This invention relates to a method and apparatus for embedding transparent action and addressing information directly onto optical data packets for optical transmission. More particularly, the invention relates to an overlay encoding scheme, which is carried on other optical data packets in WDM type transmission channels to produce a parallel data word or a serial header code which steers the data packets.
The use of digital modulation to transmit large amounts of data such as audio, video, voice, graphical and other media has created the need for a reliable and rapid data carrier means. Large amounts of information are now transmitted over the Internet, which has proven a cost effective and ubiquitous medium for data exchange. In its inception, the Internet was based on telephonic communications, which were in turn based on wire connections and electrical switching. The great amount of digital data used by multi-media has required the use of higher capability and higher speed transmission media. Fiber optic cable has proven to be an ideal backbone for the Internet because it has a large bandwidth and may carry much more data than wire cable. The theoretical capacity of a single optical fiber is vast, on the order of 25 Terahertz (1,000 Gigahertz=1 Terahertz). Today, optical fiber capacity is nearing this Terahertz range driven by unprecedented growth in the Internet that is doubling every 10 months.
The Internet uses an address protocol which requires data to be assigned addresses and divided into different packets. The data packets are then routed through the communications network to a receiving medium which has the assigned address destination. Such data transmission may take place over thousands of miles and requires numerous devices, termed routers, which function to route data traffic to the correct destination according to its addresses.
Currently the telephone communications network has an optical layer with a backbone network of high speed fiber optic cables. The optical layer is a conglomeration of numerous data signals carried long distances by cables arranged in ring and mesh topologies. The optical layer interfaces with an electronic layer of local inputs and outputs of digital information. The electronic layer uses digital switches and electronic add/drop multiplexers to route electronic signals converted from optical signals or to convert electrical signals to optical signals.
The high end of the optical spectrum standard for fiber optics is currently OC-192 , which allows data bit rates of 10 gigabits per second per channel. The OC or Optical Carrier standards are incremental increases in data rates relative to OC-1 at 51.84 Mbits/sec. The current levels of OC-1, OC-3, OC-12, OC-48 and OC-192 are specifically at 51.84 Mbits/sec, 155.52 Mbits/sec, 622.08 Mbits/sec, 2.48832 Gbits/sec, and 9.95328 Gbits/sec (or 10 Gbits/sec for simplicity). Previously, data had been transmitted through fiber optical cable using time division multiplexing (xe2x80x9cTDMxe2x80x9d) which sends signals representing data divided by slices of time. Thus, a single optical fiber could carry only one data signal at a time. In order to increase the rate at which data was transmitted, additional fibers were added or circuitry was installed to increase the speed of data transmission. Although light signals over fiber optic cable degrade less than electronic signals over wire cables, a series of repeaters (devices which read the incoming TDM signals and replicate them for further transmission) are necessary to maintain the signal at approximately 40 km increments.
In order to increase the capability or bandwidth of fiber optic without the attendant increase in data rates, circuitry or cables, wavelength multiplexing has been developed. This method encodes data signals in different wavelengths or WDM channels and simultaneously transmits these wavelengths (colors) through a single strand of fiber optic cable. Thus, a single optical fiber can hold in excess of 200 wavelengths in multi-channel systems such as DWDM (Dense Wavelength Division Multiplexing) or HDWDM (high density WDM). Typically, WDM covers 40 or less wavelength channels while DWDM reaches to 120 channels followed by even greater channel counts for HDWDM. In these schemes, each wavelength is independent and acts as one optical channel. One advantage of DWDM is the ability to carry more data without going to higher bit rates. This reduces many of the long-haul and signal-to-noise complexities faced by the TDM method while keeping incremental cost under control.
DWDM light transmission is typically generated by a laser diode array having one laser for each wavelength. At the receiving end, high-speed detectors such as PiN (P-Intrinsic-N), APD (Avalanche-Photo-Detector), or MSM (metal-silicon-metal) elements are matched to each DWDM wavelength/channel used. To ensure that all light wavelengths will propagate equally well in one fiber, the wavelengths must be spaced very close together to fit inside a given transmission window inherent to that fiber. For long range applications, single mode fibers are used to propagate only one wave mode. Single mode transmission offers the lowest losses and maximizes the long haul distances possible between repeater or regeneration sites. The single mode fiber transmission window is between 1528 nm to 1561 nm (C-band) and is typically referred to as the 1550 window. The large amount of data traveling over an Internet backbone route requires efficient transmission protocols that insure the reliability of the data at the greatest possible speed. Thus, an individual DWDM optical cable may carry numerous light signals on many different wavelength channels.
The fiber optic medium is robust and is naturally free from electrical and electromagnetic interference. However, even with the high data bandwidth enjoyed by fiber optics, increasing amounts of information require methods of more efficient data transmission that address the needs for data buffering and data grooming.
Previous generation optical fiber systems increased bandwidth by increasing data rates. This required repeaters units to amplify the signals every 40 km or less. DWDM with multiple channels permit operation at slower rates while increasing bandwidth. This allows repeater stations to be spaced further apart to 120 km distances. At each repeater station, optical signals are reconditioned by being reshaped, retimed and reamplified (xe2x80x9c3-R restorationxe2x80x9d). With DWDM, the cost of increased bandwidth is much lower than traditional TDM solutions. New wavelengths may be added at low incremental costs to match demand. Thus, DWDM allows transmission of greater data, is scalable and takes advantage of already deployed fiber.
The packets of individual optic signals must be eventually channeled to their proper destination address resulting in splitting the DWDM channel into individual data packets by demultiplexing. Routers are used to demultiplex, sort (data grooming) and then recombine optical packets into new light signals until the packets reach their intended destinations. This complex process is accomplished by first converting the light signals into electrical signals and then steering them accordingly in the electrical domain followed by a final conversion back to the light domain. Once back to light form, the signal is again launched into another fiber as the packet continues its journey. This conversion process is known as the OEO (optical-electrical-optical) and is repeated many times until a packet finally reaches its destination. High capacity data buffering plays a very important role in the OEO function since the optical signals must be held while electronic processing occurs. Conversion of data packets from one channel to another or changing the relative position of one data set to another requires sophisticated First In-First Out buffers (FIFOs) and very fast memories.
The routers may also have the ability to perform 3-R regeneration and to perform add-drop functions. At these router locations, new light data can also be injected (added) into the optical backbone or light data may be dropped at that node to service customers located in that area. In other parts of the optical network, optical add-drops and 3-R regeneration are performed as stand alone functions.
Current optical routers are heavily dependent on the OEO function. Unfortunately, this conversion adds significant delays and makes true optical packet steering extremely difficult. In most cases, steering the light signal must be accomplished in under 5 nsec to have any reasonable chance for preserving optical efficiency. OEO functions, therefore, must be minimized or eliminated in a true optical management system. In order to ensure that no optical data is lost, light buffering must be employed. Light buffering is a technique where a light packet enters a long loop of fiber to manufacture a time delay (in the nanosecond to microsecond range) to enable a supporting electrical function (such as a microcomputer) time to perform its tasks. The fiber delay loop used may extend to kilometers in length depending on the delay time required. Such optical buffering techniques are limited and do not increase system performance or replace wavelength management functions performed in the electrical domain. Thus, present systems such as the SONET (synchronous optical network) infrastructure are hybrid optical systems that must depend heavily on multiple OEO conversions to route data packets between a source and a destination.
Another delay in transmitting data using wavelength division multiplexing is the amount of time it takes for each router to correctly read the address of the packets of data. Since the DWDM method uses separate wavelength channels, each channel must be read separately in order to determine the address and thus the destination of the data. This delay is the principal bottleneck for efficient DWDM deployment and true optical packet routing.
Finally, the present methods of sending address or control codes commensurate with raw data rate speeds are inefficient and must be executed in the electrical domain. With data rates upwards of terabits present in a DWDM fiber, conventional detection techniques for address coding are forced to read all the signals in real time just to isolate a few bits of control code. This requires a terabit level engine for each fiber to perform basic signal and address code functions, rendering the approach impractical. Even if processing can be managed, the need to offload single sensor outputs with associated amplification creates many timing and phasing issues at gigabit rates when signal waveforms must be preserved to picosecond accuracies for reliable operation. These problems prevent current technology from effectively taking advantage of the power offered by light to light direct comparisons.
Thus, a need exists for a rapid light to light detector which transparently detects packet header and overlay data contents. There is a further need for an optical code detector which does not require signal conversion into an electrical medium. There is a further need for a method of addressing optical channels for rapid routing of optical signals on the fly. There is also a need for a device which allows different data signals to be added and dropped optically to efficiently route data signals. There is also a need for an optical buffer that can directly groom and route optical signals based on the steering data present in packet headers and overlay codes.
These needs may be addressed by the present invention which is embodied in an optical data decoder for detecting a data sequence from an optical signal carrying data signals at different light wavelengths and a marker wavelength signal multiplexed as a single signal. The data sequence is encoded on the different light wavelengths by modifying selected data signals. The optical data decoder has a plurality of optical detector units each corresponding to each different light wavelength carrying a data signal. Each of the optical detector units have a photo detector having an anode and a cathode, the photo detector in exposure to the data signal. A reference detector has an anode and a cathode. The anode of the reference detector is coupled to the cathode of the photo detector, and the cathode of the reference detector is coupled to the anode of the photo detector. The reference detector is exposed to the marker wavelength signal.
The invention may also be embodied in a method for transmitting a data sequence in an optical data transmission system having multiple data signals modulated on different selected light wavelengths. The multiple data signals are multiplexed into a single optical signal. A marker signal is provided which is modulated on a selected reference wavelength. Selected data signals are modified to encode the data sequence to correspond to a single selected data signal.
The invention may also be embodied in an optical router for routing data signals from an optical fiber to a selected destination. The optical fiber carries a single optical signal which has multiplexed data signals modulated at different light wavelengths, a marker wavelength signal, and a data sequence corresponding to a selected data signal encoded on the different light wavelengths of the data signals. The router has an optical buffer which has an optical data detector coupled to the optical fiber. The optical data detector has detector units which each sense light at a different wavelength and sense the marker wavelength signal. The detector produces an output indicative of the presence of a selected data sequence in the data sequence. A fiber optic delay loop holds the optical signal. A data output channel is provided. An optical switch is coupled to the optical fiber and the data channel. The fiber optic delay loop has a length sufficient to delay the optical signal for a time interval sufficient to detect the selected data code and activate the optical switch. A processor unit is coupled to the buffer and the optical switch. The processor unit reads the output of the detector of the buffer and controls the optical switch to divert the light signal to the data channel on detection of the selected data sequence.
The invention also may be embodied in an optical code detector for detecting an information code from an optical signal carried on an optic fiber. The optical signal has a header portion containing the information code encoded with different levels of light and a data portion. The optical code decoder has a plurality of optical storage devices coupled to the optical fiber. Each optical code detector stores a segment of the information code and emitting the light encoding the segment. An optical detector unit is provided for each segment of the information code and are each exposed to the segment light. The optical detector units each have a first photo detector having an anode and a cathode. A second photo detector has an anode and a cathode. The anode of the second photo detector is coupled to the cathode of the first photo detector, and the cathode of the second photo detector is coupled to the anode of the first photo detector. A light emitter array is optically coupled to the optical detector units.
The invention may also be embodied in a method for decoding information code in an optical data transmission system having a light modulated data signal having a data portion and a header containing the information code. The light signal is carried on a fiber optic cable. The information code is separated in the header into discrete light segments. The discrete light segments is determined to a predetermined pattern. A match is indicated when the predetermined pattern is the same as the discrete light segment.
The invention may also be embodied in an optical buffer for storing data signals from an optical fiber for further downstream processing. The optical fiber carries data signals at different light wavelengths and a marker wavelength signal multiplexed as a single signal, and a data sequence encoded on the different light wavelengths by modifying selected data signals. The optical buffer has an optical data detector optically coupled to the optical fiber. The optical data detector has detector units which optically sense the data sequence. The detector produces an output indicative of the presence of a selected data sequence code. A fiber optic output is provided. An optical switch has an input coupled to the optical fiber and a first output coupled to the fiber optic output, and a second output. The optical switch permits the optical signal to be routed via the first output to the fiber optic output or to the second output. A buffer fiber optical loop is coupled to the detector. The second output of the optical switch is coupled to the fiber optical loop through the second output. A processor unit is coupled to the detector and the optical switch. The processor unit reads the output of the detector and controls the optical switch to divert the optical signal to the buffer fiber loop.
It is to be understood that both the foregoing general description and the following detailed description are not limiting but are intended to provide further explanation of the invention claimed. The accompanying drawings, which are incorporated in and constitute part of this specification, are included to illustrate and provide a further understanding of the method and system of the invention. Together with the description, the drawings serve to explain the principles of the invention.