U.S. patent application number 09/731760 was filed with the patent office on 2002-06-20 for wdm optical communication network with data bridging plural optical channels between optical waveguides.
Invention is credited to Jiang, Leon Li-Feng, Montalvo, Raul B., Shanton, John Lynn III, Yu, Wenli.
Application Number | 20020075538 09/731760 |
Document ID | / |
Family ID | 24940850 |
Filed Date | 2002-06-20 |
United States Patent
Application |
20020075538 |
Kind Code |
A1 |
Jiang, Leon Li-Feng ; et
al. |
June 20, 2002 |
WDM optical communication network with data bridging plural optical
channels between optical waveguides
Abstract
The present invention relates to an optical network including a
bridge for selectively transferring information from an optical
channel carried on a first WDM optical waveguide to at least two
optical channels on a second WDM optical waveguide. The first and
second optical waveguides carry WDM optical signals each having
plural optical channels. A bridge is interposed between the first
and second optical waveguides which includes an optical add-drop
multiplexer optically communicating with each waveguide. At least
one optical channel having first and second data bits streams is
dropped from the first waveguide. The first and second data bit
streams are respectively encoded on two different optical channels
which are then added to the second optical waveguide.
Inventors: |
Jiang, Leon Li-Feng;
(Princeton Jct, NJ) ; Montalvo, Raul B.; (North
Potomac, MD) ; Shanton, John Lynn III; (Middletown,
MD) ; Yu, Wenli; (Gaithersburg, MD) |
Correspondence
Address: |
Margaret A. Burke
Seneca Networks
Legal Department
30 West Gude Drive, Suite 200
Rockville
MD
20850
US
|
Family ID: |
24940850 |
Appl. No.: |
09/731760 |
Filed: |
December 8, 2000 |
Current U.S.
Class: |
398/83 ; 398/59;
398/75 |
Current CPC
Class: |
H04J 14/0283 20130101;
H04J 14/0293 20130101; H04J 14/0216 20130101; H04J 14/0279
20130101; H04J 14/022 20130101; H04J 14/0286 20130101; H04J 14/0284
20130101 |
Class at
Publication: |
359/124 ;
359/127 |
International
Class: |
H04J 014/02 |
Claims
What is claimed is:
1. An optical network including a bridge for selectively
transferring information from an optical channel carried on a first
wavelength division multiplexed optical waveguide to at least two
optical channels on a second wavelength division multiplexed
optical waveguide comprising: a first optical waveguide carrying a
first wavelength division multiplexed optical communication signal,
the first wavelength division multiplexed optical communication
signal comprising a plurality of first optical channels; a second
optical waveguide carrying a second wavelength division multiplexed
optical communication signal, the second wavelength division
multiplexed optical communication signal comprising a plurality of
second optical channels; a bridge interposed between the first
optical waveguide and the second optical waveguide, the bridge
comprising: a first optical add-drop multiplexer optically
communicating with the first optical waveguide for selecting at
least a first optical channel from the first wavelength division
multiplexed optical signal, the first optical channel including at
least a first series of data bits and a second series of data bits
encoded on the optical channel; an optical network interface
optically communicating with the first optical add-drop
multiplexer, the first optical network interface including an
optical to electrical conversion means for taking information from
the first selected first optical channel and creating at least
first and second electrical signals, the first electrical signal
including the first series of data bits and the second electrical
signal including the second series of data bits; at least two
electrical to optical conversion elements configured such that the
first electrical signal encoded with the first series of data bits
is used to modulate a second optical channel and the second
electrical signal encoded with the second series of data bits is
used to modulate a third optical channel; one or more electrical
communication paths for routing the first and second electrical
signals to the electrical-to-optical conversion elements; a second
optical add-drop multiplexer optically communicating with the
second optical waveguide; a second optical path between the second
optical add-drop multiplexer and the at least two electrical to
optical conversion elements for receiving the second and third
optical channels and supplying them to the second optical add-drop
multiplexer such that they added to the second optical
waveguide.
2. An optical network as recited in claim 1 wherein the at least
two electrical to optical conversion elements are part of the first
optical network interface.
3. An optical network as recited in claim 1 wherein the at least
two electrical to optical conversion elements are part of a second
optical network interface which optically communicates with the
second optical add-drop muliplexer.
4. An optical network as recited in claim 3 further comprising cell
format modules and TDM format modules interposed between the first
and second optical network interfaces.
5. An optical network including a bridge for selectively
transferring information from an optical channel carried on a first
wavelength division multiplexed optical waveguide to at least two
optical channels on a second wavelength division multiplexed
optical waveguide comprising: a first optical waveguide carrying a
first wavelength division multiplexed optical communication signal,
the first wavelength division multiplexed optical communication
signal comprising a plurality of first optical channels; a second
optical waveguide carrying a second wavelength division multiplexed
optical communication signal, the second wavelength division
multiplexed optical communication signal comprising a plurality of
second optical channels; a bridge interposed between the first
optical waveguide and the second optical waveguide, the bridge
comprising: a first optical add-drop multiplexer optically
communicating with the first optical waveguide for selecting at
least a first optical channel from the first wavelength division
multiplexed optical signal, the first optical channel including at
least a first series of data bits and a second series of data bits
encoded on the optical channel; a first optical network interface
optically communicating with the first optical add-drop
multiplexer, the first optical network interface including an
optical to electrical conversion element for converting the
selected first optical channel to a first electrical signal which
includes the first and second series of data bits; means for
separating the first series of data bits from the second series of
data bits and encoding a second electrical signal with the first
series of data bits and encoding a third electrical signal with the
second series of data bits; one or more electrical communication
paths situated between the separating means and a second optical
network interface such that the second electrical signal and the
third electrical signal electrically communicate with the second
optical network interface, the second optical network interface
including at least two electrical to optical conversion elements
such that the second electrical signal encoded with the first
series of data bits is used to modulate a second optical channel
and the third electrical signal encoded with the second series of
data bits is used to modulate a third optical channel; a second
optical add-drop multiplexer optically communicating with the
second optical waveguide; a second optical path between the second
optical add-drop multiplexer and the second optical network
interface for receiving the second and third optical channels and
supplying them to the second optical add-drop multiplexer such that
they added to the second optical waveguide.
6. An optical network as recited in claim 5 further comprising cell
format modules and TDM format modules interposed between the first
and second optical network interfaces.
7. An optical network including a bridge for selectively
transferring information from an optical channel carried on a first
wavelength division multiplexed optical waveguide to at least two
optical channels on a second wavelength division multiplexed
optical waveguide comprising: a first optical waveguide carrying a
first wavelength division multiplexed optical communication signal,
the first wavelength division multiplexed optical communication
signal comprising a plurality of first optical channels; a second
optical waveguide carrying a second wavelength division multiplexed
optical communication signal, the second wavelength division
multiplexed optical communication signal comprising a plurality of
second optical channels; a bridge interposed between the first
optical waveguide and the second optical waveguide, the bridge
comprising: a first optical add-drop multiplexer optically
communicating with the first optical waveguide for selecting at
least a first optical channel from the first wavelength division
multiplexed optical signal, the first optical channel including at
least a first series of data bits and a second series of data bits
encoded on the optical channel; a first transponder interface
optically communicating with the first optical add-drop multiplexer
for receiving the first optical channel dropped from the add-drop
multiplexer and producing a corresponding first short-reach optical
signal to be output onto a first optical path from the transponder;
a first optical network interface optically communicating with the
first transponder interface, the first optical network interface
including an optical to electrical conversion element for
converting the optical signal received from the first transponder
interface to a first electrical signal which includes the first and
second series of data bits; means for separating the first series
of data bits from the second series of data bits and encoding a
second electrical signal with the first series of data bits and
encoding a third electrical signal with the second series of data
bits; one or more electrical communication paths situated between
the separating means and a second optical network interface such
that the second electrical signal and the third electrical signal
electrically communicate with the second optical network interface,
the second optical network interface including at least two
electrical to optical conversion elements such that the second
electrical signal encoded with the first series of data bits is
used to modulate a second short-reach optical signal and the third
electrical signal encoded with the second series of data bits is
used to modulate a third short-reach optical signal; a second
transponder interface optically communicating with the second
optical network interface for receiving the second and third
short-reach optical signals and converting them into second and
third optical channels; a second optical add-drop multiplexer
optically communicating with the second optical waveguide; a second
optical path between the second optical add-drop multiplexer and
the second transponder interface for receiving the second and third
optical channels and supplying them to the second optical add-drop
multiplexer such that they added to the second optical
waveguide.
8. An optical network as recited in claim 7 further comprising cell
format modules and TDM format modules interposed between the first
and second optical network interfaces.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The invention is directed to optical communication systems
in general and, more particularly, to optical networks that include
two or more waveguides each transporting a WDM optical signal
composed of plural optical channels and having a data bridge for
directing selected bit streams encoded on one optical channel from
one waveguide to plural channels carried in a WDM optical signal on
another waveguide.
[0003] 2. Description of the Related Art
[0004] As the need for communication signal bandwidth increases,
wavelength division multiplexing (WDM) has progressively gained
popularity for multiplying the transmission capacity of a single
optical fiber. A review of optical networks, including WDM
networks, can be found in Ramaswami et al., Optical Networks: A
Practical Perspective (Morgan Kaufman, .COPYRGT.1998), the
disclosure of which is incorporated herein by reference. Typically,
wavelength division multiplexed optical communication systems have
been designed and deployed in the long-haul, interexchange carrier
realm. In these long-haul optical systems, a wavelength division
multiplexed optical communication signal comprising plural optical
channels at different wavelengths travels in a single direction on
a single fiber. Because the communication traffic in such systems
commonly travels many hundreds of kilometers, the need for add-drop
multiplexing of individual channels is infrequent (if at all),
occurring at widely-spaced add-drop nodes.
[0005] Although the optical infrastructure of long-haul WDM optical
systems can accommodate future traffic needs created by increased
demand from traditional and multimedia Internet services, this
traffic must first be collected and distributed by local networks.
Currently, such local networks are predominantly structured to
carry a single wavelength, time-division multiplexed (TDM) optical
signal along a fiber network organized into various ring
structures. To route the various components of the TDM signal,
numerous electronic add-drop multiplexers are positioned along the
fiber network. At each add-drop location, the entire optical signal
is converted into an electrical signal; the portions of the
electrical signal which are destined for that add-drop point are
routed accordingly. The remaining portions of the electrical signal
are converted back to a new TDM optical signal and are output
through the electronic add-drop multiplexer. Thus, before a user
can access the bandwidth-rich WDM long-haul transport networks, he
must first pass through the bottleneck of the local networks.
[0006] Although WDM optical systems are suitable for conventional
long-haul interexchange carrier markets, metropolitan (local)
communications systems require extensive routing and switching of
traffic among various nodes positioned within interconnecting
optical fiber rings. Consequently, smaller metropolitan markets
require considerably more extensive add-drop multiplexing in order
to successfully implement wavelength division multiplexing in their
short-range systems. In addition to the difficulties posed by
frequent add-drop multiplexing channels it would be desirable to
direct channels from one DM optical waveguide to another. For
example, in a local metropolitan network, it would be desirable to
transfer traffic among adjacent rings. Further, it would be
desirable to route different portions of a single optical channel
carried by one waveguide to plural channels carried on another
waveguide. Such a device would permit effective implementation of
wavelength division multiplexing in local, metropolitan markets
requiring high volumes of signal re-routing and allow creation of
flexible network topologies.
SUMMARY OF THE INVENTION
[0007] The present invention relates to an optical network
including a bridge for selectively transferring information from an
optical channel which forms part of a first WDM optical signal
carried on a first waveguide to at least two optical channels which
forms part of a second WDM signal carried on a second optical
waveguide. A bridge is interposed between the first and second
optical waveguides. The bridge includes a first optical add-drop
multiplexer optically communicating with the first waveguide which
selects at least one optical channel from the first WDM signal. The
first optical channel carries a first series of data bits and a
second series of data bits encoded on the optical channel.
[0008] The bridge also includes a first optical network interface
which includes an optical to electrical conversion element for
converting the selected first optical channel to at least two
electrical signals which respectively include the first and second
series of data bits. The plural electrical signals may be directly
created from the optical signal or they may be derived from an
electrical signal which includes both the first and second series
of data bits which is subsequently separated into plural electrical
signals.
[0009] The electrical signals respectively encoded with the first
and second series of data bits electrically communicate with a
second optical network interface. The second optical network
interface includes at least two electrical to optical conversion
elements such that the second electrical signal encoded with the
first series of data bits is used to modulate a second optical
channel and the third electrical signal encoded with the second
series of data bits is used to modulate a third optical channel.
These optical channels are sent to a second optical add-drop
multiplexer optically communicating with the second optical
waveguide where they are added to the WDM optical signal
propagating on the second waveguide.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1 schematically depicts two WDM optical communication
waveguides having a data bridge therebetween.
[0011] FIG. 2 schematically illustrates various series of data bits
encoded on a first optical channel on a first waveguide used to
encode two different optical channels on a second waveguide.
[0012] FIG. 3 depicts a further embodiment of the data bridge of
the present invention employing a series of transponders as well as
cell format and TDM format modules.
DETAILED DESCRIPTION
[0013] Turning now to the drawings in detail in which like numerals
indicate the same or similar elements, FIG. 1 depicts a wavelength
division multiplexed optical communication network 10 according to
a first embodiment of the present invention. Optical network 10
includes waveguides 20 and 120 and a bridge 200. Each optical
transmission waveguide 20, 120 is configured to carry wavelength
division multiplexed optical communication signals, each WDM signal
comprised of plural optical channels at different wavelengths. In
accordance with traditional industry nomenclature, one of the WDM
signals propagating in a first direction is designated the
west-east WDM signal while the WDM signal propagating in the
opposite direction is designated the east-west WDM signal. The
individual optical channels in the west-east WDM optical signal are
denoted by the symbols .lambda..sub.1, .lambda..sub.2,
.lambda..sub.3 etc., while the individual optical channels in the
east-west WDM optical signal are denoted by the symbols
.lambda..sub.a, .lambda..sub.b, .lambda..sub.c, etc. for clarity of
presentation. Although not shown in FIG. 1, it is common for
optical networks to include at least two alternate optical paths--a
"work" path and a "protect" path. Only one path is depicted in FIG.
1 although it is understood that at least an additional path may be
provided along each waveguide. Each of the optical waveguides can
form part of an optical ring network or other network topologies
such as mesh networks, point-to-point networks, subtended ring
networks, or any other network topology which includes at least two
waveguides.
[0014] As used herein, the expression "wavelength division
multiplexed" or "WDM" refers to any optical system or signal
composed of plural optical channels having different wavelengths,
regardless of the number of channels in the system or signal. As
such, the term "wavelength division multiplexing" or "WDM"
encompasses all categories of WDM such as DWDM (dense wavelength
division multiplexing) and CWDM (coarse wavelength division
multiplexing).
[0015] Optical add-drop multiplexer 220 is interposed along
waveguide 20 to optically communicate with the waveguide for
receiving a wavelength division multiplexed optical signal. As used
herein, the expression "optically communicates" designates an
optical path between two elements. The optical path may be a direct
path or it may route through intermediate optical devices (e.g.,
optical isolators, additional optical circulators, filters,
amplifiers, etc.). Optical add-drop multiplexer 220 may be selected
from a number of devices depending upon the overall configuration
of optical network 10. Considerations include the number of optical
channels in the system, whether it is desired to drop a fixed
number of channels of fixed wavelengths at the same drop point (or,
conversely, a variable number of channels of different
wavelengths), etc. In the simplest case, optical add-drop
multiplexer 220 is configured to drop or add a single optical
channel of a fixed wavelength. Such an add-drop multiplexer can
take basic configuration of a three-port optical circulator and an
optical coupler with an in-fiber Bragg grating disposed in a fiber
connecting the devices. A unidirectional WDM signal enters the
first circulator; a channel to be dropped is reflected by the
grating to a drop port while the remaining channels of the WDM
signal pass through to the coupler. A channel to be added enters
the coupler and is output to the transmission waveguide where it
joins the remaining channels of the WDM optical signal. Such a
configuration is depicted in Optical Networks: A Practical
Perspective, incorporated by reference above. Of course, additional
channels may be add-dropped by adding additional gratings
corresponding to the wavelengths of the channels to be dropped (or
variable gratings whose wavelength can be changed to select
different wavelengths). While this is an example of a single
channel add-drop multiplexer which may be used with the present
invention, it is understood that any device capable of selecting
one or more optical channels from a WDM optical signal and/or
adding an optical channel to a WDM optical signal is contemplated
for use in the optical systems of the present invention.
[0016] A channel dropped from either the west-east or east-west WDM
optical signal is routed to an optical network interface 230.
Optical network interface 230 includes at least one electrical to
optical conversion element for converting the information carried
by the optical channel into one or more electrical signals. In an
exemplary embodiment, the west-east optical channel designated
.lambda..sub.1 carried on waveguide 20 is dropped by optical
add-drop multiplexer 220. As seen from the schematic depiction of
this optical channel shown in FIG. 2, .lambda..sub.1 is encoded
with various data bit streams, labeled "data bits b," "data bits
c," "data bits d," and "data bits e." The term "data," as used
herein, broadly represents any type of information to be
transmitted over an optical communication system including, but not
limited to, voice, images, video, music, text, etc. Each of the
data bit streams can be formatted in a variety of "data formats"
which may be the same or different. As defined in Telecommunication
Transmission Systems, Robert Winch, second edition, McGraw-Hill, NY
.COPYRGT. 1998), the disclosure of which is incorporated by
reference herein, a protocol is "a set of rules that control a
sequence of events which take place between equipment or layers on
the same level." ATM (Asynchronous Transfer Mode), IP (Internet
Protocol), MPLS (MultiProtocol Label Switching), TDM (Time Division
Multiplexing) are all examples of protocols used to carry data over
optical networks. Within these protocols are various data formats
which define how the individual bits of information are grouped in
a signal (e.g., header bits, payload bits, identifier bits, routing
information bits, Thus, for each protocol (e.g., ATM, IP, MPLS,
TDM, etc.) there is an associated data format for that protocol. In
the context of the present invention, the use of the terms ATM, IP,
MPLS, TDM, etc. refer to the data format associated with that
protocol unless otherwise indicated. Further discussion of
techniques for encoding optical channels with different data
formats is described in applicants' copending U.S. patent
application Ser. No. 09/688,804, the disclosure of which is
incorporated by reference herein.
[0017] The information placed on optical channel .lambda..sub.1
includes data configured in any of the data formats set forth
above; in an exemplary embodiment the optical system is constructed
so that plural data formats can be simultaneously and independently
placed on a single optical channel without conversion to another
data format prior to placement on that channel. However, it is
understood that bridge 200 may just as readily be implemented with
data of a single format or data of multiple formats which have been
converted to a single format.
[0018] The optical to electrical conversion element(s) in optical
network interfaces 230 and 250 produce an electrical signal
including all of the information from the corresponding optical
channel(s) including data bit streams b, c, d, e; these data bit
streams may be separated into plural electrical signals. Any
element capable of taking an optical signal and producing one or
more electrical signals encoded with the information from the
optical signal is contemplated for use in the present invention.
Such optical to electrical conversion elements are well known and
commercially available and will not be further described here. For
the embodiment depicted in FIG. 2, two electrical signals are
formed--one which includes data bit streams c and e and another
which includes data bit streams b and d. Alternatively, plural
electrical signals may be formed directly by the
optical-to-electrical conversion element without formation of an
intermediate electrical signal containing all the information from
the optical channel. The manner in which the electrical signals
containing the desired data bit streams is not critical; therefore,
any technique which results in the formation of electrical signals
which include the data bit streams for use in modulating optical
channels carried by the second optical waveguide.
[0019] To route the data bits encoded on .lambda..sub.1, carried by
first waveguide 20 to the second waveguide 120, first optical
network interface 230 electrically communicates with second optical
network interface 250. As used herein, the expression "electrically
communicates" denotes an electrical path between the devices
regardless of the presence of additional electrical devices
positioned therebetween. Further, particularly when data of a
single format is employed for all of the data bits, the system may
be condensed into a single optical network interface positioned
between optical add-drop multiplexers 220 and 240. The single
optical network interface would include at least one optical to
electrical conversion element and at least two electrical to
optical conversion elements; in this manner data bits encoded on
the first optical channel could be separated and placed onto two
optical channels using only one optical network interface.
[0020] Data bit streams b, c, d, and e are routed to optical
network interface 250. Optical network interface 250 includes at
least two electrical to optical conversion elements for creating
two optical channels designated .lambda..sub.a and .lambda..sub.b
in an exemplary embodiment. Any device which is capable of forming
one or more electrical signals from an optical signal is
contemplated for use in the systems of the present invention.
Optical network interface 250 encodes .lambda..sub.a with data bit
streams c and e and encodes .lambda..sub.b with data bit streams b
and d. The data bit streams may be encoded on the optical channels
through a wide variety of modulation techniques, including direct
modulation techniques (e.g., varying a current source to a laser)
or external modulation techniques (e.g., through Mach-Zehnder
modulators, electroabsorption modulators, etc.). The technique for
modulating the optical signal is not critical; therefore any
technique capable of encoding data onto an optical channel is
contemplated for use in the present invention. Optical channels
.lambda..sub.a and .lambda..sub.b are routed to optical add-drop
multiplexer 240 where they are added to the optical channels
carried by waveguide 120. The determination of which channels to
encode with which data bit streams is dependent upon the final
destination of the information; the optical network interface
determines the destination of the data and then decides which
optical channel should carry that data.
[0021] When the optical channel is selected in accordance with
SONET standards, the data bit streams are placed into a
SONET-compatible slot on the optical channel. Alternatively, other
types of optical channels may be selected such as those which use
the digital wrapper standard; however, it is understood that the
invention may be used with any technique for multiplexing data onto
an optical channel. Optical network interfaces 230 and 250 may each
comprise a single apparatus or, optionally, plural apparatus which
perform the functions described above. Further, as discussed above,
when data of a single format is used, a single optical network
interface may mutually serve waveguides 20 and 120. Although not
explicitly shown in FIG. 1, when optical channels .lambda..sub.a
and .lambda..sub.b are added to waveguide 120, the same channels
already propagating on that waveguide may be dropped. From there,
the dropped channels may be routed elsewhere in optical network 10;
alternatively, data bit streams carried on those channels may be
combined onto an optical channel to be added to waveguide 120
(especially an optical channel having the same wavelength,
.lambda..sub.1, as the channel dropped by add-drop multiplexer
220.
[0022] As indicated in FIG. 1, the same process for routing data
bit streams may also occur for one or more optical channels dropped
from waveguide 120. In an exemplary embodiment, the same number of
channels having the same wavelengths are add/dropped from each of
the optical waveguides. Data bit streams from each of the channels
that are dropped from each waveguide are encoded onto various
optical channels being added to the other waveguide. Alternatively,
an unequal number of optical channels can be add/dropped onto each
waveguide.
[0023] Turning to FIG. 3, a further embodiment of the data bridge
of the present invention is depicted. In the embodiment of FIG. 3,
the optical network interface systems 330 and 350 include two
subsystems: optical network interfaces 332 and 352 and transponder
arrays 334 and 354, respectively. Optical add-drop multiplexers 320
and 340 are interposed along optical waveguides 20 and 120; in an
exemplary embodiment, each add-drop multiplexer optically add/drops
4 optical channels from each waveguide. In this embodiment,
west-east channels dropped from waveguide 20 have the same
wavelength as east-west channels dropped from waveguide 120. In
this manner, add-drop multiplexers 320 and 340 can include channel
selectors configured for the same wavelengths. It is noted that
both a "work" and "protect" system are depicted in FIG. 3; because
these systems are substantially similar, only the "work" system is
described in this section.
[0024] Transponder arrays 334 and 354 both receive the optical
channels dropped by add-drop multiplexers 320 and 340 and produce
the optical channels to be added by the add-drop multiplexers via
optical paths 321, 322, 323, 324, 325, 326, 327, 328 and 391, 392,
393, 394, 395, 396, 397, and 398. These optical paths may be, for
example, along one or more optical waveguides such as optical
fibers. Transponder arrays 334 and 354 can include short-reach
optical interfaces and interact with the optical network interfaces
332 and 352 through these short-reach optical signals which are
carried by optical paths 371, 372, 373, 374, 375, 376, 377, 378 and
381, 382, 383, 384, 385, 386, 387, 388, respectively. Again, these
optical paths may be along one or more optical waveguides such as
optical fibers.
[0025] As in the embodiment depicted in FIG. 1, optical network
interfaces 332 and 352 convert information encoded on the optical
channels to electrical signals; in the embodiment depicted in FIG.
3, electrical signals are formed from four optical channels
selected from each of optical waveguides 20 and 120. These selected
optical channels are designated .lambda..sub.1, .lambda..sub.2,
.lambda..sub.3, .lambda..sub.4, from waveguide 20 and
.lambda..sub.a, .lambda..sub.b, .lambda..sub.c, .lambda..sub.d from
waveguide 120. In the embodiment shown in FIG. 3, the wavelengths
of .lambda..sub.1, .lambda..sub.2, .lambda..sub.3, .lambda..sub.4
are selected to be the same as the wavelengths of .lambda..sub.a,
.lambda..sub.b, .lambda..sub.c, .lambda..sub.d, respectively. When
the optical channels carry information having different data
formats, the optical network interfaces 332 and 352 can optionally
communicate with cell format modules 410, 430 and TDM format
modules 420, 440 through electrical communication paths 413, 414,
415, 416, 423, 424, 425, 426 so that data having cell or TDM
formats can be received from the optical network interfaces and be
intelligently routed to optical channels on the other optical
waveguide. Although single cell format modules 410, 430 and TDM
format modules 420, 440 are depicted in FIG. 3, a pair of cell
format and TDM modules would typically be associated with each of
the four optical channels being add-dropped by each optical
add-drop multiplexer 320, 340; the remaining modules have been
omitted for clarity of presentation. However, depending upon the
particular implementation of the system, individual modules could
be used to deal with the cell format or TDM format portions of each
of the four optical channels add-dropped on each waveguide. Routing
the respectively formatted data bit streams through the TDM or cell
format modules provides an effective technique for ensuring that
TDM formatted data is not broken up into packets or cells,
incurring additional overhead bits identifying the respective
payloads as discussed in patent application Ser. No. 09/688,804,
incorporated by reference, above. Again, it is noted that the
embodiment of FIG. 3 is used when more than one type of data format
is used in the WDM network. As in the previous embodiment, elements
410, 420, 430 and 440 can be eliminated when optical channels in
the network are encoded with a single data format. Alternatively,
individual optical channels may each have a single data format with
different channels carrying different data formats.
[0026] Electrical communication paths 411, 412, 421, and 422 allow
data to be sent across the bridge from one waveguide to another.
The discontinuity schematically indicated in these paths indicates
that other devices may be optionally positioned between the
modules, depending upon system implementation. For example, some of
the data bit streams may be routed to a module for a different
waveguide; similarly, data bit streams may be accepted from other
optical channels on other waveguides at this point in the system.
Alternatively, a series of line cards corresponding to each type of
data format (e.g., IP, MPLS, ATM, GbE, etc.) can be interposed
between the two modules 410, 430, 420, 440. Such cards are
described in further detail in applicants' copending U.S. patent
application Ser. No. 09/688,804, incorporated by reference
above.
[0027] In another alternate embodiment, a single cell format module
and TDM format module may be provided between optical network
interfaces 332 and 352 (or a pair of modules for each optical
channel. Such modules would be configured to route traffic from one
waveguide to the other or reciprocally from each waveguide to the
opposite waveguide.
[0028] In order to facilitate protection switching in the event of
equipment or transmission line failure (e.g., fiber cut), an
electrical cross-connect may optionally be provided interconnecting
the cell and TDM format modules of the work system with the optical
network interface of the protect system and interconnecting the
cell and TDM format modules of the protect system with the optical
network interface of the work system. In this way, data can be
efficiently routed to the surviving optical path to prevent service
interruption. Other electrical cross-connect configurations, such
as between optical network interfaces when cell and TDM format
modules are omitted, may also be used to enable protection
switching.
[0029] As discussed above for FIG. 1, the same process for routing
data bit streams may occur for one or more optical channels dropped
from waveguide 120 in the optical network of FIG. 3. In an
exemplary embodiment, the same number of channels having the same
wavelengths are add/dropped from each of the optical waveguides.
Data bit streams from each of the channels that are dropped from
each waveguide are encoded onto various optical channels being
added to the other waveguide. Alternatively, an unequal number of
optical channels may be add/dropped onto each waveguide.
[0030] While the above invention has been described with reference
to the particular exemplary embodiments, many modifications and
functionally equivalent elements may be substituted without
departing from the spirit and contributions of the present
invention. Accordingly, modifications and functionally equivalent
elements such as those suggested above, but not limited thereto,
are considered to be within the scope of the following claims.
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