Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
2001-12-13
2003-07-15
Chang, Audrey (Department: 2872)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S199200, C359S199200, C359S199200, C359S199200
Reexamination Certificate
active
06594045
ABSTRACT:
FIELD OF THE INVENTION
This invention relates 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
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 can control the traffic flow through the network, the ability to deliver bandwidth on demand anywhere in the network is not always possible. Over-provisioning of the network can partially 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 has to be done quickly and almost in real time, which is definitely not the reality of today.
Optical communications systems have been employing different network architectures to provide required flexible connections between 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 transmitted/received wavelengths are the same for those nodes that communicate 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 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.
To overcome the limitations of fixed wavelength networks, it has been suggested 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 i, signalling messages have to be first sent to inform node i to tune its receiver to wavelength &lgr;
j
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 Gigabit Optical Networks”, IEEE Journal of Selected Areas in Communications, Volume 14, No. 5, June 1996, p.814-823.
Another approach, where tunable devices are used at network nodes, is known as Tunable Transmitter and Fix-Tuned Receiver (TTFR) network architecture. In the TTFR approach, each node is assigned with a fixed wavelength for data reception, where the receivers at node i are only responding to the wavelength channel i (&lgr;
i
). Nodes intending to send data to node i have to tune their transmitters to wavelength &lgr;
i
. TTFR architecture has been described, e.g. in the article to Chun-Kit Chan et al. entitled “Node Architecture and Protocol of a Packet Switched Dense WDMA metropolitan Area Network”, Journal of Lightwave Technology, Vol. 17, No. 11, November 1999, pp. 2208-2218, where TTFR concept has been applied to DWDM networks.
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 is sensitive to temperature and/or current changes and therefore requires stabilization.
Thus, network architecture 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 to be expensive, less reliable and more complicated in exploitation and maintenance.
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.
SUMMARY OF THE INVENTION
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.
According to one aspect of the invention there is provided an optical network, comprising:
a plurality of N nodes;
each node has a transmitter for transmitting a set of “n
1
” wavelengths (transmitter set), and a receiver for receiving a set of “n
2
” wavelengths (receiver set), the transmitter and receiver sets are misarranged so as to differ by at least one wavelength; and
the wavelengths of transmitters and receivers at different nodes are arranged so that 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.
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 transmitter at one node and the corresponding receiver at the other node in the pair, and the second wavelength being the same for the receiver at one node and the corresponding transmitter at the other node in the pair.
Conveniently, the total number of the wavelengths used in the network is equal to “n
1
+n
2
”, and the total number of nodes is equal to N=(n
1
+n
2
)!/(n
1
!n
2
!).
The transmitter set and receiver set may have different number of wavelengths, i.e. n
1
≠n
2
, and some or all of the wavelengths of the transmitter set may differ from the wavelengths of the receiver set.
Alternatively, the transmitter set and receiver set may have same number of wavelengths, i.e. n
1
=n
2
=n, and some or all of the wavelengths of the transmitter set differ from the wavelengths the receiver set.
The number “n
1
” of the wavelengths in the transmitter set may be the same for all nodes, or alternatively the number “n
1
” of wavelengths in the transmitter set may vary for different nodes.
According to another aspect of the invention there is provided an optical network, comprising:
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, the set of wavelengths of the transmitter being different from the set of wavelengths of the receiver;
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 the other node, thereby providing a uni-directional, direct connection between the nodes.
Conveniently, wavelengths of transmitters and receivers at different nodes can be arranged so that for any pair of nodes in the network there are at least two common wavelengths, the first and second common wavelengths, the first wavelength 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 in the pair, thereby providing a bi-directional direct connection between the nodes.
Conveniently, the total number of the wavelengths used in the network is equal to “2n”, the total number of nodes is equal to N=(2n)!/(n!n!), and the number of common wavelengths for any pair of nodes is not exceeding “n&minus
Allen Denise S.
Chang Audrey
Donnelly Victoria
Tropic Networks Inc.
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