|
Negative-acknowledge Character
In data networking, telecommunications, and computer buses, an acknowledgement (ACK) is a signal that is passed between communicating processes, computers, or devices to signify acknowledgment, or receipt of message, as part of a communications protocol. Correspondingly a negative-acknowledgement (NAK or NACK) is a signal that is sent to reject a previously received message or to indicate some kind of error. Acknowledgments and negative acknowledgments inform a sender of the receiver's state so that it can adjust its own state accordingly. Acknowledgment signal types The ASCII code point for ACK is 0x06 (binary 0000 0110). By convention a receiving device sends an ACK to indicate it successfully received a message. ASCII also provides a NAK code point (0x15, binary 0001 0101) which can be used to indicate the receiving device cannot, or will not, comply with the message. Unicode provides visible symbols for these ASCII characters, U+2406 (␆) and U+2415 (␕). ACK and NAK ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Data Networking
A computer network is a collection of communicating computers and other devices, such as printers and smart phones. In order to communicate, the computers and devices must be connected by wired media like copper cables, optical fibers, or by wireless communication. The devices may be connected in a variety of network topologies. In order to communicate over the network, computers use agreed-on rules, called communication protocols, over whatever medium is used. The computer network can include personal computers, Server (computing), servers, networking hardware, or other specialized or general-purpose Host (network), hosts. They are identified by network addresses and may have hostnames. Hostnames serve as memorable labels for the nodes and are rarely changed after initial assignment. Network addresses serve for locating and identifying the nodes by communication protocols such as the Internet Protocol. Computer networks may be classified by many criteria, including the tr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bandwidth-delay Product
In data communications, the bandwidth-delay product is the product of a data link's capacity (in bits per second) and its round-trip delay time (in seconds). The result, an amount of data measured in bits (or bytes), is equivalent to the maximum amount of data on the network circuit at any given time, i.e., data that has been transmitted but not yet acknowledged. The bandwidth-delay product was originally proposed as a rule of thumb for sizing router buffers in conjunction with congestion avoidance algorithm random early detection (RED). A network with a large bandwidth-delay product is commonly known as a long fat network (LFN). As defined in , a network is considered an LFN if its bandwidth-delay product is significantly larger than 105 bits (12,500 bytes). Details Ultra-high speed local area networks (LANs) may fall into this category, where protocol tuning is critical for achieving peak throughput, on account of their extremely high bandwidth, even though their delay is no ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
User Datagram Protocol
In computer networking, the User Datagram Protocol (UDP) is one of the core communication protocols of the Internet protocol suite used to send messages (transported as datagrams in Network packet, packets) to other hosts on an Internet Protocol (IP) network. Within an IP network, UDP does not require prior communication to set up communication channels or data paths. UDP is a connectionless protocol, meaning that messages are sent without negotiating a connection and that UDP does not keep track of what it has sent. UDP provides checksums for data integrity, and port numbers for addressing different functions at the source and destination of the datagram. It has no Handshake (computing), handshaking dialogues and thus exposes the user's program to any Reliability (computer networking), unreliability of the underlying network; there is no guarantee of delivery, ordering, or duplicate protection. If error-correction facilities are needed at the network interface level, an applica ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
RC-5
The RC-5 protocol was developed by Philips in the early 1980s as a semi-proprietary consumer IR (infrared) remote control communication protocol for consumer electronics. It was subsequently adopted by most European manufacturers, as well as by many US manufacturers of specialty audio and video equipment. The other main protocol relevant to consumer electronics is the NEC protocol, which is largely used by Japanese manufacturers. The RC-5 protocol, when properly implemented, has the advantage that any CD handset (for example) may be used to control any compatible brand of CD player. By comparison, the NEC protocol assigns each brand its own unique header(s) after which may follow any desired command set; this confers the advantage that there cannot be any interference between remote handsets for pieces of equipment made by different manufacturers. Protocol details The basics of the protocol are well known. The handset contains a keypad and a transmitter integrated circuit (IC) d ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Retransmission (data Networks)
Retransmission, essentially identical with automatic repeat request (ARQ), is the resending of packets which have been either damaged or lost. Retransmission is one of the basic mechanisms used by protocols operating over a packet switched computer network to provide reliable communication (such as that provided by a reliable byte stream, for example TCP). Such networks are usually "unreliable", meaning they offer no guarantees that they will not delay, damage, or lose packets, or deliver them out of order. Protocols which provide reliable communication over such networks use a combination of acknowledgments (i.e., an explicit receipt from the destination of the data), retransmission of missing or damaged packets (usually initiated by a time-out), and checksums to provide that reliability. Acknowledgment There are several forms of acknowledgement which can be used alone or together in networking protocols: * Positive Acknowledgement: the receiver explicitly notifies the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Frame (networking)
A frame is a digital data transmission unit in computer networking and telecommunications. 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 follo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Underrun
In computing, buffer underrun or buffer underflow is a state occurring when a buffer used for communicating between two devices or processes is fed with data at a lower speed than the data is being read from it. This requires the program reading from the buffer to pause its processing while the buffer refills. Having to deal with such situations can cause undesired and sometimes serious side effects because the data being buffered is often not suited for stop-start access of this kind. In terms of concurrent programming, a buffer underrun can be considered a form of resource starvation. The term as defined above is distinct from buffer overflow, a condition where a portion of memory forms a buffer of a fixed size yet is filled with more than that amount of data, thus overwriting memory locations outside of the allocated chunk. However, buffer underrun and underflow are also sometimes used to mean buffer underwrite, where a program is tricked into writing data into memory loca ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Automatic Repeat Request
Automatic repeat request (ARQ), also known as automatic repeat query, is an error-control method for data transmission that uses acknowledgements (messages sent by the receiver indicating that it has correctly received a message) and timeouts (specified periods of time allowed to elapse before an acknowledgment is to be received) If the sender does not receive an acknowledgment before the timeout, it re-transmits the message until it receives an acknowledgment or exceeds a predefined number of retransmissions. ARQ is used to achieve reliable data transmission over an unreliable communication channel. ARQ is appropriate if the communication channel has varying or unknown capacity. Variations of ARQ protocols include Stop-and-wait ARQ, Go-Back-N ARQ, and Selective Repeat ARQ. All three protocols usually use some form of sliding window protocol to help the sender determine which (if any) packets need to be retransmitted. These protocols reside in the data link or tra ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Energy-Efficient Ethernet
In computer networking, Energy-Efficient Ethernet (EEE) is a set of enhancements to twisted-pair, twinaxial, backplane, and optical fiber Ethernet physical-layer variants that reduce power consumption during periods of low data activity. The intention is to reduce power consumption by at least half, while retaining full compatibility with existing equipment. The Institute of Electrical and Electronics Engineers (IEEE), through the IEEE 802.3az task force, developed the standard. The first study group had its call for interest in November 2006, and the official standards task force was authorized in May 2007. The IEEE ratified the final standard in September 2010. Some companies introduced technology to reduce the power required for Ethernet before the standard was ratified, using the name Green Ethernet. Some energy-efficient switch integrated circuits were developed before the IEEE 802.3az Energy-Efficient Ethernet standard was finalized. Potential savings In 2005, al ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Binary Synchronous Communications
Binary Synchronous Communication (BSC or Bisync) is an IBM character-oriented, half-duplex link protocol, announced in 1967 after the introduction of System/360. It replaced the synchronous transmit-receive (STR) protocol used with second generation computers. The intent was that common link management rules could be used with three different character encodings for messages. Six-bit Transcode looked backward to older systems; USASCII with 128 characters and EBCDIC with 256 characters looked forward. Transcode disappeared very quickly but the EBCDIC and USASCII dialects of Bisync continued in use. At one time Bisync was the most widely used communications protocol and is still in limited use in 2013. Framing Bisync differs from protocols that succeeded it in the complexity of message framing. Later protocols use a single framing scheme for all messages sent by the protocol. HDLC, Digital Data Communications Message Protocol (DDCMP), Point-to-Point Protocol (PPP), etc. e ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Header (computing)
In information technology, header is supplemental data placed at the beginning of a block of data being stored or transmitted. In data transmission, the data following the header is sometimes called the ''Payload (computing), payload'' or ''HTML element#body, body''. It is vital that header composition follows a clear and unambiguous specification or format, to allow for parsing. Examples * E-mail header: The text (body) is preceded by header lines indicating sender, recipient, subject, sending time stamp, receiving time stamps of all intermediate and the final mail transfer agents, and much more. * Similar headers are used in Usenet (NNTP) messages, and HTTP headers. * In a data packet sent via the Internet, the data (payload) are preceded by header information such as the sender's and the recipient's IP addresses, the Communications protocol, protocol governing the format of the payload and several other formats. The header's format is specified in the Internet Protocol, see IP h ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
