Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
1995-12-29
2001-09-04
Bacares, Rafael (Department: 2733)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S199200
Reexamination Certificate
active
06285475
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Cross Reference to Related Applications
This patent application is potentially related to the following commonly owned, copending applications:
1. “Method and System for Detecting Optical Faults Within the Optical Domain of a Fiber Communication Network,” Ser. No. 08/582,845 by Shoa-Kai Liu, filed on Dec. 28, 1995, and incorporated herein by reference;
2. “System and Method for Photonic Facility and Line Protection Switching,” Ser. No. 08/577,663 by John A. Fee, filed on Dec. 22, 1995, and incorporated herein by reference; and
3. “Method and System for Restoration Tributary Switching in a Fiber Network,” Ser. No. 08/582,846 by John A. Fee, filed concurrently herewith, and incorporated herein by reference.
2. Field of the Invention
The present invention relates to an optical communication network. More specifically, this invention relates to a system and method for detecting optical faults within a network.
3. Related Art
A communication network serves to transport information among a number of locations. The information is usually presented to the network in the form of time-domain electrical signals and may represent any combination of telephony, video, or computer data in a variety of formats. A typical communication network consists of various physical sites, called nodes, interconnected by information conduits, called “links.” Each link serves to carry information from one site to another site. Individual sites contain equipment for combining, separating, transforming, conditioning, and/or routing data.
The traffic of even a single link represents a formidable volume of vital data-equivalent to tens of thousands of phone calls. Sudden failure of a data link can cause a significant loss in revenues for a network owner and loss of commerce and other benefits for the network subscribers. Consequently, restoration techniques have been devised to circumvent a network link failure and to restore normal traffic flow soon.
FIG. 1
shows an example of a typical communications network
100
consisting of 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 system
100
carries data signals among the sites
101
-
105
to effectively interconnect data remote equipments
111
-
115
, i.e. computers, remote terminals, servers, etc. One or more links
120
and
121
that connect two sites are collectively referred to as a span
130
.
A span often includes multiple parallel links to increase working and spare capacity. Redundant spare links are commonly added between sites with the intent that they usually carry no data traffic but are available as alternate routes in the event of partial network failure affecting working links. If the network detects a link failure such as a fiber failure, cable cut, or transmitter/receiver nodal failure, traffic may be automatically switched from the failed link to an available spare link.
A typical implementation of a high data rate optical span is depicted in FIG.
2
. In
FIG. 2
, a given site A is connected to another site B by a span consisting of three optical fibers
230
,
232
,
234
. Two electrical data signals are presented at Site A via inputs
202
and
204
. These signals are carried through the network span and recovered at Site B as electrical signal outputs
262
and
264
respectively. For example, these data signals can be STS-48 synchronous data signals each bearing digital data at about 2.5 Gbps or the equivalent of 32 thousand telephone-quality voice channels.
At Site A, the signals enter a digital cross-connect switch
210
, and under normal conditions appear as electrical signals along connections
212
and
214
. The signal at connection
212
enters an optical Lightwave or Line Terminal Equipment (LTE)
220
shown to include an optical transmitter
221
, such as a semiconductor laser. Light emitted by the transmitter
221
is intensity-modulated by the electrical data signal that enters along connection
212
to deliver a modulated optical output signal over optical fiber
230
.
After traversing the length of fiber
230
, the optical signal arrives at Site B and enters a receiver
241
such as a photodiode. The receiver
241
is shown to be a part of an LTE
230
that amplifies and conditions the signal to render a faithful electrical reproduction at output port
252
of the original electrical data signal provided at input
202
. In a similar manner, an electrical data signal presented at input
204
is transported by LTE
222
, fiber
232
, and LTE
242
to output port
254
.
Under normal circumstances, the digital cross-connect switch DCS
260
simply connects port
252
to output port
262
to complete the end-to-end connection of input
202
to output
262
. Likewise, DCS
260
normally connects line
254
to output
264
to complete the end-to-end connection of input
204
to output
264
.
In
FIG. 2
, fibers
230
and
232
are referred to as working fibers because they both carry data traffic when all network elements are functioning properly. In contrast, fiber
234
is said to be a spare or “protect” fiber because it carries data traffic only in the event of failure of one of the working fibers
230
or
232
or of the associated LTEs
220
,
222
,
240
,
242
. Under normal circumstances, protect fiber
234
does not carry an optical data signal.
When a failure occurs along one of the working fibers
230
,
232
, digital cross-connect switches
210
and
260
switch data traffic onto the protect fiber
234
. For example, if fiber
230
becomes too damaged to transmit light, switch
210
connects input
202
to connection
216
. At the same time, DCS
260
disconnects connection
252
and connects output port
262
to connection
256
. This switching action restores end-to-end connectivity between input
202
and output
262
despite the failure of working fiber
230
.
To successfully perform restoration switching, however, it is necessary to detect failures and to coordinate switching action at each node. As shown in
FIG. 2
, a separate digital communication network is provided between sites for signaling status and switching commands between DCS
220
and DCS
260
. Controller
250
is assigned to Site A to accept alarm inputs
255
from LTE's
220
,
222
, and
224
. Controller
250
also directs the switching action of DCS
210
via control connection
253
. A similar Controller
252
resides at Site B to accept alarm inputs
256
from LTEs
240
,
242
, and
244
and to exercise control over DCS
260
via control connection
254
. Each Controller
250
,
252
is typically an imbedded microprocessor, computer, workstation, or other type of processor for controlling the switching of lightwave terminal equipment, digital cross-connect switches, and optical cross-connect switches.
Controllers
250
and
252
communicate and coordinate with each other over a separate communications link
251
. For example, status messages can be sent to indicate, acknowledge, or confirm a link or node state such as an idle, active, inactive, or detected fault state. Any digital signaling protocol can be used such as X.25, Frame Relay, ATM, B-ISDN or Common Channel Signaling 7 protocols. Alternatively, controllers
250
and
251
can communicate status messages using overhead bits or bytes within the data protocol that traverses the working fibers. Restoration algorithms and protocols applied within the controllers to restore end-to-end connectivity in response to a fault detection are well known to those skilled in the art.
Thus, the ability to restore network service depends upon the ability to detect and locate failed network components. Faults have been detected in the electrical domain at LTEs. A transmitter
221
can detect a failed laser diode, for example, by monitoring its bias current. Some transmitters also incorporate a backwave detector. This is a photodiode that picks up the
Bacares Rafael
MCI Communications Corporation
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