U.S. patent application number 09/804365 was filed with the patent office on 2001-11-22 for method and system for restoring coincident line and facility failures.
Invention is credited to Liu, Shoa-Kai, Wellbrock, Glenn.
Application Number | 20010043560 09/804365 |
Document ID | / |
Family ID | 21698274 |
Filed Date | 2001-11-22 |
United States Patent
Application |
20010043560 |
Kind Code |
A1 |
Liu, Shoa-Kai ; et
al. |
November 22, 2001 |
Method and system for restoring coincident line and facility
failures
Abstract
The system and method of the present invention provide
restoration of coincident line and facility failures. The system of
the present invention includes light termination equipment (LTE)
that is capable of detecting failures, determining the type of
component that failed, determining which restoration facility to
use based on the type of component that failed, and providing
restoration. The system of the present invention also includes
spare capacity for restoration, including protect channels and an
optical restoration network. In addition, the system of the present
invention includes an optical cross connect switch (OCCS) that is
capable of switching electrical signals to the optical restoration
network. The method of the present invention is involves detecting
a failure, determining the type of component that failed, and
sending an alarm to a centralized management center.
Inventors: |
Liu, Shoa-Kai; (Richardson,
TX) ; Wellbrock, Glenn; (Wylie, TX) |
Correspondence
Address: |
MR. PAUL ROBERTS
MCI WORLDCOM
1133 19TH STREET NW (9854/003)
WASHINGTON
DC
20036
US
|
Family ID: |
21698274 |
Appl. No.: |
09/804365 |
Filed: |
March 12, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09804365 |
Mar 12, 2001 |
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09001884 |
Dec 31, 1997 |
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6233072 |
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Current U.S.
Class: |
370/216 ;
370/225 |
Current CPC
Class: |
H04Q 11/0062
20130101 |
Class at
Publication: |
370/216 ;
370/225 |
International
Class: |
G01R 031/08 |
Claims
What is claimed is:
1. In a network subject to a previous failure and a subsequent
failure, a method for restoring the network comprising the steps
of: overcoming the previous failure using a first protection
scheme; detecting the subsequent failure; determining that the
previous failure can be overcome using a second protection scheme;
determining that the subsequent failure can be overcome using the
first protection scheme but can not be overcome by using the second
protection scheme; applying the second protection scheme to
overcome the previous failure; and applying the first protection
scheme to overcome the subsequent failure.
2. The method of claim 1 further comprising the step of:
determining that the first protection scheme is unable to overcome
the subsequent failure because the first protection scheme has
already been applied to overcoming the previous failure.
3. The method of claim 1 wherein the first protection scheme is
designed to circumvent a failure affecting a span in the network
using a spare resource within the span and the second protection
scheme is designed to circumvent a failure affecting a span in the
network using a resource outside of the span.
4. The method of claim 1 wherein the step of determining that the
previous failure can be overcome using a second protection scheme
is based upon a failure type associated with the failure.
5. The method of claim 1 wherein the step of determining that the
previous failure can be overcome using a second protection scheme
is based upon a whether the previous failure is a module failure or
a line failure.
6. The method of claim 1 wherein the step of determining that the
subsequent failure can be overcome using a first protection scheme
is based upon a failure type associated with the subsequent
failure.
7. The method of claim 1 wherein the step of determining that the
subsequent failure can be overcome using a first protection scheme
is based upon a whether the subsequent failure is a module failure
or a line failure.
Description
[0001] This application is a divisional application of pending U.S.
application Ser. No. 09/001,884 filed Dec. 31, 1997 the disclosure
of which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates generally to the reliability
and restoration of optical transmission systems.
[0004] 2. Related Art
[0005] Telecommunications networks that carry telephone calls and
data include interconnected sites or nodes that process calls and
route data. Optical transmission lines or links interconnect the
nodes.
[0006] High speed data is modulated on light waves which are
transmitted through the optical network. Any type of data can be
carried over an optical link, including but not limited to speech,
data input into or retrieved by a computer or computer database,
and any digital data. Fiber optic cables carry far greater amounts
of digital data than conventional electrical cables. A single
optical channel operating at approximately 10 Gigabits/second
(Gb/s) and transmitting data rate according to a high-speed
synchronous digital hierarchy standard, such as the SONET OC-192
protocol, carries a data rate equivalent to 129,024 voice
calls.
[0007] Multiple links are often employed between nodes to increase
communications capacity and to provide back-up in the event of
partial failures. The set of links interconnecting a given pair of
nodes is referred to as a "span."
[0008] Further bandwidth improvement can be achieved by sending
multiple modulated lightwave carriers at different frequencies
through a single fiber. This technique is known as wavelength
division multiplexing (WDM). Optical systems using WDM require
optical transmitters and receivers that operate at different light
wave frequencies. The optical transmission line, connecting an
optical transmitter and receiver, can propagate many light wave
signals of different frequencies simultaneously. For example, at
least sixteen OC-192 channels can be carried on a single fiber pair
within the co-called "erbium band." A method and system for WDM is
described in copending U.S. Application Attorney Docket No.
RIC-96-153 (1575.2550000), entitled, "Method and System for Modular
Multiplexing and Amplification in a Multi Channel Plan," filed by
Viet Le on Sep. 4, 1997, assigned to the assignee of the present
invention and incorporated by reference herein. Another optical
system is described in copending U.S. application Ser. No.
08/672,808 entitled, "System and Method for Photonic Facility and
Line Protection Switching," filed by John Fee on Jun. 28, 1996,
assigned to the assignee of the present invention, and incorporated
by reference herein.
[0009] Thus, fiber optic communications links, especially WDM
communication links, carry vast amounts of information among
distant sites to accomplish data, voice and image connectivity over
a large geographical area. Optical transmission lines, transmitters
and receivers, however, can fail. The failure of such components
can have a substantial economic and practical impact on network
users and network service providers. Therefore, in designing
communications networks, special measures are practiced to assure
utmost reliability of network components and survivability in the
event of a failure.
[0010] Two types of failures experienced in a telecommunications
network are line failures and module failures. A link in a
telecommunications network has a transmitter and a receiver, which
are also referred to as modules, and a line between the transmitter
and receiver. Line failures include damage to the physical fiber
and optical component failure, such as the malfunction of
amplification equipment situated along the fiber optic cable. Line
failures affect the communications line between two network sites.
In contrast, a failure of the transmit or receive equipment, such
as a laser diode transmitter, housed at either end of an optical
communications link is referred to as a module failure. Both line
failures and module failures may disable a link between two
nodes.
[0011] In the event of either a line or module failure, restoration
techniques are used to restore the traffic temporarily until the
failure is repaired. The restoration approach varies depending on
the failure. Traffic may be restored using line protect switching
(LPS) or network restorative switching (NRS). If the traffic is
restored using LPS, line terminating equipment (LTE) switches the
signal from the failed channel to a spare channel within the LTE.
If the traffic is restored using NRS, traffic is rerouted by
switching the traffic to different routes through the network,
based on information stored in switch tables or a pre-planned
algorithm stored in the switch or a dynamic algorithm which
discovers alternate routes at the time of a failure.
[0012] LPS is performed strictly within a span. If one
traffic-bearing link fails, the LTE's at each end of the span
switch to a protect channel or protect link reserved within the
span.
[0013] In contract to LPS, NRS involves rerouting of traffic
through a set of nodes in a mesh network and may be used to recover
even from failures wherein an entire span is disabled. A technique
for accomplishing network restoration is taught by Grover in U.S.
Pat. No. 4,956,835. NRS is a means by which spare capacity
distributed across the many spans of a network can contribute to
the survivability of span failure. Thus, network survivability is
improved while minimizing wasteful redundancy at each span.
[0014] LPS ensures resiliency to fiber cuts by employing a spare
link, referred to as the protect channel, that normally does not
carry traffic but may be used as a back-up should a traffic-bearing
link fail. The protect channel is on a different path in order to
reduce the likelihood that the protect channel will experience the
same failure as the channel in use. Creating and maintaining idle
spare capacity is costly. In order to reduce costs, one spare
channel is available for restoration of multiple traffic carrying
channels. This is called a 1:N or one-to-N protection scheme. When
one protect channel is available to restore multiple traffic
carrying channels, LPS cannot restore a failure of more than one
link. LPS is primarily aimed at restoring single link failures and
is implemented within LTE which is the local equipment that
terminates the fiber optic cable. Since LPS is localized and
simple, it is also very fast requiring only tens of milliseconds
for restoring a failed communications link.
[0015] Because telecommunications networks include high capacity
optical cables such as WDM, the networks are susceptible to
failures that disable a very large number of channels and which
cannot be restored by LPS alone causing potential high volumes of
traffic loss and significant economic impact. Accordingly, NRS is
used to restore optical networks. Exchanges have the capability to
reroute traffic automatically using switch tables or an algorithm
to other transmission paths in the network. Exchanges which have
switching capability are connected to LTE at each site and to other
transmission paths in the network. When a fiber cut or other major
fiber failure occurs disabling a span including a large number of
telecommunications links between two switching nodes, NRS is
employed by the exchange to reroute the traffic through the
restoration network to circumvent the failure until repairs are
completed.
[0016] Line protect switching (LPS) and network restorative
switching (NRS) have separate but complementary roles in a modern
network design. The LPS can quickly restore simple localized
failures without having to invoke the more complex NRS. In many
applications, the LPS can switch traffic without causing any
significant interruption to traffic. The NRS can handle network
problems of a larger scope.
[0017] However, current LPS techniques do not allow for the
restoration of failures that involve more than one channel.
Although current LPS reroutes the traffic to a spare protect
channel, only one protect channel is available to restore multiple
channels. Therefore, if the protect channel is in use restoring one
link failure, subsequent failures cannot be restored using LPS.
[0018] In addition, current NRS does not allow for restoration by
components in the optical network via a restoration network.
SUMMARY OF THE INVENTION
[0019] In the present invention, line terminal equipment (LTE)
sends an alarm to an optical cross connect switch (OCCS) controller
to restore a failure when a protect channel is in use. The OCCS
controller controls multiple optical cross connect switches (OCCSs)
and addresses alarms by determining whether they can be restored.
An OCCS is an optical switching device that interconnects numerous
optical transmission lines to an optical restoration network. An
optical restoration network includes complete restorative spans of
telecommunications links connected by the OCCSs.
[0020] The system of the present invention includes LTE, an OCCS,
and an OCCS controller that are capable of restoring a second
failure within one telecommunications cable. The LTE of the present
invention can reroute optical and electrical signals to compensate
for a failed component such as an optical transmitter, receiver, or
transmission line. The present invention includes a protect, or
spare, optical transmission line with which to replace a
corresponding failed channel. The LTE can switch to the protect
channel when a channel fails due to either line or module failure.
The LTE of the present invention is also capable of determining the
facility type of channel failures and sending an alarm to the OCCS
to reroute failure of a line via the optical restoration network if
one of the two failures is a line failure.
[0021] The OCCS of the present invention can reroute optical and
electrical signals to compensate for a channel that experiences
line failure. However, the OCCS cannot restore a channel that
experiences module failure. As a result, when two coincident
failures, a line and facility failure, occur the present invention
restores the line failure via the first OCCS switching and restores
the module failure using the protect channel.
[0022] The OCCS controller of the present invention is capable of
receiving the alarm from the LTE notifying of a failure and sending
a request to the OCCS to restore a failed line through the optical
restoration network.
[0023] The method of restoring coincident line and facility
failures is employed when a subsequent failure is detected. The
subsequent failure is analyzed to determine the facility type of
the failure. If the subsequent failure is due to a line failure, an
alarm is sent to the OCCS and the subsequent failure is restored
via the optical restoration network. If the subsequent failure is
due to a module failure, the facility type of the previous failure
is determined. If the facility type of the previous failure is
failure of a line, an alarm is sent to the OCCS and the previous
failure is restored via the optical restoration network. If the
facility type of the previous failure is also failure of a module,
an alarm is sent to the network management center indicating that a
non-restorable failure has occurred.
[0024] Further features and advantages of the invention, as well as
the structure and operation of various embodiments of the
invention, are described in detail below with reference to the
accompanying drawings.
BRIEF DESCRIPTION OF THE FIGURES
[0025] The present invention is described with reference to the
accompanying drawings, wherein:
[0026] FIG. 1 is a block diagram of an optical restoration
environment according to one embodiment of the present
invention;
[0027] FIG. 2 is a block diagram of an optical cross connect
according to one embodiment of the present invention;
[0028] FIG. 3 is a flowchart of the operation of the optical cross
connect according to one embodiment of the present invention;
[0029] FIG. 4A is a block diagram of the optical cross connect
illustrating the use of a protect channel to restore a single line
failure according to one embodiment of the present invention;
[0030] FIG. 4B is a block diagram of the optical cross connect
illustrating the response to a first and second line failure
according to one embodiment of the present invention;
[0031] FIG. 4C is a block diagram of the optical cross connect
illustrating the response to a second module failure and first line
failure according to one embodiment of the present invention;
and
[0032] FIG. 5 is a block diagram of an optical cross connect switch
controller according to one embodiment of the present
invention.
[0033] In the drawings, like reference numbers generally indicate
identical, functionally similar, and/or structurally similar
elements. The drawing in which an element first appears is
indicated by the leftmost digit(s) in the corresponding reference
number.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Table of Contents
[0034] 1.0 Overview
[0035] 2.0 Terminology
[0036] 3.0 Example Optical Restoration Environment
[0037] 4.0 Optical Cross Connect Network
[0038] 5.0 Restoration of Coincident Line Failures
[0039] 1.0 Overview
[0040] The present invention provides a system and method of
restoring subsequent failures within a telecommunications network.
A system and method are provided for sending an alarm from optical
line terminating equipment (LTE) to an optical cross connect switch
OCCS) controller. The OCCS controller addresses the alarm by
determining whether to restore the failure by sending a command to
an optical cross connect switch (OCCS). The OCCS controller can
identify the facility type of the subsequent failure and retrieve
the facility type of previous failures in order to ensure that a
protect or spare channel is made available to restore a module
failure in the event restoration of a module failure is needed.
[0041] The system and method of the present invention is
illustrated as operating in an exemplary telecommunications network
that carries digitized voice between two individuals speaking on
telephones. The present invention is further illustrated within an
exemplary optical cross connect network that is within the
telecommunications network. However, the present invention is not
limited to these environments and may be used in any network that
requires restoration such as an X.25 network transmitting data.
[0042] 2.0 Terminology
[0043] Provided below is a brief description of the terminology
used within this document. Additional description is provided in
the following sections along with exemplary implementations and
embodiments. However, the present invention is not limited to the
exemplary implementations and embodiments provided.
[0044] A "telecommunications network" is a network that carries
information. The information may be digitized voice that is carried
between two telephones or data that is carried between two
computers. Several examples of telecommunications networks follow
in the description of FIG. 1, however, a telecommunications network
is not limited to these examples.
[0045] A telecommunications network may include termination
equipment, optical cross connect switches, and optical cross
connect switch controllers. "Termination equipment" is equipment
that terminates a cable within a telecommunications network and
typically provides modulation and demodulation functionality.
Exemplary termination equipment is light termination equipment
described further with respect to FIG. 1 and FIG. 2.
[0046] An "optical cross connect switch" provides switching
functionality within an optical network. An optical network is a
network within a telecommunications network that is comprised of
transmission facilities that carry optical signals. An optical
network may provide high speed transmission and be capable of
carrying a significant amount of data.
[0047] "Optical cross connect switch controllers" accept
information from termination equipment and use the information to
provide commands to optical cross connect switches. Optical cross
connect switch controllers are processors with access to memory via
a separate or an associated memory storage device such as a hard
drive, disk, and/or standalone database. However, an optical cross
connect switch controller is not limited to these embodiments and
may be any capability to control one or more optical cross connect
switches. More detail is given about optical cross connect switch
controllers below.
[0048] A "failure" is a component that experiences operational
difficulties within the telecommunications network. A disabling
event causes the failure of one or more components within the
telecommunications network. If multiple failures occur, after the
first failure occurs, a later failure is referred to as a
"subsequent failure" and the first failure or a previous failure is
referred to as a "previous failure."
[0049] Components within the telecommunications network can be
grouped into types of components, such as lines and modules. As
used herein, the "failed facility type" characterizes a failed
component as either a "line failure" or a "module failure."
Likewise, the "previous failed facility type" as used herein may be
either a "line failure" or a "module failure."
[0050] 3.0 Example Optical Restoration Environment
[0051] FIG. 1 is a block diagram of an optical restoration
environment 101 according to one embodiment of the present
invention. Optical restoration environment 101 provides
connectivity and switching capability for telecommunications
services. An exemplary use for the optical restoration environment
101 is to restore channels in a network carrying a call placed by a
caller on a first telephone 102 to a receiver on a second telephone
120. However, optical restoration environment 101 may be used to
restore any voice or data traffic carried on a network.
[0052] Optical restoration environment 101 includes a first
telephone 102 used by a caller that is interconnected to a second
telephone 120 used by a receiver via a telecommunications network
122. Telecommunications network 122 includes a first exchange 104,
an optical cross connect 116, a second exchange 118, and an optical
restoration network 110.
[0053] The first telephone 102 is connected to a first exchange 104
within the telecommunications network 122. The first exchange 104
provides switching functionality to connect to the appropriate
telecommunications channel to establish service to the second
telephone 120. The first exchange 104 is connected to optical cross
connect 116 which is equipment that provides termination and
optical switching for channels carried on an optical
telecommunications cable 113. In addition, the optical cross
connect 116 is connected to a second exchange 118 in order to
establish connectivity via a channel link between the first
telephone 102 and the second telephone 120. The second exchange 118
is connected to the second telephone 120 to provide switching and
connectivity to second telephone 120.
[0054] According to the present invention, the optical cross
connect 116 is also connected to the optical restoration network
110 to provide restoration in the event of channel or cable
failure. The optical cross connect 116 includes a first light
termination equipment (LTE) 106 and second LTE 114. The optical
cross connect 116 also includes a first optical cross connect
switch (OCCS) 108 and a second OCCS 112. The first exchange 104 is
connected to the first LTE 106. The first LTE 106 handles call
termination, data rate conversion, and light protect switching
(LPS) restoration functions. The first LTE 106 is connected to the
first OCCS 108. The first OCCS 108 provides optical switching
capability needed for network restoration switching (NRS) via the
optical restoration network 110. The first OCCS 108 is connected to
a second OCCS 112 for connectivity to the second telephone 120. The
path between the first OCCS 108 and the second OCCS 112 is
illustrative only. As would be apparent to a person skilled in the
art, additional intermediate optical cross-connect switches and
filters can be added in a point-to-point circuit or any network
topology (eg. ring, mesh). In addition, the optical cross connect
116 includes an optical cross connect switch (OCCS) controller 111
which is connected to the first LTE 106, the second LTE 114, the
first OCCS 108, and the second OCCS 112 to provide control and
allow for rerouting via the optical restoration network 110.
[0055] The first telephone 102 and second telephone 120 are used to
place and receive calls via the telecommunications network 122. The
first telephone 102 and second telephone 120 are exemplary and may
be any equipment that can be used to initiate or receive a call via
a telecommunications network 122. Examples of other types of
equipment that can be used to initiate and receive a call via the
telecommunications network 122 are a wireless telephone, a pager, a
personal computer and a modem.
[0056] The first exchange 104 and second exchange 118 are exemplary
exchanges within the telecommunications network 122. The first
exchange 104 and second exchange 118 provide switching capability
to route a call via a telecommunications link that interconnects to
the caller's destination. The first exchange 104 and second
exchange 118 may be implemented using DMS-250 switches manufactured
by Nortel.
[0057] The telecommunications network 122 may comprise many
telecommunications networks including local exchange networks and
interexchange networks. Typically equipment used to initiate and
receive a call, such as first telephone 102 and second telephone
120, is interconnected to an exchange within a local exchange
network. Therefore, exemplary first exchange 102 and second
exchange 118 are within a local exchange network. A local exchange
network comprises switches and termination equipment within a
localized area. An example of a local exchange network is a local
telephone operating company network such as Bell Atlantic. If the
caller is calling long distance, the local exchange network will
send the call to an interexchange switch in an interexchange
network.
[0058] Similar to the local exchange network, an interexchange
network comprises a plurality of switches, also referred to as
exchanges, that are located throughout a geographic area. However,
interexchange networks typically comprise of switches throughout a
large geographic area to process long-distance telephone calls. For
example, a national interexchange network comprises switches
located throughout the nation. When a call is routed to the
interexchange network, it may be routed to one or more switches
within the interexchange network.
[0059] Optical cross connect equipment, such as exemplary optical
cross connect 116, is connected to the telecommunications cables
within telecommunications network 122, such as exemplary
telecommunications cable 113 between the first exchange 104 and
second exchange 118. The optical cross connect 116 provides
termination and switching functionality for signals carried on
optical telecommunication cable 113.
[0060] The optical cross connect 116 includes a first LTE 106 and a
second LTE 114. The first LTE 106 and second LTE 114 terminate the
telecommunications cable 113. The first LTE 106 and second LTE 114
will be described in further detail with respect to FIG. 2.
[0061] The optical cross connect 116 includes a first OCCS 108 and
a second OCCS 112. The first OCCS 108 and second OCCS 112 can by
any type of optical switch. For example, the first OCCS 108 and
second OCCS 112 may be implemented using combinations of an
integrated lithium niobate directional-coupler type switch. Other
types of suitable optical switching technology include switches
based on thermo-optic effect in polymer waveguides or silica glass,
semiconductor amplification, piezo movement, and integrated indium
phosphide. In addition, although a single first OCCS 108 and second
OCCS 112 are shown for clarity, multiple discrete switches and
couplers can be used to perform equivalent multiple-port optical
switching.
[0062] The OCCS reroutes traffic based on an algorithm. An
exemplary algorithm is the Real-Time Multiple Wavelength Routing
(RMWR) algorithm which uses collected data to select an alternate
path based on wavelength information stored in a centralized
database. RMWR is described in further detail copending U.S.
application Ser. No. 08/580,608 entitled, "Restoration System for
an Optical Telecommunications Network" filed by Shoa-Kai Liu on
Dec. 29, 1995, assigned to the assignee of the present invention,
and incorporated by reference herein. An additional description of
an algorithm used for rerouting traffic is described in U.S. Pat.
No. 4,956,835 entitled, "Method and Apparatus for Self-Restoring
and Self-Provisioning Communication Networks" filed by Grover on
Sep. 11, 1990 which is incorporated by reference herein.
[0063] The first OCCS 108 and second OCCS 112 are connected to a
telecommunications cable 113. The telecommunications cable 113
includes bidirectional optical fibers, line repeaters, and/or
amplifiers. Alternatively, the telecommunications cable 113 may
include long-haul, single mode fiber. The telecommunications cable
113 is not linked to these components and may be any transmission
medium cable of carrying signals in a telecommunications
network.
[0064] The optical restoration network 110 is connected to the
first OCCS 108 and the second OCCS 112. The optical restoration
network 110 comprises spare optical termination and cross connect
equipment for restoration of traffic if the optical cross connect
116 in use fails. The optical restoration network 110 includes a
plurality of spare components including LTEs, such as the first LTE
106 and the second LTE 114, OCCSs, such as the first OCCS 108 and
second OCCS 112, and telecommunications cables, such as
telecommunications cable 113.
[0065] The OCCS controller 114 is connected to the first LTE 106,
the second LTE 114, the first OCCS 108, and the second OCCS 112.
The OCCS controller 111 can be connected to any number of LTE and
OCCSs. The OCCS controller 111 receives information from the first
LTE 106 and the second LTE 114. If the information indicates that
traffic must be rerouted, the OCCS controller 111 sends commands to
the first OCCS 108 to reroute electrical signals via the optical
restoration network 110. The OCCS controller 111 may be implemented
using any processor or a plurality of distributed processors that
are coordinated by a communication link not shown.
[0066] 4.0 Optical Cross Connect Network
[0067] FIG. 2 is a block diagram of optical cross connect 116.
Illustrated within the first LTE 106 and the second LTE 114 are the
transmitters, 206A, 206B, 206C, . . . 206n, and the receivers,
210A, 210B, 210C, . . . 210n. Each one of the transmitters 206 is
connected to a corresponding one of the receivers 210 via one of
multiple channels 214A, 214B, 214C, . . . 214n within the
telecommunications cable 113. Also within telecommunications cable
113 is a protect channel 212. The protect channel 212 is spare and
is used for restoration if one of the channels 214 in use fails.
The protect channel 212 is connected to a transmitter 204 within
the first LTE 106 and a receiver 208 within the second LTE 114.
[0068] Although, both first LTE 106 and second LTE 114 have
transmitters and receivers, transmitters 206 are shown only in the
first LTE 106 and receivers 210 are shown only in the second LTE
114 for clarity. The transmitters and receivers are typically in an
array made up of pairs of transmitters and receivers. In FIG. 2,
each of the transmitters 206 would actually be a transmit and
receive pair.
[0069] Each of the transmitters 206 transmit a signal carrying a
digitized voice of a caller or any other data that was sent by
equipment that originated a call, which is shown in FIG. 1 as
exemplary first telephone 102. In one embodiment, the transmitters
206 are modulated lasers, such as directly modulated semiconductor
laser diodes or externally modulated lasers. Each one of the
transmitters 206 is connected to one of the multiple channels 214
within the telecommunications cable 113. The transmitters 206
transmit signals via the channels 214 within the telecommunications
cable 113 to the receivers 210.
[0070] Similar to the transmitters 206, each one of the receivers
210 is connected to one of the multiple channels 214 within
telecommunications cable 113 to receive signals from the
corresponding one of the transmitters 206. The receivers 210
demodulate electrical signals from the light wave signal of the
corresponding carrier frequency. Receivers 210 can be optical
detectors or any equipment that can receive and transduce the
transmitted signal.
[0071] In one example, each one of the channels 214 within
telecommunications cable 113 is an optical channel within a fiber
optic cable. The signals within an optical fiber are modulated
using various frequencies which allow one fiber optic cable to
carry a large number of channels. As mentioned above, this
technique is referred to as wavelength division multiplexing (WDM).
Example transmitters, receivers, and fiber optic cables and WDM are
described in further detail in the above referenced application
Attorney Docket No. RIC-96-153 (1575.2550000). In addition,
transmitters, receivers, and fiber optic cables are described in
the above referenced '808 application. Further description of
transmitters, receivers, and fiber optic cables is given by Daniel
Minoli in chapter 7 of his book entitled, "Telecommunications
Technology Handbook," Artech House, Inc. (1991) incorporated herein
by reference.
[0072] Each of the channels 214 (also referred to as traffic
carrying channels) carry normal non-restoration traffic within the
telecommunications cable 113. The protect channel 212 is an optical
channel within a fiber optic cable that is achieved by modulating a
signal at a particular frequency. Also, the transmitter 204 that
transmits via the protect channel 212 is a modulated laser like the
transmitters 206 on the other channels 214. The transmitter 204 may
be implemented using the same technologies as the transmitters 206
on the other channels 214 within the telecommunications cable 113.
Like the receivers 210 that receive signals from the traffic
carrying channels 214, the receiver 208 on the protect channel 212
demodulates the received signal. The receiver 208 may be
implemented with the same technologies as the receivers 210 that
receive signals from the other channels 214.
[0073] Both the first LTE 106 and the second LTE 114 have
processors referred to as the first LTE processor 216 and the
second LTE processor 218, respectively. The first LTE processor 216
is connected to each of the transmitters 206 to obtain information
about whether each of the transmitters 206 is in use and whether
the transmitters 206 are experiencing operational difficulties.
Similarly, the second LTE processor 218 is connected to each of the
receivers 210 to obtain information about whether each of the
receivers 210 is in use and whether the receivers 210 are
experiencing operational difficulties. The first LTE processor 216
and the second LTE processor 218 are connected to the protect
channel transmitter 204 and protect channel receiver 208,
respectively to obtain information about whether the protect
channel 212 is in use and whether the protect channel is
experiencing any operational difficulties. The first LTE processor
216 and second LTE processor 218 are any processor that can obtain
information from and coordinate among the components with a first
LTE 106 or second LTE 114.
[0074] 5.0 Restoration of Coincident Failures
[0075] FIG. 3 illustrates a restoration process 301 according to
the present invention. FIG. 3 will be described with reference to
the example of FIGS. 4A, 4B, and 4C which illustrate various
failures of channels 214 within telecommunications cable 113.
[0076] In step 304, either the first LTE 106 or the second LTE 114
detects a failure 404 in channel 214A. The first LTE 106 may detect
a failed transmitted 206. A single optical detector at the second
LTE 114 can detect a failure and send a fault signal to the second
LTE processor 210 within the second LTE 114. Failure 404 may be
detected electrically at first LTE 106 using conventional loss of
signal techniques. Alternatively, failures may be detected by
multiple optical detectors (not shown) along the channels 214. If
an optical detector detects a failure on one of the channels 214,
the optical detector will send a fault signal to the first LTE 106.
Various methods of optical failure detection including optical and
electrical detection techniques can be used including those that
are described further in co-pending U.S. application Ser. No.
08/580,391 entitled, "Method and System for Detecting Optical
Faults Within the Optical Domain of a Fiber Communication Network,"
filed by Shoa-Kai Liu on Dec. 28, 1995 which is assigned to the
assignee of the present invention and is incorporated by reference
herein.
[0077] In step 306, either the first LTE 106 or the second LTE 114,
whichever detected the failure, determines whether the protect
channel 212 is in use. A determination of whether the protect
channel 212 is in use is made to evaluate whether the protect
channel 212 is available to restore the detected failure. FIG. 4A
illustrates a single line failure in which the protect channel is
available to restore the detected failure 404. If the protect
channel 212 is not in use, the protect channel 212 is available to
restore the detected failure 404 and the first LTE 106 proceeds to
step 308. If the protect channel 212 is in use, the first LTE 106
proceeds to step 309 and sends an alarm to the OCCS controller
111.
[0078] In step 308, traffic is restored by the first LTE 106 on the
protect channel 212. FIG. 4A illustrates using the protect channel
212 to circumvent the single line failure 404. The incoming line to
the first channel 214A is interconnected to the protect channel
transmitter 204 rather than the first channel transmitter 206A. The
protect channel 212 provides connectivity that circumvents the
failed channel 214A. The protect channel receiver 208 within the
second LTE 114 receives the signal and sends the signal to the next
component that will receive the signal and provide connectivity to
the final destination, for example the second exchange 118 as shown
in FIG. 1.
[0079] FIGS. 4B and 4C illustrate multiple failures within
telecommunications cable 113. If the protect channel 212 is in use,
step 309 is performed to restore the detected failure. In step 309,
the first LTE 106 or second LTE 114, whichever detected failure
404, sends and alarm to the OCCS controller 111. The information is
sent by first LTE processor 216 or the second LTE processor 218.
The first LTE processor 216 obtains the information from one of the
transmitters 206. The second LTE processor 218 obtains the
information from one of the receivers 210. The first LTE processor
216 and the second LTE processor 218 send the OCCS controller 111
information including whether the failure is a line failure or a
module failure.
[0080] A failure on a channel 214 may be either a line failure or a
module failure. A line failure is a failure of the channel 214
between the transmitter 206 and the receiver 210. FIG. 4B
illustrates a first line failure 404 and a second line failure 406.
Transmitters 206 and receivers 210 are also referred to as modules.
A module failure is a failure of either a transmitter 206 or a
receiver 210. FIG. 4C illustrates a first line failure 404 and a
second module failure 410.
[0081] The first LTE processor 216 can determine if the
transmitters 206 (or associated receivers or modules not shown but
collocated with each of the transmitters 206 within the first LTE
106) fail. The second LTE processor 218 can determine if the
receivers 210 (or associated transmitters or modules not shown but
collocated with each of the receivers 210 within the second LTE
114) fail. If a transmitter, receiver, or other module fails, a
module failure, also referred to as an equipment failure has
occurred. Both the first LTE processors 216 and the second LTE
processor 218 can report to the OCCS controller 111 that a module
failure occurred. If a line failure occurs, the photodetector
within the one of the receivers 210 that corresponds to the failed
channel will detect a loss of light and the second LTE processor
218 can determine that a line failure occurred and report that a
line failure occurred to the OCCS controller 111.
[0082] If a line failure occurs, two alarms may be sent to the OCCS
controller 111. A photodiode within the second LTE 114 may detect a
failure by detecting a loss of light and a receiver associated with
transmitter 206 may detect a loss of communication with the second
LTE 114. If both the first LTE 106 and the second LTE 114 send
alarms for the same failure, the OCCS controller 111 can coordinate
the alarms and determine that one failure occurred.
[0083] In step 310, the OCCS controller 111 identifies the type of
the new failure using the information received from the first LTE
106 and/or the second LTE 114. The type of failure, either line or
module, is determined in order to determine how to restore the
failure. According to the present invention, line failures, such as
first line failure 404 and second line failure 406, are restored
either on the protect channel 212 or via the optical restoration
network 110. The first LTE 106 restores a single module failure 410
on a protect channel 212 as described earlier with respect to steps
306 and 308. If multiple failures occur and the protect channel 212
capacity is insufficient to restore all of the failures, in step
310 the type of failure is determined in order to ensure that if
the multiple failures include a module failure 410 and line
failures, such as first line failure 404 and second line failure
406, the module failure is restored on the protect channel 212 and
the line failures are restored on the optical restoration network
110.
[0084] If the type of new failure is a line failure, the OCCS
controller 111 proceeds to step 312 to provide restoration through
OCCS restoration actions using the optical restoration network 110.
If the type of new failure is a module failure, the OCCS controller
111 proceeds to step 314 to obtain additional information in order
to determine how to restore the failure.
[0085] In step 312, the OCCS controller 111 sends a command to the
first OCCS 108 to restore the new failure. If the new failure is a
second line failure 406 as illustrated in FIG. 4B, then the second
line failure 406 can be restored on the optical restoration network
110. Determining the facility type and rerouting the previous
failure 404 are unnecessary because the second line failure 406 can
be restored without affecting the previous failure 404.
[0086] The second line failure 406 is restored by the OCCS
controller 111 sending an alarm to the first OCCS 108. When the
first OCCS 108 receives the alarm, the first OCCS 108 switches to
reroute the optical electrical signals that were to be carried on
the failed channel 214C via the optical restoration network 110.
The optical electrical signals take a path from the transmitter
206C within the first LTE 106 through the first OCCS 108 through a
path 408 in optical restoration network 110 to the second OCCS 114
which is connected to the receiver 210C within the second LTE 114
that receives the signal. When the second line failure 406 is
repaired, the first OCCS 108 will reroute the electrical signals
back to channel 214C.
[0087] In step 314, the OCCS controller 111 retrieves the type of
previous failure. The OCCS controller 111 retrieves the information
from the first LTE processor 216 or the second LTE processor 218
that indicates whether the previous failure was a line failure or a
module failure. The type of the previous failure indicates the type
of failure that is being restored using the protect channel. As
mentioned previously, although line failures, such as first line
failure 404 and second line failure 406 typically can be restored
on a protect channel 212 or via an optical restoration network 110,
a single module failure 410 often can only be restored on a protect
channel 212. Therefore, if the new failure is a module failure 410
as was determined in step 312 and is illustrated in FIG. 4C, then
determining the type of the previous failure 404 indicates whether
the restoration in use for the previous failure 404 can be modified
to accommodate the new failure 410.
[0088] If the type of previous failure is a line failure as is
illustrated in FIG. 4C, then the OCCS controller 111 proceeds to
step 318 to restore both the previous failure 404 and the new
failure 410. If the type of previous failure is a module failure
which is not shown, then OCCS controller 111 proceeds to step 316
to send an alarm because neither the OCCS controller 111 or the
first OCCS 108 can restore both the previous failure and the new
failure.
[0089] In step 316, the OCCS controller 111 sends an alarm to a
national network management center (NNMC) or other centralized or
regional fault reporting center to report an unrestorable failure.
If the new failure is a module failure, such as module failure 410
shown in FIG. 4C, and the previous failure is a module failure then
two module failures have occurred but only one protect channel 212
is available for restoration. Assuming one protect channel is
available and no other restoration technique can be used to in
order to enable the optical cross connect 116 to restore the second
module failure, the OCCS controller 111 sends an alarm to a fault
reporting center such as the NNMC to report an unrestorable
failure.
[0090] The NNMC has staff and computer systems to detect and
restore failures that cannot be restored with the automated systems
in the telecommunications network 122. Computer systems in the NNMC
may provide restoration automatically by rerouting traffic using
switching tables within exchanges, such as first exchange 104 and
second exchange 118. If automated computer systems do not
automatically provide reroutes, they may provide information to
staff that manually implements changes to the software to reroute
traffic. For example, if multiple faults occur on
telecommunications cable 113 that cannot be restored, either
computer systems or staff may modify the switch tables in first
exchange 104 to send the traffic via different communications links
until telecommunications cable 113 is repaired. However, if the
failure is limited to one second module failure, the NNMC may do
nothing or simply block traffic from attempting to use the channel
214C that cannot be restored until the channel 214C is repaired.
Often all channels 214 within a telecommunications cable 113 are
not in use so new calls can use the remaining channels 214A, 214B,
. . . 214n.
[0091] In step 318, the OCCS controller 111 sends a command to the
first OCCS 108 to reroute the previous line failure 404. After the
previous line failure 404 has been rerouted by the first OCCS 108,
the OCCS controller 111 sends a command to the first LTE 106 to
switch the electrical signals that were carried on the second
failed channel 214C to the protect channel 212 to restore the new
module failure 410.
[0092] If the OCCS controller 111 performs step 318, then in step
310, the OCCS controller 111 identified that the new failure was a
module failure 410, and in step 314, the OCCS controller 111
retrieved information indicating that the previous failure was a
line failure 404. As mentioned previously, the scenario of a
previous first line failure 404 and a new module failure 410 is
illustrated in FIG. 4C. If the optical cross connect 116 cannot
restore single module failures via the optical restoration network
110, then the OCCS controller 111 can only restore the new module
failure 410 using the protect channel 212. As a result, restoration
by the OCCS controller 111 of both the first line failure 404 and
the module failure 410 is possible only if the first line failure
is rerouted to the optical restoration network 110 by sending an
alarm to the first OCCS 108.
[0093] The OCCS controller 111 sends a command to the first OCCS
108 to reroute the previous first line failure 404 via the optical
restoration network 110. The OCCS controller 111 may restore any
number of line failures by sending alarms to the first OCCS 108
which will reroute the electric signals via the optical restoration
network. In other words, if channels 214A, 214B, and 214D
experience line failures prior to channel 214C experiencing a
module failure, each line failure would have been restored by the
OCCS controller 111 performing earlier steps in the operation of
optical termination and cross connect equipment 301 when each
failure was experienced. The result would be that the first line
failure would be restored on the protect channel 212 by the OCCS
controller 111 performing steps 304, 306, and 308 and subsequent
line failures would be restored via the optical restoration network
110 by the OCCS controller 111 performing steps 306, 309, 310, and
312. However, regardless of the number of line failures restored
via the optical restoration network 110, when a module failure 410
is detected, if a line failure 404 is restored on the protect
channel 212, the line failure 404 is rerouted via the optical
restoration network 110 to make the protect channel 212 available
to restore the module failure 410. After the line failure 404 is
restored by the first OCCS 108 via the optical restoration network,
the first LTE 106 switches the electrical signals that were carried
on channel 214C that experienced the module failure 410 to the
protect channel 212.
[0094] The OCCS controller 111 of the present invention is
preferably implemented using a computer system 502 as shown in
block diagram form in FIG. 5. The computer system 502 includes one
or more processors, such as processor 506 connected to bus 504.
Also connected to bus 504 is main memory 508 (preferably random
access memory, RAM) and secondary storage devices 510. The
secondary storage devices 510 include, for example, a hard drive
512 and a removable storage medium drive 514 (such as a disk drive,
for example).
[0095] The functionality of the OCCS controller 111 is preferably
performed by a computer program that resides in main memory 508
while executing. When executing, this computer program enables the
computer system 502 to perform the features of the present
invention as discussed herein. Thus, the OCCS controller 111
represents a controller of the computer system 502 (and of the
processor 506). Alternatively, the functionality of the OCCS
controller 111 is predominately or entirely performed by a hardware
device, such as a hardware state machine.
[0096] In one embodiment, the present invention is a computer
program product (such as removable storage medium 516, representing
a computer storage disk, compact disk, etc.) comprising a computer
readable media having control logic recorded thereon. The control
logic, when loaded into main memory 508 and executed by processor
506, enables the processor 506 to perform the operations described
herein.
[0097] Although the OCCS controller 111 has been described with
respect to an exemplary controller and processor, the OCCS
controller 111 is not limited to this embodiment. The OCCS
controller 111 controls the OCCSs. The OCCS controller 111 may be
within an OCCS, such as first OCCS 108 and/or second OCCS 112.
Alternatively, the OCCS controller 111 could be within another
component within the telecommunications network such as first LTE
106 and/or second LTE 114. The OCCS controller 111 is any
capability to control one or more OCCSs, such as first OCCS 108 and
second OCCS 112.
[0098] While various embodiments of the present invention have been
described above, it should be understood that they have been
presented by way of example only, not limitation. Thus, the breadth
and scope of the present invention should not be limited by any of
the above-described exemplary embodiments, but should be defined
only in accordance with the following claims and their
equivalents.
* * * * *