Data set diagnostic system

DETAILED DESCRIPTION FIG.
1 depicts a communication system, or network, in which the present invention is used.
Although use of the invention is particularly advantageous in extended networks, such as that shown in FIG.
25, the principles of the invention will first be explained with reference to the simpler network of FIG.
1.
In FIG.
1, a computer 2 communicates on a time shared basis with a plurality of data terminals 3a, 3b, .
.
.
3n.
A control data set, or modem, 10 is associated with computer 2.
Tributary data sets 4a, 4b, .
.
.
4n are associated with terminals 3a, 3b, .
.
.
3n, respectively.
Computer 2 transmits information to a particular terminal via data set 10, two-wire private line 11, and the associated one of data sets 4a, 4b, .
.
.
4n.
A terminal transmits information to computer 2 via its associated data set, private line 12 and data set 10.
Data sets 4a, 4b, .
.
.
4n and 10 provide several functions.
One is to correct for distortion and other channel irregularities which may cause, for example intersymbol interference.
The other is to modulate the data which is to be transmitted into, and demodulate it out of, the passband of lines 11 and 12.
The bandwidths of lines 11 and 12 are each divided into a primary and secondary channel, as shown in FIG.
7.
The primary channel carries modulated data, start-up signals and various test signals.
The secondary channel carries diagnostic and control information between data set 10 and each of data sets 4a, 4b, .
.
.
4n.
As described in detail hereinbelow, the present invention relates principally to the communications over the secondary channel.
Data sets 4a, 4b, .
.
.
4n and 10 are illustratively, all similar in design.
By way of example, FIGS.
2-5, when arranged as shown in FIG.
6, depict data set 10.
Data set 10 includes primary and secondary circuitries which are associated with communications over the primary and secondary channels, respectively.
In particular, the primary circuitry is comprised of primary signal processing circuitry 20, primary controller 30, and primary input/output (I/O) circuitry 80