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Z-MODEM
ZMODEM is an inline file transfer protocol developed by Chuck Forsberg in 1986, in a project funded by Telenet in order to improve file transfers on their X.25 network. In addition to dramatically improved performance compared to older protocols, ZMODEM offered restartable transfers, auto-start by the sender, an expanded 32-bit CRC, and control character quoting supporting 8-bit clean transfers, allowing it to be used on networks that would not pass control characters. In contrast to most transfer protocols developed for bulletin board systems (BBSs), ZMODEM was not directly based on, nor compatible with, the seminal XMODEM. Many variants of XMODEM had been developed in order to address one or more of its shortcomings, and most remained backward compatible and would successfully complete transfers with "classic" XMODEM implementations. This list includes Forsberg's own YMODEM. ZMODEM eschewed backward compatibility in favor of producing a radically improved protocol. It perfor ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chuck Forsberg
Charles Alton "Chuck" Forsberg (May 6, 1944 – September 24, 2015) developed two data transmission protocols popular in the 1990s, for uploading and downloading files from dial-up bulletin board systems. He received a Dvorak Award for Excellence in Telecommunications in 1992 for developing ZMODEM. He was also the project engineer on the Tektronix 4010-series graphics terminals. The widely adopted ZMODEM uses a sliding window protocol. Rather than wait for positive acknowledgment after each block is sent, it sends blocks in rapid succession and resends unacknowledged blocks later. By avoiding delays due to latency, the bandwidth usable for transmission more closely approached the bandwidth of the underlying link. ZMODEM could also resume interrupted transfers without retransmitting the already-received blocks. In addition to developing the protocol, Forsberg developed software for sending and receiving files using ZMODEM. Forsberg then wrote a version, Zmodem G, which was f ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Latency (engineering)
Latency, from a general point of view, is a time delay between the cause and the effect of some physical change in the system being observed. Lag, as it is known in gaming circles, refers to the latency between the input to a simulation and the visual or auditory response, often occurring because of network delay in online games. Latency is physically a consequence of the limited velocity at which any physical interaction can propagate. The magnitude of this velocity is always less than or equal to the speed of light. Therefore, every physical system with any physical separation (distance) between cause and effect will experience some sort of latency, regardless of the nature of the stimulation at which it has been exposed to. The precise definition of latency depends on the system being observed or the nature of the simulation. In communications, the lower limit of latency is determined by the medium being used to transfer information. In reliable two-way communication syst ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
BBS File Transfer Protocols
BBS may refer to: Ammunition * BBs, BB gun metal bullets * BBs, airsoft gun plastic pellets Computing and gaming * Bulletin board system, a computer server users dial into via dial-up or telnet; precursor to the Internet * BIOS Boot Specification, a firmware specification for the boot process * Blum Blum Shub, a pseudorandom number generator * ''Kingdom Hearts Birth by Sleep'', a Disney-based video game for the PlayStation Portable Organisations United Kingdom * Birmingham Business School (University of Birmingham), a faculty * British Blind Sport, a parasports charity * British Boy Scouts, a national youth association * British Bryological Society, a botanists' learned society United States * BBS Productions, a film company of early 1970s New Hollywood * Badger Boys State, a youth camp held in Wisconsin Elsewhere * BBS Kraftfahrzeugtechnik, a German wheel manufacturer * Bahrain Bayan School * Bangladesh Bureau of Statistics * Baton Broadcast System, Canada * Bhutan Broadcas ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Run-length Encoding
Run-length encoding (RLE) is a form of lossless data compression in which ''runs'' of data (sequences in which the same data value occurs in many consecutive data elements) are stored as a single data value and count, rather than as the original run. This is most efficient on data that contains many such runs, for example, simple graphic images such as icons, line drawings, Conway's Game of Life, and animations. For files that do not have many runs, RLE could increase the file size. RLE may also be used to refer to an early graphics file format supported by CompuServe for compressing black and white images, but was widely supplanted by their later Graphics Interchange Format (GIF). RLE also refers to a little-used image format in Windows 3.x, with the extension rle, which is a run-length encoded bitmap, used to compress the Windows 3.x startup screen. Example Consider a screen containing plain black text on a solid white background. There will be many long runs of white pixel ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Kermit (protocol)
Kermit is a computer file transfer/management protocol and a set of communications software tools primarily used in the early years of personal computing in the 1980s. It provides a consistent approach to file transfer, terminal emulation, script programming, and character set conversion across many different computer hardware and operating system platforms. Technical The Kermit protocol supports text and binary file transfers on both full-duplex and half-duplex 8-bit and 7-bit serial connections in a system- and medium-independent fashion, and is implemented on hundreds of different computer and operating system platforms. On full-duplex connections, a sliding window protocol is used with selective retransmission which provides excellent performance and error recovery characteristics. On 7-bit connections, locking shifts provide efficient transfer of 8-bit data. When properly implemented, as in the Columbia University Kermit Software collection, its authors claim performance i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Synchronet
Synchronet is a multiplatform BBS software package, with current ports for Microsoft Windows, Linux, and BSD variants. Past versions also ran on MS-DOS and OS/2, but support for those platforms were dropped in version 3.0 (circa 2000). History Synchronet was originally written by Rob Swindell ( a.k.a. Digital Man) due to his desire for certain features which WWIV lacked, such as support for multiple simultaneous nodes, batch uploads and bidirectional protocol for file transfer, file transfer. The bulk of the programming for the first version of Synchronet was done during a two-month period in 1991 when Swindell was house-ridden while he recovered from surgery. The software was named for its ability to run synchronously on a network. In July 1991, the author began running his own BBS, Vertrauen, on Synchronet. Initially, he had no intention of releasing Synchronet publicly, but as word of his software spread and he received offers to buy copies of Synchronet, he eventually re ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bulletin Board System
A bulletin board system (BBS), also called computer bulletin board service (CBBS), is a computer server running software that allows users to connect to the system using a terminal program. Once logged in, the user can perform functions such as uploading and downloading software and data, reading news and bulletins, and exchanging messages with other users through public message boards and sometimes via direct chatting. In the early 1980s, message networks such as FidoNet were developed to provide services such as NetMail, which is similar to internet-based email. Many BBSes also offer online games in which users can compete with each other. BBSes with multiple phone lines often provide chat rooms, allowing users to interact with each other. Bulletin board systems were in many ways a precursor to the modern form of the World Wide Web, social networks, and other aspects of the Internet. Low-cost, high-performance asynchronous modems drove the use of online services and BBSes t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
LeechZmodem
LeechModem was a BBS file transfer protocol client. LeechModem was compatible with protocols like XMODEM (and YMODEM), but it would mischievously NAK the last packet and then abort the file transfer. The user had successfully downloaded the file, but the BBS would mistakenly not count the aborted file transfer against the user's download quota. The user would need to know and input the filesize before the transfer so the client would know when to abort. Leech-modem was designed by Sam Brown. Leech ZMODEM was suggested by Sam Brown but written by a long lost friend in Atlanta, GA. Leech ZMODEM was a LeechModem variant that was compatible with the faster ZMODEM streaming file-transfer protocol. Subsequent versions of Leech ZMODEM were authored by Sam Brown. LeechModem was used successfully for 2-3 years by a small group of people centered in the 408 area code and 203 area code. It was not until the LeechModem software was leaked that it was discovered and counter-measures were b ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
US Robotics
U.S. Robotics Corporation, often called USR, is a company that produces USRobotics computer modems and related products. Its initial marketing was aimed at bulletin board systems, where its high-speed HST protocol made FidoNet transfers much faster, and thus less costly. During the 1990s it became a major consumer brand with its Sportster line. The company had a reputation for high quality and support for the latest communications standards as they emerged, notably in its V.Everything line, released in 1996. With the reduced usage of voiceband modems in North America in the early 21st century, USR began branching out into new markets. The company purchased Palm, Inc. for its Pilot PDA, but was itself purchased by 3Com soon after. 3Com spun off USR again in 2000, keeping Palm and returning USR to the now much smaller modem market. After 2004 the company is formally known as USR. USR is now a division of UNICOM Global, and is one of the few providers left in the modem market today. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
PC Pursuit
Telenet was an American commercial packet-switched network which went into service in 1975. It was the first FCC-licensed public data network in the United States. Various commercial and government interests paid monthly fees for dedicated lines connecting their computers and local networks to this backbone network. Free public dialup access to Telenet, for those who wished to access these systems, was provided in hundreds of cities throughout the United States. The original founding company, Telenet Inc., was established by Bolt Beranek and Newman (BBN) and recruited Larry Roberts (former head of the ARPANet) as President of the company, and Barry Wessler. GTE acquired Telenet in 1979. It was later acquired by Sprint and called "Sprintnet". Sprint migrated customers from Telenet to the modern-day Sprintlink IP network, one of many networks composing today's Internet. Telenet had its first offices in downtown Washington, D.C., then moved to McLean, Virginia. It was acquired ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sliding Window
A sliding window protocol is a feature of packet-based data transmission protocols. Sliding window protocols are used where reliable in-order delivery of packets is required, such as in the data link layer (OSI layer 2) as well as in the Transmission Control Protocol (TCP). They are also used to improve efficiency when the channel may include high latency. Packet-based systems are based on the idea of sending a batch of data, the ''packet'', along with additional data that allows the receiver to ensure it was received correctly, perhaps a checksum. The paradigm is similar to a window sliding sideways to allow entry of fresh packets and reject the ones that have already been acknowledged. When the receiver verifies the data, it sends an acknowledgment signal, or "ACK", back to the sender to indicate it can send the next packet. In a simple automatic repeat request protocol (ARQ), the sender stops after every packet and waits for the receiver to ACK. This ensures packets arrive ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Channel Efficiency
Network throughput (or just throughput, when in context) refers to the rate of message delivery over a communication channel, such as Ethernet or packet radio, in a communication network. The data that these messages contain may be delivered over physical or logical links, or through network nodes. Throughput is usually measured in bits per second (bit/s or bps), and sometimes in data packets per second (p/s or pps) or data packets per time slot. The system throughput or aggregate throughput is the sum of the data rates that are delivered to all terminals in a network. Throughput is essentially synonymous to digital bandwidth consumption; it can be determined numerically by applying the queueing theory, where the load in packets per time unit is denoted as the arrival rate (), and the drop in packets per unit time is denoted as the departure rate (). The throughput of a communication system may be affected by various factors, including the limitations of the underlying analog ph ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
