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LAPB
Link Access Procedure, Balanced (LAPB) implements the data link layer as defined in the X.25 protocol suite. LAPB is a bit-oriented protocol derived from HDLC that ensures that frames are error free and in the correct sequence. LAPB is specified in ITU-T Recommendation X.25 and ISO/IEC 7776. It implements the connection-mode data link service in the OSI Reference Model as defined by ITU-T Recommendation X.222. LAPB is used to manage communication and packet framing between data terminal equipment (DTE) and the data circuit-terminating equipment (DCE) devices in the X.25 protocol stack. LAPB is essentially HDLC in Asynchronous Balanced Mode (ABM). LAPB sessions can be established by either the DTE or DCE. The station initiating the call is determined to be the primary, and the responding station is the secondary. Protocol structure Frame types *I-Frames (Information frames): Carries upper-layer information and some control information. I-frame functions include sequencing, flow ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Logical Link Control
In the IEEE 802 reference model of computer networking, the logical link control (LLC) data communication protocol layer is the upper sublayer of the data link layer (layer 2) of the seven-layer OSI model. The LLC sublayer acts as an interface between the media access control (MAC) sublayer and the network layer. The LLC sublayer provides multiplexing mechanisms that make it possible for several network protocols (e.g. IP, IPX and DECnet) to coexist within a multipoint network and to be transported over the same network medium. It can also provide flow control and automatic repeat request (ARQ) error management mechanisms. Operation The LLC sublayer is primarily concerned with multiplexing protocols transmitted over the MAC layer (when transmitting) and demultiplexing them (when receiving). It can also provide node-to-node flow control and error management. The flow control and error management capabilities of the LLC sublayer are used by protocols such as the NetBIOS Fram ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
HDLC
High-Level Data Link Control (HDLC) is a bit-oriented code-transparent synchronous data link layer protocol developed by the International Organization for Standardization (ISO). The standard for HDLC is ISO/IEC 13239:2002. HDLC provides both connection-oriented and connectionless service. HDLC can be used for point-to-multipoint connections via the original master-slave modes Normal Response Mode (NRM) and Asynchronous Response Mode (ARM), but they are now rarely used; it is now used almost exclusively to connect one device to another, using ''Asynchronous Balanced Mode'' (ABM). History HDLC is based on IBM's SDLC protocol, which is the layer 2 protocol for IBM's Systems Network Architecture (SNA). It was extended and standardized by the ITU as LAP (Link Access Procedure), while ANSI named their essentially identical version ADCCP. The HDLC specification does not specify the full semantics of the frame fields. This allows other fully compliant standards to be derived fr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
OSI Model
The Open Systems Interconnection model (OSI model) is a conceptual model that 'provides a common basis for the coordination of SOstandards development for the purpose of systems interconnection'. In the OSI reference model, the communications between a computing system are split into seven different abstraction layers: Physical, Data Link, Network, Transport, Session, Presentation, and Application. The model partitions the flow of data in a communication system into seven abstraction layers to describe networked communication from the physical implementation of transmitting bits across a communications medium to the highest-level representation of data of a distributed application. Each intermediate layer serves a class of functionality to the layer above it and is served by the layer below it. Classes of functionality are realized in all software development through all and any standardized communication protocols. Each layer in the OSI model has its own well-defined functi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Asynchronous Balanced Mode
High-Level Data Link Control (HDLC) is a Bit-oriented protocol, bit-oriented code-transparent Synchronous serial communication, synchronous data link layer Communications protocol, protocol developed by the International Organization for Standardization (ISO). The standard for HDLC is ISO/IEC 13239:2002. HDLC provides both Connection-oriented protocol, connection-oriented and Connectionless protocol, connectionless service. HDLC can be used for Point-to-multipoint communication, point-to-multipoint connections via the original master-slave modes Normal Response Mode (NRM) and Asynchronous Response Mode (ARM), but they are now rarely used; it is now used almost exclusively to connect Point-to-point (telecommunications), one device to another, using ''Asynchronous Balanced Mode'' (ABM). History HDLC is based on IBM's Synchronous Data Link Control, SDLC protocol, which is the layer 2 protocol for IBM's Systems Network Architecture (SNA). It was extended and standardized by the Int ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Data Link Layer
The data link layer, or layer 2, is the second layer of the seven-layer OSI model of computer networking. This layer is the protocol layer that transfers data between nodes on a network segment across the physical layer. The data link layer provides the functional and procedural means to transfer data between network entities and may also provide the means to detect and possibly correct errors that can occur in the physical layer. The data link layer is concerned with local delivery of frames between nodes on the same level of the network. Data-link frames, as these protocol data units are called, do not cross the boundaries of a local area network. Inter-network routing and global addressing are higher-layer functions, allowing data-link protocols to focus on local delivery, addressing, and media arbitration. In this way, the data link layer is analogous to a neighborhood traffic cop; it endeavors to arbitrate between parties contending for access to a medium, without con ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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 can transfer data frames regardless of frame contents. It can also be stated as "bit stuffing". Synchronous framing High-Level Data Link Control may work like this: * Each frame begins and ends with a special bit pattern 01111110, called a flag byte. * A bit stuffing technique is used to prevent the receiver from detecting the special flag byte in user data e.g. whenever the sender's data link layer encounters 5 consecutive 1 (one) in the data, it automatically stuffs 0 into the outgoing stream. See also *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 "c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Data Terminal Equipment
Data terminal equipment (DTE) is an end instrument that converts user information into signals or reconverts received signals. These can also be called tail circuits. A DTE device communicates with the data circuit-terminating equipment (DCE). The DTE/DCE classification was introduced by IBM. A DTE is the functional unit of a data station that serves as a data source or a data sink and provides for the data communication control function to be performed in accordance with the link protocol. Usually, the DTE device is the terminal (or a computer emulating a terminal), and the DCE is a modem or another carrier-owned device. The data terminal equipment may be a single piece of equipment or an interconnected subsystem of multiple pieces of equipment that perform all the required functions necessary to permit users to communicate. A user interacts with the DTE (e.g. through a human-machine interface), or the DTE may be the user. Connections Two different types of devices are as ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Data Circuit-terminating Equipment
A data circuit-terminating equipment (DCE) is a device that sits between the data terminal equipment (DTE) and a data transmission circuit. It is also called data communication(s) equipment and data carrier equipment. Usually, the DTE device is the terminal (or computer), and the DCE is a modem. In a ''data station'', the DCE performs functions such as signal conversion, coding, and line clocking and may be a part of the DTE or intermediate equipment. Interfacing equipment may be required to couple the DTE into a transmission circuit or channel and from a transmission circuit or channel into the DTE. Usage Although the terms are most commonly used with RS-232, several data communication standards define different types of interfaces between a DCE and a DTE. The DCE is a device that communicates with a DTE device in these standards. Standards that use this nomenclature include: * Federal Standard 1037C, MIL-STD-188 * RS-232 * Certain ITU-T standards in the V series (notably V.24 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bit Stuffing
In data transmission and telecommunication, bit stuffing (also known—uncommonly—as positive justification) is the insertion of non-information bits into data. Stuffed bits should not be confused with overhead bits. Bit stuffing is used for various purposes, such as for bringing bit streams that do not necessarily have the same or rationally related bit rates up to a common rate, or to fill buffers or frames. The location of the stuffing bits is communicated to the receiving end of the data link, where these extra bits are removed to return the bit streams to their original bit rates or form. Bit stuffing may be used to synchronize several channels before multiplexing or to rate-match two single channels to each other. Another use of bit stuffing is for run length limited coding: to limit the number of consecutive bits of the same value in the data to be transmitted. A bit of the opposite value is inserted after the maximum allowed number of consecutive bits. Since this is ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Network Address
A network address is an identifier for a node or host on a telecommunications network. Network addresses are designed to be unique identifiers across the network, although some networks allow for local, private addresses, or locally administered addresses that may not be unique. Special network addresses are allocated as broadcast or multicast addresses. These too are not unique. In some cases, network hosts may have more than one network address. For example, each network interface controller may be uniquely identified. Further, because protocols are frequently layered, more than one protocol's network address can occur in any particular network interface or node and more than one type of network address may be used in any one network. Network addresses can be flat addresses which contain no information about the node's location in the network (such as a MAC address), or may contain structure or hierarchical information for the routing (such as an IP address). Examples Exam ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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, the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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