U.S. patent application number 13/052858 was filed with the patent office on 2011-07-14 for verification of path integrity in optical switch network.
This patent application is currently assigned to VERIZON BUSINESS GLOBAL LLC. Invention is credited to John A. Fee, Frank A. McKiel, JR..
Application Number | 20110170857 13/052858 |
Document ID | / |
Family ID | 21909820 |
Filed Date | 2011-07-14 |
United States Patent
Application |
20110170857 |
Kind Code |
A1 |
Fee; John A. ; et
al. |
July 14, 2011 |
VERIFICATION OF PATH INTEGRITY IN OPTICAL SWITCH NETWORK
Abstract
To verify the integrity of optical paths through and among
optical switches, optical signals are provided with co-propagating
supplemental signals. The supplemental signals preferably have at
least one characteristic which allows distinguishing one
supplemental signal from another. Associated with a port of a
switch, means are provided for detecting a supplemental signal and
determining if the supplemental signal indicates that a desired
optical signal is passing through the port as expected and desired.
Means for imparting or changing the distinguishing characteristic
of a supplemental signal may also be employed to facilitate
verifying the passage of optical signals.
Inventors: |
Fee; John A.; (Garland,
TX) ; McKiel, JR.; Frank A.; (Colorado Springs,
CO) |
Assignee: |
VERIZON BUSINESS GLOBAL LLC
Basking Ridge
NJ
|
Family ID: |
21909820 |
Appl. No.: |
13/052858 |
Filed: |
March 21, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11265575 |
Nov 2, 2005 |
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13052858 |
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10040226 |
Jan 3, 2002 |
6980736 |
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11265575 |
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Current U.S.
Class: |
398/19 |
Current CPC
Class: |
H04Q 11/0005 20130101;
H04Q 11/0062 20130101; H04Q 2011/0043 20130101; H04B 10/073
20130101; H04Q 2011/0083 20130101 |
Class at
Publication: |
398/19 |
International
Class: |
H04B 10/08 20060101
H04B010/08 |
Claims
1. A method comprising: detecting, at an output port of an optical
switch, a supplemental signal that is co-propagated with an optical
signal, wherein the supplemental signal includes one or more
pre-determined attributes; and causing evaluation of the one or
more pre-determined attributes of the detected supplemental signal
for determining whether an alarm condition exists with respect to
the optical signal.
2. A method of claim 1, further comprising: determining whether the
optical signal has been routed correctly by the optical switch
based on the evaluation of the one or more pre-determined
attributes.
3. A method of claim 1, wherein the one or more pre-determined
attributes specify a frequency characteristic, an amplitude
characteristic, a phase characteristic, a modulation
characteristic, data represented by modulation, or a combination
thereof.
4. A method of claim 1, wherein the attribute specifies information
identifying the optical signal or an attribute of the optical
signal.
5. A method of claim 1, wherein the supplemental signal is
modulated to provide as one of the attributes data associated with
wavelength of the optical signal.
6. A method of claim 1, further comprising: storing information
about the one or more attributes of the detected supplemental
signal to maintain a historical trend; and triggering the alarm
condition based on the historical trend.
7. A method of claim 1, wherein the supplemental signal includes a
sub-carrier of the optical signal, the sub-carrier being used to
frequency, phase, or amplitude modulate the electrical signal.
8. A method of claim 1, wherein the one or more attributes are
associated with a modulation applied electrically to an electrical
signal to produce the optical signal.
9. An apparatus comprising: an optical detector coupled to an
optical switch and configured to detect, at an output port of the
optical switch, a supplemental signal that is co-propagated with an
optical signal, wherein the supplemental signal includes one or
more pre-determined attributes; and an interface configured to
cause evaluation of the one or more pre-determined attributes of
the detected supplemental signal for determining whether an alarm
condition exists with respect to the optical signal.
10. An apparatus of claim 9, wherein the evaluation of the one or
more pre-determined attributes is performed to determine whether
the optical signal has been routed correctly by the optical
switch.
11. An apparatus of claim 9, wherein the one or more pre-determined
attributes specify a frequency characteristic, an amplitude
characteristic, a phase characteristic, a modulation
characteristic, data represented by modulation, or a combination
thereof.
12. An apparatus of claim 9, wherein the attribute specifies
information identifying the optical signal or an attribute of the
optical signal.
13. An apparatus of claim 9, wherein the supplemental signal is
modulated to provide as one of the attributes data associated with
wavelength of the optical signal.
14. An apparatus of claim 9, wherein information about the one or
more attributes of the detected supplemental signal is stored to
maintain a historical trend, and the alarm condition is triggered
based on the historical trend.
15. An apparatus of claim 9, wherein the supplemental signal
includes a sub-carrier of the optical signal, the sub-carrier being
used to frequency, phase, or amplitude modulate the electrical
signal.
16. An apparatus of claim 9, wherein the one or more attributes are
associated with a modulation applied electrically to an electrical
signal to produce the optical signal.
17. An apparatus comprising: an optical matrix having a plurality
of input ports and a plurality of output ports; an optical detector
coupled to one of the output ports and configured to detect a
supplemental signal that is co-propagated with an optical signal at
the output port of the optical matrix, wherein the supplemental
signal includes one or more pre-determined attributes; and a
communication circuitry coupled to the optical detector and
configured to cause evaluation of the one or more pre-determined
attributes of the detected supplemental signal for determining
whether an alarm condition exists with respect to the optical
signal.
18. An apparatus of claim 17, further comprising: another optical
detector coupled to one of the input ports and configured to detect
the supplemental signal prior to processing by the optical
matrix.
19. An apparatus of claim 17, further comprising: an injector
coupled to one of the input ports and configured to impart the one
or more of the attributes to the supplemental signal.
20. An apparatus of claim 17, further comprising: a signal modifier
coupled to one of the input ports and configured to modify the one
or more of the attributes of the supplemental signal.
Description
RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 11/265,575, filed Nov. 2, 2005, which is a
continuation of U.S. patent application Ser. No. 10/040,226, filed
Jan. 3, 2002; the entireties of which are incorporated herein by
reference.
TECHNICAL FIELD
[0002] The present invention relates to optical communications and,
in particular, to methods for verifying correct routing of optical
signals in a network of optical communications switches.
BACKGROUND
[0003] A communications network serves to transport information
among a number of locations and typically comprises various
physical sites or `nodes`, interconnected by information conduits,
called "links." Each link serves to carry information or data from
one site to another site. Each site may contain equipment for
combining, separating, transforming, conditioning, and/or routing
data. These data may represent any combination of telephony, audio,
video, or computer data in a variety of formats.
[0004] FIG. 1 shows an example communications network 100
comprising sites 101-105 connected by links 120-121. Links are
generally implemented using electrical cables, satellites, radio or
microwave signals, or optical connections and can stretch for tens
or hundreds of miles between sites. Through these links, the
communications network 100 carries data signals among the sites
101-105 to effectively interconnect data equipments 111-115, such
as computers, remote terminals, file servers, etc. One or more
links 120 and 121 that connect two sites are collectively referred
to as a span 130. Sites 101-105 normally each comprise at least one
cross-connect switch (either electrical or optical) and are in
constant communication with a central network management system
facility 140 which monitors the flow of traffic throughout the
network.
[0005] Before the development of practical long-haul fiber links, a
network, such as network 100, was commonly implemented in an
all-electrical fashion using electrical cables or microwave paths
as links in conjunction with switches and multiplexing equipment at
the sites. A common high data rate signal to be switched and
transported intact was the DS-3 signal, as standardized by the
International Telecommunications Union (ITU), which carried data at
around 45 megabits-per-second.
[0006] It is now preferable to use optical carrier signals to carry
data along links from one site to another using optical fibers.
Optical carrier signals are of such high frequency, around
10.sup.14 Hz, that they can be modulated at very high frequencies
and can therefore carry data at an extremely high rate. For
example, a standard SONET OC-192 modulated optical signal carries
data at around 10 gigabits-per-second (10 Gbps).
[0007] FIG. 2 shows an example portion of a communications network
wherein the links connecting sites are implemented as optical fiber
links, yet the signals are switched in the electrical domain at
each site. This may be referred to as an "optical/electrical"
network. At each site the data-carrying signals are converted into
the electrical domain to be routed through the digital
cross-connect switches and perhaps processed in other ways.
Collocated with the cross-connect switches at each site are
so-called "lightwave terminal equipment" (LTE) which may comprise
optical transmitters and receivers to couple data signals into and
out of the optical fiber links.
[0008] In FIG. 2, a number of data signals to be transported are
provided along data inputs 210 at a location called Site A. Digital
cross-connect switch (DCS) 212 may combine and reformulate the data
signals to yield a composite data signal along connection 222 to
LTE 224. LTE 224 applies line-coding and may also add framing and
automatic error correction information. LTE 224 may in some cases
package asynchronous data signals into the payload envelope of a
synchronous optical transport system. Once the signal has been
prepared for transmission, LTE 224 then uses the line-coded data
signal to modulate an optical carrier emitted from an optical
transmitter 226, which usually comprises a current-modulated laser
diode. The optical signal from transmitter 226 is coupled into
optical fiber 228, which connects to distant Site B and may extend
for tens or hundreds of miles. At various points along optical
fiber 228, an optical amplifier, such as amplifier 230, or other
means may employed to strengthen the signal and to compensate for
degradation caused by imperfections in the optical path.
[0009] At Site B, the optical fiber is coupled to an optical
receiver 232 which is a part of LTE 234. By techniques that are
well known in the art, LTE 234 interprets the received optical
signal and recreates at output 236 the same data content provided
at connection 222, thus accomplishing transport of the data from
one location to another.
[0010] At Site B, the received data along output 236 enters DCS 214
whereupon the received data stream may be partially demultiplexed,
combined, and routed to be sent to other sites, or may be "dropped"
to make the received signal available to destinations in the
vicinity of Site B. Other optical links in FIG. 2 operate in a
similar manner to the link just described.
[0011] Of further note, it is common for many optical links to be
established between a given pair of sites. A set of links
interconnecting two sites are collectively referred to as a "span."
Furthermore, it is common practice, particularly in telephony
applications, to provide for corresponding pairs of directional
links to be established between sites to accomplish bi-directional
communications. A given LTE will often comprise numerous receivers
and transmitters and may even couple multiple optical carriers, at
different wavelengths, into and out of a single fiber.
[0012] In FIG. 2, the switching action of DCS 214 may accomplish
redirection of individual data signals to either Site C or Site D.
If a given data signal is introduced at Site A and is intended to
be communicated to Site C, there are a variety of mechanisms to
determine if the data signal is successfully reaching its
destination. If the signal is disconnected or severely degraded due
to a fiber cut or equipment malfunction, then electrical equipment,
such as DCS 214, will not be able to synchronize with the signal
(as is necessary to perform time slot interchange switching) and
will declare a "loss of signal" or "loss of framing" alarm. The
alarm indication will be reported whereupon a decision may be made
to reroute the signal through an alternate link. It is fortunate
that, in the electrical domain, the integrity of the signal is
inherently checked at each point where the signal is received or
switched. This allows for pinpointing the location of a failure and
for deciding effective actions to circumvent a failure in the
network.
[0013] For example, if LTE 234 or DCS 214 cannot detect or achieve
synchronization with the signal from Site A, then an alarm is
generated and reported to a network management system, such as
system 140 as was shown in FIG. 1. Based upon other alarms from LTE
234, or even LTE 224, the network management system may determine
that a failure has occurred, along fiber 228 for example, and may
direct DCS 212 and DCS 214 to utilize optical fiber 240 as an
alternate link.
[0014] As another example, assume that LTE 234 and DCS 214 indicate
successful receipt of the signal incident along fiber 228, yet LTE
244 or DCS 216 indicate loss of the signal. These conditions are
reported by the various elements to network management system 140
and correlated to determine that the failure is along fiber 242 or
at LTE 246.
[0015] The hybrid optical/electrical approach depicted in FIG. 2 is
presently in widespread use in the industry and offers substantial
advantages over the older all-electrical systems. However, it is
further desirable, for many practical reasons, to route modulated
optical signals through a network entirely in optical form, that
is, without having to convert an optical signal into an electrical
equivalent until it reaches its destination.
[0016] Conversion of an optical signal into the electrical domain
introduces many limitations. At each point where a modulated
optical signal is received and converted into an electrical
equivalent, the specific data rate and format, and in some cases
the specific carrier wavelength, must be established so that the
receiver is capable of accommodating the incoming signal. Aside
from the hardware costs involved in receiving and re-transmitting
an optical signal, the conversion to an electrical signal restricts
the type of optical signals that may be carried through the
network. When an upgrade to a higher data rate or different
modulation format is desired, the electrical domain equipment
handling signals must be changed. Furthermore, the conversion to an
electrical signal limits the ability to handle a variety of signal
bandwidths and formats which may be carried simultaneously within
the same optical network. Restoration options are thus limited in
the event of a sudden failure in the network. This was not such an
issue in the older electrical networks that carried DS3 signals
almost exclusively throughout.
[0017] Because of these limitations, manufacturers and network
owners are striving to deploy completely transparent all-optical
networks using optical cross-connect switches. These types of
switches simply couple one optical path to another without having
to receive or transduce the optical signal into an electrical
signal. Regardless of what optical signals or modulation formats
are propagated down the fiber, the optical carriers are routed by
the optical cross-connect switches. Upgrades to higher data rates
or formats can occur without any changes to the core network
switches. Mixtures of data rates and formats are readily
accommodated in a transparent all-optical network. It is desirable
to create a transparent "core network" of optical cross-connect
switches to carry and switch extremely large traffic channels.
[0018] It should be noted that some varieties of optical
cross-connect switches are entirely transparent whereas others
perform routing depending upon carrier wavelengths. However, both
varieties are advantageous for being independent of the data
modulation employed upon each optical carrier.
[0019] An example of a portion of an all-optical network is shown
in FIG. 3 and maybe compared to the optical/electrical system of
FIG. 2. Data signals presented for transmission at data inputs 310
are routed and combined into aggregate high-data rate signals
within DCS 312 and electrically coupled to LTE 316 along connection
314. LTE 316 comprises optical transmitter 318 that emits an
optical signal modulated with the data supplied by DCS 312. The
modulated optical signal from transmitter 318 propagates through
optical fiber 320 to eventually reach Site B.
[0020] At Site B, the optical signal is coupled into an input port
338 of an optical cross-connect switch (OCCS) 350 to be routed to
one of many possible output ports. The switching action of OCCS 350
determines how each signal at an input port is redirected to a
particular output port. And, because the output ports of a given
OCCS may lead to many different remote sites, the switching of OCCS
350 accomplishes routing of optical signals to different physical
destinations. In the present example, OCCS 350 may establish a
light path between input port 338 and output port 340, effectively
passing the signal from fiber 320 into fiber 328. This causes the
optical signal from transmitter 318 to be received at receiver 330
in LTE 332, meaning that the data from input 310 and DCS 312 is
available through DCS 334 and at output 336.
[0021] At Site B in FIG. 3, optical amplifier 322 is inserted in
the optical path to boost the signal before entering OCCS 350. Some
types of OCCS use a lossy switching matrix and it is advisable to
pre-amplify weak signals before entering the switch. Optical
amplifier 326 represents the common practice of amplifying optical
signals after leaving an OCCS and upon reentering a fiber link.
This compensates for losses experienced through the switch and
provides a power boost to launch the optical signal through a long
fiber link to the next site.
[0022] While the all-optical approach shown in FIG. 3 offers many
worthwhile advantages, it introduces some new challenges. As
described earlier, the traditional electrical networks and the more
recent optical-electrical networks always received and interpreted
at least portions (i.e. framing and parity information) of the data
signal. Detection of the integrity of each data signal was
inherently necessary at each point where the data signal was
received, switched, or regenerated.
[0023] In contrast, in a transparent all-optical network approach,
these aspects of the data signal are not routinely sampled. An
optical cross-connect switch, such as OCCS 350, operates "blindly"
without regard for the presence or absence of optical signals at
its input and output ports. A malfunction in OCCS 350, or a
mistaken instruction that controls OCCS 350, could cause an optical
signal to be dead-ended or to be incorrectly routed to another
site. In a network of optical cross-connect switches, the routing
of a given signal is accomplished by issuing commands to several
cross-connect switches, but there is generally no mechanism for
verifying the proper routing of the optical signal except at its
final destination.
[0024] Typically, a centralized or moderately distributed
provisioning function coordinates the action of the cross-connect
switches to accomplish routing of optical signals. The provisioning
function usually maintains a database describing how the switches
are interconnected in the network and relies upon the stored data
to decide what switching commands to issue to the switches. Optical
cross-connect switches are presumed to work properly, just like
their electronic counterparts, and the database is assumed to
accurately represent the interconnections in the network. But if a
switch fails to connect ports in response to a command or the
database inaccurately shows a link where none exists, then an
optical signal may not reach its intended destination. Furthermore,
there will be no indication of where along the path the optical
signal has been misrouted. This problem may be exacerbated when
restoration switching actions occur in the network that temporarily
alter the connection topology.
[0025] What is required is a means for verifying, in a network of
optical-domain switches, that optical data signals have been
correctly switched and routed as intended and that the optical
switching mechanisms are working properly. Furthermore, a means is
desired for determining the location of a malfunctioning element so
that traffic may be routed around it and repairs can be readily
initiated. It is also desirable that any malfunctions within the
switching mechanism of an optical switch be detected and noted
locally so that the switch may declare a localized alarm or may
alter its internal routing logic to circumvent the failure.
SUMMARY
[0026] The present invention is directed to a network of optical
cross-connect switches with improved verification of the proper
operation of the switches, the correct routing of signals in the
network, and generally the integrity of optical paths presumed to
be formed through the network. In one aspect of the present
invention, the supplemental signal is co-propagated with a
traffic-bearing optical signal. The supplemental signal is detected
at the output ports of the switch in order to verify the operation
of the switch and the correct routing of the optical signal to that
point in its path.
[0027] In another aspect of the present invention, a supplemental
signal is also detected at the input ports to the switch to verify
correct routing of optical signals reaching the switch.
[0028] In yet another aspect of the present invention, a
supplemental signal is injected at the input ports of an optical
cross-connect switch and detected at the output ports of the
optical cross-connect switch to determine correct routing of
signals through the matrix of the cross-connect switch.
[0029] In another aspect of the present invention, supplemental
signals that are already incident along input ports to a
cross-connect switch are modified and the modified supplemental
signals are detected at the output ports of the cross-connect
switch to verify correct routing of signals through the switch.
[0030] In accordance with a preferred embodiment of the present
invention the supplemental signal is an amplitude modulation
subcarrier applied to a traffic-bearing optical carrier. However,
the supplemental signal may comprise a frequency-modulation
component, as may be preferable where Raman amplification is used
along optical paths.
BRIEF DESCRIPTION OF THE DRAWINGS
[0031] The novel features believed characteristic of the invention
are set forth in the appended claims. The invention itself however,
as well as a preferred mode of use, further objects and advantages
thereof, will best be understood by reference to the following
detailed description of illustrative embodiments when read in
conjunction with the accompanying drawings, wherein:
[0032] FIG. 1 is a block diagram of a typical communications
network;
[0033] FIG. 2 depicts a portion of an electrical/optical
communications network in accordance with the prior art;
[0034] FIG. 3 depicts a portion of an all optical communications
network;
[0035] FIG. 4 is a block diagram of an optical cross-connect switch
comprising supplemental signal detectors at its output ports in
accordance with an embodiment of the present invention;
[0036] FIG. 5 is a block diagram of an optical cross-connect switch
comprising supplemental signal detectors at both its input ports
and output ports in accordance with an embodiment of the present
invention;
[0037] FIG. 6 is a block diagram of an optical cross-connect switch
comprising supplemental signal detectors at its outputs and optical
signal injectors at its input ports in accordance with an
embodiment of the present invention;
[0038] FIG. 7 is a block diagram of a optical cross-connect switch
comprising supplemental signal detectors at its output ports and
optical signal modifiers at its input ports in accordance with an
embodiment of the present invention;
[0039] FIG. 8 depicts an all optical link in a communications
network comprising a subcarrier drop-insert facility;
[0040] FIG. 9 is a block diagram of a subcarrier drop-insert
facility in accordance with an embodiment of the present
invention;
[0041] FIG. 10 is a flowchart describing a process by which a
supplemental detector validates a received supplemental signal;
[0042] FIG. 11 is a flowchart describing a process in an optical
cross-connect switch for applying a supplemental signal to an input
port, detecting the supplemental signal at an output port, and
comparing the signals to verify the correct operation of the
optical cross-connect switch;
[0043] FIG. 12 is flowchart describing a process in an optical
cross-connect switch whereby a supplemental signal is modified at
an input port, detected at an output port, and the two versions of
the signal are compared to verify proper operation of the optical
cross-connect switch and of correct routing in the path comprising
the optical cross-connect switch;
[0044] FIG. 13 is a flowchart describing a process for comparing
supplemental signals before and after passage through an optical
switching matrix; and
[0045] FIG. 14 is a flowchart describing a process whereby a
supplemental signal may be analyzed both before and after passing
through a switching matrix using only a single detector.
DETAILED DESCRIPTION
[0046] To afford one of ordinary skill in the art a clear
understanding of the present invention, various exemplary
embodiments will now be described. These exemplary embodiments
comprise optical switches, which may be of many varieties.
[0047] An optical switch may comprise a single switching element,
such as a mechanical coupling switch or a Mach-Zehnder
electo-optical switching element or a semiconductor optical
amplifier that provides gain and coupling only when powered. An
optical switch may also comprise a multitude of switching elements.
It should be generally noted that where signal ports of such
switches are referred to as being "input ports" or "output ports,"
some switches may in fact make no such distinction. Optical signals
may propagate bidirectionally through a fiber and through many
types of optical switches. Consequently, a given port may be
considered an input port with respect to a signal entering the
switch mechanism along a fiber and may also be considered an output
port with respect to another signal propagating from the switch,
emanating from the same port and into the same fiber.
[0048] Referring now to FIG. 8 of the drawings, a technique is
shown for superimposing a subcarrier signal upon a modulated
optical carrier. This technique is described in greater detail in
U.S. Pat. No. 6,285,475, but is briefly summarized herein. In FIG.
8, an optical Line Terminating Equipment (LTE) 810, comprising an
optical transmitter 818, generates an optical signal 816 that is
modulated by the summation of high data rate signal 812 and
subcarrier signal 814. In a preferred embodiment, subcarrier signal
814 is substantially lower in frequency and affects optical signal
816 with much less modulation intensity than high data rate signal
812. As this composite optical data signal 816 propagates through
an optical path, which may be a path through an all-optical
network, the subcarrier may readily be detected and extracted by
relatively inexpensive low-speed optical detectors without
requiring detection, decoding, or transducing of the co-modulated
high data rate signal. This subcarrier technique is useful for
conveying information among intermediate and terminal points along
an all-optical path and for keeping such information associated
with each particular optical carrier regardless of
wavelength-dependent routing. This technique for creating an
optical carrier with a superimposed subcarrier may be performed
within LTE 810 shown in FIG. 8.
[0049] FIG. 8 also depicts that, as optical signal 816 propagates
through optical link 820, a drop insert facility 832 may be
employed to read and alter the subcarrier portion of optical signal
816 without affecting or acting upon the associated high data rate
modulation component and without requiring the conversion of the
optical signal into an electrical signal. An optical coupler 830 is
coupled to optical link 820 to tap off therefrom a small proportion
of the energy of optical signal 816. The sampled optical signal is
input to drop insert facility 832 wherein the subcarrier modulation
is detected and processed as necessary to cause a desired modified
optical signal 826 to be sent downstream of drop insert facility
832. As will be described further in conjunction with FIG. 9, drop
insert facility 832 may assert changes to the subcarrier modulation
upon signal 816 by gain modulating an optical amplifier 834.
[0050] In FIG. 8, drop insert facility is coupled to network
management system (NMS) 140 through connection 836, by which drop
insert facility 832 may report the receipt of certain subcarrier
information or may provide alarm or status notifications. Through
connection 836, NMS 140 may also direct drop insert facility 832 in
performing modifications to the subcarrier content of signal 816.
Accordingly, optical signal 816 may undergo modifications in its
subcarrier content to yield modified optical signal 826 which then
propagates onward to other network equipment, such as optical
cross-connect switch (OCCS) 860.
[0051] To instruct in an implementation of drop insert facility
832, FIG. 9 of the drawings briefly describes an embodiment as
disclosed in U.S. Pat. No. 5,956,165 whereby the subcarrier content
of an optical signal may be altered without transducing or decoding
the high data rate modulation content of the optical signal.
[0052] In FIG. 9, a portion of optical signal 816 is tapped off by
optical coupler 830 and directed into photodiode 910, which
produces an electrical signal in response to the modulation of the
incoming optical signal. Photodiode 910 (or other forms of
detector) may be of simple and inexpensive design such that the
modulation frequency response of the detector is inadequate to
respond to the high data rate modulation but suffices to receive
the lower frequency subcarrier modulation. Amplifier 912 amplifies
the electrical signal and may impose some frequency filtering
characteristics as well. For example, the composite frequency
response of both photodiode 910 and amplifier 912 may be tailored
to allow only subcarrier modulation frequencies to appear at the
output of amplifier 912, while filtering out any frequencies above
or below the desired passband.
[0053] The resulting signal along connection 952 is coupled to
subcarrier receiver 914 and inverter 922. Subcarrier receiver 914
detects the presence of a subcarrier component and may extract
information or attributes therefrom. Subcarrier receiver 914
discriminates the raw electrical signal along connection 952 into a
data stream along connection 954, and may perform gain control,
linearization, clock recovery, and thresholding by techniques that
are well known in the art.
[0054] An error counter 916 may be coupled to subcarrier receiver
914 to observe the incidence of errors such as might occur where
digital data is conveyed by a subcarrier component of optical
signal 816. The error count or measurement from error counter 916
may be reported to a network management system or may be used
locally, for example, to affect whether received data is acted upon
or ignored. An error count or measurement from error counter 916
may also be used to gage the quality of the signal path along which
signal 816 has propagated. This aspect may be useful for monitoring
path degradation and performing fault isolation.
[0055] Another useful connection with receiver 914 is attribute
data connection 964. Through this connection receiver 914 may
provide attributes of a received subcarrier, such as frequency or
amplitude of the subcarrier. It is also possible that through this
connection receiver 914 may receive instructions as to a particular
subcarrier to be detected. Where multiple subcarriers may be
present, receiver 914 may be directed to selectively receive one of
the subcarriers based on a given frequency or a code-division
multiple access (CDMA) code.
[0056] The data output 958 of subcarrier receiver 914, which may
represent data conveyed by the subcarrier component, is coupled
into a data receive buffer 916 which collects the data and may hold
the data temporarily until controller 930 can process the data.
Controller 930 determines what data has been received, what data
must be sent, and how a subcarrier must be modified to accomplish
the sending of data as needed. Controller 930 may communicate with
a network management system to establish what data must be sent in
the subcarrier component of an outgoing optical signal 826. Along
receive data output 960, controller 930 may provide output of the
received data that has been obtained from inbound signal 816 by
subcarrier receiver 914. Along transmit data input 962, controller
930 may receive data that is to be modulated onto the outbound
updated signal 826. Controller 930 sets outgoing data into data
transmit buffer 918 so that the outgoing data be provided to new
subcarrier transmitter 920. New subcarrier transmitter 920 may
create a modulation signal having a fixed bit rate and may
therefore may draw data from data transmit buffer 920 at a given
clock rate. In one possible implementation, data transmit buffer
918 may hold an "image" of a digital signal that is to be
transmitted and new subcarrier signal 920 may continuously cycle
through the image and send the contents of data transmit buffer
918. In this manner, controller 930 need only write to data
transmit buffer whenever the transmit image must change from what
it was previously.
[0057] In any case, the data from the data transmit buffer is
converted in transmitter 920 into a form suitable for being sent as
a subcarrier signal. The output of transmitter 920 may amount to a
serial data stream or may be a subcarrier modulated in frequency,
amplitude, or otherwise, in a similar manner to received optical
signal 816. The output of transmitter 920 is coupled to a summing
point 924. Another signal entering summing point 924 is from
inverter 922. Inverter 922 accepts a raw subcarrier electrical
signal along connection 952 and creates an inverted analog signal
that is the negative of the originally received subcarrier signal
transduced by photodiode 910. The output of summing point 924
present along connection 956 is coupled to optical amplifier 834
through optical amplifier driver 934.
[0058] In the case of a fiber amplifier, such as an erbium-doped
fiber amplifier, driver 934 may comprise a pump laser whose
intensity is modulated by the input along connection 956.
Alternatively, where optical amplifier 834 is of the semiconductor
variety, driver 934 may comprise current or voltage controlling
circuitry which may be caused to vary the gain of the amplifier in
response to input along connection 956. Semiconductor amplifiers
can provide linear amplification into the 80 GHz range, meaning
that the bandwidth of a subcarrier signal may be quite high.
[0059] In either case, the coupling of an inverted form of the
original subcarrier modulation through inverter 922 and summing
point 924 causes the effective cancellation of same from the
outbound optical signal 826. Furthermore, the addition of a new
subcarrier modulation signal to summing point 924 causes the new
subcarrier information to appear on outbound optical signal 826.
The net effect is that new subcarrier information replaces that
which was received, without acting upon the high data rate aspects
of the optical carrier in any way.
[0060] Referring back now to FIG. 3 of the drawings, LTE 316
creates an optical signal by virtue of transmitter 318. The
modulated optical signal propagates through fiber 320 and enters
optical cross-connect switch (OCCS) 324 at site "B." The signal
created by transmitter 318 may comprise a supplementary signal that
is also received at input port 338 of OCCS 324. The signal entering
input port 338 may undergo switching within OCCS 324 and be
directed to any one of the output ports, such as output port 340.
Furthermore, as mentioned earlier, the supplemental signal may
carry data and comprise a unique tag that identifies the optical
signal generated by transmitter 318. The data, including the unique
tag, may be detected by relatively inexpensive low-bandwidth
detectors coupled to the optical path.
[0061] Turning now to FIG. 4, an optical cross-connect switch in
accordance with a preferred embodiment of the present invention is
shown comprising supplemental signal detectors at the output ports.
OCCS 324 is shown to comprise several elements which are typically
included in an optical cross-connect switch, namely optical matrix
410, controller 404, and communications circuitry 406. Optical
matrix 410 serves to perform connection of optical paths between
input ports and output ports of the matrix. Optical cross-connect
controller 404 exercises control over optical matrix 410. In
response to requests to connect certain input ports to certain
output ports, controller 404 coordinates the switching action of
individual switching elements in optical matrix 410 in order to
accomplish the desired interconnection. Controller 404 is also
coupled to communication circuitry 406 so that OCCS 324 may
communicate to a remote system such as a network management system
140. A network management system 140 may issue connection requests
to OCCS 324 to provision paths in the network where needed.
[0062] Optical signals to be switched by optical matrix 410 enter
the OCCS 324 along a optical fiber 320 coupled to an input port
338. As described above, an optical signal incident along optical
fiber 320 may comprise a supplemental signal generated elsewhere in
the network. This optical fiber connection then enters the optical
matrix at matrix input port 412. Typically, many such input ports
338 and corresponding matrix input ports 412 are employed within a
single OCCS 324. In addition, numerous output ports from the
optical matrix 414 are shown which are carried to output port 340
of OCCS 324 and coupled to a fiber 328. Fiber 328 typically is a
fiber link that leads to another remote optical cross-connect
switch in the network or to terminal equipment such as LTE 316 in
FIG. 3.
[0063] In accordance with a preferred embodiment of the present
invention, an optical signal having an associated supplemental
signal enters OCCS 324 along input port 338 which is coupled to
matrix input port 412. By the action of optical matrix 410 under
the control of controller 404, the signal incident at matrix input
port 412 may appear at one of the selected matrix output ports 414.
The supplemental signal incident along fiber 320 through matrix
input port 412 will have a unique attribute that may be readily
detected. For example, a supplemental signal may be distinguished
by such attributes as frequency, amplitude, phase or modulation
characteristics, including data represented by modulation. A
supplemental signal attribute may even be used to convey an
attribute of an associated optical signal. For example, a
supplemental signal may be modulated to carry data and the data may
describe the wavelength of the associated optical carrier signal
that the supplemental signal is modulated upon or otherwise
associated with. As another example, the frequency of a subcarrier
may map to a wavelength for the corresponding optical signal.
[0064] The attributes may represent information, at the very least
by way of identifying the signal. Whether an attribute of the
supplemental signal itself or the information that may be encoded
thereon by modulation, it may be generally said that a supplemental
signal may be created having one or more attributes or
characteristics that represent information content.
[0065] For an output port 414 that is intended to receive or
conduct the optical signal that was incident along fiber 320, an
associated supplemental signal detector 420 is receptive to the
supplemental signal associated with the conducted optical signal.
Upon detection of the expected supplemental signal, supplemental
signal detector 420 communicates to controller 404 via control link
422 indicating receipt of a supplemental signal and conveying
information from, or attributes of, the detected supplemental
signal. Controller 404 notes the receipt of the supplemental signal
and may maintain a historical memory of reported attributes, such
as amplitude, to look for trends that may reveal subtle or slow
degradations in the transmission of the signal.
[0066] From an external source, controller 404 may also receive
information describing whether a supplemental signal should be
expected and what attributes the supplemental signal should
exhibit. Provided with this information, controller 404 may locally
interpret whether the supplemental signal is being received as
expected and initiate a meaningful alarm notification
accordingly.
[0067] Controller 404 may compare the anticipated supplemental
signal information that was obtained from a remote system to the
supplemental signal information that was received locally by
supplemental signal detector 420. If the locally detected
supplemental signal information matches what is anticipated, then
generally no alarm indication is issued by controller 404 nor
reported to network management system 140.
[0068] The anticipated supplemental signal information may be
communicated through a network management system 140 from an
upstream transmitter, such as transmitter 318 in FIG. 3.
Alternatively, network management system 140 may actively determine
what characteristic information is to be imparted to a supplemental
signal at transmitter 318 and may also communicate to controller
404 what supplemental signal information to expect if the optical
signal from transmitter 318 is routed properly. Note that this
continuity checking determines both the integrity of optical link
320 and the correct functioning of optical matrix 410 in routing
the optical signal to the appropriate output port 414.
[0069] The supplemental signal detector 420 may be constructed in
numerous ways using an inexpensive low-bandwidth photo-detector
coupled to the optical path. One such arrangement is taught in U.S.
Pat. No. 6,285,475 and a similar arrangement is shown as part of
FIG. 9. Supplemental signal detector 420 comprises an optical tap
which removes a small portion of the signal from the optical line.
The optical signal extracted by the optical tap is coupled into a
photo-detector, such as an avalanche photo-diode or a PIN diode,
which transduces the optical signal into an electrical signal. This
electrical version of the signal may then be amplified and fed into
a detector of some nature to look for particular signal
characteristics or modulation within the supplemental signal. With
the arrangement of FIG. 4 it is possible at an OCCS 324 to
determine whether or not an optical signal is properly being
received along a fiber 320 and being coupled to a particular output
port 414. A method of operating the arrangement of FIG. 4 is
presented later in FIG. 10.
[0070] Referring now to FIG. 5 of the drawings, an OCCS 324 is
shown similar to that shown in FIG. 4. In FIG. 5 however, OCCS 324
is shown to further comprise supplemental signal detectors 520
inserted in-line between an incoming optical fiber link 320 and the
optical matrix input port 412. Supplemental signal detector 520
reports signals that it detects to controller 404, as do
supplemental signal detectors 420. The purpose of supplemental
signal detector 520 is to distinguish between supplemental signals
received along fiber 320 versus supplemental signals that have
traversed both fiber 320 and optical matrix 410. Having both signal
detectors 420 and 520 allows OCCS 324 to distinguish between
misroutings due to external causes versus misroutings due to
malfunction of optical matrix 410. FIG. 10 and FIG. 13, presented
later, describe methods by which the arrangement of FIG. 5 may be
used.
[0071] It is further contemplated that reports from numerous
supplemental signal detectors along a path or throughout a network
may be collected at a central location where the information maybe
correlated to deduce the origination and path traversal for each
supplemental signal. This form of operation may be viewed as an
all-optical counterpart for how the section and line trace overhead
is commonly used in SONET signals.
[0072] FIG. 6 of the drawings shows OCCS 324 comprising
supplemental signal injectors 620 inserted in-line between fiber
320 and matrix input port 410. Supplemental signal injector 620
imparts characteristic information or attributes to the
supplemental signal which is applied to the optical signal passing
from fiber 320 to matrix input port 412. Supplemental signal
injector 620 may receive commands from controller 404 as to what
characteristic information or attributes are to be used along a
given matrix input port 412.
[0073] After passing through optical matrix 410 along with an
associated traffic-bearing optical carrier, the supplemental signal
is detected by one of the supplemental signal detectors 420 which
reports receipt of the supplemental signal to controller 404. In
this manner, OCCS 324 may coordinate a self-contained evaluation of
the performance of optical matrix 410. Furthermore, supplemental
signal detectors 420 may be equipped to monitor the amplitude of
the carrier signals or supplemental signals and to report changes
in signal level which indicate increased attenuation through OCCS
324. This technique may be used to detect and report degradation in
the operation of OCCS 324.
[0074] In FIG. 6, optical supplemental signal injector 620 applies
a supplemental signal to the optical carrier, which may be in
addition to other supplemental signals already present on a passing
optical carrier. Supplemental signal injector may, under the
direction of controller 404, apply a signal that is distinguishable
in some respect from other supplemental signals already present on
the optical carriers passing through. A supplemental signal
detector may observe either or both of the locally and remotely
applied supplemental signals and make determinations singly or in
combination.
[0075] FIG. 7 of the drawings shows OCCS 324 comprising
supplemental signal modifier 720. Supplemental signal modifier 720
accepts supplemental signals already present in an optical carrier
incident along fiber 320 and acts to change or add information to
the signal which may then be detected by supplemental signal
detector 420 coupled to the output ports of the optical matrix 410.
This may be done so that supplemental signal detectors 420 can
simultaneously determine whether a correct signal is received along
fiber 320 and was properly routed though optical matrix 410.
[0076] Along an optical path through a network, each supplemental
signal modifier 720 may also simultaneously function as a detector
and may provide an output of detected signal information in much
the same manner as detector 420. (See the description provided for
connections 960 and 964 in FIG. 9.) In some cases where the
arrangement of FIG. 7 is used, a comparison may be made between
inbound and outbound signals as was mentioned for FIG. 5.
[0077] Furthermore, supplemental signal modifier 720 may be used to
accumulate a set of signatures along an optical path so that, by
examining the supplemental signal, one can ascertain all of the
optical cross-connect switches that the optical signal has
traversed thus far. An example of this cumulative mode of operation
is provided in U.S. Pat. No. 6,108,113. If the supplemental signal
contains an accumulation of signatures and a supplemental signal
modifier 720 adds yet another signature to the supplemental signal,
then signal detector 420 will detect a composite supplemental
signal that may be readily disassembled to determine even the
supplemental signal that was present before being modified by
modifier 720.
[0078] In other words, where the effect of the modifier on the
supplemental signal is cumulative, the need to perform separate
detection at the modifier may be obviated because the detector can
infer the supplemental signal before modification from the
supplemental signal detected after modification. Many other
variations are possible wherein the pre-modification supplemental
signal may be inferred from the post-modification signal. Another
example of this occurs where the supplemental signal comprises an
ordinal counting aspect and the modifier simply increments or
otherwise changes the count in a predictable way.
[0079] Assuming that the modification, such as a digital bit
string, is unique among the input ports, then the correct operation
of the local switching matrix is confirmed if the modification
applied by the modifier is present in the supplemental signal
detected after the matrix. Once this condition is established, then
the remainder of the supplemental signal may be compared to
expectations, with any discrepancies being attributable to routing
mistakes elsewhere in the network.
[0080] Referring now to FIG. 10 of the drawings, a process is shown
whereby an optical cross-connect switch may detect supplemental
signals and issue alarms accordingly. The process of FIG. 10 may be
executed by, for example, OCCS 324 depicted in FIG. 4 and may
execute within controller 404 of OCCS 324. Controller 404 may take
the form of a general purpose computer and the process of FIG. 10
may be implemented as software instructions operating within
controller 404.
[0081] The process of FIG. 10 starts at step 1002 upon initializing
an optical cross-connect or a network system, such as at the time
of initial power-up. The remainder of the process of FIG. 10 is a
loop that is repeated for as long as power is applied to the
system. After the system is started and initialized in step 1002,
execution proceeds immediately to step 1004. In step 1004,
information about an inbound supplemental signal is obtained from,
for example, a remote location through network management system
140. This information may indicate whether a supplemental signal is
at all expected along a given port and may further indicate
attributes of supplemental signal.
[0082] One possible attribute may be information that is expected
to be present upon the supplemental signal, in turn representing
the supplemental signal information that was applied by a
transmitter 318 in originating the optical signal. It is also
foreseen that network management system 140, or the like, may
command transmitter 318 to apply certain information to a
supplemental signal and at the same time inform an OCCS 324 as to
what information to expect in a received supplemental signal
corresponding to the same signal transmitted by transmitter 318.
Regardless of how this action takes place, step 1004 merely refers
to obtaining the information that is expected to be upon a
supplemental signal appearing at a particular port of the switch
and expected to be detected by a given supplemental signal detector
420. After obtaining this information in step 1004, step 1006 is
executed to determine if a supplemental signal is expected at all.
If no supplemental signal is expected to be detected by a given
supplemental signal detector 420, then the decision made in step
1006 is negative and execution simply returns to step 1004 and the
loop continues to, in effect, poll for whether any new information
regarding an incoming supplemental signal has been received.
[0083] If on the other hand, in step 1006, a supplemental signal is
expected to be received, then execution proceeds to decision step
1008 wherein it is determined whether a supplemental signal
detector 420 is in fact receiving a supplemental signal. If not,
then execution continues at step 1010 resulting in the issuance of
a "loss-of-signal" fault alarm to the OCCS controller 404. This
loss-of-signal indication would signify that the expected
supplemental signal is not being received where it was expected to
be received. This alarm indication may be indicative of a fault in
the network and may be reported furthermore to a network management
system 140. This information may be used at a network level by the
network management system 140 to determine that a malfunction has
occurred, to locate a malfunction, and to take actions to
circumvent a possible failure in the network. Alternatively, the
loss-of-signal alarm that originates in step 1010 may be used
locally by controller 404 to assess the operation of OCCS 324 and,
in particular, of optical matrix 410. In response to this
indication, controller 404 may take action within OCCS 324 to
circumvent a possible failure of switching elements within optical
matrix 410.
[0084] In addition to detecting loss of and expected signal at a
particular port, it is possible to monitor receipt of the errant
signal at all other ports to further pinpoint the malfunction and
to take corrective actions.
[0085] Returning to step 1008, if the determination is made that a
supplemental signal is being received as expected, then execution
proceeds to step 1012 where attributes are derived from the
supplemental signal. This would take place within supplemental
signal detector 420, for example. Attributes of the supplemental
signal may include frequency, amplitude, code-division multiple
access, or data encoded within the supplemental signal, for
example.
[0086] Process 1000 then continues execution at step 1014 wherein
the attributes of detected supplemental signal are compared to the
expected attributes obtained in step 1004 earlier. If the detected
supplemental signal attributes as determined in step 1012 do not
match the expected attributes derived in step 1004, then execution
proceeds to step 1016 and a mismatch fault alarm is issued. In a
similar fashion to the handling of the alarm created in step 1010,
a mismatch alarm created by step 1016 may be communicated to and
used by network management system 140 at the network level or by
controller 404 at the local level. When the condition exists that
the detected supplemental signal attributes are not equal to the
expected attributes, this indicates that somewhere the routing has
gone wrong and indicates a possible malfunction of optical matrix
410, of erroneous commands given to OCCS 324 from perhaps network
management system 140, or of failure of equipment "upstream" of
OCCS 324.
[0087] Therefore, the mismatch fault alarm of step 1016 may serve
many valuable purposes. It is contemplated that, in an optical
cross-connect network, the location at which the signal may have
been misrouted before reaching OCCS 324 may be determined by
observing mismatch alarms from other network elements or by reading
cumulative path information as may be encoded in information borne
on the received signal.
[0088] Returning now to step 1014, if the determination is made
that the detected supplemental signal attributes in step 1012 are
consistent with the expected supplemental signal attributes
determined in step 1004, then no alarm is issued and execution
simply returns to step 1004 which continues the loop of process
1000 for continually making the comparison of the expected
attributes to the detected attributes.
[0089] Note that process 1000 of FIG. 10 may also be readily
adapted to the OCCS 324 as shown in FIG. 5 which comprises
supplemental signal detectors at the inputs to the optical matrix
410. As will now be apparent to one of ordinary skill in the art,
the presence of supplemental signal detectors 520 prior to optical
matrix 410 allows controller 404 to distinguish possible
misroutings or malfunctions upstream of OCCS 324 from any
misroutings that may occur by malfunction of optical matrix 410 or
incorrect commands issued thereto. A method for processing detected
signals before and after an optical switch matrix is described
later in FIG. 13.
[0090] Turning now to FIG. 11 of the drawings, a process 1100 is
shown that is applicable to an OCCS that employs supplemental
signal injectors at the inputs to an optical matrix 410 as shown in
FIG. 6 of the drawings. The process of FIG. 11 starts at step 1102
upon power-up and initialization of the overall system and then
process execution proceeds immediately to step 1104 and the
remainder of process of 1100 is a loop that is executed for as long
as power is applied to the system. Process 1100 may be implemented
under software control within controller 404. In step 1104, a
supplemental signal is applied to optical carriers entering OCCS
324 along input port 338.
[0091] This supplemental signal may take many forms. In a preferred
embodiment of the present invention, the supplemental signal
injected by supplemental signal injectors 620 is a subcarrier used
to amplitude modulate the carrier and is superimposed upon the
traffic bearing high-data rate modulation already applied to the
carrier. Of course, the supplemental signal may be also imposed on
the carrier by frequency modulation or pulse modulation or other
forms. The subcarrier is preferably of substantially lower
frequency and amplitude than the high data rate modulation applied
to the optical carrier. A means for injecting in the optical domain
a subcarrier signal superimposed upon an existing optical carrier
is disclosed U.S. Pat. No. 5,956,165.
[0092] Once a supplemental signal has been added to an optical
carrier in step 1104, then, in step 1106, the optical carrier that
has been supplemented passes through the optical matrix 410.
Through optical matrix 410, the optical signal is coupled to one of
the output ports of the optical matrix and is detected by a
supplemental signal detector in step 1108. Also in step 1108, at
least one attribute of the supplemental signal is extracted from
the signal. Then, in step 1110, the attribute of the supplemental
signal as detected in step 1108 is compared to the attribute
presumably established for the supplemental signal resulting from
step 1104. If there is a mismatch between these, then execution
proceeds to step 1112 and an alarm is issued indicating the
cross-connect switch has malfunctioned. This is evidence that the
optical matrix 410 has malfunctioned because a known optical signal
was injected at an input port but did not appear at the output port
that would be appropriate if the optical matrix were operating
correctly. On the other hand, in step 1110, if the detected
supplemental signal information does equal the same information
that was applied to the supplemental signal before entering the
optical matrix, then no alarm is issued and execution continues
returns to step 1104 and process 1100 effectively continues to poll
for proper operation of the optical cross-connect switch. It is
contemplated that an arrangement is possible wherein multiple
processors or processes are used, with one performing continuous
polling and another performing troubleshooting and fault
location.
[0093] It is noteworthy that a supplemental signal locally injected
in step 1104 may be in addition to other supplemental signals
already present in an incoming optical signal. A supplemental
signal detector may observe either or both of the locally and
remotely applied supplemental signals and make determinations
singly or in combination. By the appropriate choice of attributes,
locally and remotely added supplemental signals may be
distinguished by a detector. Those of skill in the art will
appreciate that various processes described herein may be used in
combination for determining whether detected supplemental signals
are, on the whole, being received as expected. For example, it may
be possible for a supplemental signal detector to detect a remotely
added signal at one frequency and a locally injected signal at
another signal and to independently assess the correctness of each.
Where a locally injected signal is detected correctly yet a
remotely added signal component is incorrect, the optical
cross-connect switch may properly declare a routing fault external
to the switch.
[0094] Turning now to FIG. 12 of the drawings, a process 1200 is
shown by which a suitably equipped optical cross-connect switch may
receive supplemental signals from incoming optical fiber
connections, may detect supplemental information within those
signals, may modify the information content of the supplemental
signals prior to passing the information through the optical matrix
410, and then may detect the supplemental signals at the output
ports of its optical matrix. Process 1200 may be implemented for
example, as software instructions within an optical cross-connect
controller 404.
[0095] Process 1200 begins with step 1202 corresponding to initial
power up, start up and initialization of the system or of the
particular optical cross-connect switch. The remainder of process
1200 is a loop for, in effect, constantly polling to ensure correct
operation of the optical cross-connect switch and of other
components in the network.
[0096] After start up and initialization in step 1202, execution
proceeds to step 1204 wherein the supplemental information is
detected and received substantially near the input to the optical
cross-connect switch. Then, in step 1206, information regarding
what supplemental signal is expected to have been received at each
input port to the optical cross-connect switch is obtained either
locally or from a remote system, such as network management system
140. It is further contemplated that such information as to what
supplemental signal information or attributes to expect may be
derived from an upstream optical cross-connect switch along a given
optical path.
[0097] After executing step 1206, then step 1208 is executed to
determine whether the information or attributes received and
detected in step 1204 match the information or attributes that are
expected to be received in step 1206. If there is a mismatch
determined in step 1208, then execution proceeds to step 1210
whereupon a fault alarm or "line error" is declared indicating that
there is a problem with the information or the identity of the
signal coming into the optical cross-connect switch. After
declaring an alarm in step 1210, then execution returns to step
1204 so that polling continues.
[0098] Returning to step 1208, if the detected incoming
supplemental information matches what was expected to have been
received, then execution proceeds to step 1212 where the
supplemental signal is augmented or otherwise modified with
information that is a) specific to the context of OCCS 324 and b)
distinguishable from any aspects of the supplemental signal that
were already present as it entered the optical cross-connect
switch. Then, in step 1214, the modified supplemental signal is
passed through optical cross-connect matrix 410 and, in step 1216,
is detected at the output ports of the optical matrix by
supplemental signal detectors 420. Next, in step 1217, information
is determined about the supplemental signal expected to be observed
at the output port assuming the modification of step 1212 and
coupling of step 1214 have occurred correctly. Finally, in step
1218, the signal received by the supplemental signal detectors is
compared to the signal as modified in step 1212 and if they compare
favorably then execution simply returns to step 1204 and the
polling loop of process of 1200 continues.
[0099] If, on the other hand, the supplemental signal detected at a
particular output port does not match the modified supplemental
signal that was injected at a corresponding input port, this
signifies malfunction of optical matrix 410 and execution proceeds
to step 1220. If the detected supplemental signal information
happens to match the supplemental signal information that was
originally received in step 1204 prior to being modified in step
1212, then, in step 1222, an alarm is issued indicating that the
process of injecting or modifying the supplemental signal within
supplemental signal injector 720 is not working properly. T his is
a useful self-checking provision so that the traffic path is not
subjected to restoration activities if the fault actually lies
within the supplemental signal equipment itself.
[0100] Otherwise if, in step 1220, the detected supplemental signal
does not match either of the original version or the modified
version of the incoming supplemental signal then, finally, in step
1224, an alarm is issued indicating a malfunction of the optical
matrix and execution returns to step 1204 to continue the polling
as to the status of the optical cross-connect switch.
[0101] Those of ordinary skill in the art will recognize that a
similar approach to injecting or modifying supplemental signals
coming into a optical matrix and applying supplemental signal
detectors to receive and detect such signals may also be applied
even within the internal elements of an optical matrix in order to
better pinpoint switching elements that are malfunctioning.
Injection and detection of the supplemental signal may also be
accomplished in various ways and various places within the optical
cross-connect matrix. For example, if the switching elements are
electro-optic or semiconductor optical amplifiers then a slight
modulation may be applied even to the switching element in order to
superimpose modulation upon the optical carrier.
[0102] As is evident in the arrangement of FIG. 9, it is possible
that at least one implementation of a supplemental signal modifier
may also serve as a supplemental signal detector and may provide an
output to the OCCS of information arriving on the inbound optical
signal. This allows for modes of operation similar to FIG. 10 or
FIG. 13. In light of the present disclosure, those of ordinary
skill in the art may readily combine various techniques taught
herein to utilize the receive output of a supplemental signal
modifier for verifying optical signal routing.
[0103] FIG. 13 depicts a method for verifying optical signal
routing through a switch matrix and is generally applicable to any
arrangement wherein a known signal entering the matrix may be
compared to a detected signal exiting the matrix. Process 1300
begins with step 1302 upon power up and initialization of a
cross-connect switch. In step 1304, a first optical port is coupled
to a second optical port through the cross-connect matrix of the
switch. Presumably, then, an optical signal entering the first port
will be emitted from the second port substantially intact.
[0104] As described herein, it is possible that the optical signal
entering the first port may have a co-propagating supplemental
signal component. This supplemental signal may originate locally or
remotely. If such a supplemental signal exists, then it is expected
that the supplemental signal will be present at the second port
once coupling has occurred according to step 1304. If it is known,
by whatever means, what supplemental signal is present along the
first port but no matching supplemental signal is present at the
second port, then the optical matrix has clearly failed to
accomplish the intended coupling of step 1304.
[0105] It is also possible that there may be no optical signal
present at the first port or that there may be no supplemental
signal therewith. In this case, it is expected that no supplemental
signal will be present at the second port once coupling has
occurred according to step 1304. If it is known, by whatever means,
that no supplemental signal is present along the first port, yet a
supplemental signal is present at the second port, then the optical
matrix has incorrectly coupled a signal from some other port to the
second port.
[0106] Thus, after attempting a coupling in step 1304, step 1306 is
performed to compare a supplemental signal, if any, known to be
present at the first port to a supplemental signal observed at the
second port. If the known supplemental signal input at the first
port is not in agreement with the observed supplemental signal at
the second port, then a matrix malfunction fault alarm is declared
in step 1308 and the process loops back to step 1306 to continually
monitor for agreement between the input and output.
[0107] If, in step 1306, the input and output supplemental signals
are consistent with one another as described above, then no matrix
malfunction alarm need be declared and the process continues with
step 1310 to perform a comparison of signal amplitudes.
[0108] In step 1310, the amplitude of the supplemental signal at
the first port is compared to that at the second port and a net
signal loss or gain is calculated. As those of skill in the art
will appreciate, a path through an optical switch may entail loss
or gain depending on many factors, such as whether the switch uses
active elements or passive elements. Loss or gain in itself may not
present a problem, but it is expected that such loss or gain should
remain consistent through a given combination of ports. Degraded
performance of elements in the switch may cause increased loss
through the switch. Loss through a switch or along a path is
another aspect of path integrity that may be verified or monitored
in accordance with the present invention. Steps 1310 and 1312 are
performed for monitoring the loss through the switch and detecting
degradation.
[0109] Step 1312 involves comparing the loss measurement from step
1310 to historical or expected values for the loss and determining
if a noteworthy degradation has occurred. If degradation has
occurred, then, in step 1314, a matrix loss warning is issued by
the optical cross-connect switch and may be reported externally to
a network management system. Otherwise the process simply returns
to step 1306 to continue monitoring the agreement between input and
output signals. Of course, as an alternative, these steps may be
executed just once or a few times immediately after switching
activities or just occasionally after the initial switching.
[0110] As those of ordinary skill will recognize, process 1300 is
applicable at least to the arrangements depicted in FIGS. 4-7 and
may be performed cooperatively with the processes of FIGS.
10-12.
[0111] FIG. 14 of the drawings describes a process 1400 for
analyzing supplemental signals which may be useful in the case
where a supplemental signal undergoes modification yet some
attributes of the original signal may be extracted or inferred from
the modified supplemental signal. Process 1400 may be applicable,
for example, to the arrangement of FIG. 7 when the modification
performed by the supplemental signal modifiers is additive or
cumulative in nature.
[0112] Process 1400 commences at step 1402 upon the need to
evaluate proper routing of a given optical signal. Execution
immediately proceeds to step 1404 wherein an optical signal is
received at the cross-connect switch, the optical signal having an
associated supplemental signal.
[0113] Next, in step 1406, the supplemental signal undergoes
modification which may be of many varieties mentioned previously.
For example, this modification may involve appending local data to
a string of data already present in the received supplemental
signal.
[0114] In step 1408, the received optical signal, along with the
now modified supplemental signal, is passed through the switching
matrix and presumably to a particular matrix output port to which a
supplemental detector is coupled.
[0115] In step 1410, the supplemental signal is detected at the
output port where the received optical signal port is supposed to
be coupled assuming correct operation of the switch matrix. The
supplemental signal, if any, is recovered and any attributes of the
signal or information borne by the signal are rendered by the
detector.
[0116] In step 1412, the supplemental signal is further processed
to determine the attributes or information content that must have
been present on the received supplemental signal prior to
modification.
[0117] In step 1414, it is determined whether the modification
applied locally in step 1406 indeed appears in the supplemental
signal as detected in step 1410. Successful finding of the local
modification indicates continuity through the switch and implies
proper operation of the switch matrix.
[0118] If the local modification is present in the detected signal,
then execution proceeds to step 1416, to check for correct routing
of the received signal. The received supplemental signal
information determined in step 1412 is compared to expected values
for the inbound signal which may be obtained from external sources
as described earlier. If the inferred original signal agrees with
what is expected to be received at the switch, then no alarm
condition need be declared and execution simply resumes step 1404
to continue monitoring using the remainder of process 1400.
[0119] Otherwise, if the original signal is incorrect despite
proper continuity being indicated in step 1414, then a misrouting
fault alarm is issued in step 1418 and the process loops to step
1404 to continue monitoring the supplemental signal.
[0120] Returning to step 1414, if the local modification is not
evident in the detected supplemental signal, step 1420 is performed
to determine if the lack of local continuity is corroborated by the
remainder of the signal information or may be attributable to
failure of the local modifier. In step 1420, the original signal
inferred in step 1412 is compared to knowledge of what signal is
expected to be received. Assuming that the supplemental signals
along each of the many input ports are fairly unique, then
detection of a correct original signal missing only the local
modifications may indicate a failure the local modification
process. Accordingly, if the determination in step 1420 is
affirmative, then a "modifier malfunction warning" is issued in
step 1422 and then execution loops to step 1404 to continue
monitoring the supplemental signal.
[0121] If, in step 1420, it is determined that no aspects of the
detected signal are correct, then a matrix malfunction alarm is
declared in step 1424 and then execution loops to step 1404 to
continue monitoring the supplemental signal.
[0122] While this invention has been described with reference to
several illustrative embodiments, this description is not intended
to be construed in a limiting sense. Various modifications and
combinations of the illustrative embodiments, as well as other
embodiments of the invention, will be apparent to persons skilled
in the art upon reference to the description. It is therefore
intended that the appended claims encompass any such modifications
or embodiments.
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