Minimizing Bandwidth Narrowing Penalties in a Wavelength Selective Switch Optical Network

• US 20120195592A1
• Filed: 02/01/2011
• Published: 08/02/2012
• Est. Priority Date: 02/01/2011
• Status: Active Grant

• Current Assignee: Snell Holdings, LLC (Treq Labs, Inc.)
• Original Assignee: Vello Systems Incorporated
• Inventors: Barnard, Chris, Myslinski, Piotr
• Granted Patent: US 8,542,999 B2
• Time in Patent Office: Days
• US Class Current: 398/48
• CPC Class Codes: H04J 14/0204 Broadcast and select arrangements, e.g. with an optical splitter at the input before adding or dropping
• CPC Class Codes: H04J 14/0205 Select and combine arrangements, e.g. with an optical combiner at the output after adding or dropping
• CPC Class Codes: H04J 14/0206 Express channels arrangements
• CPC Class Codes: H04J 14/0209 Multi-stage arrangements, e.g. by cascading multiplexers or demultiplexers
• CPC Class Codes: H04J 14/0212 using optical switches or wavelength selective switches [WSS]
• CPC Class Codes: H04J 14/02122 Colourless, directionless or contentionless [CDC] arrangements
• CPC Class Codes: H04J 14/0256 at the optical channel layer
• CPC Class Codes: H04Q 11/0005 Switch and router aspects
• CPC Class Codes: H04Q 11/0062 Network aspects
• CPC Class Codes: H04Q 2011/0009 using wavelength filters
• CPC Class Codes: H04Q 2011/0016 using wavelength multiplexing or demultiplexing
• CPC Class Codes: H04Q 2011/0086 Network resource allocation, dimensioning or optimisation

Abstract

This invention relates to provisioning wavelength-selective switches and reconfigurable optical add-drop multiplexers to minimize the bandwidth narrowing effect from the optical filters. Novel architectures and methods are disclosed that can significantly reduce bandwidth-narrowing on channels in a reconfigurable WDM network where a large number of optical filter elements are cascaded. Instead of blocking unused channels as in the prior art, unused channels are selectively provisioned depending on the state of their adjacent channels. Unused adjacent channels of an active channel are provisioned to follow the same path as the active channels. As each channels is deployed, the channel frequency is selected so as to minimize bandwidth narrowing.

Claims

1. A method for provisioning a channel on which a client signal will be transmitted along a path from a source node through at least one intermediate node before reaching a destination node of a WDM optical network, the method comprising the following steps:

(a) selecting a signal channel and a path on which the client signal will be transmitted among a plurality of nodes of the network;

(b) configuring an optical filter at each node along the path to reflect the state of the signal channel at that node;

(c) determining, with respect to each node along the path, whether each of two channels adjacent to the signal channel is unused; and

(d) configuring the optical filter at each node along the path by setting the state of each unused adjacent channel to the same physical state as that of the signal channel,

(e) thereby effectively increasing the spectral passband of the client signal.

2. The method of claim 1, wherein the physical state of the signal channel at the source node of the path is an “

add”

state, the physical state of the signal channel at each intermediate node of the path is a “

pass through”

state and the physical state of the signal channel at the destination node is a “

blocking”

state.

3. The method of claim 2, wherein every channel is initially set to a default “

blocking”

state.

4. The method of claim 1, wherein the state of each unused adjacent channel is set to a different logical state than that of the signal channel.

5. The method of claim 1, wherein the level of attenuation of each unused adjacent channel is set to the same level of attenuation as that of the signal channel.

6. The method of claim 1, wherein the optical filter at each node along the path is a wavelength selective switch.

7. A method for minimizing bandwidth narrowing while provisioning one of a plurality of available channels on which a client signal will be transmitted along a path from a source node through at least one intermediate node before reaching a destination node of a WDM optical network, the method comprising the following steps:

(a) for each available signal channel,

(i) tentatively configuring an optical filter at each node along the path to reflect the state of the available signal channel;

(ii) tentatively configuring the optical filter at each node along the path to set the state of each unused channel adjacent to the available signal channel to the same physical state as that of the available signal channel;

(iii) determining the tentative number of bandwidth narrowing events from the perspective of the available signal channel, wherein a distinct bandwidth narrowing event would result for each channel which is adjacent to the available signal channel at a node along the path, and which has a physical state that differs from the physical state of the signal channel;

(iv) repeating step (iii) from the perspective of each of the channels adjacent to the available signal channel that is being used to transmit signals; and

(v) selecting the larger of the tentative numbers of bandwidth narrowing events determined in steps (iii) and (iv);

(b) selecting the available signal channel that yielded the smallest number of bandwidth narrowing events selected in step (a) (v); and

(c) provisioning the selected signal channel to transmit the client signal along the path.

8. A method for minimizing bandwidth narrowing after provisioning one of a plurality of available channels on which a client signal will be transmitted along a path from a source node through at least one intermediate node before reaching a destination node of a WDM optical network, the method comprising the following steps:

(a) calculating, for the provisioned signal channel, the number of existing bandwidth narrowing events with respect to each of the two channels adjacent to the provisioned signal channel, wherein a distinct bandwidth narrowing event occurs for each channel which is adjacent to the provisioned signal channel at a node along the path, and which has a physical state that differs from the physical state of the provisioned signal channel; and

(b) shifting the frequency of the provisioned signal channel toward the frequency of the channel adjacent to the provisioned signal channel having the fewest number of bandwidth narrowing events, wherein the amount of the frequency shift is a function of the number of bandwidth narrowing events calculated with respect to each of the two channels adjacent to the provisioned signal channel.

9. A system that provisions a channel on which a client signal will be transmitted along a path from a source node through at least one intermediate node before reaching a destination node of a WDM optical network, the system comprising:

(a) a signal channel transmitter that transmits a client signal among a plurality of nodes of the network on a signal channel having a predetermined frequency;

(b) an optical filter at each node along the path that is configured to reflect the state of the signal channel at that node; and

(c) a state table indicating, with respect to each node along the path, whether each of two channels adjacent to the signal channel is unused,

(d) wherein the optical filter at each node along the path is configured by setting the state of each unused adjacent channel to the same physical state as that of the signal channel, thereby effectively increasing the spectral passband of the client signal.

10. The system of claim 9, wherein the physical state of the signal channel at the source node of the path is an “

add”

state, the physical state of the signal channel at each intermediate node of the path is a “

pass through”

state and the physical state of the signal channel at the destination node is a “

blocking”

state.

11. The system of claim 10, wherein every channel is initially set to a default “

blocking”

state.

12. The system of claim 9, wherein the state of each unused adjacent channel is set to a different logical state than that of the signal channel.

13. The system of claim 9, wherein the level of attenuation of each unused adjacent channel is set to the same level of attenuation as that of the signal channel.

14. The system of claim 9, wherein the optical filter at each node along the path is a wavelength selective switch.