Optical communications – Multiplex – Optical switching
Reexamination Certificate
2000-05-11
2004-11-16
Sedighian, M. R. (Department: 2633)
Optical communications
Multiplex
Optical switching
C398S049000
Reexamination Certificate
active
06819870
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
The present invention relates generally to optical routing of data packets, and more specifically to a fiber delay line (FDL) optical buffering and routing method and system in an optical routing network.
2. Discussion of the Related Art
One of the major trends in networking in late 1990's has been a relentless growth in demand for bandwidth in both enterprise and service provider networks. Driving the need for more bandwidth is a combination of factors. More users are connecting as the commercial Internet offers a new online experience for consumers. Internet computing applications, including multi-tier distributed databases, interactive multimedia communication, and electronic commerce rely on the network and demand network resources. A new generation of high-speed Internet access is emerging to meet bandwidth demands and further amplify core bandwidth requirements.
At the same time, competitive pressures make it imperative that networking costs be reduced even as the demand for capacity and new services increases. Successful companies are constantly on the lookout for new technologies which can provide a competitive edge and increase their cost effectiveness.
Optical networking has emerged as a solution to the bandwidth crunch. In particular, one new optical technology—Dense Wavelength Division Multiplexing (DWDM)—promises to increase the capacity and performance of existing fiber optic backbones. DWDM offers a capacity upgrade solution with greater scalability and lower cost than available alternatives.
Wavelength Division Multiplexing (WDM) is a technique for increasing the information-carrying capacity of optical fiber by transmitting multiple signals simultaneously at different wavelengths (or “colors”) on the same fiber. In effect, WDM converts a single fiber into multiple “virtual fibers,” each driven independently at different wavelengths. Systems with more than a small number of channels (two or three) are considered Dense WDM (DWDM) systems. Nearly all DWDM systems operate across a range of wavelengths in the 1550 nm low-attenuation window.
A DWDM system generally includes optical transmitters (lasers), an optical multiplexer and demultiplexer, an optical amplifier and optical receivers. DWDM systems use high,resolution, or narrowband, lasers transmitting in the 1550 nm wavelength band.
The optical multiplexer combines the transmit signals at different wavelengths onto a single optical fiber, and the demultiplexer separates the combined signal into its component wavelengths at the receiver. Several technologies are currently used for optical multiplexing and demultiplexing, including thin-film dielectric filters and various types of optical gratings. Some multiplexers are constructed as completely passive devices, meaning they require no electrical input. Passive optical multiplexers behave essentially like very high precision prisms to combine and separate individual colors of the WDM signal. Like prisms, most passive optical devices are reciprocal devices, meaning they function in the same way when the direction of the light is reversed.
Typically the multiplexing and demultiplexing functions are provided by a single device, a WDM multiplexer/demultiplexer. Some multiplexers have the ability to transmit and receive on a single fiber, a capability known as bi-directional transmission.
The optical receiver is responsible for detecting the incoming lightwave signal and converting it to an appropriate electronic signal for processing by the receiving device. Optical receivers are very often wideband devices able to detect light over a relatively wide range of wavelengths from about 1280-1580 nm. This is the reason why some seemingly incompatible devices can actually inter-operate. For instance, directly connecting two otherwise incompatible network interfaces having different transmitter wavelengths is usually not a problem, even though one end may be transmitting at 1310 nm and the other at 1550 nm.
An amplifier is sometimes used to boost an optical signal to compensate for power loss, or attenuation, caused by propagation over long distances. Electronic regeneration of a WDM signal requires a separate regenerator for each wavelength on each fiber. A single optical amplifier, conversely, can simultaneously amplify all the wavelengths on one fiber.
An additional benefit of the optical amplifier is that as a strictly optical device, it is a protocol-and bit rate-independent device. In other words, an optical amplifier operates the same way regardless of the framing or bit rate of the optical signal. This allows a great deal of flexibility in that an optically amplified link can support any combination of protocols (e.g. ATM, SONET, Gigabit Ethernet, PPP) at any bit rate up to a maximum design limit.
Despite the great advances in capacity, flexibility and reliability provided to the internet by the advent of optical routing of data, congestion and data packet loss is still an ongoing problem. An analysis of Internet traffic reveals a fractal or self-similar nature, (i.e., the traffic exhibits variability in all time scales), thus the conclusion is that the internet traffic is far from well behaved and hence congestion and the dropping of data packets are unavoidable. The dropping of a data packet is often the result of blocking, which occurs when two competing packets arrive at an input of the node simultaneously and desire the same output.
Variable length packets produce additional problems, while they can be processed directly they require a routing and scheduling methodology to control buffer occupancy and do not presently provide optimal packet loss rates.
The router includes a scheduling mechanism, an optical switch matrix with control logic capable of executing a method or algorithm, employing optical buffers and a memory for retaining routing information and instructions. It should be noted that there is no random access optical memory at high speeds. Fiber delay line (FDL) optical buffers are used as optical memory in all optical routers. The optical switch matrix and FDL are the building blocks for optical packet switching.
Various techniques have been suggested by the prior art to provide random access memory at high speeds, but have not been successfully implemented. For instance deflection routing, a technique suggested to reduce the probability of blocking, has been analyzed on regular meshed networks such as Manhattan Street (MS) and Shuffle Network (SN) networks, which are suitable for local area networks (LAN) and metropolitan area networks (MAN). The deflection routing technique avoids collisions between packets by deflecting (mis-routing) one of the packets in conflict with another packet in a different direction. If buffers are not available, any mis-routed packets can be temporarily deflected to an undesired link. Thus, deflection routing allows the use of fiber links as optical buffers while maintaining bit-rate transparency.
Queuing management is another technique that has been suggested to reduce the probability of blocking of packets by managing in an intelligent way the injection of packets into the network. If an injection is possible but the packet to be injected is in conflict and the router cannot solve the conflict, the next packet in the queue, with no conflict with the flow-through packets, is selected for injection.
Another technique suggested for conflict reduction is wavelength dimensioning. This technique consists of creating a wavelength over-capacity on the network. For example, this can be achieved if the network uses 16 wavelengths per link and instead of using all of the 16 wavelengths to inject packets, a reduced number of wavelengths are employed. This technique basically reduces the traffic load per wavelength and, therefore, the probability of packet loss at every node. The optical IP routers should be capable of handling both short and long packets efficiently as the IP traffic is bimodal in nature: short packets which are typical of transactional-style f
Ge An
Tamil Lakshman S.
Alcatel
Cary Gray
Leung Christina Y
Sedighian M. R.
Sewell V. Lawrence
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