Optical communications – Multiplex – Wavelength division or frequency division
Reexamination Certificate
1999-12-23
2004-04-06
Pascal, Leslie (Department: 2633)
Optical communications
Multiplex
Wavelength division or frequency division
C370S225000, C370S218000, C370S254000, C709S223000, C398S009000, C398S034000, C398S075000
Reexamination Certificate
active
06718141
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to optical transmission systems in general and specifically to fibre optic networks employing wavelength division multiplexing.
BACKGROUND OF THE INVENTION
Telecommunications network service providers have attempted to keep pace with the exponential increase in demand for telecommunications bandwidth by relying on optical fibre digital networks.
Since 1990, the North American long distance infrastructure has been based on an optical fibre backbone known as SONET (Synchronous Optical NETwork). SONET payloads are time division multiplexed (TDM) digital signals. In North America, OC-48 optical fibres have been used, capable of supporting a SONET signal format of up to STS-48, operating at a maximum bit rate of 2.4 Gbit/s. Each OC-48 fibre is able to support approximately 32,000 simultaneous telephone calls, or 48 channels operating at the maximum electrical transmission digital signal DS-3. The current technology now supports the use of OC-192 fibres having four times the capacity of OC-48 fibres.
More recently, a technique known as wavelength division multiplexing (WDM) has been proposed to significantly increase bandwidth along the optical fibre backbone already installed. WDM involves the introduction of more than one carrier signal within a single optical fibre. These carrier signals are identified by a defining wavelength in the range of 1540 nm to 1610 nm during which the OC-48 fibre has a minimal loss characteristic. The signals are presently separated from neighbouring signals on either side by plus or minus 0.15 nm. In long-haul networks, the signals are divided into two bands, typically denoted Blue (1540 nm to 1555 nm) and Red (1555 nm to 1570 nm) respectively to provide bi-directional transmission capability. In metropolitan WDM networks, duplicate sets of fibres may be used to provide bi-directional transmission capability. Each carrier signal may be modulated by digital data at up to STS-48 data rates. In the case of dense WDM (DWDM) systems, there may be as many as 32 separate channels per fibre, although this number will increase as the technology continues to improve.
While solving the problem of bandwidth availability, at least for the present, WDM presents a significant challenge to the network service provider in terms of determining the physical connectivity of the network for the purposes of maintenance, fault isolation, network-fill usage, performance monitoring and protection readiness.
First, the WDM network necessarily entails an increase in the complexity of the network topology which is proportionate to the increase in traffic capacity of such networks over non-WDM optical networks and even electrical communications networks.
Second, network topology has conventionally been charted by manual datafilling techniques, that is, additions to, deletions from or other modifications to the existing network topology were recorded manually at the network's central office. Even with non-WDM networks, such techniques were frequently characterized by inaccuracy due to errors in the manual keying of the connectivity data and obsolescence since the manually entered data can become easily out of date as the physical fibre connections are constantly changed. Not infrequently, a correct and up to date topology was not recorded until all or part of the network failed and the topology was manually retraced during the repair effort. Moreover, manual datafilling is an expensive and time-consuming endeavour.
Third, because optical networks are inherently transparent to the embedded payload signal, any payload could in theory be carried along the network without extensive hardware redeployment when the service is changed. This same transparency characteristic means that the network service provider is unable to accurately monitor the signal connectivity of the network, even with an accurate topology of the various network elements or nodes.
The challenges are even more significant in identifying and isolating faults along the network. Fault isolation and repair necessarily requires a detailed and accurate record of the network topology, which, as indicated above, is not often available when manual datafilling methods are used to maintain network connectivity data. More significantly, the increased traffic capacity and the transparency of WDM optical networks with regard to signal connectivity render obsolete such traditional fault isolation techniques as manual signal tracing and require the development of new techniques to identify and isolate network faults.
SUMMARY OF THE INVENTION
It is therefore desirable to provide a WDM network with the capability of determining the network's physical topology and signal connectivity in an automated and ongoing manner.
It is also desirable to provide a WDM network with the capability of fault isolation in an automatic and ongoing manner.
It is further desirable to provide a WDM network where individual nodes can detect the connectivity of incoming optical signals and based on their own internal connectivity, broadcast downstream the new signal connectivity.
The invention may be summarized according to a broad aspect as a wavelength division multiplexed (WDM) network having a plurality of network nodes interconnected by WDM compatible optical fibre segments which carry a plurality of WDM compatible wavelengths capable of being modulated by signals, comprising: a configuration propagation system for propagating configuration data of each network node along the network; and a mapping processor for monitoring and processing the configuration data of each network node whereby the configuration for the entire network may be determined.
The invention may be summarized according to a second broad aspect as for use in a WDM network having a plurality of network nodes interconnected by WDM compatible optical fibre segments which carry a plurality of WDM compatible wavelengths capable of being modulated by signals, a configuration signal processor associated with at least one of the network node for generating configuration data, and mapping processor for determining the configuration of the entire network, a configuration signal containing the configuration data for modulating a WDM compatible configuration wavelength reserved throughout the network, whereby the configuration signal processor of a network node may insert configuration data into the configuration signal and the mapping processor may retrieve the configuration data from the configuration signal and determine the configuration of the entire network.
The invention may be summarized according to a third broad aspect as for use in a WDM network having a plurality of network nodes interconnected by WDM compatible optical fibre segments which carry a plurality of WDM compatible wavelengths a capable of being modulated by signals, a configuration signal containing configuration data for modulating a WDM compatible configuration wavelength reserved throughout the network, and a mapping processor for determining the configuration of the entire network,a configuration signal processor associated with a network node for generating configuration data and inserting the configuration data into the configuration signal, whereby the mapping processor may retrieve the configuration data for each network node from the configuration signal and determine the configuration of the entire network.
The invention may be summarized according to a fourth broad aspect as for use in a WDM network having a plurality of network nodes interconnected by WDM compatible optical fibre segments which carry a plurality of WDM compatible wavelengths capable of being modulated by signals, a configuration signal processor associated with at least one of the network nodes for generating configuration data and a configuration signal containing configuration data for modulating a WDM compatible configuration wavelength reserved throughout the network,a mapping processor for retrieving and processing the configuration data for each network node from the configuration s
Nortel Networks Limited
Pascal Leslie
Payne David C.
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