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Digital Data Communications Message Protocol
Digital Data Communications Message Protocol (DDCMP) is a byte-oriented communications protocol devised by Digital Equipment Corporation in 1974 to allow communication over point-to-point network links for the company's DECnet Phase I network protocol suite. The protocol uses full or half duplex synchronous Synchronization is the coordination of events to operate a system in unison. For example, the conductor of an orchestra keeps the orchestra synchronized or ''in time''. Systems that operate with all parts in synchrony are said to be synchrono ... and asynchronous links and allowed errors introduced in transmission to be detected and corrected. It was retained and extended for later versions of the DECnet protocol suite. DDCMP has been described as the "most popular and pervasive of the commercial byte-count data link protocols". See also * DEX References Overview of the protocolProtocol specification(courtesy of DEC) ;Notes Network protocols {{compu-netw ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Byte-oriented Protocol
Byte-oriented framing protocol is "a communications protocol in which full bytes are used as control codes. Also known as character-oriented protocol." For example UART communication is byte-oriented. The term "character-oriented" is deprecated, since the notion of character has changed. An ASCII character fits to one byte (octet) in terms of the amount of information. With the internationalization of computer software, wide characters became necessary, to handle texts in different languages. In particular, Unicode characters (or strictly speaking code points) can be 1, 2, 3 or 4 bytes in UTF-8, and other encodings of Unicode use two or four bytes per code point. See also * Bit-oriented protocol A bit-oriented protocol is a communications protocol that sees the transmitted data as an ''opaque'' stream of bits with no semantics, or meaning. Control codes are defined in terms of bit sequences instead of characters. Bit oriented protocol ca ... References Data transmission [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Communications Protocol
A communication protocol is a system of rules that allows two or more entities of a communications system to transmit information via any kind of variation of a physical quantity. The protocol defines the rules, syntax, semantics and synchronization of communication and possible error recovery methods. Protocols may be implemented by hardware, software, or a combination of both. Communicating systems use well-defined formats for exchanging various messages. Each message has an exact meaning intended to elicit a response from a range of possible responses pre-determined for that particular situation. The specified behavior is typically independent of how it is to be implemented. Communication protocols have to be agreed upon by the parties involved. To reach an agreement, a protocol may be developed into a technical standard. A programming language describes the same for computations, so there is a close analogy between protocols and programming languages: ''protocols ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Digital Equipment Corporation
Digital Equipment Corporation (DEC ), using the trademark Digital, was a major American company in the computer industry from the 1960s to the 1990s. The company was co-founded by Ken Olsen and Harlan Anderson in 1957. Olsen was president until forced to resign in 1992, after the company had gone into precipitous decline. The company produced many different product lines over its history. It is best known for the work in the minicomputer market starting in the mid-1960s. The company produced a series of machines known as the PDP line, with the PDP-8 and PDP-11 being among the most successful minis in history. Their success was only surpassed by another DEC product, the late-1970s VAX "supermini" systems that were designed to replace the PDP-11. Although a number of competitors had successfully competed with Digital through the 1970s, the VAX cemented the company's place as a leading vendor in the computer space. As microcomputers improved in the late 1980s, especially ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Network Topology
Network topology is the arrangement of the elements ( links, nodes, etc.) of a communication network. Network topology can be used to define or describe the arrangement of various types of telecommunication networks, including command and control radio networks, industrial fieldbusses and computer networks. Network topology is the topological structure of a network and may be depicted physically or logically. It is an application of graph theory wherein communicating devices are modeled as nodes and the connections between the devices are modeled as links or lines between the nodes. Physical topology is the placement of the various components of a network (e.g., device location and cable installation), while logical topology illustrates how data flows within a network. Distances between nodes, physical interconnections, transmission rates, or signal types may differ between two different networks, yet their logical topologies may be identical. A network’s physical topology ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
DECnet
DECnet is a suite of network protocols created by Digital Equipment Corporation. Originally released in 1975 in order to connect two PDP-11 minicomputers, it evolved into one of the first peer-to-peer network architectures, thus transforming DEC into a networking powerhouse in the 1980s. Initially built with three layers, it later (1982) evolved into a seven-layer OSI-compliant networking protocol. DECnet was built right into the DEC flagship operating system OpenVMS since its inception. Later Digital ported it to Ultrix, as well as Apple Macintosh and IBM PC running variants of DOS and Microsoft Windows under the name DEC Pathworks, allowing these systems to connect to DECnet networks of VAX machines as terminal nodes. While the DECnet protocols were designed entirely by Digital Equipment Corporation, DECnet Phase II (and later) were open standards with published specifications, and several implementations were developed outside DEC, including ones for FreeBSD and Lin ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Duplex (telecommunications)
A duplex communication system is a point-to-point system composed of two or more connected parties or devices that can communicate with one another in both directions. Duplex systems are employed in many communications networks, either to allow for simultaneous communication in both directions between two connected parties or to provide a reverse path for the monitoring and remote adjustment of equipment in the field. There are two types of duplex communication systems: full-duplex (FDX) and half-duplex (HDX). In a full-duplex system, both parties can communicate with each other simultaneously. An example of a full-duplex device is plain old telephone service; the parties at both ends of a call can speak and be heard by the other party simultaneously. The earphone reproduces the speech of the remote party as the microphone transmits the speech of the local party. There is a two-way communication channel between them, or more strictly speaking, there are two communication chann ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Synchronization
Synchronization is the coordination of events to operate a system in unison. For example, the conductor of an orchestra keeps the orchestra synchronized or ''in time''. Systems that operate with all parts in synchrony are said to be synchronous or ''in sync''—and those that are not are '' asynchronous''. Today, time synchronization can occur between systems around the world through satellite navigation signals and other time and frequency transfer techniques. Navigation and railways Time-keeping and synchronization of clocks is a critical problem in long-distance ocean navigation. Before radio navigation and satellite-based navigation, navigators required accurate time in conjunction with astronomical observations to determine how far east or west their vessel traveled. The invention of an accurate marine chronometer revolutionized marine navigation. By the end of the 19th century, important ports provided time signals in the form of a signal gun, flag, or dropping ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Asynchronous Communication
In telecommunications, asynchronous communication is transmission of data, generally without the use of an external clock signal, where data can be transmitted intermittently rather than in a steady stream. Any timing required to recover data from the communication symbols is encoded within the symbols. The most significant aspect of asynchronous communications is that data is not transmitted at regular intervals, thus making possible variable bit rate, and that the transmitter and receiver clock generators do not have to be exactly synchronized all the time. In asynchronous transmission, data is sent one byte at a time and each byte is preceded by start and stop bits. Physical layer In asynchronous serial communication the physical protocol layer, the data blocks are code words of a certain word length, for example octets ( bytes) or ASCII characters, delimited by start bits and stop bits. A variable length space can be inserted between the code words. No bit synchroni ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
DEX (protocol)
DEX (data exchange) is a format for collecting audit and event data from vending machines. DEX was introduced in the late 1980s by bottlers who provided product to vending machines. It was intended to improve auditing of vending machines, simplify inventory management. DEX records cash in/out, product movement and other audit data. The format was adopted as a standard by the National Automatic Merchandising Association The National Automatic Merchandising Association, or NAMA, is the American national trade association of the convenience services industry, including vending, micro markets, office coffee service, and foodservice management. Headquartered in Arling ... Technology Committee after it was already in use by bottlers. It was included in NAMA VDI version 1.0, announced in 2009. [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
