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56kbps
A 56 kbit/s line is a digital connection capable of carrying 56 kilobits per second (kbit/s), or 56,000 bit/s, the data rate of a classical single channel digital telephone line in North America. In many urban areas, which have seen wide deployment of faster, cheaper technologies, 56 kbit/s lines are generally considered to be an obsolete technology. Speed derivation The figure of 56 kbit/s is derived from its implementation using the same digital infrastructure used since the 1960s for digital telephony in the public switched telephone network, which uses a sampling rate of 8,000 Hz for PCM audio with 8-bit audio bit depth to encode analogue signals into a digital stream of 64,000 bit/s. However, in the T-carrier systems used in the US and Canada, a technique called bit-robbing uses, in every sixth frame, the least significant bit for Channel Associated Signaling (CAS). This effectively renders the lowest bit of the 8 speech bits unusable for data transm ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Kilobit
The kilobit is a multiple of the unit bit for digital information or computer storage. The prefix ''kilo-'' (symbol k) is defined in the International System of Units (SI) as a multiplier of 103 (1 thousand), and therefore, :1 kilobit = = 1000 bits. The kilobit has the unit symbol kbit or kb. Using the common byte size of 8 bits, 1 kbit is equal to 125 bytes. The kilobit is commonly used in the expression of data rates of digital communication circuits as kilobits per second (kbit/s or kb/s), or abbreviated as ''kbps'', as in, for example, ''a 56 kbps PSTN circuit'', or ''a 512 kbit/s broadband Internet connection''. The unit symbol kb (lowercase 'b') is typographically similar to the international standard unit symbol for the kilobyte, i.e. kB (upper case 'B'). The International Electrotechnical Commission (IEC) recommends the symbol bit instead of b. The prefix ''kilo-'' is often used in fields of computer science and information technology wit ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
T-carrier
The T-carrier is a member of the series of carrier systems developed by AT&T Bell Laboratories for digital transmission of multiplexed telephone calls. The first version, the Transmission System 1 (T1), was introduced in 1962 in the Bell System, and could transmit up to 24 telephone calls simultaneously over a single transmission line of copper wire. Subsequent specifications carried multiples of the basic T1 (1.544 Mbit/s) data rates, such as T2 (6.312 Mbit/s) with 96 channels, T3 (44.736 Mbit/s) with 672 channels, and others. Although a ''T2'' was defined as part of AT&T's T-carrier system, which defined five levels, T1 through T5, only the T1 and T3 were commonly in use.1999 ad: On the left, in an aisle seat, a man who very much "filled" his airline seat while on the right side of the aisle is a height-challenged man whose shoe toes barely reach the floor Transmission System 1 The T-carrier is a hardware specification for carrying multiple time-division mul ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Telecommunications Standards
Telecommunication is the transmission of information by various types of technologies over wire, radio, optical, or other electromagnetic systems. It has its origin in the desire of humans for communication over a distance greater than that feasible with the human voice, but with a similar scale of expediency; thus, slow systems (such as postal mail) are excluded from the field. The transmission media in telecommunication have evolved through numerous stages of technology, from beacons and other visual signals (such as smoke signals, semaphore telegraphs, signal flags, and optical heliographs), to electrical cable and electromagnetic radiation, including light. Such transmission paths are often divided into communication channels, which afford the advantages of multiplexing multiple concurrent communication sessions. ''Telecommunication'' is often used in its plural form. Other examples of pre-modern long-distance communication included audio messages, such as coded drumbea ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
List Of ITU-T V-series Recommendations
The ITU-T V-Series Recommendations on Data communication over the telephone network specify the protocols that govern approved modem communication standards and interfaces. ''Note:'' the '' bis'' and ''ter'' suffixes are ITU-T standard designators of successive iterations of a standard (''bis'' and ''ter'' are derived from the Latin for "twice" and "thrice"). General standards ''Applies to V.1–V.9'' *V.1 is an ITU-T recommendation, entitled ''Equivalence between binary notation symbols and the significant conditions of a two-condition code.'' *V.2 is an ITU-T recommendation, approved in November 1988, titled ''Power levels for data transmission over telephone lines.'' *V.4 is an ITU-T recommendation, approved in November 1988, titled ''General structure of signals of International Alphabet No. 5 code for character oriented data transmission over public telephone networks.'' *V.5 was an ITU-T recommendation, approved in November 1988, titled ''Standardization of data signall ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Switch56
{{Unreferenced, date=December 2009 Nortel's Switch56 was a networking protocol built on top of the telephone cabling hardware of their Digital Multiplex System and other telephone switches. The name comes from the fact that Switch56 carried 56 kbit/s of data on its 64 kbit/s lines, as opposed to most systems, including ISDN, where the entire 64 kbit/s bandwidth was available for data. The speed was a side effect of Nortel using a 2-wire cable to carry both voice and switching commands, as opposed to other systems where the command data was carried on a separate set of low-speed lines. Switch56 "folded" the two sources of data into one, placing a single bit from the command channel onto the end of every 7 bits of data, similar to the original T-carrier supervision scheme. This data was split out at the "far end" as 56 kbit/s and 8 kbit/s subchannels. Switch56 was built on top of the basic Nortel hardware to allow computers to put data into the existing telephony network. Although slo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Integrated Services Digital Network
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] |
Modem
A modulator-demodulator or modem is a computer hardware device that converts data from a digital format into a format suitable for an analog transmission medium such as telephone or radio. A modem transmits data by Modulation#Digital modulation methods, modulating one or more carrier wave signals to encode digital information, while the receiver Demodulation, demodulates the signal to recreate the original digital information. The goal is to produce a Signal (electronics), signal that can be transmitted easily and decoded reliably. Modems can be used with almost any means of transmitting analog signals, from light-emitting diodes to radio. Early modems were devices that used audible sounds suitable for transmission over traditional telephone systems and leased lines. These generally operated at 110 or 300 bits per second (bit/s), and the connection between devices was normally manual, using an attached telephone handset. By the 1970s, higher speeds of 1,200 and 2,400 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Channel Associated Signaling
Channel-associated signaling (CAS), also known as ''per-trunk signaling'' (PTS), is a form of digital communication signaling. As with most telecommunication signaling methods, it uses routing information to direct the payload of voice or data to its destination. With CAS, this routing information is encoded and transmitted in the same channel as the payload itself. This information can be transmitted in the same band (in-band signaling) or a separate band (out-of-band signaling) to the payload. Call setup will be comparatively slower since signaling channels are shared thus congestion can be faced. CAS potentially results in lower available bandwidth for the payload. For example, in the PSTN the use of out-of-band signaling within a fixed bandwidth reduces a 64 kbit/s DS0 to 56 kbit/s. Because of this, and the inherent security benefits of separating the control lines from the payload, telephone systems introduced since the 1960s rely more on common-channel signaling (CCS). The ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Least Significant Bit
In computing, bit numbering is the convention used to identify the bit positions in a binary number. Bit significance and indexing In computing, the least significant bit (LSB) is the bit position in a binary integer representing the binary 1s place of the integer. Similarly, the most significant bit (MSB) represents the highest-order place of the binary integer. The LSB is sometimes referred to as the ''low-order bit'' or ''right-most bit'', due to the convention in positional notation of writing less significant digits further to the right. The MSB is similarly referred to as the ''high-order bit'' or ''left-most bit''. In both cases, the LSB and MSB correlate directly to the least significant digit and most significant digit of a decimal integer. Bit indexing correlates to the positional notation of the value in base 2. For this reason, bit index is not affected by how the value is stored on the device, such as the value's byte order. Rather, it is a property of the numeri ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Frame (telecommunications)
A frame is a digital data transmission unit in computer networking and telecommunication. In packet switched systems, a frame is a simple container for a single network packet. In other telecommunications systems, a frame is a repeating structure supporting time-division multiplexing. A frame typically includes frame synchronization features consisting of a sequence of bits or symbols that indicate to the receiver the beginning and end of the payload data within the stream of symbols or bits it receives. If a receiver is connected to the system during frame transmission, it ignores the data until it detects a new frame synchronization sequence. Packet switching In the OSI model of computer networking, a frame is the protocol data unit at the data link layer. Frames are the result of the final layer of encapsulation before the data is transmitted over the physical layer. A frame is "the unit of transmission in a link layer protocol, and consists of a link layer header followed by a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bit-robbing
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. Context The T1 circuit is divided into 24 channels, each carrying 8,000 samples per second, each 8 bits long. The Super Frame (SF) consist of 12 frames of 24 channels. The DS1 designation consist of 24 frames called, Extended Super Frame (ESF). In either designation, these channels are multiplexed together and sample at 8000bit/s. In the superframe, ten frames are utilized entirely for voice/data and two are utilized partially for voice. Hence, each of the two partial frames yields bit/s = 56kbit/s for voice data per channel, compared to the bit/s = 64kbit/s per channel in the other frames. Intuitively, 5 out of 6 frames have 8-bit resolution equal to 64kbit/s (8 bits × 8,000 samples pe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Analogue Signal
An analog signal or analogue signal (see spelling differences) is any continuous signal representing some other quantity, i.e., ''analogous'' to another quantity. For example, in an analog audio signal, the instantaneous signal voltage varies continuously with the pressure of the sound waves. In contrast, a digital signal represents the original time-varying quantity as a sampled sequence of quantized values which imposes some bandwidth and dynamic range constraints on the representation. The term ''analog signal'' usually refers to electrical signals; however, mechanical, pneumatic, hydraulic and other systems may also convey or be considered analog signals. Representation An analog signal uses some property of the medium to convey the signal's information. For example, an aneroid barometer uses rotary position as the signal to convey pressure information. In an electrical signal, the voltage, current, or frequency of the signal may be varied to represent the information. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
