U.S. patent application number 14/626550 was filed with the patent office on 2016-07-28 for joint signal-routing and power-control for an optical network.
The applicant listed for this patent is Alcatel-Lucent USA Inc.. Invention is credited to Zizhong Cao, Paul Claisse, Rene-Jean Essiambre, Muralidharan Kodialam, Tirunell V. Lakshman.
Application Number | 20160219350 14/626550 |
Document ID | / |
Family ID | 56321227 |
Filed Date | 2016-07-28 |
United States Patent
Application |
20160219350 |
Kind Code |
A1 |
Kodialam; Muralidharan ; et
al. |
July 28, 2016 |
JOINT SIGNAL-ROUTING AND POWER-CONTROL FOR AN OPTICAL NETWORK
Abstract
We disclose a signal-routing method directed at improving the
throughput of an optical network by taking into account the fiber
nonlinearity in the process of solving a joint signal-routing and
power-control problem for the optical network. Based on the
obtained solution, a network controller may set the signal-routing
configurations of the various network nodes and the optical gains
of the various optical amplifiers to enable the optical network to
carry the traffic in a manner that results in a higher throughput
than that achievable with the use of conventional signal-routing
and/or power-control methods.
Inventors: |
Kodialam; Muralidharan;
(Marlboro, NJ) ; Essiambre; Rene-Jean; (Red Bank,
NJ) ; Claisse; Paul; (Skillman, NJ) ;
Lakshman; Tirunell V.; (Marlboro, NJ) ; Cao;
Zizhong; (Miller Place, NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Alcatel-Lucent USA Inc. |
Murray Hill |
NJ |
US |
|
|
Family ID: |
56321227 |
Appl. No.: |
14/626550 |
Filed: |
February 19, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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62106419 |
Jan 22, 2015 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04J 14/0221 20130101;
H04Q 11/0066 20130101; H04J 14/0257 20130101; H04J 14/0271
20130101; H04Q 11/0062 20130101; H04J 14/0227 20130101 |
International
Class: |
H04Q 11/00 20060101
H04Q011/00 |
Claims
1. An optical communication method comprising: determining a
plurality of optical paths for a traffic matrix to be routed
through an optical network, wherein each optical path of the
plurality satisfies a feasibility condition defined by a first
threshold value and a second threshold value, the first threshold
value being configured to specify an optical signal-to-noise ratio,
and the second threshold value being configured to specify an
optical nonlinearity threshold; determining a universal set of
powers, each power in said set corresponding to a respective span
in the plurality of optical paths and representing an optical power
level in that respective span, with each power in said set being
determined based on the first and second threshold values; and
routing the traffic matrix through a subset of the plurality of
optical paths.
2. The method of claim 1, further comprising configuring network
nodes located on optical paths of the subset to direct optical
signals configured to carry traffic flows corresponding to the
traffic matrix along respective optical paths of the subset.
3. The method of claim 2, further comprising configuring optical
amplifiers located on the optical paths of the subset to amplify
the optical signals in a manner that causes an optical launch power
for each respective span in the subset to approximate a respective
power from the universal set of powers.
4. The method of claim 2, wherein each of the optical nodes located
on the optical paths of the subset comprises a respective
reconfigurable optical add/drop multiplexer.
5. The method of claim 2, wherein the optical nodes located on the
optical paths of the subset include one or more optical nodes
equipped with respective OEO signal regenerators.
6. The method of claim 2, wherein at least one of the optical
signals is WDM signal.
7. The method of claim 1, wherein optical paths allocated to carry
traffic flows corresponding to the traffic matrix do not have an
optical path not belonging to the plurality of optical paths that
satisfy the feasibility condition.
8. The method of claim 1, wherein the optical network is a
transparent optical network.
9. The method of claim 1, wherein the optical network is a
translucent optical network.
10. The method of claim 1, wherein the feasibility condition is
given by the following inequality: i .di-elect cons. q a i b i
.ltoreq. NL T OSNR T ##EQU00023## where a i = hvB ref F i T i ; b i
= .gamma. i ( 1 - T i ) .alpha. i ; ##EQU00024## i denotes a span;
q denotes an optical path; OSNR.sub.T is the first threshold value;
NL.sub.T is the second threshold value; hv is an energy of one
photon of optical frequency v; B.sub.ref is a reference bandwidth;
F.sub.i is a noise figure for the span; .alpha..sub.i is a fiber
loss coefficient for the span; T.sub.i is optical transmittance of
the span; and .gamma..sub.i is a nonlinear coefficient for the
span.
11. The method of claim 1, wherein each power in the universal set
of powers is determined in accordance with the following equation:
P i * .apprxeq. a i b i OSNR T NL T ##EQU00025## where a i = hvB
ref F i T i ; b i = .gamma. i ( 1 - T i ) .alpha. i ; ##EQU00026##
i denotes a span; OSNR.sub.T is the first threshold value; NL.sub.T
is the second threshold value; hv is an energy of one photon of
optical frequency v; B.sub.ref is a reference bandwidth; F.sub.i is
a noise figure for the span; .alpha..sub.i is a fiber loss
coefficient for the span; T.sub.i is optical transmittance of the
span; and .gamma..sub.i is a nonlinear coefficient for the
span.
12. The method of claim 1, wherein, for an optical path, the
feasibility condition is checked by: obtaining a respective span
metric for each span of the optical path; summing the respective
span metrics to generate an aggregated metric for the optical path;
and comparing the aggregated metric with a reference metric defined
by the first and second threshold values.
13. The method of claim 1, further comprising: generating a
plurality of routing solutions by specifying a plurality of
different traffic matrices and repeating the steps of determining
the plurality of optical paths, determining the universal set of
powers, and routing for each of said different traffic matrices;
and storing the plurality of routing solutions in a non-volatile
memory.
14. The method of claim 13, further comprising: obtaining a current
traffic matrix to be routed through the optical network; and
retrieving from the non-volatile memory one of the plurality of
routing solutions corresponding to the current traffic matrix.
15. The method of claim 14, further comprising: configuring network
nodes to direct optical signals configured to carry traffic flows
corresponding to the current traffic matrix along respective
optical paths specified in said one of the plurality of routing
solutions; and configuring optical amplifiers located on the
respective optical paths to amplify the optical signals in a manner
that causes an optical launch power for each respective span to
approximate a respective power from the universal set of powers
corresponding to said one of the plurality of routing
solutions.
16. The method of claim 1, wherein the routing is performed using a
fully polynomial-time approximation scheme.
17. A non-transitory machine-readable medium, having encoded
thereon program code, wherein, when the program code is executed by
a machine, the machine implements a computer-aided signal-routing
method, the computer-aided signal-routing method comprising:
determining a plurality of optical paths for a traffic matrix to be
routed through an optical network, wherein each optical path of the
plurality satisfies a feasibility condition defined by a first
threshold value and a second threshold value, the first threshold
value being configured to specify an optical signal-to-noise ratio,
and the second threshold value being configured to specify an
optical nonlinearity threshold; determining a universal set of
powers, each power in said set corresponding to a respective span
in the plurality of optical paths and representing an optical power
level in that respective span, with each power in said set being
determined based on the first and second threshold values; and
routing the traffic matrix through a subset of the plurality of
optical paths.
18. The non-transitory machine-readable medium of claim 17, wherein
the computer-aided signal-routing method further comprises:
generating a plurality of routing solutions by specifying a
plurality of different traffic matrices and repeating the steps of
determining the plurality of optical paths, determining the
universal set of powers, and routing for each of said different
traffic matrices; and storing the plurality of routing solutions in
a non-volatile memory.
19. The non-transitory machine-readable medium of claim 18, wherein
the computer-aided signal-routing method further comprises:
obtaining a current traffic matrix to be routed through the optical
network; and retrieving from the non-volatile memory one of the
plurality of routing solutions corresponding to the current traffic
matrix.
20. An optical network comprising: a plurality of network nodes
optically interconnected by a plurality of optical links, each
comprising one or more fiber spans; and a network controller
operatively coupled to the plurality of network nodes and
configured to: determine a plurality of optical paths for a traffic
matrix to be routed through the plurality of optical links, wherein
each optical path of the plurality of optical paths satisfies a
feasibility condition defined by a first threshold value and a
second threshold value, the first threshold value being configured
to specify an optical signal-to-noise ratio, and the second
threshold value being configured to specify an optical nonlinearity
threshold; determine a universal set of powers, each power in said
set corresponding to a respective span in the plurality of optical
paths and representing an optical power level in that respective
span, with each power in said set being determined based on the
first and second threshold values; and route the traffic matrix
through a subset of the plurality of optical paths.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority from U.S. Provisional
Patent Application No. 62/106,419 filed on Jan. 22, 2015, and
entitled "JOINT ROUTING AND POWER-CONTROL FOR AN OPTICAL NETWORK,"
which provisional patent application is incorporated herein by
reference in its entirety.
BACKGROUND
[0002] 1. Field
[0003] The present disclosure relates to optical communication
equipment and, more specifically but not exclusively, to routing
optical signals in an optical network.
[0004] 2. Description of the Related Art
[0005] This section introduces aspects that may help facilitate a
better understanding of the disclosure. Accordingly, the statements
of this section are to be read in this light and are not to be
understood as admissions about what is in the prior art or what is
not in the prior art.
[0006] The physical layer of an optical network typically suffers
from various linear and nonlinear impairments, such as power loss,
dispersion, crosstalk, cross-phase modulation, four-wave mixing,
etc. The adverse effects of these impairments are especially
pronounced in optically transparent and optically translucent
networks that are typically configured to keep the communication
signal in the optical domain as long as possible and/or employ
optical-to-electrical-to-optical signal regeneration very sparsely.
However, signal-routing methods that are directed at improving the
network efficiency by taking into account the physical-layer
impairments are not sufficiently developed yet.
SUMMARY OF SOME SPECIFIC EMBODIMENTS
[0007] Disclosed herein are various embodiments of a signal-routing
method directed at improving (e.g., optimizing) the throughput of
an optical network by taking into account the fiber nonlinearity in
the process of solving a joint signal-routing and power-control
problem for the optical network. Based on the obtained solution, a
network controller may set the signal-routing configurations of the
various network nodes and the optical gains of the various optical
amplifiers to enable the optical network to carry the traffic in a
manner that results in a higher throughput than that achievable
with the use of conventional signal-routing and/or power-control
methods.
[0008] According to one embodiment, provided is an optical
communication method comprising the steps of: determining a
plurality of optical paths for a traffic matrix to be routed
through an optical network, wherein each optical path of the
plurality satisfies a feasibility condition defined by a first
threshold value and a second threshold value, the first threshold
value being configured to specify an optical signal-to-noise ratio,
and the second threshold value being configured to specify an
optical nonlinearity threshold; determining a universal set of
powers, each power in said set corresponding to a respective span
in the plurality of optical paths and representing an optical power
level in that respective span, with each power in said set being
determined based on the first and second threshold values; and
routing the traffic matrix through a subset of the plurality of
optical paths.
[0009] According to another embodiment, provided is a
non-transitory machine-readable medium, having encoded thereon
program code, wherein, when the program code is executed by a
machine, the machine implements a computer-aided signal-routing
method, the computer-aided signal-routing method comprising the
steps of: determining a plurality of optical paths for a traffic
matrix to be routed through an optical network, wherein each
optical path of the plurality satisfies a feasibility condition
defined by a first threshold value and a second threshold value,
the first threshold value being configured to specify an optical
signal-to-noise ratio, and the second threshold value being
configured to specify an optical nonlinearity threshold;
determining a universal set of powers, each power in said set
corresponding to a respective span in the plurality of optical
paths and representing an optical power level in that respective
span, with each power in said set being determined based on the
first and second threshold values; and routing the traffic matrix
through a subset of the plurality of optical paths.
[0010] According to yet another embodiment, provided is an optical
network comprising: a plurality of network nodes optically
interconnected by a plurality of optical links, each comprising one
or more fiber spans; and a network controller operatively coupled
to the plurality of network nodes and configured to: determine a
plurality of optical paths for a traffic matrix to be routed
through the plurality of optical links, wherein each optical path
of the plurality of optical paths satisfies a feasibility condition
defined by a first threshold value and a second threshold value,
the first threshold value being configured to specify an optical
signal-to-noise ratio, and the second threshold value being
configured to specify an optical nonlinearity threshold; a
universal set of powers, each power in said set corresponding to a
respective span in the plurality of optical paths and representing
an optical power level in that respective span, with each power in
said set being determined based on the first and second threshold
values; and route the traffic matrix through a subset of the
plurality of optical paths.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] Other aspects, features, and benefits of various disclosed
embodiments will become more fully apparent, by way of example,
from the following detailed description and the accompanying
drawings, in which:
[0012] FIGS. 1A-1B show block diagrams of an optical network in
which various embodiments may be practiced;
[0013] FIG. 2 shows a pictorial view of a fiber span in the optical
network of FIG. 1 together with the corresponding span parameters
that may be used for routing optical signals through that fiber
span according to an embodiment of the disclosure;
[0014] FIG. 3 shows a portion of the optical network of FIG. 1
configured to carry two different commodities according to an
embodiment of the disclosure;
[0015] FIG. 4 shows a flowchart of a signal-routing method that can
be used in the optical network of FIG. 1 according to an embodiment
of the disclosure;
[0016] FIGS. 5A-5B show a pseudo-code that can be used to implement
the signal-routing method of FIG. 4 according to an embodiment of
the disclosure; and
[0017] FIG. 6 shows a graph abstraction that can be used to modify
the pseudo-code shown in FIGS. 5A-5B according to an embodiment of
the disclosure.
DETAILED DESCRIPTION
[0018] FIGS. 1A-1B show block diagrams of an optical network 100 in
which various embodiments may be practiced. More specifically, FIG.
1A shows an overall schematic view of network 100 showing its
physical and network layers corresponding to the Open System
Interconnection (OSI) model. FIG. 1B shows a block diagram of an
optical link 140 between two nodes 110 in network 100.
[0019] A physical layer 102 of network 100 is illustratively shown
in FIG. 1A as comprising seven nodes 110.sub.1-110.sub.7
interconnected by a plurality of optical links 140. In various
alternative embodiments, the number of nodes 110 in network 100 may
be different from seven. In an example embodiment, a node 110 may
be implemented using a reconfigurable optical add/drop multiplexer
(ROADM).
[0020] An optical link 140.sub.ij shown in FIG. 1B is configured to
connect nodes 110.sub.i and 110.sub.j, where i, j=1, 2, . . . , 7
and i.noteq.j. For illustration purposes, optical link 140.sub.ij
is shown as being a bidirectional link having two unidirectional
sub-links 142 and 144. Sub-link 142 is configured to transport
optical signals from node 110.sub.i to node 110.sub.j. Sub-link 144
is similarly configured to transport optical signals from node
110.sub.j to node 110.sub.i. In an example embodiment, each of
sub-links 142 and 144 comprises a plurality of fiber spans 146 and
a plurality of tunable optical amplifiers 150. In some embodiments,
some optical links 140 in network 100 may be unidirectional
links.
[0021] A network controller 130 operates to control the routing
configurations of the various nodes 110 and the optical gains of
the various optical amplifiers 150 using a plurality of control
paths 132. A plurality of control signals 134 (see FIG. 1B)
transmitted via control paths 132 are used to control (e.g., set,
change, etc.) the signal-routing configurations of nodes 110. A
plurality of control signals 136 (also see FIG. 1B) transmitted via
control paths 132 are similarly used to control the optical gains
of optical amplifiers 150.
[0022] Routing decisions in network 100 may be made using a routing
protocol corresponding to a network layer 104, wherein each node
110.sub.i is represented by a corresponding router 160.sub.i.
Routers 160 are interconnected by a plurality of virtual links 170.
Note that a virtual link 170 may or may not have a one-to-one
correspondence to one of optical links 140 in physical layer 102.
In the latter case, a single virtual link 170 may be mapped onto
two or more optical links 140.
[0023] In some embodiments, noise and nonlinearity may be the two
main factors that contribute to the degradation of optical signals
in network 100. A respective subset of amplifiers 150 can be
configured to ensure that the optical signal-to-noise ratio (OSNR)
is greater than a minimum threshold that permits proper detection
and decoding of an optical signal at a respective end receiver.
However, unlike wireless networks, where the signal-to-noise ratio
can often be improved by simply increasing the transmit power, in
optical networks, such as network 100, an increased transmit power
may lead to increased effects of nonlinearity, such as the Kerr
nonlinearity. Various embodiments of a signal-routing method
disclosed herein are directed at improving (e.g., optimizing) the
throughput of network 100 by explicitly taking into account the
fiber nonlinearity in the process of solving a joint signal-routing
and power-control problem for the network. Based on the obtained
solution, controller 130 operates to set the signal-routing
configurations of the various nodes 110 and the optical gains of
the various optical amplifiers 150 to enable network 100 to carry
the traffic in a manner that results in a higher throughput than
that achievable with the use of conventional signal-routing and/or
power-control methods.
[0024] Optical amplifiers 150 operate to boost the optical signal
power, with a side effect being that the optical noise is amplified
as well. The launch optical power applied to an optical fiber is
determined by the output of the optical amplifier 150 located at
the end of the preceding fiber span 146 (see FIG. 1B). Since
different spans 146 may have different fiber lengths and/or
different fiber characteristics, each optical amplifier 150 may be
configured to have individual optical-gain settings that are
different from the settings of other optical amplifiers 150.
[0025] Each fiber span 146 may be configured to carry multiple
wavelength-division-multiplexed (WDM) channels, with each WDM
channel having allocated thereto a predetermined bandwidth. For
simplification purposes, we will assume (without undue limitation)
that the launch optical powers for different WDM channels are
approximately equal to one another for any given fiber span 146.
Hereafter, in the mathematical description that follows, we use
index i to designate different fiber spans 146, and use the symbol
P.sub.i to designate the launch optical power per WDM channel in
fiber span i. In an example embodiment, the value of P.sub.i is
determined and set by controller 130, e.g., using method 400 (FIG.
4).
[0026] If the modulation and coding schemes are fixed, then the
data rate for each channel is also fixed. Since the number of WDM
channels on each link 140 is typically known and constant, one can
model each link 140 as having a fixed data rate. The data rate for
link e in the network is denoted by the symbol c.sub.e. In an
example embodiment, all fiber spans 146 may have the same capacity
(e.g., corresponding to a "100G network"). However, routing methods
disclosed herein are also capable of handling a more-general
network configuration, wherein different fiber spans are configured
to have different capacities.
[0027] The traffic that network 100 needs to carry may be specified
in the form of a traffic matrix that lists different
source-destination pairs and the corresponding traffic demands or
volumes. The traffic corresponding to each source-destination pair
is hereafter referred to as a respective "commodity." We use index
k to designate the different commodities.
[0028] Let s(k), t(k), and d.sub.k represent the source node 110,
the destination node 110, and the amount of traffic that network
100 needs to carry for commodity k, respectively. Let Q.sub.k
represent the set of paths for commodity k. Each path
q.epsilon.Q.sub.k originates at s(k), terminates at t(k), and
comprises a respective plurality of fiber spans 146. The expression
i.epsilon.q indicates that span i is on path q.
[0029] A conventional approach to determining whether or not a
traffic matrix can be routed through a non-optical network with
given link capacities is to solve a multi-commodity flow problem.
However, the situation is significantly more complex for an optical
network, such as network 100. For example, in network 100, the set
of paths that can be used to route flows depends on the power
settings of optical amplifiers 150 at the different fiber spans
146, which is not the case in a non-optical network. As already
indicated above, the power setting may be shared by all WDM
channels that are being transmitted through that particular optical
amplifier 150. The two conditions that a path in network 100 needs
to satisfy in order to be feasible can be formulated as follows:
[0030] A. the path needs to have a sufficiently large OSNR, e.g.,
greater than a first specified threshold; and [0031] B. the
nonlinear phase shift (which can be used as a proxy for the amount
of degrading interference caused by nonlinear signal distortions)
in the path needs to be sufficiently small, e.g., lower than a
second specified threshold. The values of the first and second
thresholds may depend on the data rate on each link.
[0032] FIG. 2 shows a pictorial view of a fiber span 146 and a
corresponding optical amplifier 150 (also see FIG. 1B) together
with the corresponding span parameters that may be used for routing
optical signals through that fiber span according to an embodiment
of the disclosure. Assuming that the fiber span shown in FIG. 2 is
span i, the following parameters can be used to characterize the
span for signal-routing and power-control purposes: (i) the noise
figure F.sub.i; (ii) the fiber length L.sub.i; (iii) the fiber loss
coefficient .alpha..sub.i; (iv) the transmittance T.sub.i; and (v)
the nonlinear coefficient .gamma..sub.i. As indicated in FIG. 2,
the transmittance T.sub.i can be expressed as
T.sub.i=exp(-.alpha..sub.iL.sub.i). The launch power P.sub.i can be
adjusted as necessary, e.g., to optimize the operation of network
100.
[0033] The launch power P.sub.i determines the OSNR as well as the
nonlinear phase shift for span i. The contribution to the overall
OSNR from span i considered in isolation is given by Eq. (1):
OSN R i = T i P i hvB ref F i ( 1 ) ##EQU00001##
where hv is the energy of one photon of optical frequency v, and
B.sub.ref is the reference bandwidth (e.g., 12.5 GHz at 1550 nm).
Eq. (1) assumes that (i) all parameters are expressed in linear
units; (ii) insertion losses between optical amplifier 150 and the
fiber of span 146 are small; and (iii) the noise figure F.sub.i is
independent of the signal powers at the input and output of the
optical amplifier. Note that according to Eq. (1), the OSNR for
span i increases with an increase of the launch power P.sub.i.
Fiber nonlinearity for span i is measured using the nonlinear phase
shift .phi..sub.i, which is given by Eq. (2):
.phi. i = .gamma. i .alpha. i P i ( 1 - T i ) ( 2 )
##EQU00002##
Note that according to Eq. (2), the nonlinear phase shift for span
i also increases with an increase of the launch power P.sub.i.
[0034] Using Eqs. (1) and (2), the above-stated path-feasibility
conditions (A) and (B) can be converted into a mathematical form as
follows:
i .di-elect cons. q hvB ref F i T i P i .ltoreq. OSN R T ( 3 a ) i
.di-elect cons. q .gamma. i .alpha. i P i ( 1 - T i ) .ltoreq. NL T
( 3 b ) ##EQU00003##
where OSNR.sub.T is the OSNR threshold, and NL.sub.T is the
nonlinearity (e.g., nonlinear phase-shift) threshold. Eq. (3a)
substantially states that a feasible path q provides sufficient
OSNR to make the optical signal decodable at the end receiver. Eq.
(3b) substantially states that a feasible path q does not cause a
prohibitively large accumulation of nonlinear distortions in the
optical signal.
[0035] FIG. 3 shows a portion 300 of network 100 configured to
carry two different commodities (labeled k and k') according to an
embodiment of the disclosure. The path corresponding to commodity k
originates at node s(k) and terminates at node t(k). The path
corresponding to commodity k' originates at node s(k') and
terminates at node t(k'). Both paths include span i. As a result,
the launch power of span i affects signal characteristics of both
commodities. This attribute of a shared span typically limits the
range of power settings that may be used for a span analogous to
span i, e.g., because for some power settings, the path
corresponding to commodity k may be feasible while the path
corresponding to commodity k' may not be feasible. For example,
when the path corresponding to commodity k' is longer than the path
corresponding to commodity k, it tends to cause a greater
cumulative nonlinear phase shift at a particular power setting (see
Eq. (3b)). On the other hand, if the power used for span i is
lowered to reduce the nonlinear phase shift, then the path
corresponding to commodity k may become infeasible due to not
meeting the OSNR threshold (also see Eq. (3a)). This example
illustrates the fact that the set of paths that can be used to
route the various commodities in network 100 is a function of the
power settings used in various optical amplifiers 150, or
equivalently, the launch power at an individual fiber span is a
function of the paths that traverse that span. It follows then
that, for optimal results, the problems of setting the optical
gains and selecting the routing paths for different commodities may
need to be solved jointly or in interdependent manner.
[0036] FIG. 4 shows a flowchart of a signal-routing method 400 that
can be used in network 100 (FIG. 1) according to an embodiment of
the disclosure. In an example embodiment, method 400 is directed at
(i) finding a set of paths in network 100 along which flows
corresponding to different commodities can be routed in an
efficient manner and (ii) determining and setting appropriate power
levels P.sub.i for different corresponding spans i. The search is
constrained to the paths that satisfy both Eq. (3a) and Eq.
(3b).
[0037] In an example embodiment, method 400 can be executed by or
at network controller 130. Based on the results of the executed
method 400, network controller 130 can then use control paths 132
to appropriately configure nodes 110 and amplifiers 150. Method 400
may be re-executed as necessary when the traffic matrix changes
and/or the span parameters indicated in FIG. 2 are altered for any
of the fiber spans 146, e.g., due to a hardware reconfiguration,
repair, or upgrade.
[0038] In an alternative embodiment, some of the processing of
method 400 may be executed using a processor external to network
controller 130, with the obtained results being stored in a memory
(not explicitly shown in FIG. 1A) accessible to the network
controller. In this embodiment, network controller 130 may be
configured to retrieve an appropriate set of results from the
memory instead of generating them dynamically and/or in situ. The
memory may be pre-loaded with multiple sets of results, e.g.,
corresponding to different possible traffic matrices. Upon
obtaining the traffic matrix that needs to be routed, network
controller 130 may retrieve the set of results corresponding to
that particular traffic matrix and, if necessary, execute the
remaining portions of method 400 using an internal processor and/or
other appropriate hardware resources hosted by or accessible to the
network controller.
[0039] For illustration purposes and without undue limitation, the
following description is given for an embodiment in which all
processing of method 400 is performed at network controller
130.
[0040] As used herein the term "feasible path" refers to a path q
corresponding to a commodity specified by the traffic matrix that
satisfies the following condition:
i .di-elect cons. q a i b i .ltoreq. NL T OSN R T ( 4 )
##EQU00004##
where a.sub.i and b.sub.i are the span parameters defined by Eqs.
(5a)-(5b):
a i = hvB ref F i T i ( 5 a ) b i = .gamma. i ( 1 - T i ) .alpha. i
( 5 b ) ##EQU00005##
The parameter a.sub.i can illustratively be interpreted as the
contribution of span i to the noise power spectral density within
the reference bandwidth. The parameter b.sub.i can illustratively
be interpreted as the effective nonlinearity accumulation in span i
per unit of signal power. Eq. (6) gives a mathematical definition
of the set of feasible paths:
= { q : i .di-elect cons. q a i b i .ltoreq. NL T OSN R T } ( 6 )
##EQU00006##
[0041] At step 402 of method 400, controller 130 operates to obtain
sets of parameters a.sub.i and b.sub.i for each span i in network
100. In one embodiment, controller 130 may be configured to
calculate the parameters a.sub.i and b.sub.i using Eqs. (5a)-(5b).
In an alternative embodiment, controller 130 may be configured to
retrieve the sets of parameters a.sub.i and b.sub.i from a memory
containing all necessary parameters of network 100 in an
appropriately accessible form. A person of ordinary skill in the
art will understand that the memory may be preloaded with all
necessary parameters of network 100 prior to the execution of
method 400, e.g., when the network is deployed, modified, upgraded,
and/or tested.
[0042] At step 404 of method 400, controller 130 determines the
universal set of powers P.sub.i* for various paths q corresponding
to the traffic matrix. As used herein the term "universal power"
refers to an optical launch power P.sub.i for span i that
approximately (e.g., within .+-.10%) satisfies Eq. (7):
P i * .apprxeq. a i b i OSN R T NL T ( 7 ) ##EQU00007##
A useful property of the universal set of powers P.sub.i* is that
setting the optical launch powers P.sub.i to P.sub.i* (i.e.,
P.sub.i=P.sub.i*) does not make any path q non-feasible due to the
effects of interrelatedness of the optical powers on the paths
corresponding to different commodities that are explained above in
reference to FIG. 3. A mathematical proof of this property can be
found, e.g., in the above-cited U.S. Provisional Patent Application
No. 62/106,419.
[0043] As is evident from Eq. (7), the determination of the
universal set of powers P.sub.i* carried out at step 404 relies on
the sets of parameters a.sub.i and b.sub.i obtained at step 402 and
also on the thresholds OSNR.sub.T and NL.sub.T. In some
embodiments, the thresholds OSNR.sub.T and NL.sub.T may have fixed
predetermined values. In some other embodiments, the values of
thresholds OSNR.sub.T and NL.sub.T may themselves be adjustable
parameters of the routing algorithm, in which case method 400 may
be iteratively cycled through steps 404 and 406 until an
appropriate iteration-stopping condition is satisfied.
[0044] At step 406 of method 400, controller 130 is configured to
solve the problem of routing the traffic matrix through the set of
feasible paths q (see Eq. (6)) in network 100 in a manner that
tends to approximately minimize (e.g., to within a predetermined
tolerance) the resulting maximum link utilization in the
network.
[0045] In an example embodiment, step 406 is directed at finding an
approximate solution to the below-described mathematical
problem.
[0046] The routing matrix gives the amounts of flow d.sub.k that
need to be transmitted through network 100 for each commodity k.
The maximum possible link utilization is one (or 100% of the link
capacity). If the maximum link utilization required for routing a
traffic matrix is smaller than one, then the traffic matrix is
routable. Conversely, if the maximum required link utilization is
greater than one, then the traffic matrix is not routable. An
alternative formulation of these routability conditions may be
based on scaling each entry in the traffic matrix by a factor
.theta.. The problem to be solved then may be directed at finding
the maximum value of the factor .theta. for which .theta. times the
traffic matrix can still be routed. In this formulation,
.theta..sup.-1 represents the maximum link utilization when the
traffic matrix is routed. If the maximum value of .theta. is
greater than one, then the traffic matrix is routable. Otherwise,
the traffic matrix is not routable.
[0047] The following linear program with a set of constraints can
represent the problem of finding the maximum value of the factor
.theta.:
max .theta. q .di-elect cons. Q k F x q = .theta. k , .A-inverted.
k ( 8 a ) k e .di-elect cons. q .di-elect cons. Q k F x q .ltoreq.
c e , .A-inverted. e ( 8 b ) x q .gtoreq. 0 , .A-inverted. q ( 8 c
) ##EQU00008##
where x.sub.q denotes the flow volume on path q; Q.sub.k denotes
the set of paths available for commodity k in network 100; c.sub.e
is the data rate for link e; and d.sub.k is the flow volume for
commodity k. Constraints (8a) ensure that the flows are routed only
along the paths from the set (also see Eq. (6)). Constraints (8b)
ensure that the routed flows do not exceed the corresponding link
capacities. Note that all routing for commodity k takes place at
the intersection of Q.sub.k and the set (i.e. at
Q.sub.k.andgate.).
[0048] In an example embodiment, the above-formulated linear
program can be implemented and solved, e.g., as further described
below in reference to FIG. 5. In alternative embodiments, other
suitable algorithmic implementations are also possible.
[0049] Upon being executed by controller 130, step 406 identifies
an approximately optimal subset of paths q from the set and
provides the corresponding flow volumes x.sub.q to be sent along
each of these paths to carry the traffic corresponding to the
traffic matrix.
[0050] At step 408 of method 400, controller 130 uses control paths
132 to appropriately configure nodes 110 and amplifiers 150. More
specifically, nodes 110 are configured to direct the various flows
corresponding to the traffic matrix along the subset of paths
identified at step 406. Amplifiers 150 are configured to generate
the optical launch powers on the various fiber spans of these paths
such that these optical launch powers are approximately set to the
levels of the respective powers P.sub.i* determined at step
404.
[0051] FIGS. 5A-5B show a pseudo-code 500 that can be used to
implement step 406 of method 400 (FIG. 4) according to an
embodiment of the disclosure. More specifically, pseudo-code 500
realizes a fully polynomial-time approximation scheme (FPTAS) for
the linear program formulated above in reference to Eqs. (8a)-(8c).
An FPTAS for a maximization problem, such as that of step 406 of
method 400, is capable of providing an approximate solution that is
within a factor of (1-.omega.) of the true optimum solution for any
specified tolerance co. The required time for finding this
approximate solution is polynomial in the number of problem
parameters and 1/.omega..
[0052] The FPTAS corresponding to FIGS. 5A-5B is a primal-dual
algorithm, and one can write the dual to the problem of step 406 of
method 400 as follows. The dual variables are denoted l.sub.e and
z.sub.k. The dual variables l.sub.e are associated with the
constraints of Eq. (9):
q : e .di-elect cons. q x q .ltoreq. c e , .A-inverted. e ( 9 )
##EQU00009##
The dual variables z.sub.k are associated with the constraints of
Eq. (10):
q .di-elect cons. Q k x q = d k , .A-inverted. k ( 10 )
##EQU00010##
These constraints ensure that the span capacities are not exceeded
and that the flow volume allocated for commodity k is sufficient
for the demand specified by the traffic matrix. The dual problem to
be solved can then be formulated using Eqs. (11a)-(11d) as
follows:
min .eta. ( L ) = e c e l e ( 11 a ) e .di-elect cons. q l e
.gtoreq. z k , .A-inverted. k .A-inverted. q .di-elect cons. Q k (
11 b ) k d k z k .gtoreq. 1 ( 11 c ) l e , z k .gtoreq. 0 ,
.A-inverted. e .A-inverted. k ( 11 d ) ##EQU00011##
[0053] Let
.phi. ( L ) = ^ k d k .mu. k ( L ) ##EQU00012##
denote the sum of the products of traffic volumes and shortest path
lengths for each commodity. Then, the dual problem formulated by
Eqs. (11a)-(11d) can also be interpreted as being directed at
finding:
min .sigma. = .eta. ( L ) .phi. ( L ) ( 12 ) ##EQU00013##
Let .sigma.* denote the value of the minimum defined by Eq. (12).
One can scale the traffic demands and link capacities such that
.sigma.*.gtoreq.1.
[0054] The algorithm defined by pseudo-code 500 starts out by
setting the initial values of dual variables l.sub.e in accordance
with Eq. (13):
l e = .delta. c e ( 13 ) ##EQU00014##
where .delta. is a predetermined constant (also see FIG. 5A). The
value of l.sub.e can be interpreted as the length of link e. The
algorithm then attempts to simulate sending the flow for each
commodity k, in turn, along the respective shortest feasible path.
The problem of determining the shortest feasible path is
NP-complete, but permits the use of an efficient approximation
algorithm. Once the flow is sent, the dual lengths of all the links
on the shortest feasible path are incremented as indicated in
pseudo-code 500 (see FIG. 5B). The process of sending the flows and
adjusting the dual lengths is repeated iteratively until a
termination condition is met. A mathematical proof that the
algorithm defined by pseudo-code 500 solves the above-formulated
dual problem can be found, e.g. in the above-cited U.S. Provisional
Patent Application No. 62/106,419.
[0055] With a careful choice of the values of .omega.', .epsilon.,
and .delta. for the algorithm defined by pseudo-code 500, the total
number of phases can be bounded by N.sub.p=O(.omega..sup.-2). The
total number of iterations is approximately
N.sub.l=O(.omega..sup.-2D). The total number of steps is
approximately N.sub.s=O(.omega..sup.-2(D+E)). In various steps of
the algorithm, a constrained shortest path computation and other
updates indicated in FIG. 5 are performed.
[0056] Various embodiments disclosed above are primarily designed
for transparent optical networks, in which a candidate path is
feasible if and only if the above-discussed path constraints are
satisfied from end-to-end. However, in some networks, the use of
end-to-end constraints may lead to a routing failure, e.g., because
the corresponding network simply does not have or cannot support a
sufficient number of routes that satisfy such constraints. This
routing failure can be remedied, e.g., by converting an optically
transparent network into an optically translucent one, wherein a
relatively small number (compared to the number of nodes) of signal
regenerators are used to absorb the dispersed optical signals,
reconstruct original signals in the electrical domain, and convert
the reconstructed signals back into optical signals. In this
manner, the range of optical transmission can be greatly extended,
and more of feasible candidate paths can be considered and utilized
during the routing processing. As a downside, this network
conversion requires a relatively large capital expenditure for
deploying and operating optical-to-electrical-to-optical (OEO)
signal regenerators.
[0057] The algorithm defined by pseudo-code 500 can be modified,
e.g., as further described below, for use in translucent optical
networks. To enable a person of ordinary skill in the art to make
and use these modifications, we first explain how OEO signal
regenerators and their capacities can be represented in the graph G
used in pseudo-code 500. It is assumed that each of the OEO signal
regenerators is attached to some node 110. Locations of the nodes
110 equipped with OEO signal regenerators are known a priori and
supplied to the modified pseudo-code as an additional input in the
section labeled "Input" (see FIG. 5A). In practice, only a small
fraction of nodes 110 are equipped with OEO signal regenerators
and, in some embodiments, said OEO signal regenerators are capable
of regenerating only a limited number of channels
c.sub..nu..sup..tau..
[0058] FIG. 6 shows a graph 600 that can be used to modify
pseudo-code 500 (FIGS. 5A-5B) according to an embodiment of the
disclosure. We assume that the OEO signal regenerator (denoted by
the symbol .nu.') is attached at a certain node 110 (denoted by the
symbol .nu.) and is configured to be inserted into flows that pass
through the node on-demand, rather than by fixed (always ON)
allocation. As such, the OEO signal regenerator is represented in
graph 600 using a loop composed of two links e=.nu..fwdarw..nu.'
and e'=.nu.'.fwdarw..nu.. The corresponding link capacity is
c.sub.e=c.sub.e'=c.sub..nu..sup..tau..
[0059] In a modified pseudo-code 500, all OEO signal regenerators
configured as indicated in FIG. 6 are grouped into a set V.sub.r,
and the corresponding links e and e' are added to the link set E.
When an optical signal arrives at node .nu., it may either be
applied directly for the next fiber span or enter the loop ee' to
be regenerated in OEO signal regenerator .nu.'. Only some flows are
directed through the regenerator loops, and the corresponding
capacity restrictions can be added to pseudo-code 500 in a
relatively straightforward manner.
[0060] As a next modification of pseudo-code 500, one can adapt
Hassin's constrained shortest path algorithm to support the added
regenerator functionality. This algorithm is disclosed, e.g., in R.
Hassin, "Approximation schemes for the restricted shortest path
problem," Mathematics of Operation Research, 17 (1):36-42, 1992,
which is incorporated herein by reference in its entirety. Hassin's
algorithm follows a dynamic programming approach: it starts from
the source node s(k), then iteratively increases the search range l
and updates the minimum cumulative dispersion
g v = ^ i .di-elect cons. p v a i b i ##EQU00015##
along the least dispersed paths p.sub..nu. from s(k) to every other
node .nu. within the search range |p.sub..nu.|<l, and terminates
as soon as it finds a path p.sub.t(k) from s(k) to t(k) that
satisfies the dispersion constraint
g t ( k ) .ltoreq. NL T OSNR T . ##EQU00016##
The resulting path p.sub.t(k) is the constrained shortest path.
[0061] The following equations mathematically describe the
above-indicated modifications of pseudo-code 500.
g s ( k ) = 0 , l = 0 , 1 , 2 , , p t ( k ) ( 14 a ) g v ( l ) =
.infin. , .A-inverted. v .di-elect cons. V - s ( k ) , l = 0 , 1 ,
2 , , p t ( k ) ( 14 b ) g v ( l ) = min { g v ( l - 1 ) , min e =
v ' v ( g v ' ( l - l e ) + i .di-elect cons. e a i b i ) } ,
.A-inverted. v .di-elect cons. V - s ( k ) , l = 0 , 1 , 2 , , p t
( k ) ( 14 c ) ##EQU00017##
where Eqs. (14a) and (14b) provide the initial conditions of the
search, and Eq. (14c) gives an iterative update. The use of OEO
signal regenerators causes the cumulative dispersion to reset to
zero at each of the regenerator nodes from set V.sub.r, as
reflected in Eqs. (15a)-(15d):
g s ( k ) = 0 , l = 0 , 1 , 2 , , p t ( k ) ( 15 a ) g v ( l ) =
.infin. , .A-inverted. v .di-elect cons. V V r - s ( k ) , l = 0 ,
1 , 2 , , p t ( k ) ( 15 b ) g v ( l ) = min { g v ( l - 1 ) , min
e = v ' v ( g v ' ( l - l e ) + i .di-elect cons. e a i b i ) } ,
.A-inverted. v .di-elect cons. V - s ( k ) , l = 0 , 1 , 2 , , p t
( k ) ( 15 c ) g v = 0 , if min e = v ' v ( g v ' ( l - l e ) + i
.di-elect cons. e a i b i ) .ltoreq. NL T OSNR T , .A-inverted. v
.di-elect cons. V r , l = 0 , 1 , 2 , , p t ( k ) ( 15 d )
##EQU00018##
In this manner, an OEO signal regenerator .nu.'.epsilon.V.sub.r is
activated as soon as a feasible path from s(k) to .nu. that
conforms to the cumulative nonlinearity constraint is found, and
starts serving as a reset point for all candidate paths passing
through it. Consequently, the scope of the constrained shortest
path is no longer restricted to candidate paths without
regenerators. Such an extension of the scope does not mean that any
paths can utilize OEO signal regenerators. Instead, the
above-indicated limited capacities of the OEO signal regenerators
need to be efficiently allocated to those traffic demands that
could not be routed without OEO signal regenerators or would highly
benefit from the use of OEO signal regenerators. This can be
achieved through iterative adjustments of the length system L and
reallocation of traffic flows, e.g., as indicated in pseudo-code
500.
[0062] According to an example embodiment disclosed above in
reference to FIGS. 1-6, provided is an optical communication method
(e.g., 400, FIG. 4) comprising the steps of: determining (e.g.,
402+404+406, FIG. 4) a plurality of optical paths for a traffic
matrix to be routed through an optical network (e.g., 100, FIG. 1),
wherein each optical path of the plurality satisfies a feasibility
condition defined by a first threshold value and a second threshold
value, the first threshold value being configured to specify an
optical signal-to-noise ratio, and the second threshold value being
configured to specify a nonlinear phase shift; determining (e.g.,
404, FIG. 4) a universal set of powers, each power in said set
corresponding to a respective span (e.g., 146, FIG. 1B) in the
plurality of optical paths and representing an optical power level
in that respective span, with each power in said set being
determined based on the first and second threshold values; and
routing (e.g., 406, FIG. 4) the traffic matrix through a subset of
the plurality of optical paths.
[0063] In some embodiments of the above method, the method further
comprises the step of configuring (e.g., as part of 408, FIG. 4)
network nodes (e.g., 110, FIG. 1A) located on optical paths of the
subset to direct optical signals configured to carry traffic flows
corresponding to the traffic matrix along respective optical paths
of the subset.
[0064] In some embodiments of any of the above methods, the method
further comprises the step of configuring (e.g., as another part of
408, FIG. 4) optical amplifiers (e.g., 150, FIG. 1B) located on the
optical paths of the subset to amplify the optical signals in a
manner that causes an optical launch power for each respective span
in the subset to approximate (e.g., to within .+-.10%) a respective
power from the universal set of powers.
[0065] In some embodiments of any of the above methods, each of the
optical nodes located on the optical paths of the subset comprises
a respective reconfigurable optical add/drop multiplexer (e.g., as
110.sub.1, FIG. 1A).
[0066] In some embodiments of any of the above methods, the optical
nodes located on the optical paths of the subset include one or
more optical nodes equipped with respective OEO signal regenerators
(e.g., as indicated in FIG. 6).
[0067] In some embodiments of any of the above methods, at least
one of the optical signals is WDM signal.
[0068] In some embodiments of any of the above methods, optical
paths allocated to carry traffic flows corresponding to the traffic
matrix do not have an optical path not belonging to the plurality
of optical paths that satisfy the feasibility condition.
[0069] In some embodiments of any of the above methods, the optical
network is a transparent optical network.
[0070] In some embodiments of any of the above methods, the optical
network is a translucent optical network.
[0071] In some embodiments of any of the above methods, the
feasibility condition is given by the following inequality:
i .di-elect cons. q a i b i .ltoreq. NL T OSNR T ##EQU00019##
where
a i = hvB ref F i T i ; b i = .gamma. i ( 1 - T i ) .alpha. i ;
##EQU00020##
i denotes a span; q denotes an optical path; OSNR.sub.T is the
first threshold; NL.sub.T is the second threshold; hv is an energy
of one photon of optical frequency v; B.sub.ref is a reference
bandwidth; F.sub.i is a noise figure for the span; .alpha..sub.i is
a fiber loss coefficient for the span; T.sub.i is optical
transmittance of the span; and .gamma..sub.i is a nonlinear
coefficient for the span.
[0072] In some embodiments of any of the above methods, each power
in the universal set of powers is determined in accordance with the
following equation:
P i * .apprxeq. a i b i OSNR T NL T ##EQU00021##
where
a i = hvB ref F i T i ; b i = .gamma. i ( 1 - T i ) .alpha. i ;
##EQU00022##
i denotes a span; OSNR.sub.T is the first threshold; NL.sub.T is
the second threshold; hv is an energy of one photon of optical
frequency v; B.sub.ref is a reference bandwidth; F.sub.i is a noise
figure for the span; .alpha..sub.i is a fiber loss coefficient for
the span; T.sub.i is optical transmittance of the span; and
.gamma..sub.i is a nonlinear coefficient for the span.
[0073] In some embodiments of any of the above methods, the method
is executed at a controller (e.g., 130, FIG. 1A) of the optical
network.
[0074] In some embodiments of any of the above methods, for an
optical path, the feasibility condition is checked by: obtaining
(e.g., 402, FIG. 4; Eqs. (4)-(5)) a respective span metric for each
span of the optical path; summing (e.g., as in the left side of Eq.
(4)) the respective span metrics to generate an aggregated metric
for the optical path; and comparing the aggregated metric with a
reference metric defined by the first and second threshold values
(e.g., as indicated by Eq. (4)).
[0075] In some embodiments of any of the above methods, the method
further comprises the steps of: generating a plurality of routing
solutions by specifying a plurality of different traffic matrices
and repeating the steps of determining the plurality of optical
paths, determining the universal set of powers, and routing for
each said different traffic matrices; and storing the plurality of
routing solutions in a non-volatile memory.
[0076] In some embodiments of any of the above methods, the method
further comprises the steps of: obtaining a current traffic matrix
to be routed through the optical network; and retrieving from the
non-volatile memory one of the plurality of routing solutions
corresponding to the current traffic matrix.
[0077] In some embodiments of any of the above methods, the method
further comprises the steps of: configuring (e.g., as part of 408,
FIG. 4) network nodes (e.g., 110, FIG. 1A) to direct optical
signals configured to carry traffic flows corresponding to the
current traffic matrix along respective optical paths specified in
said one of the plurality of routing solutions; and configuring
(e.g., as another part of 408, FIG. 4) optical amplifiers (e.g.,
150, FIG. 1B) located on the respective optical paths to amplify
the optical signals in a manner that causes an optical launch power
for each respective span to approximate (e.g., to within .+-.10%) a
respective power from the universal set of powers corresponding to
said one of the plurality of routing solutions.
[0078] In some embodiments of any of the above methods, the routing
is performed using a fully polynomial-time approximation scheme
(e.g., 500, FIG. 5).
[0079] According to another example embodiment disclosed above in
reference to FIGS. 1-6, provided is a non-transitory
machine-readable medium, having encoded thereon program code,
wherein, when the program code is executed by a machine, the
machine implements a computer-aided signal-routing method, the
computer-aided signal-routing method comprising the steps of:
determining (e.g., 402+404+406, FIG. 4) a plurality of optical
paths for a traffic matrix to be routed through an optical network
(e.g., 100, FIG. 1), wherein each optical path of the plurality
satisfies a feasibility condition defined by a first threshold
value and a second threshold value, the first threshold value being
configured to specify an optical signal-to-noise ratio, and the
second threshold value being configured to specify a nonlinear
phase shift; determining (e.g., 404, FIG. 4) a universal set of
powers, each power in said set corresponding to a respective span
(e.g., 146, FIG. 1B) in the plurality of optical paths and
representing an optical power level in that respective span, with
each power in said set being determined based on the first and
second threshold values; and routing (e.g., 406, FIG. 4) the
traffic matrix through a subset of the plurality of optical
paths.
[0080] In some embodiments of the above non-transitory
machine-readable medium, the computer-aided signal-routing method
further comprises the steps of: generating a plurality of routing
solutions by specifying a plurality of different traffic matrices
and repeating the steps of determining the plurality of optical
paths, determining the universal set of powers, and routing for
each of said different traffic matrices; and storing the plurality
of routing solutions in a non-volatile memory.
[0081] In some embodiments of any of the above non-transitory
machine-readable media, the computer-aided signal-routing method
further comprises the steps of: obtaining a current traffic matrix
to be routed through the optical network; and retrieving from the
non-volatile memory one of the plurality of routing solutions
corresponding to the current traffic matrix.
[0082] According to yet another example embodiment disclosed above
in reference to FIGS. 1-6, provided is an optical network (e.g.,
100, FIG. 1A) comprising: a plurality of network nodes (e.g., 110,
FIG. 1A) optically interconnected by a plurality of optical links
(e.g., 140, FIG. 1A), each comprising one or more fiber spans
(e.g., 146, FIG. 1B); and a network controller (e.g., 140, FIG. 1A)
operatively coupled to the plurality of network nodes and
configured to: determine (e.g., 402+404+406, FIG. 4) a plurality of
optical paths for a traffic matrix to be routed through the
plurality of optical links, wherein each optical path of the
plurality of optical paths satisfies a feasibility condition
defined by a first threshold value and a second threshold value,
the first threshold value being configured to specify an optical
signal-to-noise ratio, and the second threshold value being
configured to specify a nonlinear phase shift; determine (e.g.,
404, FIG. 4) a universal set of powers, each power in said set
corresponding to a respective span (e.g., 146, FIG. 1B) in the
plurality of optical paths and representing an optical power level
in that respective span, with each power in said set being
determined based on the first and second threshold values; and
route (e.g., 406, FIG. 4) the traffic matrix through a subset of
the plurality of optical paths.
[0083] While this disclosure includes references to illustrative
embodiments, this specification is not intended to be construed in
a limiting sense. Various modifications of the described
embodiments, as well as other embodiments within the scope of the
disclosure, which are apparent to persons skilled in the art to
which the disclosure pertains are deemed to lie within the
principle and scope of the disclosure, e.g., as expressed in the
following claims.
[0084] Unless explicitly stated otherwise, each numerical value and
range should be interpreted as being approximate as if the word
"about" or "approximately" preceded the value or range.
[0085] It will be further understood that various changes in the
details, materials, and arrangements of the parts which have been
described and illustrated in order to explain the nature of this
disclosure may be made by those skilled in the art without
departing from the scope of the disclosure, e.g., as expressed in
the following claims.
[0086] Although the elements in the following method claims, if
any, are recited in a particular sequence with corresponding
labeling, unless the claim recitations otherwise imply a particular
sequence for implementing some or all of those elements, those
elements are not necessarily intended to be limited to being
implemented in that particular sequence.
[0087] Reference herein to "one embodiment" or "an embodiment"
means that a particular feature, structure, or characteristic
described in connection with the embodiment can be included in at
least one embodiment of the disclosure. The appearances of the
phrase "in one embodiment" in various places in the specification
are not necessarily all referring to the same embodiment, nor are
separate or alternative embodiments necessarily mutually exclusive
of other embodiments. The same applies to the term
"implementation."
[0088] Also for purposes of this description, the terms "couple,"
"coupling," "coupled," "connect," "connecting," or "connected"
refer to any manner known in the art or later developed in which
energy is allowed to be transferred between two or more elements,
and the interposition of one or more additional elements is
contemplated, although not required. Conversely, the terms
"directly coupled," "directly connected," etc., imply the absence
of such additional elements.
[0089] The embodiments covered by the claims in this application
are limited to embodiments that (1) are enabled by this
specification and (2) correspond to statutory subject matter.
Non-enabled embodiments and embodiments that correspond to
non-statutory subject matter are explicitly disclaimed even if they
formally fall within the scope of the claims.
[0090] The described embodiments are to be considered in all
respects as only illustrative and not restrictive. In particular,
the scope of the disclosure is indicated by the appended claims
rather than by the description and figures herein. All changes that
come within the meaning and range of equivalency of the claims are
to be embraced within their scope.
[0091] A person of ordinary skill in the art would readily
recognize that steps of various above-described methods can be
performed by programmed computers. Herein, some embodiments are
intended to cover program storage devices, e.g., digital data
storage media, which are machine or computer readable and encode
machine-executable or computer-executable programs of instructions
where said instructions perform some or all of the steps of methods
described herein. The program storage devices may be, e.g., digital
memories, magnetic storage media such as a magnetic disks or tapes,
hard drives, or optically readable digital data storage media. The
embodiments are also intended to cover computers programmed to
perform said steps of methods described herein.
[0092] The functions of the various elements shown in the figures,
including any functional blocks labeled as "controllers" and
"processors," may be provided through the use of dedicated hardware
as well as hardware capable of executing software in association
with appropriate software. When provided by a processor, the
functions may be provided by a single dedicated processor, by a
single shared processor, or by a plurality of individual
processors, some of which may be shared. Moreover, explicit use of
the term "processor" or "controller" should not be construed to
refer exclusively to hardware capable of executing software, and
may implicitly include, without limitation, digital signal
processor (DSP) hardware, network processor, application specific
integrated circuit (ASIC), field programmable gate array (FPGA),
read only memory (ROM) for storing software, random access memory
(RAM), and non volatile storage. Other hardware, conventional
and/or custom, may also be included. Similarly, any switches shown
in the figures are conceptual only. Their function may be carried
out through the operation of program logic, through dedicated
logic, through the interaction of program control and dedicated
logic, or even manually, the particular technique being selectable
by the implementer as more specifically understood from the
context.
[0093] It should be appreciated by those of ordinary skill in the
art that any block diagrams herein represent conceptual views of
illustrative circuitry embodying the principles of the disclosure.
Similarly, it will be appreciated that any flow charts, flow
diagrams, state transition diagrams, pseudo code, and the like
represent various processes which may be substantially represented
in computer readable medium and so executed by a computer or
processor, whether or not such computer or processor is explicitly
shown.
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