rate. This allows modems to connectfaster. MNP-10 boosts performance by shrinking and expanding the sizeof a data block as line conditions degenerate or improve. ZyXEL hasmodems with its ZyCellular protocol. AT&T Paradyne uses ETC (enhancedthroughput cellular).Cellular SecurityCellular telephone traffic, including data from cellular modems, iseasy to intercept with inexpensive equipment. In the past even RadioShack sold receivers capable of receiving cellular transmissions. Federallaws now prevent the sale of such devices, but many units still remainin use. While the chances of interception may be small, they are still veryreal. Unless some form of encryption is used, cellular modem users needto be careful about what they send over a cellular phone.CDPDThe advent of digital cellular phone systems provided a wholenew class of wireless technology called CDPD (cellular digital packetdata). CDPD is compelling businesses and consumers to convert from©2001 by The Fairmont Press, Inc. All rights reserved.