The present invention relates, generally, to a communication system for transmitting both data and television signals to and from one or more user work stations. More particularly, the invention relates to a communication system employing an industry standard local area network (LAN) or wide area network (WAN) to communicate on a broad spectrum of frequencies.
As used hereinafter, the term "backbone communication network" is intended to mean an electrical signal transmission facility which makes electrical signals available to a plurality of user work stations but which is not directly connected to any work station. The backbone network may form a part of a local area network (LAN) or wide area network (WAN).
The term "baseband signals" is intended to mean information signals within the frequency range of 0 to 100 MHz. Computer data is normally transmitted by baseband signals. The term "broadband signals" is intended to mean information signals at a frequency higher than the highest baseband frequency--typically in the frequency range of
100 to 500 MHz. If the upper limit of the baseband range terminates at 50 MHz, the lower limit of the broadband range can commence at this frequency. Video information (i.e., television) is normally transmitted by broadband signals.
A so-called "baseband network" is designed to transmit baseband signals, whereas a "broadband network" is designed to transmit broadband signals.
The term "balanced signal mode" or "balanced mode" is intended to mean a signal condition wherein the amplitudes of the signals applied on each of the wires of a "twisted pair" cable are oppositely poled relative to the cable shield or ground.
The term "unbalanced signal mode" or "unbalanced mode" is the signal condition wherein the applied signal amplitudes are likewise or similarly poled on each of the wires of a twisted pair cable relative to the cable shield or ground.
The term "equally unbalanced signal mode" or "equally unbalanced mode" is the signal mode wherein the signal amplitudes are likewise poled and of equal amplitude on each of the wires in the twisted pair cable relative to the cable shield or ground.
As so-called "multimedia" are incorporated into desktop computers (also known as "personal computers" or "PC's") and as "videoconferencing" is merged into user work stations which incorporate a PC, the increased system integration requires a substantial increase in the quantity of transmitted information as compared to the information conventionally transmitted on an industry standard local area network (LAN) or wide area network (WAN).
To this end, it is known to transmit both baseband and broadband signals on a common backbone network which, in turn, is connected to a plurality of user work stations by a distribution network. The U.S. Pat. No. 4,885,747 to Foglia discloses a so-called "filter coupler" or "F-coupler" by which the baseband signals are transmitted between a backbone network and a PC via a twisted pair shielded cable in a balanced mode and the broadband signals are transmitted between the same backbone network and the same PC via the same shielded cable in an unbalanced mode. The disclosure of this U.S. patent is incorporated herein by reference.
Among the drawbacks of the communication system disclosed in the U.S. Pat. No. 4,885,747 is the requirement that a specific type of twisted pair shielded cable must be used as the transmission line between a backbone network and each individual user work station. As specified by IBM Corp., this transmission line is so-called "type 9" wire. This requires, in some cases, recabling an entire floor or an entire building to accommodate this system.