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| United States Patent |
5,367,394
|
|
Chuter
, et al.
|
November 22, 1994
|
Test apparatus
Abstract
A test apparatus is designed for use with a TPON system including a headend
station connected via a fibre optic network to a plurality of
terminations. The test apparatus is a self-contained unit including a
connection for linking the apparatus to a termination, a first detection
circuit which detects status signals generated by the termination, and a
second detection circuit which detects alarm signals generated in the
head-end station and transmitted to the termination in a downstream data
frame. The test apparatus in response to the first and second test
circuits provides an output which indicates the condition of the
termination. In one example, a series of indicator lamps formed on the
housing for the test apparatus are lit to provide the appropriate output.
| Inventors:
|
Chuter; Jeremy B. (Suffolk, GB2);
Hale; Michael A. (Essex, GB2);
Clarke; Donald E. A. (Essex, GB2)
|
| Assignee:
|
British Telecommunications public limited company (London, GB2)
|
| Appl. No.:
|
050028 |
| Filed:
|
April 29, 1993 |
| PCT Filed:
|
November 21, 1991
|
| PCT NO:
|
PCT/GB91/02060
|
| 371 Date:
|
April 29, 1993
|
| 102(e) Date:
|
April 29, 1993
|
| PCT PUB.NO.:
|
WO92/10036 |
| PCT PUB. Date:
|
June 11, 1992 |
Foreign Application Priority Data
| Nov 22, 1990[GB] | 9025399 |
| Nov 23, 1990[GB] | 9025492 |
| Current U.S. Class: |
398/33; 370/241; 398/15; 398/94; 714/712 |
| Intern'l Class: |
H04B 010/08 |
| Field of Search: |
359/110,125,132,137,143,167
371/20.1,29.1
370/13
|
References Cited [Referenced By]
U.S. Patent Documents
| 4516216 | May., 1985 | Armstrong | 364/514.
|
| 5046807 | Sep., 1991 | Unitt | 359/137.
|
| 5153764 | Oct., 1992 | Faulkner et al. | 359/167.
|
| Foreign Patent Documents |
| 0137339 | Aug., 1983 | JP | 359/110.
|
| 0143619 | Jun., 1990 | JP | 359/110.
|
| 2229881 | Oct., 1990 | GB | 359/110.
|
| WO88/09093 | Nov., 1988 | WO.
| |
| 2007432 | Apr., 1992 | WO | 359/110.
|
Other References
Patent Abstrcts of Japan, No. JP58164357, Sep. 29, 1983, Kazumi, "Title
Monitoring Control System".
IEEE Global Telecommunications Conference, Globecom 85, vol. 3, No. 44.5, 4
Dec. 1985, New Orleans, Louisiana, pp. 4451-4456, D. G. Allan et al,
"Design of Integrated Surveillance Systems for High Capacity Fiber
Systems".
|
Primary Examiner: Chilcot, Jr.; Richard E.
Assistant Examiner: Negash; K.
Attorney, Agent or Firm: Nixon & Vanderhye
Claims
We claim:
1. A test apparatus for use with a passive optical network (PON) system
having a head-end station connected via a fibre optic network to a
plurality of terminations, each termination including means to carry out
self-diagnostic procedures and to generate status signals for transmission
to the head-end station, said test apparatus comprising:
means for direct connection with one of said terminations at the site of
the connected termination and for data communication with that
termination,
first detection means to detect status signals generated by the termination
connected thereto,
second detection means to detect alarm signals in a data frame transmitted
from the head-end station via the PON and received at the termination
connected thereto, and
indication means responsive to the first and second detection means to
provide an output indicative of the condition of the termination connected
thereto.
2. A test apparatus according to claim 1, for use with a PON system in
which the head-end station and the terminations include means to transmit
and receive data frames having a plurality of basic frames preceded by a
header portion, each downstream basic frame including control channels
addressed to different respective terminations, and each control channel
including one or more bits in a predetermined position which are set by
the head-end station to indicate an alarm condition;
said second detection means including means for reading bits in the
predetermined bit position in frames received at the termination connected
thereto.
3. A test apparatus according to claim 1, for use with a PON system in
which each termination includes a dedicated asynchronous serial interface
for data communication,
said means for data communication including means to control transfer of
data via said interface.
4. A test apparatus according to any one of the preceding claims, including
means for generating a signal for transmission via the connected
termination to the head-end station.
5. A test apparatus according to claim 1 including means for generating a
laser inhibit signal for transmission to the termination to turn off a
laser optical source within the termination.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to test apparatus, and, in particular, to
apparatus suitable for use in conjunction with a passive optical network
(PON) system.
2. Related Art
The applicant's International patent applications numbers GB 90/01758
(WO91/08623) and GB 91/00100 describe a TPON (Telephony on a Passive
Optical Network) system designed to carry data via a Bit Transport System
(BTS). The TPON system includes a head-end station having a time division
multiple access (TDMA) master which assembles incoming exchange traffic
into TDMA frames. These frames are broadcast via an optical stage onto a
fibre network. Each of a number of terminations connected to the network
recognizes and responds to an appropriately addressed portion of the data
in the broadcast frame and ignores the remainder of the frame.
The header portion of each frame includes regions used for the monitoring
and control of the system. In particular, as described in the above
mentioned applications, upstream TDMA frames may include a ranging check
pulse transmitted by a termination. In response to this ranging check
pulse the head-end station transmits control signals to the termination to
modify the timing of transmissions from the termination so as to correct
for any variations in the time of receipt of the transmissions. The
transmission from a termination is arranged to be delayed, with respect to
the receipt of a TDMA frame, by a certain amount as determined by the
head-end station such that the terminal transmission is in its correct
place in the upstream TDMA frame received at the head-end station. The
head-end station is typically arranged to generate an alarm signal if the
terminal transmission delay as measured by the receipt of the ranging
pulse falls outside a predetermined range. The head-end station may also
transmit a diagnostic signal onto the network, as described in our
International patent application number GB 91/01815.
While monitoring and control procedures of the type outlined above are
effective once the TPON system is fully installed and running they are not
in themselves capable of providing all the diagnostic functions necessary
for a termination whilst that termination is being installed. Moreover
those diagnostic functions which can be carried out provide an output in
the form of alarm signals or other indications of the state of the network
only at the head-end station. The relevant information is not then
available directly for use by, for example, an engineer installing a
termination at a position remote from the head-end station.
BRIEF SUMMARY OF THE INVENTION
According to the present invention there is provided a test apparatus for
use with a PON system comprising a head-end station connected via a fibre
optic network to a plurality of terminations, each termination being
arranged to carry out self-diagnostic procedures and to generate status
signals for transmission to the head-end station, the apparatus being
characterised by means for data communication with a said termination,
first detection means arranged to detect, in use, status signals generated
by the termination, second detection means arranged to detect, in use,
alarm signals in a data frame transmitted from the head-end station via
the fibre optic network and received at the termination, and indication
means responsive to the first and second detection means to provide an
output indicative of the condition of the termination.
The present invention provides a test apparatus capable of carrying out
local diagnostic tests on a termination, and also of providing local
access to diagnostic procedures carried out by the head-end station. Such
an apparatus greatly facilitates the work, for example, of an engineer
installing a new termination by making it possible for that engineer to
carry out a range of diagnostic tests on site.
In a test apparatus for use with a PON system in which the head-end station
and the terminations are arranged to transmit and receive data frames
comprising a plurality of basic frames preceded by a header portion, each
downstream basic frame including control channels addressed to different
respective terminations, and each control channel including one or more
bits in a predetermined position which are set by the head-end station to
indicate an alarm condition, preferably the second detection means
includes means for reading bits in the predetermined bit position in a
frame received at the termination.
In a test apparatus for use with a PON system in which each termination
includes a dedicated asynchronous serial interface for data communication,
in use, with a test apparatus, preferably the means for data communication
is arranged to control, in use, transfer of data via said interface.
Preferably the test apparatus includes means for generating a signal for
transmission via the termination to the head-end station. Preferably the
test apparatus includes means for generating a laser inhibit signal for
transmission to the termination to turn off a laser optical source within
the termination.
BRIEF DESCRIPTION OF THE DRAWINGS
An apparatus in accordance with the present invention will now be described
in detail with reference to the accompanying drawings in which:
FIG. 1 is a block diagram of a TPON system;
FIGS. 2a and 2b are downstream and upstream TDMA frames respectively;
FIG. 3 is a diagram showing a termination and test apparatus in greater
detail; and
FIG. 4 is a plan of the tester of FIG. 3.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS OF THE INVENTION
A TPON system comprises a head-end station 1, a number of terminations 2,
and a passive fibre optic network 3 linking the head-end station 1 to the
terminations (e.g., subscriber stations or outstations) 2. Although, for
clarity, only three terminations are shown, in practice many more
terminations will be connected to a single head-end station. Typically the
head-end station is located in a local telephone exchange and the
terminations 2 are subscriber stations in domestic or commercial premises
or street cabinets in the neighbourhood of the local exchange.
The head-end station 1 broadcasts data over the fibre network 3 as time
division multiple access (TDMA) frames having a predetermined format. The
frames include control channels addressed to specific ones of the
terminations 2 to control, amongst other parameters, the amplitude and
timing of the optical signals transmitted onto the fibre network 3 by the
terminations 2.
In the upstream direction, each termination 2 transmits data in a
predetermined time slot, which data is assembled into a TDMA frame at the
head-end station 1.
FIGS. 2a and 2b show the format of downstream and upstream frames,
respectively. Basic data is communicated in eighty basic frames BF1 . . .
BF80. The basic frames BF1 . . . BF80 are preceded by a header portion H
which, in the upstream direction, includes a phase-2 ranging section R,
720 bits long. Each termination 2 is arranged to transmit onto the fibre
network 3 a ranging pulse timed to arrive at a respective predetermined
position within the ranging section R. The head-end station 1 determines
the phase of each arriving ranging pulse and then transmits control
signals to the respective termination 2, in the control portion of the
basic frames, to advance or retard the timing of the transmission.
In the downstream direction, the header portion includes a region D which,
as described in our above mentioned patent application number GB 91/01815,
includes an optical time domain reflectometry (OTDR) diagnostic signal.
The head-end station 1 detects any return of the OTDR signal occurring as
the result of a partial or complete break in the network.
Each control channel in the downstream basic frames includes three mode
bits which may be used, as described in further detail below, to
communicate alarm signals from the head-end station 1 to a termination 2
for detection by a test apparatus T connected to the termination 2.
FIG. 3 shows the test apparatus T and the respective termination 2 in
greater detail.
The front end of the termination 2 comprises an optical stage OS comprising
an optical receiver RX which receives optical signals from the network and
using an appropriate photodetector converts them to electrical signals,
and an optical transmitter TX, which carries out the converse process,
using an optical source such as a laser diode to convert electrical
signals into optical signals for transmission onto the network in the
upstream direction. Data from the optical stage OS is received and decoded
in a Bit Transport System (BTS) slave S which recognizes those portions of
incoming TDMA frames having an address appropriate to the particular
termination 2. The corresponding traffic data is then decoded and output
to a line interface L. The BTS slave S also carries out various control
and supervisory functions in response to control data in the incoming TDMA
frame. In particular, it generates ranging pulses for transmission to the
head-end station 1, and adjusts the timing of transmissions of data from
the termination 2 in response to control signals generated and transmitted
from the head-end station 1.
After the termination 2 has been installed at a desired location, a test
unit T is connected to the termination, as shown in FIG. 3. The tester T
includes a controller C arranged to communicate data with the termination
2 via a UART interface TI/F. The test procedures fall into two categories.
Firstly, local self-diagnostic test procedures are carried out by the
termination independently of the head-end station. The BTS slave S carries
out a number of diagnostic procedures to ascertain, for example, that the
optical stage is operational and responds appropriately to an output from
the BTS slave S. Similarly the BTS slave S will check that there is
electrical continuity between the slave S and the optical stage OS and
between the slave S and the line interface L. When the appropriate
diagnostic procedures have been completed then the slave S sends a series
of alarm indications to the tester T via the interface TI/F to indicate
whether or not each of the tested features is functioning satisfactorily.
In response to these alarm signals, the tester T generates a display to
indicate to the engineer using the tester T the hardware status of the
termination. In the present example the casing of the tester T shown in
FIG. 4 includes columns of LED lamps L1-L5, L11-L15 and these are
illuminated to indicate the results of the tests.
After the successful completion of the local test procedures, the tester T,
either automatically or in response to a control input from the user (via
push button ALM2), carries out a second category of testing in conjunction
with the head-end station. The controller C generates a signal for
transmission via the termination to the head-end station. The head-end
station responds to receipt of this signal from the tester T and carries
out a number of diagnostic and control procedures including, for example,
using the ranging pulses transmitted from the particular termination to
synchronise the termination to the head-end clock, interrogating the BTS
slave to determine the identifying code of the termination, and
determining whether the amplitude of ranging pulses transmitted from the
termination falls in the desired operating range.
Depending upon the results of the tests, the head-end station sets the
values of three predetermined mode bits in the control channel transmitted
to the termination 2. These mode bits indicate whether or not the ranging
process has been successfully completed and, if not, also indicates the
nature of the failure. These mode bits are received at the BTS slave S
where they are read via the interface TI/F by the tester T.
The tester unit T decodes the test bits and again generates an appropriate
display to indicate the result of the diagnostic procedures. In the
present example, the second column of lamps L11-L15 is used to indicate
the results of the tests carried out using the head-end station, whilst
the column of lamps L1-L5 is used to indicate the results of the tests
carried out locally within the termination 2.
Tables 1 and 2 below list the test functions and corresponding display
outputs for the local and system tests respectively. Table 3 lists the
values assigned to the mode bits by the head-end station in accordance
with the results of the ranging procedure. In addition to the functions
listed in the tables the tester provides the following functions, actuated
by push buttons mounted on the case: LTEST - lamp test, this illuminates
all the LED's in a slave unit; LINH - laser inhibit, this turns off the
laser in the termination's optical stage OS; ALM2 - status alarm 2--this
transmits a service request signal via the termination 2 to the head-end
station to cause it to carry out the aforementioned second category of
diagnostic and control procedures.
TABLE 1
______________________________________
HARDWARE STATUS
BTS signal name
Colour State Description
______________________________________
PWRUP GREEN ON System enabled
(powered up).
MFCRC GREEN ON Valid Cyclic
Redundancy Check
(CRC) received.
This indicates
that the SLAVE
is synchronised
to the MASTER.
RXINVALID GREEN ON Optics receiver
is recovering
valid clock and
data.
RXDATALOW YELLOW ON Received laser
power high
enough to allow
correct
operation of the
receiver. If
this is off, and
RXINVALID is on,
then light level
is marginal, but
enough for the
receiver to
work.
BITCLK YELLOW PULSED Bit clock from
line interface
to analogue
line. Has no
effect on
ranging process.
______________________________________
TABLE 2
______________________________________
RANGING STATUS
Function Colour State Description
______________________________________
START YELLOW ON BTS MASTER is
attempting to
range the
optical end.
NOISE RED ON BTS MASTER
detected
unexpected,
`noise`, pulses
in the Phase 1
area.
NO PHASE 1 RED ON BTS MASTER did
not detect a
returned Phase 1
pulse from the
optical end.
CENTERING RED ON BTS MASTER
detected a
control
problem - Phase
2 pulse
centering
failed.
DONE GREEN ON Optical end was
successfully
interrogated -
not necessarily
configured for
traffic.
______________________________________
TABLE 3
______________________________________
Ranging code
Mode Description
______________________________________
0 7 No error - ie unit passed.
1 6 Noise in the Phase 1 area.
2 5 No Phase 1 pulse received.
3 4 .vertline.
4 3 .vertline.
Phase 2 centering
failure.
5 2 .vertline.
-- 1 Unit configured
(initialised).
______________________________________
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