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Modified AMI Code
Modified AMI codes are a digital telecommunications technique to maintain system synchronization. Alternate mark inversion (AMI) line codes are modified by deliberate insertion of bipolar violations. There are several types of modified AMI codes, used in various T-carrier and E-carrier systems. Overview The clock rate of an incoming T-carrier is extracted from its bipolar line code. Each signal transition provides an opportunity for the receiver to see the transmitter's clock. The AMI code guarantees that transitions are always present before and after each mark (1 bit), but are missing between adjacent spaces (0 bits). To prevent loss of synchronization when a long string (computer science), string of zeros is present in the payload (computing), payload, deliberate bipolar violations are inserted into the line code, to create a sufficient number of transitions to maintain synchronization; this is a form of run length limited coding. The receive terminal equipment recognizes the bi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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System
A system is a group of interacting or interrelated elements that act according to a set of rules to form a unified whole. A system, surrounded and influenced by its open system (systems theory), environment, is described by its boundaries, structure and purpose and is expressed in its functioning. Systems are the subjects of study of systems theory and other systems sciences. Systems have several common properties and characteristics, including structure, function(s), behavior and interconnectivity. Etymology The term ''system'' comes from the Latin word ''systēma'', in turn from Greek language, Greek ''systēma'': "whole concept made of several parts or members, system", literary "composition"."σύστημα" , Henry George Liddell, Robert Scott, ''A Greek–English Lexicon'', on Pers ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Data
Data ( , ) are a collection of discrete or continuous values that convey information, describing the quantity, quality, fact, statistics, other basic units of meaning, or simply sequences of symbols that may be further interpreted formally. A datum is an individual value in a collection of data. Data are usually organized into structures such as tables that provide additional context and meaning, and may themselves be used as data in larger structures. Data may be used as variables in a computational process. Data may represent abstract ideas or concrete measurements. Data are commonly used in scientific research, economics, and virtually every other form of human organizational activity. Examples of data sets include price indices (such as the consumer price index), unemployment rates, literacy rates, and census data. In this context, data represent the raw facts and figures from which useful information can be extracted. Data are collected using technique ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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MLT-3 Encoding
MLT-3 encoding (Multi-Level Transmit) is a line code (a signaling method used in a telecommunication system for transmission purposes) that uses three voltage levels. An MLT-3 interface emits less electromagnetic interference and requires less bandwidth than most other binary or ternary interfaces that operate at the same bit rate (see PCM for discussion on bandwidth / quantization tradeoffs), such as Manchester code or Alternate Mark Inversion. MLT-3 cycles sequentially through the voltage levels −1, 0, +1, 0. It moves to the next state to transmit a 1 bit, and stays in the same state to transmit a 0 bit. Similar to simple NRZ encoding, MLT-3 has a coding efficiency of 1 bit/baud, however it requires four transitions (baud) to complete a full cycle (from low-to-middle, middle-to-high, high-to-middle, middle-to-low). Thus, the maximum fundamental frequency is reduced to one fourth of the baud rate. This makes signal transmission more amenable to copper wires. The lack of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Hybrid Ternary Code
In telecommunications, the hybrid (H-) ternary line code is a line code that operates on a hybrid principle combining the binary non-return-to-zero-level (NRZL) and the polar return-to-zero (RZ) codes. The H-ternary code has three levels for signal representation; these are positive (+), zero (0), and negative (−). These three levels are represented by three states. The state of the line code could be in any one of these three states. A transition takes place to the next state as a result of a binary input 1 or 0 and the encoder's present output state. The encoding procedure is as follows. # In general, the encoder outputs + level for a binary 1 input and a − level for a binary 0 input. # However, if this would result in the same output level as the previous bit time, a 0 level is output instead. # Initially, the encoder output present state is assumed at 0 level when the first bit arrives at the encoder input. The new line-coding scheme violates the encoding rule of NRZ-L ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Bipolar Encoding
In telecommunication, bipolar encoding is a type of return-to-zero (RZ) line code, where two nonzero values are used, so that the three values are +, −, and zero. Such a signal is called a duobinary signal. Standard bipolar encodings are designed to be DC-balanced, spending equal amounts of time in the + and − states. The reason why bipolar encoding is classified as a return to zero (RZ) is that when a bipolar encoded channel is idle the line is held at a constant "zero" level, and when it is transmitting bits the line is either in a +V or -V state corresponding to the binary bit being transmitted. Thus, the line always returns to the "zero" level to denote optionally a separation of bits or to denote idleness of the line. Alternate mark inversion One kind of bipolar encoding is a paired disparity code, of which the simplest example is alternate mark inversion. In this code, a binary 0 is encoded as zero volts, as in unipolar encoding, whereas a binary 1 is encoded alte ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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DS-3
Digital Signal 3 (DS3 or T3 line) is a digital signal level 3 T-carrier. The data rate for this type of signal is 44.736 Mbit/s (45 Mb). It can transport 28 DS1 level signals within its payload. It can transport 672 DS0 level channels within its payload. Such circuits are the usual kind between telephony carriers, both wired and wireless, and typically by OC1 optical connections. Cabling DS3 interconnect cables must be made with true 75-ohm coaxial cable and connectors. Cables or connectors which are 50 ohms or which significantly deviate from 75 ohms will result in signal reflections which will lower the performance of the connection, possibly to the point of not workingGR-139-CORE ''Generic Requirements for Central Office Coaxial Cable'', defines type 734 and 735 cables for this application. Due to losses, there are differing distance limitations for each type of cable. Type 734 has a larger center conductor and insulator for lower losses for a given distance. The ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Digital Signal 1
Digital Signal 1 (DS1, sometimes DS-1) is a T-carrier signaling scheme devised by Bell Labs. DS1 is the primary digital telephone standard used in the United States, Canada and Japan and is able to transmit up to 24 multiplexed voice and data calls over telephone lines. E-carrier is used in place of T-carrier outside the United States, Canada, Japan, and South Korea. DS1 is the logical bit pattern used over a physical T1 line; in practice, the terms ''DS1'' and ''T1'' are often used interchangeably. Overview T1 refers to the primary digital telephone carrier system used in North America. T1 is one line type of the PCM T-carrier hierarchy. T1 describes the cabling, signal type, and signal regeneration requirements of the carrier system. The signal transmitted on a T1 line, referred to as the DS1 signal, consists of serial bits transmitted at the rate of 1.544 Mbit/s. The type of line code used is called Alternate Mark Inversion (AMI). Digital Signal Designation is the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Primary Rate Interface
The Primary Rate Interface (PRI) is a telecommunications interface standard used on an Integrated Services Digital Network (ISDN) for carrying multiple DS0 voice and data transmissions between the network and a user. PRI is the standard for providing telecommunication services to enterprises and offices. It is based on T-carrier (T1) transmission in the US, Canada, and Japan, while the E-carrier (E1) is common in Europe and Australia. The T1 line consists of 23 bearer (B) channels and one data (D) channel for control purposes, for a total bandwidth of 24x64-kbit/s or 1.544 Mbit/s. The E1 carrier provides 30 B- and one D-channel for a bandwidth of 2.048 Mbit/s. The first timeslot on the E1 is used for synchronization purposes and is not considered to be a B- or D-channel. The D-channel typically uses timeslot 16 on an E1, while it is timeslot 24 for a T1. Fewer active bearer channels, sometimes called user channels, may be used in fractional T1 or E1 services. ISDN ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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ISDN
Integrated Services Digital Network (ISDN) is a set of communication standards for simultaneous digital transmission of voice, video, data, and other network services over the digitalised circuits of the public switched telephone network. Work on the standard began in 1980 at Bell Labs and was formally standardized in 1988 in the CCITT "Red Book". By the time the standard was released, newer networking systems with much greater speeds were available, and ISDN saw relatively little uptake in the wider market. One estimate suggests ISDN use peaked at a worldwide total of 25 million subscribers at a time when 1.3 billion analog lines were in use. ISDN has largely been replaced with digital subscriber line (DSL) systems of much higher performance. Prior to ISDN, the telephone system consisted of digital links like T1/ E1 on the long-distance lines between telephone company offices and analog signals on copper telephone wires to the customers, the " last mile". At the time, t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Slip (telecommunication)
In telecommunications, a slip is a positional displacement in a sequence of transmitted symbols that causes the loss or insertion of one or more symbols. Slips are usually caused by inadequate synchronization of the two clocks controlling the transmission or by poor reception of the signal. References * Federal Standard 1037C Federal Standard 1037C, titled Telecommunications: Glossary of Telecommunication Terms, is a United States Federal Standard issued by the General Services Administration pursuant to the Federal Property and Administrative Services Act of 1949, ... Synchronization Telecommunication theory {{Telecomm-stub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Digital Signal 0
Digital Signal 0 (DS0) is a basic digital signaling rate of 64 kilobits per second (kbit/s), corresponding to the capacity of one analog voice-frequency-equivalent communication channel. The DS0 rate, and its equivalents E0 in the E-carrier system and T0 in the T-carrier system, form the basis for the digital multiplex transmission hierarchy in telecommunications systems used in North America, Europe, Japan, and the rest of the world, for both the early plesiochronous systems such as T-carrier and for modern synchronous systems such as SDH/ SONET. The DS0 rate was introduced to carry a single digitized voice call. For a typical phone call, the audio sound is digitized at an 8 kHz sample rate, or 8000 samples per second, using 8-bit pulse-code modulation for each of the samples. This results in a data rate of 64 kbit/s. Because of its fundamental role in carrying a single phone call, the DS0 rate forms the basis for the digital multiplex transmission hierarchy in telecommunica ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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Robbed-bit Signaling
In communications systems, robbed-bit signaling (RBS) is a scheme to provide maintenance and line signaling services on many T1 digital carrier circuits using channel-associated signaling (CAS). The T1 carrier circuit is a type of dedicated circuit currently employed in North America and Japan. Overview T1 is a protocol for digital transmission over telephone networks. A T1 circuit combines 24 DS0 channels through time-division multiplexing. Data is transmitted in frames, where each frame contains an 8-bit sample of each of the 24 channels, plus one extra framing bit for a total of 193 bits. Each channel carries 8,000 samples per second. The frames are transmitted either in sequences of 12 frames, known as superframes (SF), or sequences of 24 frames, known as extended superframes (ESF). Robbed-bit signaling is a method to provide signaling information alongside data within a superframe. Robbed-bit signaling uses the least-significant bit of every channel in every sixth frame ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |