Optical communications – Multiplex – Optical switching
Reexamination Certificate
2000-05-24
2004-06-01
Pascal, Leslie (Department: 2633)
Optical communications
Multiplex
Optical switching
C398S068000, C398S077000
Reexamination Certificate
active
06744984
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to telecommunication networks, and more particularly, to a system and method for providing a channel capacity expansion mechanism for high-speed data transmission over an optical network.
Optical networks are high-capacity telecommunications networks based on optical technologies and components that provide routing, grooming, and restoration at the wavelength level. They provide higher capacity communication networks for new applications such as the Internet, video and multimedia interaction, and advanced digital services at a reduced cost. Wavelength Division Multiplexing (WDM) technology is widely used in optical networks to provide additional capacity on existing fibers. Using the WDM technology, the components of the optical network are defined according to how the wavelengths are transmitted, groomed, or implemented in the network.
WDM technology combines many signals, or “virtual” fibers, onto a single physical fiber by transmitting each signal at a different frequency. Furthermore, with the improvement of optical filters and other laser technology, the number of effective channels on a single physical fiber for carrying the signals is continually increasing. Currently, dense wavelength division multiplexing (DWDM) technology allows a single fiber to provide 40 or 80 channels for carrying signals. Consequently, by implementing DWDM systems and optical amplifiers, networks can now provide a variety of channels with different bit rates, e.g., OC-48 or OC-192, over a single fiber.
One major problem in designing a DWDM system is creating a channel spacing plan. Although the, International Telecommunication Union (ITU) has published a standard set of frequencies based on different channel spacing, the 50 GHz and 100 GHz plans are still the most commonly used. Furthermore, as these systems are rapidly deployed, it is likely that both OC-48 and OC-192 channels will be carried. However, at a low channel spacing plan such as 50 GHz, OC-192 channels can not be adjacent because an interference will ensue (referred to as “neighboring channel interference”). Moreover, this interference problem cannot be prevented by filtering mechanisms. Due to this neighboring channel interference, the available number of OC-192 channels for a channel spacing plan of 50 GHz is almost cut in half.
Another common problem in DWDM communication networks is the transmission traffic congestion problem due to unexpected heavy loads on a particular transmission route. In such situations, one or more alternative routes are needed to bypass the congested route. It is thus desirable that channel capacities on the alternative routes can be expanded to the maximum for effectively and smoothly completing the transmissions.
It is further desired to provide a mechanism to further increase the channel capacity of multiple transmission routes of a WDM system with minimum neighboring channel interference.
SUMMARY OF THE INVENTION
In response to these and other problems, an improved system and method is disclosed for providing high-speed, high capacity data communication over a Wave Division Multiplexing (WDM) network with an efficient re-routing capability.
When all light channels between two nodes in the network are loaded with transmission jobs, a transmission traffic jam, or congestion, is created. In order to avoid the congested route, a new alternative route is need to alleviate the heavily load. One example of the present invention selects an alternative route to direct the traffic away from the congested route, and further expand the channel capacity of the alternative route by modulating or encoding the light channels in the alternative route with orthogonal codes.
In order to select the alternative route, at least one intermediate routing point must be identified. Assuming the congested route has a starting point and a destination point, the intermediate routing point is determined based on communication channel availability between the starting node and the intermediate routing point, and further between the intermediate routing point and the destination point. Encoding one or more light channels between the starting node and the intermediate routing point with a set of orthogonal codes will significantly expand the communication channel availability. The same can be achieved by encoding one or more light channels between the intermediate routing point and the destination point. These encoding processes help to improve system manageability and route flexibility.
In another example of the present invention, the light channels on the alternative route do not have to be encoded until needed. That is, the system has a choice of using existing light channels without orthogonally encoding them if there are enough channels for directing the transmission traffic away from the congested route.
REFERENCES:
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patent: 5940379 (1999-08-01), Startup et al.
patent: 6160651 (2000-12-01), Chang et al.
patent: 6215765 (2001-04-01), McAllister et al.
patent: 6504832 (2003-01-01), Koo et al.
Alcatel Optical Networks Technical Papers,DWDM Channel Spacing Do You know How Much Capacity You're Really Getting, Paper No. AD98-04, pp. 1-8.
Faruque Saleh
Homayoun Fereidoun
Haynes & Boone LLP
Nortel Networks Limited
Pascal Leslie
Tran Dzung
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