. Bell telephone magazine . to come, consider that high speed digitaltransmission systems, with their capacity for carryingmany different signals at once, will provide the mostefficient, the most economical and the highest qual- ity means of meeting these new needs looming onthe horizon. Because all kinds of signals — voice, TV, data —become alike once theyre converted into streams ofelectronic pulses, we can interleave pulses from dif-ferent sources and send several different kinds ofsignals over the same channel. We can monitor thequality of transmission, regenerate the pulses everymile or s
. Bell telephone magazine . to come, consider that high speed digitaltransmission systems, with their capacity for carryingmany different signals at once, will provide the mostefficient, the most economical and the highest qual- ity means of meeting these new needs looming onthe horizon. Because all kinds of signals — voice, TV, data —become alike once theyre converted into streams ofelectronic pulses, we can interleave pulses from dif-ferent sources and send several different kinds ofsignals over the same channel. We can monitor thequality of transmission, regenerate the pulses everymile or so and then convert them from pulse formback to their original form at the destination, says At Bell Laboratories digital transmission laboratory in Holmdel, Francis Rusin watches a transmission system of the future take of the one-day T4, this experimental system transmits 3,456 voice channels or two TV programs at once via the laserbeam in left foreground, and operates at 224 million pulses per second. 24 Richard A. Kelley, who is director of the digitaltransmission laboratory in Holmdel. Imagine that youre the postmaster in a local postoffice, confronted with the Christmas avalanche ofpackages. Theyre all sizes, shapes and , too, that you have a machine which canbreak down all packages into small units of the samesize and weight, give them identifying numbers, thenshoot them out through a tube to a distant postoffice. There another machine sorts them out, re-stores them to their original shapes and sizes, andgives them to the parcel post carrier. Obviously, you cant actually do that with pack-ages. But essentially that is what pulse code modula-tion does with electronic signals. Digital transmissionnot only allows us to fit signals from many differentsources on the same channel but it also eliminatesinterference between signals carrying different kindsof information, adds Mr. Kelley. The technique can also be valuable for other rea-sons. Fo
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