Testing of ISDN line via auxiliary channel signaling

Details Testing of ISDN line via auxiliary channel signaling Testing of ISDN line via auxiliary channel signaling

1997-12-03

2001-02-06

Jung, Min (Department: 2739)

Multiplex communications

Diagnostic testing

Loopback

C370S524000, C379S021000

Reexamination Certificate

active

06185191

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to telecommunication systems, and is particularly directed to a communication and testing control mechanism, that is incorporated within a craftsperson's test set having an architecture of the type described in the above-referenced '117 application, for facilitating the testing of an ISDN communication circuit.
BACKGROUND OF THE INVENTION
As described in the above-referenced '117 application, a variety of telecommunication test units have been proposed for testing digital signalling circuits. Such digital signaling circuits may include, but are not limited to, those transporting high bit-rate digital subscriber line (HDSL) signals, asymmetrical digital subscriber line (ADSL) signals, digital data service (DDS) signals and integrated services digital network (ISDN) signals. Unfortunately, such conventional test units are relatively cumbersome and hardware-intensive devices, that are customarily resident in a telcom service office or other fixed system installation, affording only a single point of access to the circuit to be tested.
A non-limiting example of such a conventional test unit is described in the U.S. Pat. No. 5,208,846, to Hammond et al, entitled: “Subscriber Loop Tester for Telephone Switching Systems.” In order to be connectable with different types of telecommunication circuits, the Hammond et al test unit contains different types of line interfaces/jacks. Determining which jack is to be used requires that the test system operator have a priori knowledge of the communication link to which the test set is to be coupled. Without this knowledge, the user does not know to which jack the line should be connected, and cannot readily configure the test unit to support a particular user interface and associated termination hardware.
As noted above, because conventional test units are relatively large and fixed pieces of equipment, they are not readily suited for use in the field (i.e., they are not portable). As a consequence, they are not readily interfaced with any accessible location of a communication link. This relatively poor facility of transport and ready connection to any location along a link to be tested also limits the practicality and effectiveness of such test units.
These shortcomings have become a particular concern to telecommunication service providers, especially with the continuing expansion and demand for integrated services digital network (ISDN) services. Not only is there currently a need for a practical, portable test set that is capable of testing already installed ISDN circuits, but one which can perform ‘dry loop’ line testing, prior to its use for ISDN service; namely, there is a need for an ISDN test device that will permit a circuit to be ‘prequalified’ (as ISDN-capable), before ISDN equipment is purchased and connected to the line to be used for ISDN service.
Advantageously, the portable test set described in the above-referenced '117 application employs a communication architecture that is readily interfaced with virtually any location of a link/circuit to be tested, so as to allow testing of the link, irrespective of its configuration (e.g., two-wire vs. four-wire), or the type of signals that may be conveyed over the link (analog or digital). In addition to circuitry for testing the operation of a standard analog (POTS) line, the portable test set described in the '117 application contains a digital communications controller and associated digital signalling interface components, including both ‘U’ interface and ‘S/T’ interface circuits.
Thus, the test set can be interfaced with either a two-wire network link or a four-wire customer premises link, and may transmit and receive ISDN bearer channel messages over either type of circuit. The contents of the bearer channel messages may be defined to evoke prescribed responses from a companion test set coupled to another portion (relatively far end) of the communication circuit of interest, so that the circuit linking the two test sets may be tested. When two test sets are coupled to spaced apart locations of the circuit/line under test, they may operate in respective master and slave modes, allowing a craftsperson using the master test set to initiate a bit error rate test (BERT) from one end of the circuit, and derive a measure of the operational performance characteristic of the in-between segment of the circuit.
SUMMARY OF THE INVENTION
The present invention is directed to an enhancement of the ISDN communication and testing capability of the test set described in the '117 application, that not is only capable of performing line prequalification and post installation testing, but does so in a manner that simplifies the interaction between the user/craftsperson and the test set, thereby minimizing line testing inaccuracies (which often depend upon the skill and familiarity of the technician with ISDN communications) and improving performance.
Pursuant to a first aspect of the present invention, dry loop prequalification testing of a (two-wire) ISDN U-interface is conducted by coupling a test set as a line termination (LT) unit to a central office end of the line, and using the embedded operations channel (eoc) to conduct a prescribed message exchange sequence with a network termination (NT) unit (such as another test set, or a NT-
1
device) at the customer premises. In this dry loop mode of eoc testing of the two-wire ISDN line from the central office, there is no connection between the U-interface and the central office switch (and therefore no powering of the two-wire line by the central office). All signalling is effected from the test set's two-wire ‘U’ interface chip. Where another test set of the type described in the '117 application is coupled to the ISDN line at the customer premises, the line is also disconnected from any terminal equipment at that point. A typical, but non-limiting, case would involve the use of one or a pair of test sets to ISDN-prequalify one or more lines of a bundle of two-wire pairs within already installed communication cable.
In accordance with the eoc-based message exchange sequence, a user or craftsperson operating a sourcing test set (as an LT device at the central office) activates a MENU key on the test set keypad, which causes the test set's LCD display panel to display a list of options available to the user, one of which is a bit error test (BERT). The BERT option is selected via a numeric key on the keypad associated with the listing in the displayed menu option. In response to this key command selecting the BERT option, the control software executed by the test set's supervisory microcontroller causes the display unit to display a list of prescribed parameter options (including the data rate to be employed (e.g., 56 Kbaud or 64 Kbaud), the length of time the test is to be run, and which bearer channel (B
1
, B
2
or both B
1
and B
2
) is to be looped back for conducting the BERT). Via the keypad, parameter values for the listed menu are entered.
Once the list of parameter options has been entered, the user simply operates a soft START key displayed on the test unit's display screen, which automatically causes a master-slave message exchange sequence to take place, beginning with the transmission of a first message (CLEAR ALL LOOPBACKS) over the embedded operations channel (eoc) to the far end device. In response to this message, the far end (slave) device clears all loopbacks (on each of the B
1
, B
2
channels), and transmits a return message (LOOPBACKS CLEARED) to inform the master site that all loopbacks have been cleared.
In response to receiving the LOOPBACKS CLEARED return message, the master test set transmits an ACTIVATE LOOPBACK message to the far end device. The ACTIVATE LOOPBACK message identifies which bearer channel(s) is to be looped back (as previously menu-selected by the user). In response to the ACTIVATE LOOPBACK message, the slave device loops back the channel or channels specified in the eoc message and returns a mess

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