jected to annoying and uncomfortable bursts of sound
SYSTEM FOR SIMULTANEOUS ANALOG AND generated by the CID data transmission.
DIGITAL COMMUNICATIONS OVER AN A heretofore system that has addressed this CID/CW
ANALOG CHANNEL problem uses a technique of muting all sound to the
5 conversing parties while the caller i.d. information is
BACKGROUND OF THE INVENTION being transmitted. This system has the advantage of
This invention relates in general to devices for pro- providing an error free channel for the CID data com
viding simultaneous transmission of analog communica- munication, but it has a significant disadvantage in that
tion and sporadic bursts of digital data over a band- it causes the conversation to be muted for the three to
width limited analog channel, and in particular to such 10 four seconds it takes to transmit the CID information,
devices that remove from the band available for the Another heretofore proposed system for CID/CW
analog communications only those frequencies neces- involves using a spread spectrum signal for CID data
sary to accomplish the data transmissions and only dur- transfer mixed with the voice signal. This system is too
ing the data transmissions. expensive and too complicated to implement. More
A need exists for a way to transfer, from time to time, 15 over, the spread spectrum signal will be heard as noise
bursts of digital data over an analog channel simulta- to the user reducing the clarity of the voice communica
neously with analog communications without degrad- tion during CID transfer.
ing the fidelity of the analog communications except The present invention avoids the muting without only slightly during the bursts of digital data. Such a creating noise and is able to transmit CID information need exists in the art of telephone communications, 20 over a channel with no interruption in voice communiparticularly with the introduction of a feature com- cation and without subjecting the conversing parties to monly called "caller identity delivery" also known as the aforesaid annoying and uncomfortable burst of "caller i.d." (hereinafter sometimes referred to as sound. It has the further advantage of not reducing the "CID"). This feature provides a user with certain iden- band of frequencies available on the channel for voice tifying information of a caller, such as telephone num- 25 communications except only slightly during the brief ber and/or the name of the caller. This identifying rn- CID data transmissions. It ^so provides an error free formation, i.e. data, is transmitted digitally from a tele- h for the data communications. phone company to its users telephone equipment via Qther advanta ^ attributes ^ either discussed the same voice frequency channels used for voice com- m Qr can be ,eaned from ... of ^ herdn_ munication for display on their respective equipment. In 30 ° . ° the case where the user is not using the telephone when T> • J c i_- • a caller rings, the CID information is transferred be- PreTM me*ods °f f hTMmS ^ tween the first and second ring signals. The user can mlss,0vn of sf?t?TMd *^J%? ... then view the information to decidewhether to answer Pat Nos" ^f.'3,11' 4>512>013 4,280,020. These the telephone 35 mventlons multiplex the data and the analog signal The techniques for transmitting digital data over an therebv continuously degrading the quality of the anaanalog channel such as a voice frequency channel are ^S112!
well known in the art. For example transmission of the SUMMARY OF THE INVENTION digital data can be, and is most commonly, accomplished using a technique called "FSK" or frequency 40 ^ obiect of this invention is to maintain the maxishift keying. For another example, digital data can also mum possible fidelity of an analog signal traversing an be transmitted over such channels by a technique called analog channel while providing error free data commu"PSK" or phase shift keying. Both of these techniques nications during spurious intervals without muting the utilize a portion of the frequency spectrum available on analog signal.
the channel. 45 A, further object of this invention is to provide a A conflict can arise when a user has the CID feature system for transmitting a digital signal simultaneously and also has a telephone feature commonly called "call with an analog signal without errors that could be introwaiting." (The combination of the two features is com- duced by the analog signal, and with only a slight monly called "caller i.d. on call waiting" hereinafter change to the frequency spectrum of the analog signal, sometimes referred to as "CID/CW"). If a user's equip- 50 A further object of this invention is to provide a ment is connected to another party, the call waiting system for clear and error free intermittent data cornfeature alerts the user to the presence of a waiting call munications by switching into the system notch filters by a distinctive audible indication. The user can then that attenuate the data transfer frequencies, and after elect to receive the waiting call by a known keying the data communications are complete, the notch filters operation. The conflict arises whenever the user is tele- 55 are switched out of the system thereby providing maxiphoned by a caller while the user is engaged in a tele- mum analog fidelity of the voice signal, phone conversation with another party and the caller's These and other objects are achieved by a system for CID information is transmitted to the user's receiver. simultaneously transmitting analog and digital signals The CID transmission takes place almost automatically via an analog channel comprising a transmitting end after the user is alerted to the new call so that this infor- 60 comprising means for removing from the analog signal mation can be used to help decide whether to take the those frequency components used to construct the diginew call. Since both the analog signals of the conversa- tal signal resulting in a first interim signal, the removal tion between the user and the other party, and the digi- of said frequency components being for the purpose of tal signals corresponding to the caller's CID informa- preventing errors which could be caused by the prestion are transmitted over the same analog channel, there 65 ence of said frequency components in the analog signal, can be audible interference between the two while the means for producing a second interim signal comprising CID information is being transmitted. The user and the at least a combining of the first interim signal and the other party involved in the conversation can be sub- digital signal, and means for transmitting the second