Code-based filtering mechanism for reducing data-induced...

Details Code-based filtering mechanism for reducing data-induced... Code-based filtering mechanism for reducing data-induced...

1999-06-18

2004-03-23

Chin, Wellington (Department: 2664)

Multiplex communications

Diagnostic testing

Loopback

C379S022010

Reexamination Certificate

active

06711136

ABSTRACT:

FIELD OF THE INVENTION
The present invention is application relates in general to digital telecommunication networks and systems, and is particularly directed to the integration of one or more digital control code-based filtering routines into a test code sequence-based latching loopback mechanism of a digital data device, for reducing and/or preventing a data-induced latching loopback condition.
BACKGROUND OF THE INVENTION
FIG. 1
diagrammatically illustrates a reduced complexity example of a telecommunications network for delivering digital data service (e.g., 64 Kpbs service) from a remote location to data terminal equipment at a customer (end user) site. The network includes a source of digital communication data, such as a DDS service unit
110
, which is coupled to a communication path switch
112
, shown as a digital access cross-connect system (DACS), that terminates a ‘west’ end of a T-carrier link (such as a T-
1
fiber optic link)
111
. It should be noted that data may be coupled to the end user by way of a variety of data service units, such as but not limited to office channel unit data ports (OCUDP)s, digital signal
0
data ports (DS
0
DP)s, data service unit data ports (DSUDP)s, digital data service terminals (DDST)s, data service unit/channel service units (DSU/CSU)s, and similar equipment, such as frame relay (FR) equipment with built-in interfaces, shown at
130
.
The DACS
112
is operative to steer the (64 Kbps) data stream from the DDS service unit
110
into DS
0
channels of the T-carrier link
111
for distribution to remote customers by means of a channel bank
114
that terminates an ‘east’ end of the T-
1
link
111
. For this purpose, the channel bank
114
includes an office channel unit (OCU)
115
that directs a respective DS
0
channel over a 64 Kpbs connection
113
to a DSU/CSU
116
. The DSU/CSU
116
is coupled over a link
117
to data terminal equipment (DTE) or user interface
118
.
When maintenance is required on a data transport connection between the channel bank
114
and the customer's data terminal equipment
118
, it is customary practice to employ a test unit
120
of a network operating center, which provides diagnostic and trouble isolation functions, for transmitting various (in-band) interrogation and test or control code sequences to one or more of the digital data devices installed along the digital data transport path. In the illustrated network, digital data devices
115
,
116
monitor the data stream transmitted from the channel bank
114
for the presence of such control code sequences, and respond in accordance with the operational function dictated by a received control code sequence.
Where the test code sequence is defined to invoke a loopback, the digital data device responds by going into the particular type of loopback specified by the loopback control byte sequence. In the network diagram of
FIG. 1
, non-limiting examples of the loopback of interest include an OCU loopback at data path location
130
, a channel loopback at data path location
132
, or a DSU loopback at data path location
134
. The loopback control code sequences may be defined in accordance with well known network specifications, such as AT&T publication Technical Reference TR 62310 “DS
0
Digital Local Channel Description and Interface Specification”, August 1993.
The particular sequences employed have names and abbreviations as described in ANSI T1.107-1995 document and include: Transmission in Progress (“TIP”), Loopback Select (“LSC”), Loopback Enable (“LBE”), and Far End Voice (“FEV”). Each of these control code sequences is a stream of repeated bytes, where the bytes are predefined. For an illustration of the use of such in-band code sequences to interrogate and/or control the operation of one or more telecommunication services channel units, attention may be directed to the U.S. Patents to S. Killian et al, Nos. 5,390,179 and 5,574,723, entitled: “Remote Provisioning of Telephone Channel Unit Using Inband Digital Code Sequences Transmitted Over Tandem Link,” assigned to the assignee of the present application and the disclosures of which are herein incorporated.
FIG. 2
illustrates an example of a typical latching loopback test code sequence
210
, that is comprised of a set of repeated individual code sequences, sequentially transmitted as: a TIP sequence
212
—a don't care sequence X—an LSC sequence
214
—a don't care sequence X—an LBE sequence
216
—a don't care sequence X—a FEV sequence
218
. The don't care byte sequences X that are transmitted between the control code sequences
212
,
214
,
216
and
218
may be of different lengths and have different byte values.
One TIP code sequence is the repeated byte sequence: S
0111010
, S
0111010
, . . . , S
0111010
, where the TIP byte S
0111010
is repeated sequentially a prescribed number of times (e.g., at least 35 times). The bit “S” is a don't care (or X) value. Similarly, according to the above-referenced TR 62310 document, the number of LSC bytes in a loopback select sequence may comprise at least 35 bytes; the number of LBE bytes in a loopback enable sequence may comprise at least 100 LBE bytes; and the number of FEV bytes in a far end voice sequence may comprise at least 32 bytes.
FIG. 3
is a state diagram showing the operation of a conventional latching loopback mechanism employed by a currently commercially available digital data device, such as an Adtran D4 OCU DP, manufactured by Adtran Corp., Huntsville, Ala., to respond to the latching loopback code sequence of FIG.
2
.
FIG. 4
shows a prior art state transition table associated with the state diagram of FIG.
3
. As shown in the state diagram of
FIG. 2
, the digital data device of interest is initially in the monitor state
310
.
During the course of the transmission of data over the network, if a prescribed majority M out of N TIP sequence (e.g., M/N=31/32) is detected by the digital data service device's control processor, a TIP VALID transition
312
is invoked, and the conditional operational state of the device transitions from its initial monitor state
310
to the select state
320
. Namely, TIP VALID true means that M (e.g., 31) TIP bytes have been detected within a plurality of N (e.g., 32) sequential bytes being received from the digital data path.
Once in the select state
320
, if a prescribed majority M out of N LSC sequence (e.g., M/N=31/32) is detected, an LSC VALID condition
322
is invoked, and the conditional operational state of the device transitions from the select state
320
to the enable state
330
. While in the enable state
330
, if a prescribed majority M out of LBE sequence (e.g., M/N=93/96) is detected, an LBE VALID transition
332
is invoked, and the device state transitions from the enable state
330
to the FEV state
340
. Finally, in the FEV state
340
, if a prescribed majority M out of LBE sequence (e.g., M/N=7/8) is detected, an FEV DETECTED condition
342
is invoked, and the device state transitions from the FEV state.
340
to the latching loopback state
350
.
In order to exit the latching loopback state
350
(and return to the monitor state
310
), a TIP VALID condition
312
must be asserted true, or a manual reset is required. Also shown in the state diagram of
FIG. 3
are additional TIP VALID sequence paths
312
emanating from each of intermediate states
320
,
330
and
340
, and transitioning back to the select state
320
. Pursuant to the TR 62310 document, the state diagram of
FIG. 3
further contains respective ‘watchdog’ timer paths
360
, for aborting the latching loopback procedure from any of intermediate states
320
,
330
, and
340
, in order to reduce the probability of false loopback sequence detection from the contents of a monitored data stream.
A respective watchdog time path
360
is true (binary ‘1’) when the watchdog timer expires before the next expected byte sequence has been detected. For example, when in the select state
320
the LSC sequence is expected. If LSC VALID
322
is

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