Note: Descriptions are shown in the official language in which they were submitted.
CA 02411630 2002-11-08
Attorney Docket No. TR-086
FLEXIBLE OPTICAL NETWORK ARCHITECTURE AND OPTICAL ADD/DROP
MULTIPLEXER/DEMULTIPLEXER THEREFOR
RELATED APPLICATIONS
[0001] This patent. application claims benefit from ZJ.S.
Provisional Patent Application Serial. No. 60/292,589 to Liu
filed on 23 May 2001; from U.S. Patent Application Serial
No. 09/953,952 to Liu filed on 18 September 2001; and from
U.S. Patent Application Serial No. 10/013,676 to Liu filed
on 13 December 2001.
FIELD OF THE INVENTION
[0002] This invention relatE's to optical networks, and
in particular, to flexible optical network architecture and
add/drop multiplexer therefor, which provide flexible
connection between the network nodes.
BACKGROUND OF THE INVENTION
2~0 [0003] Optical Packet Networks (OPN) typically have
Synchronous Optical Network (SONET) ring architecture with
DWDM techniques integrated inside the rings to increase: the
network capacity and to support multi-ring connections and
the multiple services requests. Although the OPN management
2:p can control 'the traffic flow through the network, the
ability to deliver banc.-lwidth on demand anywhere in the
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network is not always possible. Over-provisioning of the
network can partiall~r solve this problem, but only at the
expense of the increase of the network costs and less
effective utilization of the network resources.
Additionally, the update and re~-provisioning of the
equipment ha.s to be done quick-'._y an~~L almost in real time,
which is definitely not the reality of today.
[0004] Optical communications systems have been
employing different network arc:hit.ectures to provide
required flexible connections betwef=_n the network nodes and
bandwidth on demand services. For example, in a fixed
wavelength network, where each node transmits and receives
channels at fixed wavelengths, the t~ransmit.ted/received
wavelengths are the same for those nodes that communicate
1.S with each other. This Network architecture requires
multiple transmitters and receivers at each node, or
otherwise it does not have flexibility to provide multiple
connections between different nodes. It is also costly and
inefficient to upgrade such a network, e.g. to accommodate
21) new channels or to establish new connections, as it will
require the addition of extra transmitters/receivers at the
nodes. As a result, with this network architecture, it is
difficult to satisfy the ever-increasing demand for network
growth.
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[0005] To overcome the limitations of fixed wavelength
networks, it; has been suggeste~~ to use tunable wavelength
transmitters and/or receivers to provide higher flexibility
of the network connections. For example, in a Fixed-tuned
Transmitter and Tunable Receiver (FTTR? approach, each node
is assigned with a specific wavelength for data
transmission, while a. receiver is a tunable device capable
of receiving' one of several data streams at different
wavelengths generated by the transmitters. To transmit data
from node j to node l, signalling m~.ssages have to be first
sent to inform node l to tune its receiver to wavelength
for data reception. FTTR network architecture has been
deployed, e.g. in a European experimental system named
Rainbow-II networks and published in an article by Eric
Hall et al. entitled "The Rainbow-II Cigabi.t Optical
Networks", IEEE Journal of Selected Areas in
Communications, Volume 14, No. 5, June 1996, p.814-823.
[0006] Another app:roach., where tunable devices are used
at network nodes, is known as Tunable Transmitter and F'ix-
Tuned Receiver (TTFR) network architecture. In the TTFR.
approach, ea~~h node i;s assigned with a fixed wavelength. for
data reception, where the receivers at node l are only
responding to the wavelength channel. l (7~i). Nodes intending
to send data to node .l have to tune their transmitters to
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wavelength a,i. TTFR ar~.hit.ecture has been described, e.g. in
the article to Chun-Kit Chan or a1. entitled "Node
Architecture and Protocol of a Packet Switched Dense WDMA
metropolitan Area Network", Journal of Lightwave
Technology, Vol. 17, No. ~L1, November 1999, pp. 2208-2218,
where TTFR concept has been applied to DWDM networks.
[0007] The major drawback of tunable devices is their
high cost and low reliability compared to the fixed
wavelength devices. Additionally, the process of wavelength
tuning has finite response time, it i.s sensitive to
temperature and/or current changes ~~.nd therefore requires
stabilization.
[0008] Thus, network architE:cture using fixed wavelength
devices can provide quick and reliable connections, but
fail to provide flexibility and cost effective solutions to
accommodate network growth and utilization. In contrast,
known network architectures using tunable devices can
provide flexibility of network connections, but tend tc> be
expensive, less reliable and more complicated in
exploitation and maintenance.
[0009] Accordingly, there is a need in industry for the
development of an alternative optical network and node
architecture, which would deliver inexpensive, flexible and
reliable network connections.
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SUHiMARY OF THE INVENTION
[0010] Therefore there is an object of the invention to
provide an optical network architecture which would provide
flexibility of the network connections while being simple
and cost effective.
[0011] According to one ripe=ct of: the invention there is
provided an optical network, comprising:
[0012] a .plurality of N nodes;
[0013] each node leas a transmitter for transmitting a
set of "n1" wavelengths (transmitter set), and a receiver
for receiving a set of "'n2" wavelengths (receiver set), the
transmitter and receiver sets are misarranged so as to
differ by at least one wavelength; and
[0014] the wavelengths of transmitters and receivers at
different nodes are arranged so than for any pair of nodes
there is at least one common wavelength which is the same
for the transmitter at one node and the receiver at the
other node, thus providing a direct connection between the
nodes.
21) [0015] Beneficially, it is arranged that for any pair of
nodes there are at least two common wavelengths, the first
and second common wavelengths, the first wavelength being
the same for the transmi..tter at one node and the
corresponding receiver at the other node in the pair, and
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the second wavelength being the same for the receiver <~t
one node and the corresponding transmitter at the other
node in the pair.
[0016] Conveniently, the total number of the wavelengths
S used in the network is equal tc: "nl+n2", and the total
number of nodes is equal to N =- (nl+n2) ! / (n1! n2! ) .
[0017] The transmitter set a.nd receiver set may have
different number of wavelength:, i.a. nl~n2, and some or all
of the wavelengths of the tram>mitter set may differ from
the wavelengths of the receiver set.
[0018] A1 ternatively, the transmitter set and receiver
set may have same number of wavelengths, i.e. nl=n2=n, and
some or all of the wavelengths of the transmitter set
differ from the wavelengths the receiver set.
1.5 [0019] The number "n.1" of the wavelengths in the
transmitter set rnay b~e the same for ail nodes, or
alternatively the number "n1" of wavelengths in the
transmitter set may vary for different nodes.
[0020] According to another aspect of the invention
there is provided an o~>t:ical network, comprising:
[0021] a plurality of nodes, each node having a
transmitter for transmitting a set of "n" wavelengths, and
a receiver for receiving another set of "n" wavelengths,
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the set of wavelength's of the transmitter being differ~snt
from the set: of wavelengths of the receiver;
[0022] wavelengths of transmitters and receivers at
different nodes being arranged so that for any pair of
nodes there is at least one common wavelength which is the
same for one: of the transmitter and receiver at one node
and one of the respective receiver and transmitter at t:he
other node, thereby providing a uni-directional, direct
connection between the nodes.
[0023] Conveniently, wavelengths of transmitters and
receivers at different nodes can be arranged so that for
any pair of nodes in the network thr:re are at least two
common wavelengths, the first and. second common
wavelengths, the first wavelenc;th is the same for the
transmitter at one node and the corresponding receiver at
the other node in the pair, and the second wavelength is
the same for the receiver at one node and the corresponding
transmitter at the other node ire the pair, thereby
providing a bi-directional direct connection between the
nodes .
(0024] Conveniently, the total number of the wavelengths
used in the network is equal to "2n", the total number of
nodes is equal to N = ~;~y !/(n!n!~, and the number of
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common wavelengths for any pair of nodes is not exceeding
"n-1".
[0025] The number of wavelengths used by transmitters or
receivers at each node may be conveniently equal to n=2,3,
4 to 10, or any other number o:E wavelengths, which would
provide required connection between the nodes in the
network.
[0026] Preferably, transmitters and receivers at the
network nodes are fixed wavelength devices, which generate
or receive signals at fixed wavel.engt.hs. Alternatively,
some or all of the transmitters and,/or receivers may be
tunable or switchable wavelength devices, which allow
tuning or switching of the wavelength within a required
wavelength range.
[0027] The network architecture described above can be
applied to various types of optical networks, e.g. a
wavelength division multiplexing (WDM;~ network, including
ring, multi-ring, mesh, bus and star network topologies;.
[0028] According to another aspect of the invention
2n there is provided a node for an. optical network, comprising
a transmitter for transmitting a set. of "n1" wavelengths,
and a receiver for receiving another set of "n2"
wavelengths, the set of wavelengths of the transmitter
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differing from the set of wavelengths of the receiver by at
least one wavelength;
[0029] the wavelengths of the transmitter and receiver
at the said node are arranged so that for any pair of nodes
in the network, where the said node is one of the two nodes
in the pair, there is at least one common wavelength which
is the same for one c:~f the transmitt=er and receiver at the
said node and one of the respec=tive receiver and
transmitter at the other node wwn the pair.
[0030] Ccnvenientl.y, the wavelengths of the transmit=ter
and receiver at the node are ax:ranged so that for any pair
of nodes in the network, where t=he paid node is one of the
two nodes in the pair', there ax-a at least two common
wavelengths, the first and second common wavelengths, t=he
first wavelength is the same for the transmitter at the
said node and the corresponding receiver at the other node
in the pair, and the second wavelength is the same for the
receiver at the said node and the corresponding transmitter
at the other node in the pair.
[0031] Conveniently, nl=n2=n, and the set of wavelengths
of the transmitter is different from the set of wavelengths
of the receiver.
[0032] Advantageously, the node described above further
comprises an optical add/drop multiplexer/demultiplexer
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(OADM) including means for dropping wavelengths from the
network at the node and means f=or adding wavelengths to the
network from the node. Conveniently, the means for dropping
wavelengths includes means for dropping one wavelength at a
time, comprising a set of "n2" optical filters adjusted to
the wavelengths of the receiver, and the means for adding
wavelengths includes means for adding one wavelength at a
time, comprising another set of "n1" optical filters or
optical couplers suitable to operate at the wavelengths of
1~~ the transmitter. Optionally, a node may further comprise a
wavelength converter to provide indirect connection between
the nodes through other nodes in the network.
[0033] According to yet another aspect of the invention
there is provided an optical add/drop
l:> multiplexer/demultiplexer for a node described above,
comprising:
(0034] means for dropping wavelengths from the network to
the node comprising a set of "n~" optical filters suitable
for operation at the wavelengths of the receiver set; and
20 [0035] means for adding wavelengths to the network from
the node comprising one of the following:
[0036] a :yet "n1" optical filters suitable for operation
at the wavelengths of the transmitter set; and
l0
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[0037] a set of "n_~r' optical couplers suitable for
operation at the wavelengths of the transmitter set.
[0038] According to yet another aspect of the invent: ion
there is provided a method of providing direct connections
between the nodes in an optical network having a plurality
of nodes, the method comprising the steps of:
[0039] for each node, providing a transmitter for
transmitting a set of "n,." wavelengths, and a receiver for
receiving another set of "n2" wavelengths, and selecting the
wavelengths of the transmitter and the receiver so as t.o
differ by at least one wavelength;
[0040] se:Lecting w<~velengths of t.:ransmitters and
receivers at different nodes so that: for any pair of nodes
there is at least one common wavelength which is the same
1:p for one of the transmitter and the receiver at one node,
and one of the respective receiver and transmitter at the
other node, thus providing a direct connection between the
nodes.
[0041] Beneficially, it is selected so that nl=n2=n, the
wavelengths of the tr<~rasmitter set is different from the
wavelengths of the receiver set. Advantageously, the step
of selecting the wave:Leragths of transmitters and receivers
at different nodes is performed so as to provide that for
any pair of nodes there are at least. two common
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wavelengths, the first and second cc>mmon wavelengths, t:he
first wavelength is the same for thr-_~~rransmitter at one
node and the corresponding receiver at the other node in
the pair, and the second wavelength is the same for the
S receiver at one node and the corresponding transmitter at
the other node in the pair. Conveniently, the method
described above further comprises the step of arranging the
total number of wavelengths used in the network to be equal
to "2n".
[0042] Conveniently, the optical network described above,
can be built as an overlay of a multi~-ring network so that
the nodes of the optical network are the nodes in the
multi-ring network, thereby providing a flexible connection
between the nodes in the multi-ring network.
1.5 [0043] The network architecture described above has the
following advantages. It requires less wavelength resources
to support t:he same number of nodes in the network than
other known solutions, and it is moz:e cost effective anal
reliable.
BRIEF DESCRIPTION OF THE DRAWINGS
[0044] The invention will now be described in greater
detail with :reference t:o the attached drawings, in which:
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FIGURE 1 is a diagram illustrating a network
architecture and connections between the nodes according to
a first embodiment of the invention;
FIGURE 2 is a blo:~k diagram of one form of an optical
add/drop multiplexer/demultiplexer (OADM) used at the node
of the network of FIGURE 1;
FIGURE 3 is a block diagram of another form of an
optical add/drop multiplexer/demultiplexer (OADM) used at
the node of the network of FIGURE 1;
FIGURE 4 is a diagram illustrating flexible
connections between the' rings i.n a m.ulti-ring network i.n
accordance with the connection scheme of the first
embodiment of the invention;
FIGURE 5 is a diagram of a band interchange modules of
FIGURE 4; and
FIGURE 6 is a diagram illustrating more than one
connection between the modes by using wavelength
converters.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0045] A schematic c:liagram of a network 10 according to
the first embodiment of the invention is shown in Figure 1.
The network 10 includes six nodes designated by reference
numerals 12, 14, 16, 18, 20 and 22 respectively. Each node
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has a transmitter for t~ransmitt-ing <~ set of n1=2
wavelengths, and a receiver for receiving another set of
nz=2 wavelengths, and i.t: is conveniently selected that
nl=nz=n=2, and the set. of wavelengths of the transmitter
being different from the set of wavelengths of the
receiver. The total number of wavelengths used by
transmitters and receivers at each node is equal to 2n = 4
(~1, ~z, ~.3, ~4) , which is also equal to the total number of
wavelengths used in the network. 10. Further to the above,
l~~ the wavelengths of transmitters and receivers at the nodes
are assigned in such a mariner so that for any pair of nodes
in the network there .ar-e at least two common wavelengths,
the first and second common wavelengths, the first
wavelength is the same for the transmitter at one node and
1:~ the corresponding receiver at the other node in the pair,
and the second wavele:ngt_°~ is the same for the receiver at
one node and the corresponding tran:~mitter at the other
node in the pair, thereby providing a direct bi-directional
connection between the nodes.
20 [0046] Figure 1 and Table 1 illustrate the assignment of
four wavelengths (~,1, ~,Y ~.3, ~.4) to the transmitters TX and
receivers RX at the nodes, where index x = 1, 2, ... 6
relates to the nodes 12 t.o 22 respectively. Namely, the
node 12 has <~ transmitter T1 (~", ~,~) and a receiver R1 (~,1,
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whose corresponding wavelengths are shown in brackets,
node 14 has T2 ( ~,2 , ~,~ ) and RZ ( J~1, ~; ) , node 16 ha s T3 ( ~.
~,2 ) and R3 ( a~l , ~,.~ ) , noc~.e 18 ha s T.a ( ~, 3 , ~,l ) and R4 ( ~.2 ,
~4 ) ,
node 2 0 has TS ( ~,1, ~,4 ) and RS ( ~,3 , n.~ ) , and node 2 2 has T6
(~,1, ~,2) and R6 (~,3, ~,~) respectuvely. Connections between
the nodes are made through the-~r common wavelengths, e..g.
node 12 provides a bi.-directional cc>nnection to the other
five nodes 14, 1.6, 18, 20 and 2.2 in t:he network by
receiving signals on wavelengths ic:hannels) 7~1 & ~,2 and
transmitting signals on wavelengths (channels) 7~3 & ~,4. In
more detail, referring to the c:onnec:tion scheme of Figure
1, node 12 would receive signals on wavelengths ~.1 and ;~,2,
namely on wavelength ~,, from nodes 18, 20 and 22, and on
wavelength ~,2 from nodes 14 and 16. On the transmission.
side, node 12 would send signa=~s on wavelengths ~,3 and ~,4,
namely, on wavelength.,~3 to nodes 14, 20 and 22, and on.
wavelength 7~,4 to nodes 15 and 18. Thus, for nodes 12 and 14
the common wavelengths are ~,2 and 7~3, for nodes 12 and :16
the common wavelengths are ~,4 and ~,2, for nodes 12 and :18 -
2.0 ~,4 and ~,1, f or node s 1. 2 and 2 0 -- i~,,~ and 7~1, and f or node s 12
and 20 - x,3,4 and X1,2. ,::onnections between other nodes in the
network are established in a s_lmilar manner and illustrated
in Table 1.
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[0047] Thus, the network 10 uses combinations of four
wavelengths by two at. each node to ,~>rovide quick and
flexible connections in a six-node network in the manner
described above.
S
TABLE 1. Flexible connections between 6 nodes
Node Receiver TransmitterIllustratian ReceiverTransmitter
of Connections
._ ______...____..__.
12 R1 ~~y .11 y3' Rl y' T1 (~,s~
~~) ~p._ ~z) ~a)
l '~4 l
W _
14 R2 (~,n Tz (~z, ~.__.__ --R' 'fa (~2~
~,j) ~,a) -__ - (~,, Via)
~;)
-
16 R3 ~~I T3 ~~2, ~ R3 ~~i T3 ~~2~ ~3)
~ ~~E) ~3 ~ ~ ~4)
- __.._ ___ _. ._
18 R4 ~~2~ T4 ~~I,l R~ ~y, T4 ~~1 ~
~) a a, 5'~ __.__ ~) ~3)
~.
20 R _ S RS ~y, ~'S ~~,1~
~~2~ ~3) TS ~~1,1~ ~;) ~4)
~"1~ ...
22 R6 ~~3~ T6 ~~I s R6 ~~;~ T6 ~~1 a
~~4) ~~~ ~4) ~.?)
(0048] A block diagram of the OADM 30 used at the node
of the network 10 is illustrated in Figure 2. It includes a
band add/drop filter 32 for receiving an incoming band of
four wavelength channels entering the node, transmittir~g
the band to the other nodes (not shc.wn~, and routing the
received band inside the node far further processing. The
filter 32 has two inputs and two outputs, namely an input
34 for receiving the band, an output 36 for transmitting
the band outside the node, an output 38 for dropping the
1 E,
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band at the node, and, an input 40 foxy adding the processed
band to the filter 32 and further t~~> the network 10.
(0049] Th.e output 33 of the band filter 32 is connected
to a three-way switch. 42 having three outputs 44, 46 and
48. The first output 4a of the swit~~:h 42 provides
connection of the switch to an opti~~:al channel drop filter
50, which is adjusted, tc one oi= the wavelengths of the
receiver at the node, e.g. to wavelw:ngth ~l at node 12. The
second output 46 of the three-way switch 42 is connected to
another optical channel drop f=_lter 52, which is adjusted
to the other' wavelength of the receiver at the node, e..g.
to wavelength ~,z at node 12. Conveniently, the total number
of the optical channel drop filters required at each node
is equal to the number cf the wavelengths utilized by the
receiver at the node. Each of t:he filters 50 and 52 has two
outputs, the first pair of the filters' outputs 54 and 56
is connected. to corresponding receiv~er(s) at the node, e.g.
to the receiver Rl(~l,~z) at node 12, and the other pair of
the filters' outputs 58 and 60 is connected to a two-way
switch 62. The switcr: 62 combines t:rie two wavelengths
dropped at filters 50 and 52 and se:c~ds them to another two-
way switch 64 whose outputs 66 and 68 are respectively
connected to optical channel add filters 70 and 72. ThE=_
filters 70 a.nd 72 add channels transmitted at the node,,
In
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being respectively adjusted to the wavelengths of the
transmitter at the node, e.g. filter 70 is adjusted to
wavelength 7~3, and fi:lt.er 72 to wavelength ~,4 at node 12.
The respective outputs 74 and 76 of filters 70 and 72 are
connected to another two-way switch 78, which combines the
dropped and added channels and sends them to yet another
two-way switch 80. Additionally, the switch 80 receives the
channels) intended to pass thr-ough the node from the
output 48 of the switch 42, thus completing the formation
of the required band of four wavelengths to be sent to the
network through the band filter 32. Conveniently, the total
number of optical channel add falters required at the node
is equal to the number of wavel.ength.s used by the
transmitter at the node.
[0050] The OADM 30 operates in the following manner. The
band of four (2n) wave_Lengths i.s selected by the band
add/drop filter 32 and sent to the three-way switch 42 for
further selection of individual channels, which are
supposed to be dropped at the node, and those channels,
which are intended to pass through the node and to be
returned back to the natwork. C'.hannels to be dropped are
filtered by corresponding channel drop filters SO and 52
and further sent to the corres~>onding receivers. Channels
to be added at the node are received from the corresponding
l~
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transmitter at the node and combined in the switch 80 with
channels being dropped and with the pass-through channels,
thus forming another band of four wavelengths to be sent to
the network.
[0051] A block diagram of another form of the OADM 130,
which can be used at the node of the network 10, is
illustrated in Figure 3. It is similar to the OADM 30 of
Figure 2, and similar elements are designated by same
reference numerals incremented by 100_ The OADM 130
includes a band add/drop filter 132 for receiving an
incoming band of four wavelength ChanTlels entering the
node, transmitting the band to the other nodes (not shown),
and routing the received band inside the node for further
processing. 'The filter 132 has twa inputs and two outputs,
1.5 namely an input 134 for receiving the band, an output 136
for transmitting the band outside the node, an output 138
for dropping the band at the node, and an input 40 for
adding the processed :band to the filter 132 and further to
the network 10.
[0052] The output 138 of the band filter 132 is
connected to a three-way switch 142 .having three outputs
144, 146 and 148. The first output 146 of the switch 142
provides connection of the switch to an optical channel
drop filter :150, which is adjusted t:o one of the
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wavelengths of the receiver at the :node, e.g. to wavelength
~,1 at node 1:z. The second output 14E~ of the three-way switch
142 is connected to another optical channel drop filter
152, which is adjusted to the other wavelength of the
receiver at the node, e.g. to vaavelength ~,2 at node 12.
Conveniently, the total number of t:he optical channel drop
filters required at ear_h node i.s equal t:o t:he number of: the
wavelengths utilized by the rec:eive:r at the node. Each of
the filters 150 and 152 has two outputs (i.e. two pair: of
outputs), the first pair of the filters' outputs 154 and
156 is connected to corresponding receivers) at the node,
e.g. to the receiver R,(h1,~,2) at node 12. Conveniently, it
can be done by using a coupler 157 as shown in Figure ?..
The other pair of the filters' outputs 158 and 160 is
connected to a coupler 162, which combines the two
wavelengths dropped at filters 150 and 152 and sends them
to optical couplers 170 and 172 from its output 173. The
couplers 170 and 172 receive trAe dropped channels and also
add channels ~,k and ~."; transmitt:ed at the node, the couplers
2~0 being respectively suitable to operate at the wavelengths
of the transmitter at the node, e.g.. coupler 170 is adding
the wavelength ~,~, and coupler 172 :i:~ adding the wavelength
~,4 at node 12. The combined dropped and added channels are
sent to yet .another two-way switch 180 from the output 179
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of the coupler 172. Additionally, t:he switch 180 receives
the channels) intended to pass through the node from the
output 148 cf the switch 142, thus completing the formation
of the required band of four wavelengths to be sent to the
network through the band filter 132. Conveniently, the
total number of optical couplex:s required at the node is
equal to the number cf wavelengths used by the transmitter
at the node, and the total number o:f optical filters
required at the node is equal t:o the number of wavelengths
used by the receiver at the node.
[0053] The OADM 130 operated> in the following manner .
The band of four (nl+n~) wavelengths is selected by the band
add/drop filter 132 and sent to the three-way switch 142
for further selection of individual channels, which are'
supposed to be dropped at the node, and those channels
which are intended to pass through the node and to be
returned back to the network. C:har~nels to be dropped are
filtered by corresponding channel drop filters 150 and 152
and further sent to the corresponding receivers. Channels
to be added at the node are received from the corresponding
transmitter at the node, added via corresponding couplers
170 and 172, and combined in the swatch 180 with channels
being dropped and with the pass-through channels, thus
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forming another band of four wavelengths to be sent to the
network.
[0054] Thus, the OADM, comprising a set of "n2" optical
filters operating at wavelengths of the receiver and
another set of "n1" optical fi7.ters or couplers operating at
wavelengths of the tz°ansmitter and performing multiplexing
and demultiplexing of:' optical ~~hanne~ls, is provided.
[0055] In a modification to the embodiment, the optical
network 10 can be build as an overlay on top of another
l0 multi-ring network so that the nodes 12, 14, 15, 18, 20 and
22 of the optical network 10 are also the nodes in the
multi-ring network, thereby providing a flexible connection
between the nodes in the multi-ring network. This
modification of the ~~rdoodiment is illustrated in Figures 4
and 5, which shows a multi-ring net: work 200 having first
and second ring netwoxks 202 a.nd 204.. The first ring
network 202 includes modes 12, Z4 and 18 of the network 10,
and the second ring network 204 includes nodes 16, 20, 22
of the network 10. The exchange of optical bands between
the rings 202 and 204 is performed by using a band
interchange module 210 suitable for Transfer of four
wavelengths, the structure of the interchange module being
shown in Figure 5. ~'he band interchange module can be
either swit.chable or fixed. If it i.s switchable, each ring
22
CA 02411630 2002-11-08
Attorney Docket No. TR-086
can have up to six dynamic active nodes, working
independently before the switch is turned on. It also
allows avoiding the need for a hub izpde at the border of
the rings for traffic exchange, which may become a
bottleneck with the growth of traffic. More than two rings
in the mufti-ring network can r>e connected in a similar
manner, thus providing a flexible connection between the
multiple rings.
[0056] In the embodiment described above, the network
architecture is arranged to provide bi-directional
connection between the network nodes. Tt is also
contemplated that assignment of wavelength in the network
can be made so that wavelengths of transmitters and
receivers at different nodes are arranged so that for any
I.5 pair of nodes there is one common wavelength which is the
same for one of the transmitter and receiver at one node
and one of t:he respective receiver and transmitter at the
other node, thus providing a direct connection between the
nodes, which can be either a uni-directional connection or
a bi-directional connection.
[0057] While the embodiment described above illustrates
the assignment of wavelengths in the network so that an.y
pair of nodes has two common wavelengths, it is understood
that the number of common wavelengths can be higher or
23
CA 02411630 2002-11-08
Attorney Docket No. TR-086
lower than the above number depending on the network
requirements. One illustrative example of wavelength
assignments between the nodes allowing serving more than
six nodes is shown in Table 2 below.
Table 2 Flexible connection between 8 nodes using 4 wavelengths
Node Receiver Transmitter IllustrationReceiver Transmitter
of
Connections
.__. -__-__-_ u-
#1 R, (y, ~l.t O3, ~.q~ Rt W, ~z) Tt (~s,
~z) -._.._ ___'~ Via.)
-
#2 Rz (y, ~ Rz (~~, ~z) Tz ~~2,
~s) Tz (~z, ~a~ ~q.)
#3 R3 ~~t,l, Ir3 ~~2, ~3) ~__..- R3 (~1, ~q) T3 ~~2,
~4) ~- ~~ ~~,)
_...-__ _-_ _
_-
#4 Rq ~~.2, / Rq ~~2, ~q) T4 ~~1,
~4) I~4 ~~I, ~.3' ~ ~'~)
_
-__- __
#s RS yz, ~ R5 (~,~, T5 (~t,
~3) ~rj (~~, a,.,~ ~,~y ~.q.)
__.___
#6 R6 ~~3, :!~~ R~ ~ag, ~,q~T6 ~~i,
~4) I~~6 ~~1, ~ ~2)
~
.
#7 R7 ~~I, ~r7 ~~,I, ~,o. a.3) R7 ~~I, ~3, T7 ~~I,
~3, ~~q) ~ ~4) ~2, ~3)
#8 Rg ~~2, I~17 ~~I, ~~ ~~'~~q~ T7 ~~I,
~3, ~'~q) ~~,1~ RX (~~ ~2., ~4)
.- -
_-_-__-. ~____ L__ __._____
__
[0058] Although the network of the embodiment described
above has been implemented by using four wavelengths
(channels) in total an;3 supports :connections between si.x
nodes, it is contemplated that a similar approach can be
applied to a network which would use "'nl+n2°' wavelengths in
total, and whose total number of nodes would be equal t:o N
- (nl+n2) ! / (n1 ! n2 ! ) . One! exemplary illustration of using more
than four wavelength i:~ shown i.n table 3 below, which
24
CA 02411630 2002-11-08
Attorney Docket No. TR-086
illustrates how to provide connections between 20 node: by
using six different wavelength:>.
Table 3 Fully flexible connection between 20 Nodes using fi wavelengths
Rx ~,6 ~,5 Tx ill ~ ~ Rx ~,6 Tx ~,l ~,2
~,4 ~,2 h_3_ ~,5 7~4 ~,3
Rx ~6 ~.5 Tx ~, l Rx ~,6 Tx ~, l ~,2
~,3 ~,2 ~,4 ~,5 7~3 ~,4
_
Rx ~,6 ~,3 Tx 7~1 R:x i~6 Tx ~,I ~,2
~,4 ~,2 ~_5 ~,3 7~4 ~5
Rx ~S ~,4 Tx hl ~,2 R:x_~5 Tx ~,l ~,2
~,3 ~,6_ ~,4 ~,3 ~,6
Rx ~,6 ~5 Tx ~,1 Rx_~_,6 Tx ~,1 ~,3
~,2 ~,3 ~.4_ ~5 ~,2 ~,4
Rx 7~6 ~3 Tx ~,1 R:x_ ~,6 rf x ~,1 ~,5
~,2 ~,5 ~.4_ ~,3 7~2 ~4
Rx 7~5 ~,4 T x ~,1 _Rx ~. Tx ~,1 ~,6
~,2 ~,6 ~, ~_~~4_~, ~,3
3 2_
Rx 7~6 ~4 Tx ~,1 R.x t~f~ T_x ~, l ~,5
~,2 ~,5 ~.~ ~_,47~2 ~,3
Rx 7~4 ~,3 Tx ~,1 R:x i~4 '_fx ~,1 ~,5
~,2 ~,5 ~.6 ~_,3_~,2 ~,6
Rx 7~5 ~3 Tx ~,1 /~ R:x_;~,5_~_,3_~,2_Tx ~,1 ~,6
~,2 ~,6 ~,_4 ~,4
Rx ~,1 ~,2 Tx ~,6 I~ x ~ '(x ~,6 ~,5
~,3 ~,5 ~, ,1 ~,2 ~,4
4 ~,3
Rx ~ 1 ~.2 _ ~ _ _
~,4 Tx ~.6 ~,4 Tx ~,6 ~,5
~,5 i~L R x ~,3
3 ~ I
a~2
i
Rx ~,1 ~2 Tx ~,6 ~ _ _
7~5 ~,3 n.4 _ Tx ~,6 ~,3
_ ~,4
_
R: x ;~~
1_~2_~,5
Rx ~,1 ~,2 Tx ~5 ~,4 ~ R_x';~,1 Tx ~,5 ~,4
~,6 i~~3._ ~_,2 ~,G ~,3
Rx ~, l ~,3 Tx A,6 R x_;~,1 Tx ~,6 ~,5
~,4 ~S i~~_2. ~_~3 ~,4 7~2
~
Rx ~,1 7~5 Tx A,6 R:_x. ~, Tx ~,6 ~,3
~,4 ~3 ~~2 l w_5_~,~ ~,2
Rx ~,1 ~.6 Tx ~,5 R x_;~_,1 Tx ~,5 ~,4
~,3 ~,4_7~~_2 ?~6 ~,3 ~,2
~
Rx ~,1 ~,5 Tx ?~6 R: x ;~. Tx ~,6 ~,4
~,3 ~,4 X42 l_~.5 ~,2
~,3
Rx ~, t 7~5 Tx A_,4 R: x ~,1_?~_5_~,6'Tx ~,4 ~,3
~,6 ~,3 n,2 7~2
Rx ~,1 ~,6 Tx ~,5 R x ;~ Tx ~,5 ~,3
~,4 ~,3 ~.~2 l 7~6 ~,2
~,4
[0059] Ira a modification to the embodiment described
above, it is possible to ~~et up t:wo o:r more connections
between the nodes at the same time if the intermediate
nodes have wavelength.~~onverters. The nodes, which provide
the wavelength conversion, operate as hops, and the
additional cost involved is the cost. of transpanders at.
each node. E.y a way c~f example, Figure 6 illustrates
establishing of two connections between the nodes 12 and
CA 02411630 2002-11-08
Attorney Docket No. TR-086
20, wherein the first connection is established by direct
communication between the node; a.t the wavelength ~,3, and
the second connection is establ.i.shed. through the nodes 18
and 14 by using the wavelength conversions ~.~ to ~,1 and ~,1 to
~,2 respectivE=ly. Simi_I_arly, two connections from the node 20
to the node 12 can be clone at the w<~velength ~,3 (direct
connection) and via nodes 16 and 22 using wavelength
converters as illustrated in Figure 6. The OADM structure
shown in Figures 2 and 3 has tc> be :lightly modified tc>
support adding and dropping of two channels, otherwise
being similar to that ~~f Figure~~ 2 and 3.
[0060] Various comb:inat.ions and arrangements of
components in the network may ~~lso be contemplated. For
example, fixed wavelength devices (transmitters and/or
receivers) at certain nodes may be replaced with tunable
devices to provide additional flexibility of network
connections.
[0061] Although the approacrto network architecture: has
been described with regard to an optical mesh network,
2~~ alternatively, it can be applied to other types of
networks, e.g. ring networks, ox any other known optical
network, which would require achievirag flexible connections
by using limited network resourr_es.
26
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Attorney Docket No. TR-086
[0062] Although specific embodiments of the invention
have been described in detail, it wall be apparent to one
skilled in the art that variations and modifications to the
embodiments may be made within the scope of the following
claims.
27
