Asynchronous communication can be non-electronic or electronic. It describes any form of communication that involves a measurable time interval between the sending and receiving of the content of any message.

Asynchronous (Non-electronic) Communication

Asynchronous non-electronic communication is exemplified in letter writing, and the physical movement of messages from one location to another.

Asynchronous Electronic Communication

Asynchronous electronic communication is the sending of data blocks, for example symbols, characters or data packets, at any point in time, using variable time interval separating the transmission of the blocks. The most significant aspect of asynchronous communications is variable bit rate, or that the transmitter and receiver clock generators do not have to be exactly synchronized.. A clock generator is a circuit that produces a timing signal (known as a clock and behaves as such) for use in synchronizing a circuits operation. ...

Physical layer

In asynchronous serial communication at 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 synchronization signal is required. This is sometimes called character oriented communication. Examples are the RS232C serial standard, and MNP2 and V.2 modems and older. Asynchronous serial communication describes an asynchronous transmission protocol in which a start signal is sent prior to each byte, character or code word and a stop signal is sent after each code word. ... This article does not cite any references or sources. ... In computer hardware terminology, word size (word length) is the number of bits that a CPU can process at one time (the word). ... An octet is a group consisting of eight (8) elements, but it has several more specific meanings (usually given by a specific field or application): Music In music, an octet is a musical ensemble consisting of eight musicians. ... This article refers to the unit of binary information. ... There are 95 printable ASCII characters, numbered 32 to 126. ... This article or section is in need of attention from an expert on the subject. ...

The opposite is isochronous or synchronous serial communication, where a separate clock signal is transferred. Example of this is the X.21 electrical interface between modem and computer. Alternatively the clock signal may be retrieved from a self-clocking line code method such as 8B/10B encoding used in Firewire and Manchester code used in Ethernet. The clock signal timing may also be retrieved from a bit synchronization bit pattern in the beginning of large data blocks or data frames, see below. Other examples of synchronous serial communication are modems using MNP3 or V.5 standards or later. Isochronous means having an equal time difference or occurring simultaneously. ... In synchronous digital electronics, such as most computers, a clock signal is a signal used to coordinate the actions of two or more circuits. ... X.21 is a digital signaling interface recommended by ITU-T that includes specifications for DTE/DCE physical interface elements, alignment of call control characters and error checking, elements of the call control phase for circuit switching services, data transfer at up to 2 Mbit/s, and test loops. ... In telecommunications and electronics, a self-clocking signal is one that can be decoded without need for a separate clock signal or other source of synchronization. ... In telecommunication, a line code is a code chosen for use within a communications system for transmission purposes. ... In telecommunications, 8B/10B is a line code that maps 8-bit symbols to 10-bit symbols to achieve DC-balance and bounded disparity, and yet provide enough state changes to allow reasonable clock recovery. ... The 6-pin and 4-pin FireWire Connectors FireWire is Apple Inc. ... In telecommunication, Manchester code (also known as Phase Encoding, or PE) is a form of data communications line code in which each bit of data is signified by at least one voltage level transition. ... Ethernet is a large, diverse family of frame-based computer networking technologies that operates at many speeds for local area networks (LANs). ... In telecommunications, a frame is a packet which has been encoded for transmission over a particular link. ... A modem (from modulate and demodulate) is a device that modulates an analog carrier signal to encode digital information, and also demodulates such a carrier signal to decode the transmitted information. ... This article or section is in need of attention from an expert on the subject. ...

Non-coherent modulation methods do not require a receiver reference clock signal that is phase synchronized with the sender carrier wave. In this case, the asynchronously transferred blocks (see the definition above) are modulation symbols. The opposite is coherent modulation. Phase synchronization is the process by which two or more cyclic signals tend to oscillate with a repeating sequence of relative phase angles. ... This article or section does not adequately cite its references or sources. ...

Data link layer and higher

Asynchronous communication at the data link layer or higher protocol layers is known as statistical multiplexing or packet mode communication, for example asynchronous transfer mode (ATM). In this case the asynchronously transferred blocks are called data packets, for example ATM cells. The opposite is circuit switched communication, which provides constant bit rate, for example ISDN and SONET/SDH. This article does not cite any references or sources. ... Statistical multiplexing is similar to time-division multiplexing (TDM), except that, rather than arbitrarily assigning a time slot to each signal, each signal is assigned a slot according to priority and need. ... Wikipedia does not yet have an article with this exact name. ... Asynchronous Transfer Mode (ATM) is a cell relay, Circuit switching network and data link layer protocol which encodes data traffic into small (53 bytes; 48 bytes of data and 5 bytes of header information) fixed-sized cells. ... In computer networking and telecommunications, packet switching is a communications paradigm in which packets (messages or fragments of messages) are individually routed between nodes, with no previously established communication path. ... In telecommunication, the term circuit switching has the following meanings: 1. ... ISDN is also short for isosorbide dinitrate Integrated Services Digital Network (ISDN) is a type of circuit switched telephone network system, designed to allow digital (as opposed to analog) transmission of voice and data over ordinary telephone copper wires, resulting in better quality and higher speeds, than available with analog... Synchronous optical networking, is a method for communicating digital information using lasers or light-emitting diodes (LEDs) over optical fiber. ...

The packets may be encapsulated in a data frame, with a frame synchronization bit sequence indicating the start of the frame, and sometimes also a bit synchronization bit sequence, typically 01010101, for identification of the bit transition times. Note that at the physical layer, this is considered as synchronous serial communication. Examples of packet mode data link protocols that can be/are transferred using synchronous serial communication are the HDLC, Ethernet, PPP and USB protocols. In telecommunications, a frame is a packet which has been encoded for transmission over a particular link. ... Frame synchronization: While receiving a stream of framed data, frame synchronization is the process by which incoming frame alignment signals, , distinctive bit sequences (a syncword), are identified, , distinguished from data bits, permitting the data bits within the frame to be extracted for decoding or retransmission. ... In telecommunications, a self-synchronizing code is a line code in which the symbol stream formed by a portion of one code word, or by the overlapped portion of any two adjacent code words, is not a valid code word. ... It has been suggested that the section HDLC from the article Measuring_data_throughput be merged into this article or section. ... Ethernet is a large, diverse family of frame-based computer networking technologies that operates at many speeds for local area networks (LANs). ... In computing, the Point-to-Point Protocol, or PPP, is commonly used to establish a direct connection between two nodes. ... Note: USB may also mean upper sideband in radio. ...

Application layer

An asynchronous communication service or application does not require constant bit rate. Examples are file transfer, email and the World Wide Web. An example of the opposite, a synchronous communication service, is realtime streaming media, for example IP telephony, IP-TV and video conferencing. FTP or file transfer protocol is a commonly used protocol for exchanging files over any network that supports the TCP/IP protocol (such as the Internet or an intranet). ... E-mail, or email, is short for electronic mail and is a method of composing, sending, and receiving messages over electronic communication systems. ... WWWs historical logo designed by Robert Cailliau The World Wide Web is a system of interlinked, hypertext documents accessed via the Internet. ... Streaming media is multimedia that is continuously received by, and normally displayed to, the end-user while it is being delivered by the provider. ... IP Telephony, also called Internet telephony, is the technology that makes it possible to have a telephone conversation over the Internet or a dedicated Internet Protocol (IP) network instead of dedicated voice transmission lines. ... It has been suggested that IP Media be merged into this article or section. ... Categories: Wikipedia cleanup | Groupware | Telecommunications stubs ...

See also

• Asynchronous serial communication
• Asynchronous transfer mode (ATM)
• Plesiochronous
• Plesiochronous Digital Hierarchy (PDH)
• Asynchronous system
• Asynchronous circuit
• Asynchrony
• Anisochronous
• Baud rate