GB2427518A

GB2427518A - Optical add-drop multiplexer in which data input at a plurality of different ports is dropped using a common bank of transponders

Info

Publication number: GB2427518A
Application number: GB0512388A
Authority: GB
Inventors: Richard Munro Dorward; Steven Benedict Alleston
Original assignee: Marconi Communications Ltd; Marconi Co Ltd; Ericsson AB
Current assignee: M (DGP1) Ltd; Ericsson AB
Priority date: 2005-06-20
Filing date: 2005-06-20
Publication date: 2006-12-27
Also published as: GB0512388D0

Abstract

The invention relates to the field of telecommunications networks and in particular to a node of such a network which is arranged to allow one set of transponders to address a plurality of line ports. The node comprises a series of signal blockers which are arranged to be selectively operable on command to route traffic to different ports of the node and to the set of transponders for adding/dropping signals from the node. Such an arrangement also permits sharing of equipment of the node such as a multiplexer, a demultiplexer, and splitters.

Description

Telecommunication Network The invention relates to a telecommunications network and in particular to a node of a telecommunications network according to the preamble of Claim 1. Known telecommunications networks operating using Wavelength Division Multiplexing (WDM) include nodes to add or drop optical signals to or from the network. Such a node typically has two or more line directions for routing traffic. An optical cross connection within the node allows individual wavelengths carrying traffic to be routed on these different line directions. The known cross connection can also selectively terminate wavelengths. The most common architecture for such a node is a Reconfigurable Optical Add/Drop Multiplexer (ROADM) as shown in Figure 1, generally designated 10. The node 10 has a first port 12 and a second port 14 both of which can pass an incoming and outgoing multiplexed optical signal. For simplicity only the signal travelling East to West as seen in Figure 1 will be discussed in detail. An incoming multiplexed signal 16 on the second port 14 is split into two secondary multiplexed signals 18, 24 by a splitter 17. The secondary signal 18 is selectively filtered at a first multiplexer/demultiplexer 20 and is terminated on a first bank of transponders 22, whilst the secondary signal 24 is passed on to a wavelength blocker 26.The wavelength blocker 26 selectively attenuates those channels within the secondary multiplexed signal 24 which have been dropped by the first multiplexer/demultiplexer 20. By attenuating the dropped channels, the same wavelength can then be re-used by reinserting them after the wavelength blocker 26 using a second bank of transponders 23 and a second multiplexer/demultiplexer 25. Optical amplifiers 28 and power monitoring units 30 at the ports 12, 14 are used, respectively, to overcome and allow control of any optical losses. The problem with the arrangements of Figure 1 is that each port requires its own bank of transponders and multiplexers/demultiplexers to provide the required functionality. Accordingly the number of transponders and multiplexers/demultiplexers grow proportionally with the number of ports. Such transponders and multiplexers/demultiplexers are expensive which increases the capital costs, and increases the amount of equipment that is required for operation of each node of the network. Such an increase in equipment increases the probability of failures occurring within the node. The present invention aims to solve the problems of the known arrangement by providing an architecture that permits a bank of transponders to be shared by a plurality of ports. According to the invention, this problem is solved by the characterising portion of Claim 1. Such an arrangement can provide the advantage of reducing the cost of a node of a WDM telecommunications networks. The invention provides a technical solution to the problem of allowing one set of transponders to address a plurality of line ports in a multi-port WDM node. Such an arrangement also permits sharing of equipment of the node such as a multiplexer, a demultiplexer and splitters of the node. Other features of the invention will be apparent from the following description of a preferred embodiment shown by way of example only in the accompanying drawings, in which; - Figure 1 is a schematic diagram of the architecture for an optical add/drop node according to the prior art. - Figure 2 is a schematic diagram of the architecture for a two-port optical adddrop node according to a first embodiment of the present invention. - Figure 3 is a schematic diagram of the architecture for a three-port optical adddrop node according to a second embodiment of the present invention. - Figure 4 is a schematic diagram of the architecture of a three-port add-drop node according to a third embodiment of the present invention. Referring to Figure 2 there is shown a schematic diagram of the architecture for a twoport optical add-drop node according to a first embodiment of the present invention, generally designated 40. Features corresponding to the dual port arrangement of Figure 1 are shown with like reference numerals. In Figure 2 it can be seen that the ports 12, 14 share one multiplexter/demultiplexer 42 having one bank of transponders 44. A first incoming multiplex signal 16 to the second port 14 is split into two secondary multiplexed signals 24, 34 by a splitter 17, the secondary signals 24, 34 being substantially identical. The secondary signal 34 continues on to a blocker 46 which can selectively block the secondary signal 34 on command. The secondary signal 24 continues on to a blocker 26 which can also selectively block the secondary signal 24 on command. A second incoming multiplexed signal 48 to the first port 12 is split into secondary signals 50 and 52 by a splitter 54, the secondary signals 50, 52 being substantially identical. The secondary signal 52 continues on to a blocker 56 which can selectively block the secondary signal 52 on command. The secondary signal 50 continues on to a blocker 58 which can also selectively block the secondary signal 50 on command. The blockers 46, 56 are then operated to selectively block one or other of the secondary signals 34 and 52 such that the transponders 44 are shared between the ports 12, 14 on an individual basis and not as a bank. The blockers 46, 56 feeding the transponders 44 are operated selectively on a per wavelength basis and so that they do not block the entire signal 34, 52. In this way only parts of one of the signals 34, 52 is passed to a shared splitter 60 which then passes the signal on to shared multiplexer/demultiplexer 42 to be terminated at the shared transponders 44. The wavelengths of the secondary signal 24 or the secondary signal 50 that are not dropped by the transponders 44 are then allowed to pass through either of the blockers 26, 58 respectively.Amplifiers 28 may be located between the shared splitter 60 and the shared multiplexer/demultiplexer 42 to counter and control any attenuation that may have occurred. The arrangement of the signal blockers which are selectively operable on command permit routing of traffic to different ports of the node and to the bank of transponders for adding/dropping signals from the node. In a similar manner any new signals 62 added to the node 40 via the transponders 44 are first combined at the shared multiplexer/demultiplexer 42 and then passed to the shared splitter 60. The shared splitter 60 then splits the new signal 62 into two substantially identical secondary signals 64, 66 which each continue on to a respective blocker 68, 70. Depending on whether the new signal 62 is destined for the first port 12 or the second port 14 the blockers 68, 70 are then operated to selectively block parts of one or other of the signals 64, 66. The architecture of the node 40 of Figure 2 permits the bank of transponders 44 to be shared by the ports 12, 14 for dropping and adding telecommunications traffic to and from the node 40. By selective activation of the blockers 26, 46, 56, 58, 68, 70 each of the shared transponders 44 can address either of the line directions. In Figure 3 a schematic diagram of the architecture for a three-port optical add-drop node is shown according to a second embodiment of the present invention, generally designated 80. Features corresponding to the dual port arrangement of Figure 2 are shown with like reference numerals. In Figure 3 a third port 82 is shown in communication with the first and second ports 12, 14. The three ports 12, 14, 82 share one multiplexer/demultiplexer 42 having one bank of transponders 44. The first incoming signal 16 is split into three secondary signals 24, 34, 84 by the splitter 17. Each of these three signals 24, 34, 84 are substantially identical and continue on to a respective blocker 26, 46, 86 which can pass the signal 24, 34, 84 on command. A second incoming multiplexed signal 48 to the first port 12 is split into three secondary signals 50, 52, 87 by the splitter 54.The secondary signals 50, 52, 87 are substantially identical. The secondary signal 87 continues on to a blocker 88 which can also selectively block the secondary signal 87 on command. Figure 3 also shows a third incoming signal 90 to the third port 82 which is split into three secondary signals 92, 94, 96 by a splitter 98. The secondary signals 92, 94, 96 are substantially identical. Each of the secondary signals 92, 94, 96 continue on to a respective blocker 100, 102, 104 which can pass the signal on command. The three blockers 46, 56, 102 are then operated to selectively block two of the secondary signals 34, 52, 94. In this way only one of the signals 34, 52, 94 is passed to the shared splitter 60 which then passes the signal on to the shared multiplexer/demultiplexer 42 to be terminated at the shared transponders 44. The wavelengths of the secondary signal 24, 84, 50, 87, 92 or 96 that are not dropped by the transponders 44 are then allowed to pass through either of the blockers 26, 86, 58, 88, 100 or 104 respectively. In a similar manner any new signals 62 added to the node 80 via the transponders 44 are first combined at the shared multiplexer/demultiplexer 42 and then passed to the shared splitter 60. The shared splitter 60 then splits the new signal 62 into three substantially identical secondary signals 64, 66, 106 which each continue on to a respective blocker 68, 70, 108. Depending on whether the new signal 62 is destined for the first port 12, or the second port 14, or the third port 82, the blockers 68, 70, 108 are then operated to selectively block two of the signals 64, 66, 106. The architecture of the node 80 of Figure 3 permits the bank of transponders 44 to be shared by the three ports 12, 14, 82 for dropping and adding telecommunications traffic to and from the node 80. By activation of the blockers 26, 46, 56, 58, 68, 70, 86, 88, 100, 102, 104, 108 any one of the shared transponders 44 can selectively address either of the line directions. Figure 4 is a schematic diagram of the architecture of a three-port add-drop node according to an alternative embodiment of the present invention, generally designated 120. Features corresponding to the arrangements of Figures 2 and 3 are shown with like reference numerals. In Figure 4 three ports 12, 14, 82 are in communication with one another and share two multiplexer/demultiplexers 42, 43 each having one bank of transponders 44, 45. The first incoming signal 16 is split into two secondary signals 24, 34 by the splitter 17. Each of these two signals 24, 34 are substantially identical and continue on to a respective blocker 26, 46 which can pass the signal on command. If part of the incoming signal 16 is to be dropped at the node 120 the splitter 17 splits the signal 16 into a further secondary signal 124 which continues on to the shared splitter 60 via a blocker 126.The further secondary signal 124 is then dropped at the transponders 44. In a similar manner a second incoming multiplexed signal 48 to the first port 12 is split into two secondary signals 50, 52 by a splitter 54. The secondary signals 50, 52 are substantially identical. The secondary signals 50, 52 continues on to respective blockers 58, 56 which can selectively block the secondary signals 50, 52 on command. If part of the incoming signal 48 is to be dropped at the node 120 the splitter 54 splits the signal 48 into a further secondary signal 128 which continues on to the second shared splitter 130 via a blocker 132. The further secondary signal 128 is then dropped at the transponders 45. In a similar manner a third incoming signal 90 to the third port 82 is also shown which is split into two secondary signals 92, 94 by a splitter 98. The secondary signals 92, 94 are substantially identical. Each of the secondary signals 92, 94 continue on to a respective blocker 100, 102 which can pass the signal on command. If part of the incoming signal 90 is to be dropped at the node 120 the splitter 98 splits the signal 90 into a further secondary signal 134 which continues on to the shared splitter 130 via a blocker 136. The further secondary signal 134 is then dropped at the transponders 45. It will be appreciated that the further secondary signal 134 could alternatively be arranged to be dropped at the transponders 44. To pass a signal to the first bank of transponders 44 from either of the first port 12 and the third port 82 the two blockers 132, 136 are operated to selectively block one of the secondary signals 128, 134. The signal then passes on to the shared splitter 130 which then passes the signal on to the shared multiplexer/demultiplexer 43 to be terminated at the transponders 45. Any new signals 62 added to the node 120 via the transponders 44, 45 are first combined at either of the shared multiplexer/demultiplexer 42, 43 and then passed to the respective shared splitter 60, 130. For the first bank of transponders 44 the shared splitter 60 then splits the new signal 62 into two substantially identical secondary signals 64, 66 which each continue on to a respective blocker 68, 70. Depending on whether the new signal 62 is destined for the first port 12, or the second port 14, or the third port 82, the blockers 68, 70 are then operated to selectively block one of the signals 64, 66. For the second bank of transponders 45 the shared splitter 130 splits the new signal 62 into two substantially identical secondary signals 138, 140 which each continue on to a respective blocker 142, 144.Depending on whether the new signal 62 is destined for the first port 12, or the second port 14, or the third port 82, the blockers 142, 144 are then operated to selectively block one of the signals 138, 140. The architecture of the node 120 of Figure 4 permits the two banks of transponders 44, 45 to be shared by the three ports 12, 14, 82 for dropping and adding telecommunications traffic to and from the node 120. By activation of the blockers 26, 46, 56, 58, 68, 70, 100, 102, 122, 126, 132 136, 142, 144 each of the shared transponders 44, 45 can selectively address the line directions 14 and 82, and 12 and 82, respectively. The nodes described in the embodiments of Figures 2 - 4 are preferably dynamically reconfigurable via control software. This avoids the requirement for manual patching of connections. Such dynamic reconfiguration is known to the skilled person and shall not described further herein.

Claims

1. A telecommunications network node (40) comprising; a plurality of ports (12, 14) adapted for passing telecommunications traffic; each port (12, 14) having a splitter (54, 17) adapted to split an incoming multiplexed signal (16, 48) to the port (12, 14) into a plurality of substantially identical multiplexed signals (24, 34, 50, 52); the node including a demultiplexer (42); the demultiplexer (42) in communication with a bank of transponders (44) for dropping traffic from the node (40, 80); characterised in that the bank of transponders (44) is arranged to drop traffic from more than one port (12, 14).

2. A node according to Claim 1, wherein each of the plurality of multiplexed signals (24, 34, 50, 52) is adapted to be input to a respective signal blocker (26, 46, 58, 56).

3. A node according to Claim 2, wherein at least one blocker (26, 46, 58, 56) is arranged to selectively block a portion of its associated multiplexed signal (24, 34, 50, 52) on command.

4. A node according to Claim 3 including a further splitter (60) associated with the bank of transponders (44).

5. A node according to any preceding Claim and further including a multiplexer (42) for adding traffic to the node (40) via the bank of transponders (44).

6. A node according to Claim 5, wherein the multiplexer (42) is provided with an additional splitter (60) for splitting the added traffic into a plurality of additional multiplexed signals (64, 66).

7. A node according to Claim 6, wherein each additional multiplexed signal (64, 66) is adapted to be input to a respective additional signal blocker (68, 70).

8. A node according to Claim 7, wherein each additional signal blocker (68, 70) is operative to selectively block at least a portion of each additional multiplexed signal (64, 66) on command for routing each additional multiplexed signal (64, 66) to one of the ports (12, 14).

9. A node according to any preceding Claim, wherein the signal blocker (26, 58) associated with one of the multiplexed signals (24, 50) is arranged to pass different wavelengths of the incoming multiplexed signal (16, 48) to those dropped at the bank of transponders (44).

10. A node according to any preceding Claim and further including a plurality of banks of transponders (44, 45) wherein each bank of transponders (44, 45) is arranged to drop traffic from a plurality of ports (12, 14, 82).

11. A telecommunications network including a node according to any preceding Claim.