U.S. patent application number 13/944401 was filed with the patent office on 2013-11-14 for dynamic assignment of wavelengths in agile photonic networks.
This patent application is currently assigned to Alcatel Lucent. The applicant listed for this patent is Mukul Katiyar, Rajender Rao Nednur, Anthony Vernon Walker Smith, Kotikalapudi Sriram, Jonathan Titchener. Invention is credited to Mukul Katiyar, Rajender Rao Nednur, Anthony Vernon Walker Smith, Kotikalapudi Sriram, Jonathan Titchener.
Application Number | 20130302033 13/944401 |
Document ID | / |
Family ID | 48999814 |
Filed Date | 2013-11-14 |
United States Patent
Application |
20130302033 |
Kind Code |
A1 |
Sriram; Kotikalapudi ; et
al. |
November 14, 2013 |
Dynamic Assignment Of Wavelengths In Agile Photonic Networks
Abstract
In an automatically switched optical network, the wavelengths
are assigned to optical path based on their intrinsic physical
performance and on the current network operating parameters. The
wavelength performance information is organized in binning tables,
based primarily on the wavelength reach capabilities. A network
topology database provides the distance between the nodes of the
network, which is used to determine the length of the optical path.
Other network operating parameters needed for wavelength selection
are also available in this database. Once a bin corresponding to
the path length is identified in the binning table, the wavelength
for that path is selected based on length only, or based on the
length and one or more additional parameters. The optical path
performance is estimated for the selected wavelength, and the
search continues if the estimated path performance is not
satisfactory. Several available wavelengths are searched and of
those, the wavelength that is most used along the optical path in
consideration or alternatively network-wide is selected and
assigned. This method helps minimize wavelength fragmentation. The
binning tables may have various granularities, and may be organized
by reach, or by reach, wavelength spacing, the load on the
respective optical path, the fiber type, etc.
Inventors: |
Sriram; Kotikalapudi;
(Marlboro, NJ) ; Katiyar; Mukul; (Piscataway,
NJ) ; Titchener; Jonathan; (Green Brook, NJ) ;
Nednur; Rajender Rao; (North Brunswick, NJ) ; Smith;
Anthony Vernon Walker; (Ottawa, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Sriram; Kotikalapudi
Katiyar; Mukul
Titchener; Jonathan
Nednur; Rajender Rao
Smith; Anthony Vernon Walker |
Marlboro
Piscataway
Green Brook
North Brunswick
Ottawa |
NJ
NJ
NJ
NJ |
US
US
US
US
CA |
|
|
Assignee: |
Alcatel Lucent
Murray Hill
NJ
|
Family ID: |
48999814 |
Appl. No.: |
13/944401 |
Filed: |
July 17, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10128092 |
Apr 23, 2002 |
8521022 |
|
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13944401 |
|
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|
09909265 |
Jul 19, 2001 |
7171124 |
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10128092 |
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Current U.S.
Class: |
398/49 |
Current CPC
Class: |
H04J 14/0221 20130101;
H04J 14/0267 20130101; H04J 14/0284 20130101; H04J 14/0283
20130101; H04J 14/0269 20130101; H04J 14/0257 20130101; H04J
14/0246 20130101; H04Q 11/0005 20130101 |
Class at
Publication: |
398/49 |
International
Class: |
H04Q 11/00 20060101
H04Q011/00 |
Claims
1.-24. (canceled)
25. In a automatically switched optical network, a routing
management block comprising: means for storing wavelength
performance information according to type, extent and granularity
search criteria; means for storing updated network resources
information; and a wavelength assignment module for determining the
length of an optical path by searching said updated network
resources information and selecting a wavelength for said optical
path based on said wavelength performance information.
26. A routing management block as in claim 25, wherein said
wavelength performance information comprises a wavelength binning
table with a plurality of reach bins, a reach bin comprising one or
more wavelengths classified according to a reach range.
27. A routing management block as in claim 26, wherein each said
reach bin further comprises a plurality of load sets, each load set
comprising one or more wavelengths classified according to a load
range.
28. A routing management block as in claim 25, wherein said
wavelength performance information comprises a signal quality
versus reach (Q-Reach) graph.
29. A computer readable database medium having a binning table
database for storing wavelength performance information and for
causing a computer to process said binning table database so as to
assign a wavelength to an optical path in a automatically switched
optical network, said binning table database comprising: a
plurality of reach bins, a reach bin storing one or more
wavelengths classified according to a reach range; and in each said
reach bin, a plurality of sets, each set comprising one or more
wavelengths organized according to a wavelength performance
parameter.
30. The computer readable database medium as claimed in claim 29,
wherein said wavelength performance parameter is the effective load
of said optical path.
31. The computer readable database medium as in claim 29, wherein
said wavelength performance parameter is the wavelength spacing
available for said wavelength plan.
32. (canceled)
Description
PRIORITY PATENT APPLICATION
[0001] This patent application is a continuation in part of the
co-pending U.S. patent application Ser. No. 09/909,265, entitled
"Wavelength Routing and Switching Mechanism for a Photonic
Transport Network", Smith et al., filed Jul. 19, 2001, assigned to
Innovance Networks, docket 1021.
RELATED U.S. PATENT APPLICATION
[0002] U.S. Patent Application "Wavelengths assignment in an
optical WDM network", (Solheim et al.), Ser. No. Not available yet,
filed Dec. 12, 2001 assigned to Innovance Networks, docket
1011.
[0003] U.S. Patent Application "Regenerator Placement Mechanism For
Wavelength Switched Optical Networks" (Rider et al.), Ser. No. not
available yet, filed Mar. 13, 2002 and assigned to Innovance
Networks, docket 1045.
FIELD OF INVENTION
[0004] The invention is directed to an agile photonic network (also
known as automatically switched optical network ASON, or as all
optical network), and in particular to a system and method for
assigning wavelengths to a connection in such networks.
BACKGROUND OF THE INVENTION
[0005] The most relevant trends in the optical networking area are
the increase in the network capacity and the increase in
transmission reach. A higher network capacity is obtained by
increasing the channel rate and multiplexing more traffic in time
domain, known as TDM (time division multiplexing), and/or by
increasing the channel density, known as WDM (wavelength division
multiplexing).
[0006] Advances in transmitter and receiver design, evolution of
optical amplification, employment of distributed Raman
amplification combined with various dispersion compensation
techniques, new encoding and modulation techniques, digital wrapper
technology, etc., enabled development of ultra-long reach ULR
networks, where an optical signal needs to be regenerated at 3,000
km or more.
[0007] However, current WDM networks use point-to-point
connectivity, where all channels are OEO
(optical-to-electrical-to-optical) converted at each node. In this
architecture, the advantages of the ULR cannot be fully exploited.
Thus, OEO conversion at all intermediate nodes along a trail is not
necessary in the majority of cases, since the modern ULR techniques
allow optical signals to travel distances greater than the distance
between two or more successive nodes without regeneration. Thus,
important cost savings may be obtained by eliminating the equipment
used for the unnecessary OEO conversion.
[0008] There is a need to reduce the cost of the network nodes by
maximizing the distance traveled by the signals in optical format,
to take advantage of the emerging ULR techniques and to provide a
more efficient use of the network equipment.
[0009] There is a trend towards a new generation of optical
networks, that will provide the customers with the ability to
automatically establish an end-to-end connection at a push of a
button. This new architecture has, among numerous other advantages,
the ability to treat each connection differently, so as to provide
the respective user with an individualized class of service, with
the corresponding revenue differentiation. End-to-end connection
granularity means that the nodes of the network need to be able to
switch the connection in optical format, while automatically
regenerating the signal only when necessary. This approach
dramatically reduces the node complexity, and consequently the
network cost.
[0010] Automatic switching and regeneration result in regenerators
and wavelengths becoming two of the most important resources of the
photonic networks. In general, they could be allocated to a
connection according to certain rules, which are mostly dictated by
the class of service for the respective connection, and by the
particular architecture of the network. Methods to economically use
these resources and minimize blocking of new connection requests
are crucial to cost reduction and operational efficiency of
photonic networks.
[0011] Determination of the number of regenerators and their nodal
allocations is one aspect of efficient resource management in
photonic networks. Regenerators need to be switched into an
end-to-end connection so that the signal is regenerated and
restored to superior quality before propagation and transmission
impairments corrupt the signal entirely.
[0012] Further, in switched optical networks, the selection and
assignment of the right wavelength to each optical path for the
best possible utilization of available wavelengths depends on
several factors. These factors include (a) maintaining a current
view of the current network connectivity; and (b) since "not all
wavelengths are equal", providing the network with the knowledge of
the individual wavelength performance.
[0013] Knowing the current wavelength allocation allows the network
to select one or more unused wavelengths to serve a new connection.
This is even more important having in view that this allocation is
dynamic, the connections being set-up and removed by users at
arbitrary moments. Knowing the individual performance of all
wavelength available in the network and the pertinent topology
information (fiber type, link loading, etc), allows matching a
wavelength to an optical path, which allows further reduction of
the network costs.
[0014] Nonetheless, the selection and assignment of the right
wavelength for each optical path for the best possible utilization
of available wavelengths is a complex problem. A meaningful
solution to this complex problem is needed to facilitate the best
possible use of wavelengths as a resource while satisfying
connection setup demands.
SUMMARY OF THE INVENTION
[0015] It is an object of the invention to provide an agile network
with dynamic assignment of wavelengths to an end-to-end
connection.
[0016] According to one aspect of the invention, an automatically
switched optical network operating according to a wavelength plan
is provided with a method of assigning a wavelength to an optical
path, comprising: organizing all wavelengths provided by the
wavelength plan in a binning table according to the natural
wavelength reach and a specified wavelength parameter; determining
the length of the optical path and the value of the wavelength
specific parameter for that optical path; and searching the binning
table to select a wavelength for the optical path based on
availability of the wavelength on the optical path, the length of
the optical path and the value of the parameter.
[0017] According to another aspect, the invention provides a
routing management block that comprises means for storing
wavelength performance information; means for storing updated
network resources information; and a wavelength assignment module
for determining the length of an optical path based on the updated
network resources information and selecting a wavelength for the
optical path based on the wavelength performance information.
[0018] Still further, the invention provides an automatically
switched optical network operating according to a wavelength plan
with a binning table that includes wavelength performance
information, the binning table comprising a plurality of reach
bins, a reach bin comprising one or more wavelengths classified
according to a reach range; and, in each the reach bin, a plurality
of sets, each the set comprising one or more wavelengths organized
according to a wavelength performance parameter.
[0019] Additionally, the invention deals with determination of the
most used of the available wavelengths over an optical path, and
assignment of the most used wavelength to the optical path in order
to minimize wavelength fragmentation. The notion of "most used" can
be applied only over the optical path in consideration or over the
network as a whole. One novel aspect of the present invention is
the way the concept of minimization of wavelength fragmentation is
used in conjunction with navigation of wavelength-binning tables in
the context of switched optical networks.
[0020] Advantageously, the wavelength assignment mechanism
according to the invention allows fast, automatic establishment of
new connections based on the current network architecture,
connectivity and loading and also on conditions in the connection
request. Finding an appropriate wavelength-path match is performed
in a meaningful way, using searching techniques with various
degrees of sophistication. Selection of a wavelength for each
optical path is performed with optimal use of current network
resources, while ensuring that the quality of the selected trail is
adequate for the respective call.
[0021] The wavelength searching and selection techniques according
to the invention allow reducing the time-to-bandwidth (TTB).
Furthermore, the wavelength searching and selection techniques are
designed with a view to reduce network resource utilization, by
minimizing wavelengths fragmentation, which lowers the need for
regenerators, reduces call blocking, and hence contributes to
network service costs reduction, while increasing the
quality-of-service.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] The foregoing and other objects, features and advantages of
the invention will be apparent from the following more particular
description of the preferred embodiments, as illustrated in the
appended drawings, where:
[0023] FIG. 1 shows the main modules involved in the routing and
switching services of a photonic network, and their
interaction;
[0024] FIG. 2A shows a plurality of optical paths for an end-to-end
A-Z trail, including regenerating nodes;
[0025] FIG. 2B shows some ways to enhance performance of A-Z trail
of FIG. 2A;
[0026] FIG. 3A shows an example of a cell of a complex
wavelength-reach table;
[0027] FIG. 3B is a flowchart illustrating a method of selecting a
wavelength using tables as shown in FIG. 3A;
[0028] FIG. 4A illustrates how wavelength fragmentation is
addressed in the context of an optical path;
[0029] FIG. 4B is a flowchart illustrating a method for minimizing
wavelength fragmentation in the context of an optical path;
[0030] FIG. 4C shows an optical path with multiple links (hops) and
multiple fibers on some of the links;
[0031] FIG. 5A illustrates how wavelength fragmentation is
addresses in the context of the entire network;
[0032] FIG. 5B is a flowchart illustrating a method for minimizing
wavelength fragmentation over an entire switched optical
network;
[0033] FIG. 6A is an example of a signal quality versus reach (Q-R)
plot; and
[0034] FIG. 6B is a flowchart illustrating a method for upgrading a
wavelength using a fine-grained wavelength reach table;
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0035] The following description is of a preferred embodiment by
way of example only and without limitation to combination of
features necessary for carrying the invention into effect.
[0036] The following definitions are used throughout this
specification: "Dial", "Redial", "Call" or "connection request"
refers to a request for exchanging traffic between two nodes. It
includes conditions such as the source and destination nodes,
traffic bandwidth and rate, the class of service CoS, the type of
routing, explicit constraints, etc.
[0037] "Photonic network" is a network where an end-to-end
connection is established along a trail whereby the traffic may be
automatically switched at all or some intermediate nodes in optical
format. The nodes of a photonic network could be optical add/drop
multiplexing (OADM) nodes that provide add, drop and optical
passthrough, or could be optical cross-connect nodes that provide
add, drop and optical switching of the passthrough traffic.
[0038] A "connection" is a logical route from a source node,
generically referred to as node A to a destination node,
generically referred to as node Z. A "route" or "trail" refers to a
specific route for the A-Z connection.
[0039] A "wavelength plan" refers to the set of wavelengths
available network-wide. A wavelength plan specifies the
telecommunication window on which the network operates (e.g.
C-band, L-band), the wavelengths available in the respective
window, and the wavelength spacing, etc. For example, the
wavelength plan could provide .about.100 wavelengths on a 50 GHz
grid from 1567 nm to 1610 nm (i.e. L-band) which yields .about.1
Tb/s per optical line amplifier.
[0040] A "regeneration node" is a node that OEO converts the
traffic on the route passing through that node for wavelength
conversion (relevant to this invention) or signal conditioning. The
photonic network to which this invention applies (hereinafter
referred as the "photonic network") has the ability to determine if
a connection needs wavelength conversion (or/and traffic
regeneration), looks for a regenerator available at one or more
intermediate nodes along the A-Z trail and allocates regenerator(s)
to the respective route to correctly deliver the signal to its
destination. To this end, some or all nodes of the photonic network
are provided with a pool of regenerators that are automatically
switched into a connection as needed. Since the regenerators and
the wavelength converters of the photonic network have a similar
hardware design, they are collectively referred to in this
specification as regenerators.
[0041] An "optical path" or "regenerator segment" refers to the
fiber and the equipment between a transmitter and the next
receiver, i.e. between two successive regenerators.
[0042] A "link" refers to the equipment (could be optical
amplifiers, dispersion compensators, etc) and fiber between two
successive photonic nodes. A link may include one or more fibers
and the associate equipment.
[0043] The term "loading" is a measure of the number of channels
carried by a certain fiber/link. "Wavelength spacing" provides the
distance between two consecutive wavelengths. Link loading and
wavelength spacing are inter-related notions.
[0044] "Network topology information" includes information on
network equipment and connectivity, fiber type for each link,
wavelengths availability per link, the number and type of
transponders and regenerators at each node and their availability,
etc. It is generically illustrated by data topology system DTS 15
in FIG. 1.
[0045] FIG. 1 is a logical overview of a network and element
management system for a photonic network, showing the modules
pertinent to the invention. A detailed description on how the
routing and switching mechanism of FIG. 1 operates is provided in
the parent case Docket 1021. A brief description follows.
[0046] A call management block 11 provides a routing management RM
10 with a connection request that specifies the source node A and
the sink node Z. A request also defines certain conditions, and
generally includes constraints associated with the class of
services (CoS) of the call/user.
[0047] Routing management platform 10 comprises a routing module
(RM) 22, a regenerator placement module (RPM) 23 and a wavelength
assignment module (WAM) 24. After receiving the call from block 11,
a routing management controller (RMC) 21 operates modules RM 22,
RPM 23 and WAM 24 to generate a list 26 of possible best trails
between nodes A and Z. The RMC 21 analyzes and orders the trails
according to their cost and/or chances of success, and returns them
to call manager 11 one by one. Block 11 attempts to set-up the
connection along one of these trails; if the first trail on the
list fails to set-up, block 11 requests the next trail from list 26
and so on, until a trail is successfully setup.
[0048] RPM 23, which is the subject of patent application Docket
#1045, decides where to place regenerators along the A-Z trail
based on regenerator and wavelength availability. As described in
patent application Docket 1045, RPM 23 also has the ability to
change an initial placement of regenerators taking into account the
distance-dependent nature of the wavelengths.
[0049] The WAM 24 assigns wavelengths to each optical path of the
respective end-to-end A-Z trail, based on wavelength rules 25,
wavelength availability from DTS 15, and on pre-stored information
about wavelength performance, as shown at 20. Thus, the wavelength
assignment mechanism addresses wavelength contention in order to
reduce wavelength blocking; considers wavelength-reach performance
of the available channels; and assigns wavelengths with appropriate
reach profiles for each optical path of the respective route.
[0050] Since the trail performance cannot be determined until after
the wavelength assignment module (WAM) 24 assigns wavelengths to
each path of the trail, RPM 23 may invoke WAM 24 multiple times for
corroborating the decisions regarding the placement of regenerators
with the optimal wavelength assignment, as these two modules 23, 24
perform inter-dependent functions.
[0051] A Q calculator 18 is available for use by the modules of the
routing management platform 10. The Q calculator is a module
provided by the optical link engineering (OLE) module 19, for
calculating a quality factor Q based upon knowledge of the topology
from DTS 15, optical devices specified and measured parameters
generically shown by database 14.
[0052] During route selection, Q-calculator 18 estimates the Q
value for each trail in the list 26 so that the routing management
can order the trails based on this value. When a wavelength is
considered for an optical path, its estimated optical quality, or Q
value, is used to determine the acceptability of the wavelength. If
the estimated Q.sub.est value falls short of a required Q.sub.th
value, then the wavelength is not selected for that path.
Alternatively, both RPM 23 and WAM 24 collectively attempt some
corrective measures for enhancing the end-to-end performance of the
respective trail, to avoid searching for a new trail.
[0053] At the time the connection is set-up, Q calculator 18
determines a measured Q value Q.sub.meas, which reflects the
optical path conditions in the network more realistically. If
Q.sub.meas<Q.sub.th, RPM 23 and WAM 24 collectively attempt some
corrective measures, or the trail is abandoned in favor of another
one from list 26.
[0054] FIGS. 2A and 2B are provided for a brief description of the
RPM 23 and WAM 24 interaction. FIG. 2A shows an end-to-end
connection from node N1 to node N11 routed along an A-Z trail. The
source and destination nodes have transponders, which are optical
terminals (a long reach transmitter Tx-receiver Rx pair), for
adding on or dropping off a connection to/from the switched optical
network from/to the network clients. In the example of FIG. 2A, A-Z
trail uses two regenerators (wavelength converters) R1 and R2
located at nodes N4 and N8, so that A-Z trail has three optical
paths, denoted with OP1, OP2 and OP3. As also shown in FIG. 2A, a
continuous wavelength .lamda.i, .lamda.j, and .lamda.k is allocated
to each respective optical path, as seen later. R1 is switched in
the trail since .lamda.i is not available on link N4-N5 (e.g. is
used by another connection on link N4-N5, or cannot reach node Z),
and R2 is provided since .lamda.j is not available on link N8-N9
(e.g. is used by another connection on link N8-N9, or cannot reach
node Z)
[0055] After WAM 24 performed an initial wavelength assignment, the
Q calculator (18 in FIG. 1) provides an estimate Q.sub.est of the
quality of all optical paths OP1, OP2 and OP3 for the selected
wavelength set. If all Q.sub.est values exceed a predetermined
threshold Q.sub.th ("pass"), the trail A-Z passes the quality test
and wavelengths .lamda.i, .lamda.j, and .lamda.k are selected and
assigned to OP1, OP2, OP3, respectively.
[0056] However, if as FIG. 2B shows, Q.sub.est on OP2 (.lamda.j) is
less than Q.sub.th, a number of options are available to address
this problem. As shown by arrow "a", RPM 35 may shorten OP2 by
"re-placing" regenerator R1 from node N4 to node N5, so that path
OP2 gets a better chance of passing the Q test. Thereafter, Q
calculator 18 determines the new Q.sub.estvalues for OP1' (N1 to
N5), OP2' (N5 to N8), and if these pass (Q.sub.est>Q.sub.th),
wavelength set .lamda.i, .lamda.j, and .lamda.k is selected.
[0057] If either of OP1' and OP2' fails, R1 is returned at node N4
and RPM 35 "re-places" the regenerator R2 to the previous node,
i.e. from node N8 to node N7, again to shorten OP2. This is shown
by arrow "b". Q calculator 18 determines the new Q.sub.est values
for OP2'' (N4 to N7), OP3'' (N7 to N11), and if these pass
(Q.sub.est>Q.sub.th), wavelength set .lamda.i, .lamda.j, and
.lamda.k is initially selected.
[0058] If one of the new Q.sub.est values "fails", R1 and R2 are
maintained as in the initial regenerator placement solution, and
WAM 24 attempts to upgrade wavelength .lamda.j to .lamda..sub.up,
shown by arrow "c". This means that a wavelength .lamda..sub.up
with a higher reach, if available, is selected and proposed for
possible assignment for the problem link OP2. If Q.sub.est on OP2
passes for the upgraded wavelength, the wavelength set .lamda.i,
.lamda..sub.up, and .lamda.k is selected to service the A-Z
connection.
[0059] However, if the upgraded wavelength .lamda..sub.up also
"fails", then the RPM 23 may decide to add one more regenerators to
the A-Z trail to create four optical paths with shorter distances.
Then, the steps of the basic method described above are repeated
for the new optical paths. It is also to be noted that a wavelength
upgrade may be attempted before regenerator re-placement; it could
result in a less time consuming solution.
[0060] It is also to be noted that similar corrective actions may
be performed if the set-up of a selected trail fails.
[0061] WAM 24 is designed having in mind network resource
optimization (e.g. regenerators and wavelengths) and also reduction
of the path/route computational times, with the ultimate goal of
saving costs. The selection and assignment of an optimal wavelength
for each optical path can be performed using intelligent methods,
by providing the WAM with:
[0062] (1) a priori wavelength performance information, organized
for various types of searches, and various granularities.
[0063] (2) ways of systematic navigation of the wavelength
performance information for searching and selecting an appropriate
wavelength for an optical path, and
[0064] (3) methods of optimizing the wavelength selection at the
optical path level, or/and at the network level.
[0065] Providing and Organizing Wavelength Performance
Information
[0066] Wavelengths differ from each other in their optical
characteristics, such as dispersion, noise figure, etc.
Characteristics exhibited by a particular wavelength also generally
differ if propagated over different fiber types. Based on these
characteristics, the wavelengths may be grouped in sections of
reach (also called here bins), where each section corresponds to a
different range of reach distances. The wavelength performance
information to be accounted for can be expanded to include other
intrinsic characteristics of the transmission medium beyond the
reach, so as to obtain bins with a finer granularity. According to
an embodiment of the invention, the wavelength performance
information 20 is for example arranged in tables with rows,
columns, cells and stored in the database 25 for consultation by
the wavelength assignment module 24. It is to be noted that the
tables may be stored in any other location that is accessible to
WAM 24. While it is also possible to use alternative ways of
presenting and accessing this information, it is important to set
it according to the type, extent and granularity of the search. The
term table is used generically to identify any such organized
wavelength performance data.
[0067] Table 1 is an example of a wavelength-binning table
organized according to the wavelength reach range only. This table
provides information regarding all wavelengths that are projected
to traverse various distance ranges in a fiber, i.e. 0-250 km,
251-500 km, etc., while meeting a certain optical signal quality
requirement, e.g. the above mentioned Q.sub.th. This information
does not take into account operational issues such as dirty
fibers.
TABLE-US-00001 TABLE 1 1 j - 1 j j + 1 M Ordered Search Reach Range
R(j) Set 1-250 km 251-250 501-750 km 4251-4500 km 1 1.sup.st Search
Set .lamda._Set(1, 1) .lamda._Set(1, , j) .lamda._Set(1, M) 2
2.sup.nd Search Set .lamda._Set(2, 1) .lamda._Set(2, , j)
.lamda._Set(2, M) 3 3.sup.rd Search Set .lamda._Set(3, 1)
.lamda._Set(3, , j) .lamda._Set(3, M) indicates data missing or
illegible when filed
[0068] The bins may be further categorized in accordance with
wavelengths spacing. One characteristic of the optical signals is
the cross phase modulations (XPM). Due to XPM, the optical signals
that are of similar frequencies degrade each other's performance.
As the wavelengths get "closer", the signal degradation increases
due to an increased XPM.
[0069] It is therefore advantageous to pre-arrange the order in
which the optical channels are assigned to a connection A-Z by
organizing in advance the sequence in which wavelengths in one bin
are proposed for allocation. For example, wavelengths with wider
spacing should be used to setup optical connections initially, when
the network is commissioned, and wavelengths with narrower spacing
should be used to setup optical connections later.
[0070] Table 2 illustrates a wavelength-binning table organized
according to wavelength reach range and wavelength spacing. Here,
the wavelengths are grouped in columns of reach and three rows for
three different spacing values, i.e. 50, 100, and 200 GHz.
TABLE-US-00002 TABLE 2 ##STR00001## ##STR00002##
[0071] Each link or fiber in the optical path has a load, which is
defined as the ratio between the total number of wavelengths in use
divided by the sum of unassigned wavelengths and those in use. This
ratio is preferably expressed as a percentage. The notions of
wavelength-spacing or load values are inter-related. To achieve a
load-balanced wavelength fill on a link, the wavelengths in each
reach bin could be grouped into loading bins. Load-balanced
wavelength fill refers to using larger spacing between assigned
wavelengths at lower loads and then making use of the wavelengths
in-between as the load increases. The bins may also be categorized
according to link load values as shown in Table 3.
TABLE-US-00003 TABLE 3 ##STR00003## ##STR00004##
[0072] The columns in Table 3 correspond to reach ranges, and the
rows correspond to link load ranges, i.e. 0-25%, 26-50% and 51-100%
link loads, respectively. For the same reach (the sets in the same
column), the sets for higher load include the sets for lower loads.
For example, the wavelength set .lamda._Set(2, j) contains
.lamda._Set(1, j), while .lamda._Set(3, j) contains .lamda._Set(2,
j) and .lamda._Set(1, j).
[0073] Since the optical characteristics of different fiber types
(e.g. TrueWave.TM., LEAF.TM., DSF, etc.) vary, different fiber
types generally have different wavelength binning tables. Tables 4A
and 4B show examples of how the wavelengths in each bin of the
spectrum used in the network are equidistantly spaced by increments
of four, two, or one, based on load for TrueWave.TM. and LEAF.TM.
fibers, respectively.
TABLE-US-00004 TABLE 4A True Wav Route Length % Loade <1000 km
1000 km-2000 km 2000 km-3500 km 0-25% 1, 5, 9, 91, 11, 15, 19, 23,
47, 51, 55, 59, 63, 95, 99 27, 31, 39, 43, 67, 71, 75, 79 81, 85,
89 26-50% Above + Above + Above + 3, 7, 93 13, 17, 21, 25, 49, 53,
57, 61, 65, 29, 33, 37, 41, 69, 73, 77 43, 45, 83, 87 51-100% any
1-10 or any 11-45, 81-90 Any 46-80 91- indicates data missing or
illegible when filed
TABLE-US-00005 TABLE 4B LEAF Route Length % Load <1000 km 1000
km-200 2000 km-3500 km 0-25% 3, 99 5, 9, 85, 89, 93 13, 17, 21, 25,
29, 33, 37, 41, 45, 49, 53, 57, 61, 65, 69, 73, 77, 81 26-50% Above
+ Above + Above + 1, 5, 97, 99 7, 87, 91, 95 11, 15, 19, 23, 27,
31, 35, 39, 43, 47, 51, 55, 59, 63, 67, 71, 75, 79, 83 51-100 any
1-5 o any 11-45, 8 Any 10-84 96-100 90 indicates data missing or
illegible when filed
[0074] Tables 20 can be constructed based on fiber link engineering
studies, fiber measurements and analysis. More fine-grained
versions, where for example the reach range are on the order of a
few hundred kilometers or less, can also be prepared. A
fine-grained table is based on narrow ranges of reach values.
Presently, the wavelength reach tables are coarse-grained in their
reach range values, e.g. reach range bins are .about.1000 km wide.
The granularity of these tables is changing based on new fiber
measurements and analysis. It is anticipated that these tables will
become fine-grained in the near future, with the reach range on the
order of a few hundred kilometers or less.
[0075] Thus, tables 20 may be updated/expanded as more accurate and
additional information on various performance parameters of the
transport medium (the fiber) become available.
[0076] Other versions of the tables may be used, and some examples
are described next. The nodes of the photonic network are generally
provided with a drop tree, for demultiplexing and routing the drop
channels (local traffic) to the local user. The drop tree may use
for example a gateway input/output GIO module that distributes
selectively the channels to an associated receiver, and a GIO with
a tunable post compensator TPC, which enables extended reach for a
range of wavelengths. Such a GIO is referred to as a GIO-ER. Since
the node is provided with these two hardware options, the
wavelength reach tables may be further modified to reflect these
options. If a GIO-ER is available, then a wavelength can appear
twice in the wavelength-binning table, in two different reach bins
depending on the gateway device used.
[0077] As shown in FIG. 3A, each (i,j)-bin in a wavelength reach
table can now be divided into two bins, one of which contains a set
of wavelengths, .lamda._Set(i,j), corresponding to a configuration
that uses GIO, and the other contains a set of wavelengths,
.lamda._ER_Set(i,j), corresponding to use of GIO-ER. This
modification to the wavelength reach tables results in slight
changes to the way the tables are navigated.
[0078] FIG. 3B is a flowchart illustrating a method of selecting a
wavelength using tables as shown in FIG. 3A. The RPM 23 requests a
wavelength search for a specified trail. In step 31, the WAM 24
searches the wavelength performance information 20 to find a set of
wavelengths that are available and suitable for the trail. As
discussed above, the wavelength performance information may be
organized in tables, or in other formats suitable for searches. If
table navigation failed to return a wavelength for the respective
optical path, branch NO of decision block 32, then in at step 33,
WAM 24 checks if a GIO-ER is available at both end-nodes of the
optical path.
[0079] If k>0 as shown by branch YES of decision block 32, a
wavelengths is selected for the respective OP, step 37, according
to the rules described next, and the routing management 10 proceeds
with the next operation, step 38.
[0080] If there is no available GIO-ER at one end, branch NO of
decision block 33, it is concluded that no wavelength is available
at all for this optical path, and a regenerator replacement, or a
wavelength upgrade are tried, step 36. If none of these corrective
actions returns a wavelength for the respective optical path, the
trail may be abandoned in favor of the next one on list 26.
[0081] If there are available GIO-ERs, branch YES of decision block
33, a modified wavelength reach table as illustrated in FIG. 3A is
searched in step 34 to determine wavelength availability in
sub-bins containing wavelengths with improved, higher reach denoted
with .lamda._ER_Set(i,j). Once one or more (k>0), wavelengths
were identified in this table, branch YES of decision block 35, the
WAM selects a respective wavelength, step 37 and the routing
management 10 proceeds with the next operation, step 38. If no
wavelengths are found (k=0), the WAM returns operation to RPM 23,
step 36 as shown by branch NO of decision block 35.
[0082] It is recommended to use the GIO device as a default case
whenever a wavelength is available, as the GIO-ER variant is more
expensive. To show this, FIG. 3B illustrates the steps involving
GIO-ER in dotted lines.
[0083] Searching for an Appropriate Wavelength for an Optical
Path
[0084] The ways the wavelength performance information is used
(step 31 on FIG. 3B) depends on the connection request, the
characteristics of the selected trail, the type and granularity of
the wavelength performance information (wavelength binning tables),
the time allocated to the search (navigation through a table) for a
valid wavelength, etc. When only the length (D) of an optical path
is known, the search is performed in Table 1 starting in column W
where the wavelength reach R(j) corresponds to the length of the
optical path D, and k wavelengths with R(j).gtoreq.D are returned
by the search. For example, the unused wavelengths in the bin with
501 km<R(j)<750 km are considered for an optical path that
has 700 km.
[0085] Table 2 is used when the reach of all wavelengths for
various wavelength spacing is known. To perform a search, the entry
cell is given by the respective reach column R(j), in a row
corresponding to the widest wavelength-spacing, i.e., 200 GHz. Then
the search continues through the bins corresponding to the
immediate next wider spacing within the same column (j) and so on
until all cells in column (j) are examined. If no available
wavelength is found in column (j), the search extends to column
(j+1) corresponding to the next higher reach range and the widest
spacing, as shown by the arrow.
[0086] When the length of the link D and the link loading are
provided, Table 3 is used. Use of Table 3 helps to keeps the
cross-phase modulation (XPM) to the minimum, as the loads are
constantly monitored and available wavelengths are picked such that
XPM is kept to a minimum. Still, XPM cannot be completely avoided
at higher loads, but the present technique allows for smooth
increase in XPM without adverse effects as the load increases. The
entry cell can be determined according to D, or according to both D
and load.
[0087] For a D-only search, the search starts preferably from the
bin, or cell within the column with an appropriate reach, in a row
corresponding to the lowest load, e.g. 0-25%, and continues through
bins corresponding to the immediate next higher load within the
same column. For example, as shown on Table 3, if the optical path
has 400 km, the search for an unused wavelength for that path
starts with bin .lamda._Set(1,j); the wavelengths in column (j)
provide a reach between 251 and 500 km, and result in the lowest
loading.
[0088] If no acceptable wavelength is found in column (j), the
search moves to the bin corresponding to the next higher reach
range (j+1), starting again with the lowest link load in cell (bin)
.lamda._Set(1,j+1), as indicated by the arrow in Table 3.
[0089] Alternatively, this search may start from the cell
designated by reach, also using an estimated load calculated based
on the current link load values. It is to be noted that an optical
path may include multiple links, and sometimes multiple fibers
between two adjacent nodes. A method for determining the effective
current load for an optical path is described later.
[0090] This systematic way of navigating through the
wavelength-binning tables allows for organized, time saving
searches to find and validate a group of available wavelengths
suitable for assignment to an optical path.
[0091] Each time a wavelength is considered for assignment to an
optical path, its estimated optical quality or Q.sub.est value is
used to determine the initial acceptability of the wavelength, as
described above in connection with FIG. 2B. This procedure is
repeated until k acceptable wavelengths are found. k is
programmable, and selected so as to limit the number of acceptable
wavelengths and the search time.
[0092] Optimizing the Wavelength Selection
[0093] WAM attempts to select the best wavelength out of the k
acceptable wavelengths based on rules. For example, it is
advantageous to select wavelength from the most used wavelengths in
the network, in order to minimize the wavelength fragmentation,
which results in better network economics. This is mainly because
less fragmentation results in a lower number of regenerators needed
for wavelength conversion. A lower wavelength fragmentation also
reduces the call (connection) blocking.
[0094] The most used wavelengths can be determined considering only
the wavelengths usage on the cross-links relative to the optical
path under consideration, or by considering the wavelengths usage
on all links in the network.
[0095] FIG. 4A illustrates an example of an optical path OP
connecting nodes N1 to N5; the transmitter Tx at node N1 and the
receiver Rx at node N5 can be the respective terminal of a
transponder or a regenerator. In this example out of five
wavelengths .lamda.1 to .lamda.5, wavelengths .lamda.1 and .lamda.4
are already used on this path by other connections, so that the set
of k wavelengths that are available for a new connection include
.lamda.2, .lamda.3 and .lamda.5. Of these available wavelengths,
this example also assumes that, .lamda.2 is used on two cross-links
(at node N2), .lamda.3 on six cross-links (at node N2, N3 and N4),
and .lamda.5 on two cross-links (at node N1). It is apparent that
in this example .lamda.3 is most used relative to the optical path.
Hence, assigning .lamda.3 to for the new optical path, rather than
.lamda.2 or .lamda.5 is most beneficial, because it minimizes
fragmentation of wavelengths .lamda.2 or .lamda.5.
[0096] FIG. 4B is a flowchart of a method for minimizing wavelength
fragmentation determined considering the wavelengths usage on the
cross-links. Wavelength selection begins as shown at step 40, when
WAM 24 determines the distance between the optical terminals, e.g.
nodes N1 and N5 in FIG. 4A. It also identifies all wavelengths that
are used on cross-links at the nodes along the optical path, namely
nodes N1-N4. This information is available from the data topology
system 15 (see FIG. 1).
[0097] At the same time, the links of the path are identified
(links N1-N2, N2-N3, N3-N4 and N4-N5 in FIG. 4A), step 41, and the
effective load of each link in path OP is calculated as described
later, shown in step 42.
[0098] At step 43, the wavelength reach table of choice is
consulted for identifying the wavelengths that are free for the
entire OP, i.e. are not used on any of the links N1-N2, N2-N3,
N3-N4 and N4-N5 by other connections. The respective reach table is
used as indicated above, according to the estimated effective load,
required reach, wavelength spacing, and/or fiber type, etc, to find
k wavelengths that are free and have a reach R.gtoreq.D. If less
than k wavelengths are available, then a set of as many wavelengths
as possible are considered by the WAM 24. (This is also denoted
with k in the flow-chart for simplification)
[0099] However, if no free wavelength is available for path OP, as
shown by branch NO of decision block 44, then the routing
management 10 may try to solve this problem by re-placing the
regenerators, or by switching in a wavelength converter at a
certain intermediate node N2-N4 of the optical path, as shown by
step 45. This is the object of the co-pending US Patent Application
Docket 1045 identified above. Alternatively, a wavelength upgrade
may be attempted, as seen later.
[0100] If k>0, the WAM 24 proceeds to step 46. Now, all nodes
and cross-links of optical path OP are identified, and also all the
wavelengths that are in use on the cross-links are listed, to
determine a link usage value for each wavelength identified in step
41. The list of wavelength usage for the available wavelengths is
determined in step 46. For the example of FIG. 4A, the usage is:
.lamda.2=2, .lamda.3=6, and .lamda.5=2. As indicated above, the
usage value is based on the number of times each wavelength is used
in the cross-links of the optical path.
[0101] A step 47, the wavelength .lamda.3 having the highest usage
value among the k (three) available wavelengths (.lamda.2,
.lamda.3, .lamda.5) is identified, and selected for the path OP.
WAM 24 then returns operation to RM 10 for the next assignment,
step 48.
[0102] As shown in step 42, the effective load value for the entire
optical path is needed for optimizing wavelength selection on each
optical path. Some of the links of the OP may carry a different
number of wavelengths as shown on link N3-N4 which carries
.lamda.1, .lamda.4 and .lamda.10. The effective load for the entire
optical path is determined based on the current load value of each
link of the respective path. The load of a link is defined as the
ratio between the total number of wavelengths in use divided by the
sum of unassigned wavelengths and those in use.
[0103] FIG. 4C shows an example of an optical path OP with multiple
links Link1 to Link4, and multiple fibers on some of the links, for
explaining how the effective load value for the optical path is
determined in step 42 of FIG. 4B. In this example, links Link2 and
Link3 have each two fibers Fiber1 and Fiber2.
[0104] The effective load for an optical path comprising various
fiber-types and links with multiple fibers is determined in a
two-step process:
[0105] (1) for links that have multiple fibers, the link load is
considered the minimum of the loads on all fibers
Load.sub.Link2=Min(Fiber1, Fiber2)
[0106] (2) for the entire path, the load is considered the maximum
of the loads on all links: Load.sub.OP=Max(Link1, Link2, Link3,
Link4) Alternatively, loads on the links along a certain path may
be averaged, and the path load is in this case a weighted sum:
Load.sub.OP=w1Link1+w2Link2+w3Link3+w4Link4). In this case, the
weights are proportional to the respective link lengths.
[0107] FIG. 5A illustrates how wavelength assignment is optimized
considering the wavelengths usage on all links in the photonic
network. The most used wavelengths are now defined with respect to
the number of links on which they are used throughout the network.
The example of FIG. 5A considers .lamda.1 and .lamda.2 as only
available wavelengths for the OP P-Q. Network-wide, both .lamda.1
and .lamda.2 are being used on eight links. However, .lamda.1 is
used on five optical paths C-D, E-F, G-H, I-J and M-N (five
contiguous sets of nodes), and .lamda.2 is used only on two optical
paths A-B and K-L (two contiguous sets of nodes). This observation
suggests that use of .lamda.1 is currently more scattered around in
the network than the use of .lamda.2. Assigning .lamda.1 to the
optical path P-Q would result in lesser fragmentation network-wide,
as compared to assigning .lamda.2 to this path.
[0108] It should be recognized that sometimes two contiguous sets
of nodes over which a wavelength is used can cross each other and
this needs,to be factored into the computation of the individual
participation of a wavelength to network fragmentation.
[0109] FIG. 5B is a flowchart illustrating a method of selecting
wavelengths for a new connection with minimization of fragmentation
over an entire photonic network. This flow-chart is described in
connection with the example of FIG. 5A. First, the WAM 24
determines the distance D between nodes P and Q in step 50, from
the DTS 15. All wavelengths that are not used on optical path P-Q,
and that have a reach D or more are identified in step 52. As
before, this operation implies navigating through one of the tables
described above. If no wavelength may be assigned to path P-Q, as
shown by branch NO of decision block 53, WAM 24 returns the
operation to routing management for a regenerator replacement,
wavelengths upgrade, or for selecting another trial from list 26,
step 57.
[0110] At the same time, as shown by step 51, WAM 24 identifies all
active optical paths in the switched optical network, again using
the DTS 15. The number of links used for each wavelength is also
determined in this step.
[0111] If a certain number of wavelengths k>0 has been
identified in step 53, WAM estimates a usage measure for each
wavelength in step 54. The usage measure may be estimated in a
number of ways; an example is provided here.
[0112] For example, WAM may determine the total number of links
over which a wavelength is used in the network. In the example of
FIG. 5A, both .lamda.1 and .lamda.2 are used on eight links. Next,
WAM determines the number of contiguous nodes over which each
wavelength is used. In the example of FIG. 5A, .lamda.1 is used on
five optical paths, with the maximum number of contiguous nodes of
3 (for optical path C-D, I-J, and M-N which have 3 nodes), while
the number of contiguous nodes for .lamda.2 is five (for optical
paths A-B and L-K, which have five nodes each). The number of
contiguous nodes is a measure of continuity of a wavelength in the
network, and inversely correlates to fragmentation. Thus, while
.lamda.1 and .lamda.2 are equally used in terms of number of links,
.lamda.2 has a higher count of contiguous nodes. Accordingly,
.lamda.2 can be argued to be less fragmented than .lamda.1. The
network operator may select one option or a combination of both. It
is also apparent that other ways of determining the wavelength
usage measure network-wide are possible. After the most used
wavelength has been selected for OP in step 55, the WAM returns
operation to the RM 10 for the next assignment, step 56.
[0113] If a fine-grained wavelength-binning table is available,
then finding an upgraded wavelength may also take granularity into
consideration. To achieve this, a Q-R (signal quality versus reach)
graph is provided according to the invention, shown in FIG. 6A.
This graph is provisioned based on a priori link engineering
studies, and may also be pre-stored for example in database 25. It
may again be provided for various types of fibers; varies with the
fiber type.
[0114] The Q-R plot of FIG. 6A is used to determine the number of
bins (n) that should be skipped in a fine-grained
wavelength-binning table for efficiently searching the available
wavelengths and finding a wavelength that can be expected to
make-up the difference in reach, or the short-fall in Q value.
[0115] FIG. 6B is a flow-chart showing the process of finding a
wavelength upgrade using the Q-R graph and a wavelength binning
table with fine granularity. Let's assume that a wavelength
.lamda..sub.j was selected for optical path OP, using whatever
selection method. Let's also assume that on set-up, the measured
performance of OP is acceptable, step 60, i.e.
Q.sub.meas>Q.sub.th. In this case, .lamda..sub.j is assigned to
the respective optical path, as shown by the YES branch of decision
block 61 and step 62. If on the other hand, using .lamda..sub.j
does not result in the expected performance for OP, branch NO of
decision block 61, WAM 24 will attempt a wavelength upgrade, step
63. Now, WAM 24 determines .DELTA.Q in step 64, which is the amount
by which Q.sub.meas for the previously selected wavelength
.lamda..sub.j was lower compared with the required value Q.sub.th.
Next, in step 65, WAM determines the distance .DELTA.R using Q-R
graph of FIG. 6A. .DELTA.R gives the distance by which wavelength
search must advance in the fine-granularity wavelength reach
table.
[0116] To determine n (the number of bins that should be skipped),
the incremental distance .DELTA.R is divided to the reach
granularity `r` available for the respective table, so that
n=.DELTA.R/r as shown in step 66. This means that WAM 24 advances
the search to cell (n+i) along the range dimension, as shown by
step 67. Here `i` is the range of the bin corresponding to the
previously selected wavelength .lamda..sub.j. From this point on,
the new wavelength .lamda..sub.up is selected by navigating the
table as explained before, shown by step 68.
* * * * *