Optical waveguides – With optical coupler
Reexamination Certificate
2001-09-21
2004-04-06
Zarroli, Michael C. (Department: 2839)
Optical waveguides
With optical coupler
C359S199200, C370S395400
Reexamination Certificate
active
06718080
ABSTRACT:
FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not Applicable.
BACKGROUND OF THE INVENTION
This invention relates generally to a method and apparatus for switching and grooming of data units, over a plurality of communications links with a plurality of transmission rates, in a communications network in a timely manner while providing low switching complexity and performance guarantees.
Circuit-switching networks, which are still the main carrier for real-time traffic, are designed for telephony service and cannot be easily enhanced to support multiple services or carry multimedia traffic in their native packet formats. Circuit-switching is based on very accurate clock frequency for byte-by-byte switching. This enables circuit-switching networks to transport data streams at constant rates with a small delay jitter. Finally, the clock accuracy for SONET requires increasingly more accuracy as the lines transmission speed increases.
Packet switching networks handle bursty data more efficiently than circuit switching, due to their statistical multiplexing of the packet streams. However, current packet switches and routers operate asynchronously and provide “best effort” service only, in which end-to-end delay and jitter are neither guaranteed nor bounded. Furthermore, statistical variations of traffic intensity often lead to congestion that results in excessive delays and loss of packets, thereby significantly reducing the fidelity of real-time streams at their points of reception. Finally, current packet switches and routers electronically process the header of each packet to be routed and switched, which requires high processing power and limits the scalability of the packet switching network.
Circuit switches use time for routing. A time period is divided into very small time slices, each containing only one byte. The absolute position of each time slice within each time period determines where that particular byte is routed.
In accordance with some aspects of the present invention, time-based switching/routing supports a more sophisticated and flexible timing than circuit switching. Consequently, time-based switching provides better support of video-based multimedia applications. The time frames used for time-based switching in the present invention has larger time duration than the time slot used in circuit switching—consequently, time-based switching is much simpler than circuit switching. The present invention also supports routing based on control information included in at least one of headers and trailers of selected ones of the time frames, which current circuit switching cannot provide for.
Moreover, the present invention uses Common Time Reference (CTR). The CTR concept is not used in circuit switching. Using CRT has far reaching implications when comparing circuit switching and the current invention. For example, CR ensures deterministic no slip of time frames, while enabling deterministic pipeline forwarding of time frames. This is in contrast to circuit switching, where (1) there are time slot slips, and (2) deterministic pipeline forwarding is not possible.
In U.S. Pat No. 5,418,779 Yemini et al. disclose a switched network architecture that uses time. Time is used in order to determine when a plurality of switches can transmit over a predefined routing tree to one destination. This kind of tree is known as “sink” tree since the destination switch functions as a “sinks” for the transmission from all switches. The time interval in which the plurality of switches transmits to a selected “sink” destination switch is called time band. In different time bands the plurality of switches are transmitting to a different single “sink” destination switch. Network switches change their configuration between time bands in order to build the proper “sink” tree during each time band. The present invention does use neither “sink” trees nor time bands for transmission over “sink” trees.
Yemini's invention may not be realizable in communications networks with end-to-end propagation delays that are not much smaller than the time band durations. In general, in Yemini's invention the end-to-end propagation delays introduce a non-trivial scheduling problem that may or may not have a solution. Furthermore, Yemini's invention does not discuss or specify how to take into consideration the link propagation delays and the end-to-end propagation delays. Consequently, general topology switched network cannot be built the way it is taught by Yemini's et al. invention.
Yemini's invention has another problem, which is congestion, that is the direct result of using “sink” trees. Data units received from different upstream switches contend for a single outgoing link towards the root of the “sink” tree. The present invention does not have any congestion. This is a direct consequence of using in the current invention completely different system operation principles and methods.
For example, in Yemini's et al. patent there is no pipeline forwarding: data units do not proceed in a lock-step fashion through the communications network, as it is the case in the present invention. The lack of pipeline forwarding leads to the above mentioned scheduling and congestion problems. Such problems are due to the fact that incoming time bands of Yemini's invention are not aligned in different input ports of the network's switches. Furthermore, it was not specified what are the temporal relationship of the same and different time bands on different “sink” tree switches when the link propagation delay and the end-to-end propagation delay are not zero. In contrast, time frames in the present invention are aligned with a Common Time Reference (CTR) on every switch.
In optical data communications with a single wavelength a single data stream is transduced into a series of pulses of light carried over an optical fiber. These pulses of light are of a single wavelength. This single wavelength vastly under-utilizes the capacity of the optical fiber, which is capable of carrying a large number of signals each at a unique wavelength. Due to the nature of propagation of light signals, the optical fiber can carry multiple wavelengths simultaneously. The process of carrying multiple discrete signals via separate wavelengths of light on the same optical fiber is known in the art as wavelength division multiplexing (WDM). Many optical components, including, but not limited to, WDM multiplexers, WDM demultiplexers, star couplers, tunable lasers, filters, waveguide grating routers (WGRs) are deployed in optical networks featuring WDM, and consequently used in the embodiments presented in this disclosure. [T. E. Stern and K. Bala, “Multiwavelength Optical Networks: a Layered Approach,” Prentice Hall PTR, Upper Saddle River, N.J., USA, ISBN 020130967X. R. Ramaswami and K. N. Sivarajan, “Optical Networks: a Practical Perspective,” Morgan Kaufmann Publishers, San Francisco, Calif., USA, ISBN 1-55860-445-6. H. J. R. Dutton, “Understanding Optical Communications,” Prentice Hall PTR, Upper Saddle River, N.J., USA, ISBN 0-13-020141-3].
The present invention permits a novel combination of: (1) time-based switching and routing and (2) WDM technology. WDM is including the capabilities for (1) dynamic tunable wavelength transmission, (2) dynamic and static wavelength switching, and (3) tunable wavelength reception.
The increasing demand for communications capacity has led to the deployment of Wavelength Division Multiplexing (WDM), which requires extremely high capacity switches. Lambda or static wavelength switches address this need by switching a whole wavelength from an input optical fiber link to an output optical fiber link without requiring any processing of the transmitted data units. WDM with whole lambda_switching will be deployed in the network's optical core. However, switching of whole lambdas (e.g., lambdas of OC-192) is inefficient and costly for three reasons:
1. N square problem: the number of lambdas needed to accommodate all the possible connections among all access points i
Baldi Mario
Ofek Yoram
Sitrick & Sitrick
Synchrodyne Networks, Inc.
Zarroli Michael C.
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