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Protocol Spoofing
Protocol spoofing is used in data communications to improve performance in situations where an existing protocol is inadequate, for example due to long delays or high error rates. Spoofing techniques In most applications of protocol spoofing, a communications device such as a modem or router simulates ("spoofs") the remote endpoint of a connection to a locally attached host, while using a more appropriate protocol to communicate with a compatible remote device that performs the equivalent spoof at the other end of the communications link. File transfer spoofing Error correction and file transfer protocols typically work by calculating a checksum or CRC for a block of data known as a ''packet'', and transmitting the resulting number at the end of the packet. At the other end of the connection, the receiver re-calculates the number based on the data it received and compares that result to what was sent from the remote machine. If the two match the packet was transmitted correctl ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Protocol (computing)
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 are t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Telebit
Telebit Corporation was a US-based modem manufacturer, known for their TrailBlazer series of high-speed modems. One of the first modems to routinely exceed 9600 bit/s speeds, the TrailBlazer used a proprietary modulation scheme that proved highly resilient to interference, earning the product an almost legendary reputation for reliability despite mediocre (or worse) line quality. They were particularly common in Unix installations in the 1980s and 1990s. The high price of the Telebit modems was initially not a concern as their performance was equally high compared to other systems. However, as new designs using V.32 and V.32bis began to arrive in the early 1990s, Telebit's price/performance ratio was seriously eroded. A series of new designs followed, but these never regained their performance lead. By the mid-1990s the company had been part of a series of mergers and eventually disappeared in 1998 after being acquired by Digi International. Startup Telebit was founded by Paul B ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
TCP Westwood
TCP Westwood (TCPW) is a sender-side-only modification to TCP New Reno that is intended to better handle large bandwidth-delay product paths (large pipes), with potential packet loss due to transmission or other errors (leaky pipes), and with dynamic load (dynamic pipes). TCP Westwood relies on mining the ACK stream for information to help it better set the congestion control parameters: Slow Start Threshold (ssthresh), and Congestion Window (cwin). In TCP Westwood, an "Eligible Rate" is estimated and used by the sender to update ssthresh and cwin upon loss indication, or during its "Agile Probing" phase, a proposed modification to the well-known slow start phase. In addition, a scheme called Persistent Non Congestion Detection (PNCD) has been devised to detect persistent lack of congestion and induce an Agile Probing phase to expeditiously utilize large dynamic bandwidth. The resultant performance gains in efficiency, without undue sacrifice of fairness, friendliness, and stabi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Internetwork Packet Exchange
Internetwork Packet Exchange (IPX) is the network layer protocol in the IPX/SPX protocol suite. IPX is derived from Xerox Network Systems' IDP. It also has the ability to act as a transport layer protocol. The IPX/SPX protocol suite was very popular through the late 1980s and mid-1990s because it was used by Novell NetWare, a network operating system. Due to Novell NetWare's popularity, IPX became a prominent protocol for internetworking. A big advantage of IPX was a small memory footprint of the IPX driver, which was vital for DOS and Windows up to Windows 95 due to the limited size at that time of conventional memory. Another IPX advantage is easy configuration of its client computers. However, IPX does not scale well for large networks such as the Internet. As such, IPX usage decreased as the boom of the Internet made TCP/IP nearly universal. Computers and networks can run multiple network protocols, so almost all IPX sites also run TCP/IP, to allow Internet connectivity ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dial-on-demand Routing
Dial on Demand Routing (DDR) is a routing technique where a network connection to a remote site is established only when needed. In other words, if the router tries to send out data and the connection is off, then the router will automatically establish a connection, send the information, and close the connection when no more data needs to be sent. DDR is advantageous for companies that must pay per minute for a WAN setup, where a connection is always established. Constant connections can become needlessly expensive if the company does not require a constant internet connection. How it works There are two parts to establishing a connection with DDR: the physical connection and the digital connection. The physical connection consists of the actual cable that connects computers on the network and the network interface card that allows for communication over these cables. DDR uses existing Public Switched Telephone Network (PSTN) lines – or the network of all public circuit-sw ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Xpress Transport Protocol
Xpress Transport Protocol (XTP) is a transport layer protocol for high-speed networks promoted by the XTP Forum developed to replace TCP. XTP provides protocol options for error control, flow control, and rate control. Instead of separate protocols for each type of communication, XTP controls packet exchange patterns to produce different models, e.g. reliable datagrams, transactions, unreliable streams, and reliable multicast connections. Long latency is one of the major problems in satellite communications. Couple this with possible environmental variables and sometimes asymmetrical bandwidth conditions, the quality of service in satellite communications is sometimes lacking. XTP addresses these issues in a variety of ways such as a Selective Retransmission algorithm that deals with loss recovery. This works by the receiver detecting missing data packets and transmitting a list of those missing packets to the sender, who then is able to quickly resend missing packets as needed ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
TCP Congestion Control
Transmission Control Protocol (TCP) uses a network congestion-avoidance algorithm that includes various aspects of an additive increase/multiplicative decrease (AIMD) scheme, along with other schemes including slow start and congestion window (CWND), to achieve congestion avoidance. The TCP congestion-avoidance algorithm is the primary basis for congestion control in the Internet. Per the end-to-end principle, congestion control is largely a function of internet hosts, not the network itself. There are several variations and versions of the algorithm implemented in protocol stacks of operating systems of computers that connect to the Internet. To avoid congestive collapse, TCP uses multi-faceted congestion-control strategy. For each connection, TCP maintains a CWND, limiting the total number of unacknowledged packets that may be in transit end-to-end. This is somewhat analogous to TCP's sliding window used for flow control. Additive increase/multiplicative decrease The a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Geostationary
A geostationary orbit, also referred to as a geosynchronous equatorial orbit''Geostationary orbit'' and ''Geosynchronous (equatorial) orbit'' are used somewhat interchangeably in sources. (GEO), is a circular geosynchronous orbit in altitude above Earth's equator ( in radius from Earth's center) and following the direction of Earth's rotation. An object in such an orbit has an orbital period equal to Earth's rotational period, one sidereal day, and so to ground observers it appears motionless, in a fixed position in the sky. The concept of a geostationary orbit was popularised by the science fiction writer Arthur C. Clarke in the 1940s as a way to revolutionise telecommunications, and the first satellite to be placed in this kind of orbit was launched in 1963. Communications satellites are often placed in a geostationary orbit so that Earth-based satellite antennas do not have to rotate to track them but can be pointed permanently at the position in the sky where the sat ... [...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 (shortened to LFN). As defined in , a network is considered an LFN if its bandwidth-delay product is significantly larger than 105 bits (12,500 bytes). 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 dela ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Echo Cancellation
Echo suppression and echo cancellation are methods used in telephony to improve voice quality by preventing echo from being created or removing it after it is already present. In addition to improving subjective audio quality, echo suppression increases the capacity achieved through silence suppression by preventing echo from traveling across a telecommunications network. Echo suppressors were developed in the 1950s in response to the first use of satellites for telecommunications. Echo suppression and cancellation methods are commonly called acoustic echo suppression (AES) and acoustic echo cancellation (AEC), and more rarely line echo cancellation (LEC). In some cases, these terms are more precise, as there are various types and causes of echo with unique characteristics, including acoustic echo (sounds from a loudspeaker being reflected and recorded by a microphone, which can vary substantially over time) and line echo (electrical impulses caused by, e.g., coupling between t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Modem
A modulator-demodulator or modem is a computer hardware device that converts data from a digital format into a format suitable for an analog transmission medium such as telephone or radio. A modem transmits data by Modulation#Digital modulation methods, modulating one or more carrier wave signals to encode digital information, while the receiver Demodulation, demodulates the signal to recreate the original digital information. The goal is to produce a Signal (electronics), signal that can be transmitted easily and decoded reliably. Modems can be used with almost any means of transmitting analog signals, from light-emitting diodes to radio. Early modems were devices that used audible sounds suitable for transmission over traditional telephone systems and leased lines. These generally operated at 110 or 300 bits per second (bit/s), and the connection between devices was normally manual, using an attached telephone handset. By the 1970s, higher speeds of 1,200 and 2,400 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Microcom Networking Protocol
The Microcom Networking Protocols, almost always shortened to MNP, is a family of error-correcting protocols commonly used on early high-speed (2400 bit/s and higher) modems. Originally developed for use on Microcom's own family of modems, the protocol was later openly licensed and used by most of the modem industry, notably the "big three", Telebit, USRobotics and Hayes. MNP was later supplanted by v.42bis, which was used almost universally starting with the first v.32bis modems in the early 1990s. Overview Although Xmodem was introduced 1977, as late as 1985 ''The New York Times'' described XMODEM first, then discussed ''MNP'' as a leading contender, and that 9600 baud modems "are beginning to make their appearance." By 1988, the ''Times'' was talking about 9600 and 19.2K, and that "At least 100 other brands of modems follow" MNP (compared to Hayes' use of LAP-B). Error correction basics Modems are, by their nature, error-prone devices. Noise on the telephone line, a common ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
