Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
1999-12-16
2003-07-01
Pascal, Leslie (Department: 2633)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S199200, C359S199200, C359S199200, C359S199200, C359S199200, C359S199200, C385S016000, C385S017000, C385S024000, C370S228000, C370S225000, C370S216000
Reexamination Certificate
active
06587235
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to optical communication systems. It particularly relates to a capacity-efficient restoration architecture for an optical communication system.
2. Background Art
The operations, administration, maintenance, and provisioning of optical fiber communication systems are described in the Synchronous Optical Network/Synchronous Digital Hierarchy (SONET/SDH) standards as specified by American National Standards Institute (ANSI) and International Telecommunication Union—Telecommunication Standardization Sector (ITU-T). SDH is specified in ITU-T G.707 Recommendation, Network node interface for the SDH.
Typical optical fiber communication systems comprise a combination of transmitters, receivers, optical combiners, optical fibers, optical amplifiers, optical connectors, and splitters. Wavelength Division Multiplexing (WDM) or Dense Wavelength Division Multiplexing (DWDM) systems also comprise couplers to enable multiple wavelength transmission over the same optical fiber. Typical optical system configurations include mesh networks and ring networks. Ring networks commonly comprise two fiber pairs connecting a plurality of nodes in a loop. One fiber pair carries bi-directional aggregate traffic between pairs of nodes in the ring. The second fiber pair is used to re-route traffic when there is a failure in the ring on a shared basis. A two-fiber ring is also available in which half the capacity within a fiber is reserved for traffic restoration. Mesh networks commonly comprise a plurality of nodes wherein a node can be connected to more than two nodes in the network enabling enhanced network reliability and higher capacity efficiency when a link failure occurs.
Optical fibers carry far greater amounts of information than carried by other communication media (e.g., electrical cables). Under the Synchronous Optical Network (SONET') standard, the commonly used OC-48 protocol operates at 2.488 Gbps supporting a capacity equivalent to over 32,000 voice circuits. The next highest protocol, OC-192, operates at 9.953 Gbps supporting a capacity equivalent to over 128,000 voice circuits. Therefore, robustness and reliability is required from such high-capacity, long-haul systems. Indeed, most Transatlantic cable systems (TAT), undersea systems which carry international telecommunication traffic, are required to have at least 25 year reliability.
However, since reliability is never absolute most optical systems require a restoration scheme to maintain some level of system performance despite fiber outages, amplifier failures, and some other equipment failure. Several common restoration schemes commercially used include those specified in the SONET standard in a point-to-point single link configuration or a ring network configuration.
Examples of these standardized traditional protection schemes are shown in
FIGS. 1
,
2
. Particularly,
FIG. 1
shows a typical one-line point-to-point 1:1 protection system in a Dense Wavelength Division Multiplexing (DWDM) scheme wherein nodes A, B are linked nodes within an optical fiber communication system. The system shown operates in accordance with the SONET/SDH standard, the standard for synchronous data transmission on optical media.
The protection system architecture
100
includes protection switches
110
,
190
, working and protection link
150
, and dense wavelength division multiplexers (DWDMs)
120
,
160
. Working and protection link
150
commonly comprises a single or multiple (cable bundle of fibers) optical fiber connection between nodes A, B. Protection switches
110
,
190
commonly comprise optical-to-electrical transducers and/or optical layer cross-connection switches that provide communication service connectivity between the protection system
100
and other communication devices (e.g., customer premises equipment). There exists a one-to-one correspondence between working channels (lines)
130
,
170
and protection channels (lines)
140
,
180
. However, both working and protection channels
130
,
170
,
140
,
180
are multiplexed by the DWDMs on to a single optical fiber connection between DWDMs
120
,
160
for one direction (e.g., A to B). Another corresponding fiber is typically used for the other direction traffic from B to A.
In response to a failure in the transmitter or receiver or cabling for a working line, the SONET/SDH signals carried by working lines
130
,
170
are switched from the working lines
130
,
170
to the protection lines
140
,
180
by protection switches
110
,
190
. However, since both working lines
130
,
170
and protection lines
140
,
180
are carried by the same working and protection link
150
, a fiber cut in link
150
or a failure in DWDMs
120
,
160
or in an optical amplifier for link
150
completely terminates optical communication services between nodes A, B over link
150
. To resume service, alternate routing (not shown) would be necessary that can be accomplished through ring switch or mesh restoration means.
FIG. 2
shows the same protection configuration but now with a two-line point-to-point 1:1 protection architecture
200
. The protection system architecture
200
includes protection switches
210
,
295
working link
250
and protection link
260
, and DWDMs
220
,
270
. DWDMs
220
,
270
multiplex working lines
230
,
280
and protection lines
240
,
290
on to separate working link
250
and protection link
260
between nodes A, B.
For this protection scheme, in response to a failure in the transmitter or receiver or cabling for a working line as well as an optical amplifier or DWDM failure, the SONET/SDH signals carried by working lines
230
,
280
are switched from the working lines
230
,
280
to the protection lines
240
,
290
by protection switches
210
,
295
. However, again, to resume service when both working and protection links
250
,
260
both fail or are cut because the fibers in lines
250
and
260
are in the same cable, alternate routing (not shown) would be necessary that can be accomplished through ring switch or mesh restoration means.
Both 1-line or 2-line 1:1 DWDM systems shown in
FIGS. 1
,
2
are inefficient in terms of utilization of protection capacity. Both systems use 100% idle capacity that either does not generate any revenue or provides low-grade service on the protection lines. This low-grade service can be preempted when there is a failure of the primary revenue-generating service.
FIGS. 3
,
4
again show a commonly-used optical restoration system architecture that provides communication services in accordance with the SONET standard. Particularly,
FIG. 3
shows a one-line 1:N protection system using DWDM. The protection system architecture
300
includes protection switches
310
,
390
working and protection link
350
, and DWDMs
340
,
360
. Nodes A, B within the system are interconnected by working and protection link
350
. In the 1:N protection scheme, there is one dedicated protection channel (line)
330
,
380
for each group of N (N>1) working channels (lines)
320
,
370
. A typical example may be ten groups of 4 (N=4) working channels therein resulting in 10 protection channels for a total number of 40 working channels. In the illustrative example shown in FIG.
2
(
a
), a transmitter/receiver failure on one of a group of N working channels
320
,
370
is protected by switching to a protection channel
330
,
380
dedicated for that group. Again, due to the one-line scheme for working and protection link
350
, an optical amplifier failure or fiber cut results in a termination of communication services between nodes A, B over link
350
. Working channels
320
,
370
must be re-routed using a ring or mesh restoration network (not shown).
Similarly,
FIG. 4
shows a two-line 1:N (N>1) protection system using DWDM. The protection system architecture
400
includes protection switches
410
,
495
working link
450
and protection link
460
, and DWDMs
440
,
470
. Nodes A, B within the system are interconnecte
Chaudhuri Sid
Cortez Bruce Gilbert
Zelingher Simon S.
AT&T Corp.
Pascal Leslie
Phan Hanh
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