Optical communication switch node

Optical: systems and elements – Deflection using a moving element – Using a periodically moving element

Reexamination Certificate

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Details

C359S199200, C359S199200

Reexamination Certificate

active

06594050

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention is directed to an optical switch node. In particular, the present invention is directed to a self-routing switching node based on an optical associative memory and noncoherent pattern recognition techniques.
2. Description of Related Art
The increasing demand for high capacity communication links is being driven by data-intensive services on the Internet. For example, high capacity communications transmitted through links include multimedia information, multiparty video conferencing, video-on-demand, telemedicine, and database searching. Digital data transfer rates over commercial point-to-point fiber optic media currently run into the gigabit-per-second range, and will soon surpass the 10 Gb/s rate. While this represents an advance of just a single order of magnitude, the distinction between 1 Gb/s and 10 Gb/s is significant as the data rate for optically transmitted signals is currently overtaking the speed of commercially available electronics technology. Given the demand for multi-Gb/s speeds and the inability of conventional electronic equipment to keep pace with fiber optic transmission speeds, the development of novel Gb/s optoelectronic data processing components constitutes a critical technology area.
ATM Standard
A significant amount of data is currently transmitted using the Asynchronous Transfer Mode (ATM) communications standard. ATM is a self-routing means of sending data over a network. Instead of relying on a single external controller to route data through the entire network from a source to a destination, ATM places a routing header of five bytes onto the front of a packet of data. The basic data unit in the ATM network is called a “cell” that has a fixed size of 53 bytes including a “payload” (the data portion) of 48 bytes and the “header” of 5 bytes. Each node in the network typically has a modest number of inputs and outputs (e.g., between 4 and 100). At each node in the network, the header information is read so that the node can autonomously decide where to send the packet next in the network. By consulting a switch routing table in the node, the packet “finds” its way from its source to its final destination.
ATM technology has its history in the development of broadband ISDN in the 1970s and 1980s. From a technical view, ATM is an evolution of packet switching. Similar to packet switching for data (e.g., X.25, frame relay, transmission control protocol [TCP]/Internet protocol [IP]), ATM integrates the multiplexing and switching functions, and is typically a good match for bursty traffic (in contrast to circuit switching). Additionally, ATM allows communication between devices that operate at different speeds. Unlike packet switching, ATM generally supports high-performance, multimedia networking and has been implemented in a broad range of networking devices including PCs, workstations, server network interface cards, switched-Ethernet and token-ring workgroup hubs, workgroup and campus ATM switches, ATM enterprise network switches, ATM multiplexers, ATM-edge switches, and ATM-backbone switches.
ATM is also a capability that can be offered as an end-user service by service providers (as a basis for tariffed services) or as a networking infrastructure for these and other services. The most basic service building block is the ATM virtual circuit, which is an end-to-end connection that has defined end points and routes, but does not include dedicated bandwidth. Bandwidth is allocated on demand by the network as users have traffic to transmit.
The ATM connection standard organizes different streams of traffic in separate calls, thereby allowing the user to specify the resources required and the network to allocate resources based on these needs. Multiplexing multiple streams of traffic on each physical facility (between the end user and the network or between network switches), combined with the ability to send the streams to many different destinations, results in cost savings through a reduction in the number of interfaces and facilities required to construct a network.
ATM standards define (1) virtual path connections (VPCs), which contain (2) virtual channel connections (VCCs). A virtual channel connection (or virtual circuit) is the basic unit, which carries a single stream of cells, in order, from user to user. A collection of virtual circuits can be bundled together into a virtual path connection. A virtual path connection can be created from end-to-end across an ATM network. In this case, the ATM network does not route cells belonging to a particular virtual circuit. All cells belonging to a particular virtual path are routed the same way through the ATM network, thus resulting in faster recovery in case of major failures.
An ATM network also uses virtual paths internally for the purpose of bundling virtual circuits together between switches. Two ATM switches may have many different virtual channel connections between them, belonging to different users. These can be bundled by the two ATM switches into a virtual path connection that serves the purpose of a virtual trunk between the two switches. The virtual trunk is then handled as a single entity by, perhaps, multiple intermediate virtual path cross connects between the two virtual circuit switches.
Virtual circuits are statically configured as permanent virtual circuits (PVCs) or dynamically controlled via signaling as switched virtual circuits (SVCs). They can also be point-to-point or point-to-multipoint, thus providing a rich set of service capabilities. SVCs are often the preferred mode of operation in a network because they can be dynamically established, thereby minimizing reconfiguration complexity.
Switching
As discussed above, with the development of the ATM standard as the specification for a broadband communication network, the switching requirements of a network in terms of speed and function have increased significantly. In this regard, packet switching is based on the concept of statistical multiplexing onto the digital links, which implies that the use of large and very fast memories is of paramount importance. Even more important than the concept of statistical multiplexing is the fact that packet switching is performed on a packet-by-packet basis and not a connection-by-connection basis as with circuit switching. In circuit switched networks, the control memories of TSIs and TMSs are under the control of a central CPU that changes their configurations as connections are set up and torn down. With packet switching, however, each packet carries its own identifier called a “routing table” that instructs the node where the packets have to be switched (routed). Therefore, a large amount of processing is required in a packet-switched node, and the connecting network of a packet switching node is likely to change its input/output connection pattern with a rate related to the transmission time of a packet. Based on the well-known seven layer protocol architecture of the OSI model, the routing function for classical X.25 low-speed networks belongs to the network layer, whereas the forwarding one is associated with the data link and physical layers.
Optical Switching
Optical space switches are analogic devices that physically route an optical flow from an input to a selected output. Most of the present electronic switches are instead essentially based on the digital cross-points (e.g., based on CMOS, fast access RAM and electronic buffers). The optical switches are in a sense more similar to the earliest electromechanical or semi-electronic implementations of a crossbar network in the space domain than to the modern fully electronic switches operating both in the time and space domains.
Large switching matrices are composed by connecting small switching devices (switching elements) according to various architectures. Photonic space switching matrices are subdivided according to the kind of interconnection optical hardware being used (e.g., free-space, optical fibers or integrated optical waveguides

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