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Burst Mode Clock And Data Recovery
The passive optical network (PON) uses tree-like network topology. Due to the topology of PON, the transmission modes for downstream (that is, from optical line termination, (OLT) to optical network unit (ONU)) and upstream (that is, from ONU to OLT) are different. For the downstream transmission, the OLT broadcasts optical signal to all the ONUs in continuous mode (CM), that is, the downstream channel always has optical data signal. One given ONU can find which frame in the CM stream is for it by reading the header of the frame. However, in the upstream channel, ONUs can not transmit optical data signal in CM. It is because that all the signals transmitted from the ONUs converge (with attenuation) into one fiber by the power splitter (serving as power coupler), and overlap among themselves if CM is used. To solve this problem, burst mode (BM) transmission is adopted for upstream channel. The given ONU only transmits optical packet when it is allocated a time slot and it needs to tra ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Passive Optical Network
A passive optical network (PON) is a fiber-optic telecommunications technology for delivering broadband network access to end-customers. Its architecture implements a point-to-multipoint topology in which a single optical fiber serves multiple endpoints by using unpowered (''passive'') fiber optic splitters to divide the fiber bandwidth among the endpoints. Passive optical networks are often referred to as the '' last mile'' between an Internet service provider (ISP) and its customers. Components and characteristics A passive optical network consists of an optical line terminal (OLT) at the service provider's central office (hub) and a number of optical network units (ONUs) or optical network terminals (ONTs), near end users. A PON reduces the amount of fiber and central office equipment required compared with point-to-point architectures. A passive optical network is a form of fiber-optic access network. In most cases, downstream signals are broadcast to all premises sharing ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Optical Line Termination
{{unreferenced, date=April 2016 An optical line termination (OLT), also called an optical line terminal, is a device which serves as the service provider endpoint of a passive optical network. It provides two main functions: # to perform conversion between the electrical signals used by the service provider's equipment and the fiber optic signals used by the passive optical network. # to coordinate the multiplexing between the conversion devices on the other end of that network (called either optical network terminals or optical network units). The diagram below depicts an OLT within a fiber-optic network. Features OLTs include the following features: * A downstream frame processing means for receiving and churning an Asynchronous Transfer Mode cell to generate a downstream frame, and converting a parallel data of the downstream frame into a serial data thereof. * A wavelength division multiplexing means for performing an electro/optical conversion of the serial data of the down ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Optical Network Unit
Optics is the branch of physics that studies the behaviour and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behaviour of visible, ultraviolet, and infrared light. Because light is an electromagnetic wave, other forms of electromagnetic radiation such as X-rays, microwaves, and radio waves exhibit similar properties. Most optical phenomena can be accounted for by using the classical electromagnetic description of light. Complete electromagnetic descriptions of light are, however, often difficult to apply in practice. Practical optics is usually done using simplified models. The most common of these, geometric optics, treats light as a collection of rays that travel in straight lines and bend when they pass through or reflect from surfaces. Physical optics is a more comprehensive model of light, which includes wave effects such as diffraction and interference that cannot be acc ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Continuous Transmission Mode
Continuous transmission mode is a telecommunications mode where a good part of the communication transmission links are of the continuous-mode type, in which the signal is present at all times. In more quantitative terms, continuous transmission mode takes place: *at constant bit rate Constant bitrate (CBR) is a term used in telecommunications, relating to the quality of service. Compare with variable bitrate. When referring to codecs, constant bit rate encoding means that the rate at which a codec's output data should be con ..., *when the communication channel is active for times much longer than both: **the time needed to set up the channel itself, and/or **the time needed to transmit any file or record or any other sequence of information bearing bits. Telecommunications techniques {{telecomm-stub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Time Division Multiple Access
Time-division multiple access (TDMA) is a channel access method for shared-medium networks. It allows several users to share the same frequency channel by dividing the signal into different time slots. The users transmit in rapid succession, one after the other, each using its own time slot. This allows multiple stations to share the same transmission medium (e.g. radio frequency channel) while using only a part of its channel capacity. Dynamic TDMA is a TDMA variant that dynamically reserves a variable number of time slots in each frame to variable bit-rate data streams, based on the traffic demand of each data stream. TDMA is used in the digital 2G cellular systems such as Global System for Mobile Communications (GSM), IS-136, Personal Digital Cellular (PDC) and iDEN, and in the Digital Enhanced Cordless Telecommunications (DECT) standard for portable phones. TDMA was first used in satellite communication systems by Western Union in its Westar 3 communications satellite ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Clock Recovery
In serial communication of digital data, clock recovery is the process of extracting timing information from a serial data stream itself, allowing the timing of the data in the stream to be accurately determined without separate clock information. It is widely used in data communications; the similar concept used in analog systems like color television is known as carrier recovery. Basic concept Serial data is normally sent as a series of pulses with well-defined timing constraints. This presents a problem for the receiving side; if their own local clock is not precisely synchronized with the transmitter, they may sample the signal at the wrong time and thereby decode the signal incorrectly. This can be addressed with extremely accurate and stable clocks, like atomic clocks, but these are expensive and complex. More common low-cost clock systems, like quartz oscillators, are accurate enough for this task over short periods of time, but over a period of minutes or hours the drift in ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Injection Locked Oscillator
Injection locking and injection pulling are the frequency effects that can occur when a harmonic oscillator is disturbed by a second oscillator operating at a nearby frequency. When the coupling is strong enough and the frequencies near enough, the second oscillator can capture the first oscillator, causing it to have essentially identical frequency as the second. This is injection locking. When the second oscillator merely disturbs the first but does not capture it, the effect is called injection pulling. Injection locking and pulling effects are observed in numerous types of physical systems, however the terms are most often associated with electronic oscillators or laser resonators. Injection locking has been used in beneficial and clever ways in the design of early television sets and oscilloscopes, allowing the equipment to be synchronized to external signals at a relatively low cost. Injection locking has also been used in high performance frequency doubling circuits. H ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Clock Signal
In electronics and especially synchronous digital circuits, a clock signal (historically also known as ''logic beat'') oscillates between a high and a low state and is used like a metronome to coordinate actions of digital circuits. A clock signal is produced by a clock generator. Although more complex arrangements are used, the most common clock signal is in the form of a square wave with a 50% duty cycle, usually with a fixed, constant frequency. Circuits using the clock signal for synchronization may become active at either the rising edge, falling edge, or, in the case of double data rate, both in the rising and in the falling edges of the clock cycle. Digital circuits Most integrated circuits (ICs) of sufficient complexity use a clock signal in order to synchronize different parts of the circuit, cycling at a rate slower than the worst-case internal propagation delays. In some cases, more than one clock cycle is required to perform a predictable action. As ICs become mo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
