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Loopback
Loopback (also written loop-back) is the routing of electronic signals or digital data streams back to their source without intentional processing or modification. It is primarily a means of testing the communications infrastructure. Loopback can take the form of communication channels with only one communication endpoint. Any message transmitted by such a channel is immediately and only received by that same channel. In telecommunications, loopback devices perform transmission tests of access lines from the serving switching center, which usually does not require the assistance of personnel at the served terminal. Loop around is a method of testing between stations that are not necessarily adjacent, wherein two lines are used, with the test being done at one station and the two lines are interconnected at the distant station. A patch cable may also function as loopback, when applied manually or automatically, remotely or locally, facilitating a loop-back test. Where a syst ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Localhost
In computer networking, localhost is a hostname that refers to the current computer used to access it. The name ''localhost'' is reserved for loopback purposes. It is used to access the network services that are running on the host via the loopback network interface. Using the loopback interface bypasses any local network interface hardware. Loopback The local loopback mechanism may be used to run a network service on a host without requiring a physical network interface, or without making the service accessible from the networks the computer may be connected to. For example, a locally installed website may be accessed from a Web browser by the URL ''http://localhost'' to display its home page. IPv4 network standards reserve the entire address block (more than 16 million addresses) for loopback purposes. That means any packet sent to any of those addresses is looped back. The address is the standard address for IPv4 loopback traffic; the rest are not supported by ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
RS-232
In telecommunications, RS-232 or Recommended Standard 232 is a standard introduced in 1960 for serial communication transmission of data. It formally defines signals connecting between a ''DTE'' (''data terminal equipment'') such as a computer terminal or PC, and a ''DCE'' ('' data circuit-terminating equipment'' or '' data communication equipment''), such as a modem. The standard defines the electrical characteristics and timing of signals, the meaning of signals, and the physical size and pinout of connectors. The current version of the standard is ''TIA-232-F Interface Between Data Terminal Equipment and Data Circuit-Terminating Equipment Employing Serial Binary Data Interchange'', issued in 1997. The RS-232 standard had been commonly used with serial ports and serial cables. It is still widely used in industrial communication devices. A serial port complying with the RS-232 standard was once a standard feature of many types of computers. Personal computers used them ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bogon Filtering
Bogon filtering is the practice of blocking packets known as bogons, which are ones sent to a computer network claiming to originate from invalid or bogus IP addresses, known as bogon addresses. Etymology The term ''bogon'' stems from hacker jargon, with the earliest appearance in the Jargon File in version 1.5.0 (dated 1983). It is defined as the quantum of ''bogosity'', or the property of being bogus. A bogon packet is frequently bogus both in the conventional sense of being forged for illegitimate purposes, and in the hackish sense of being incorrect, absurd, and useless. An alternative etymology suggests that 'bogon' derives from a portmanteau of "bogus logon", or a logon from a place you know no one can actually logon. Types of bogon addresses Areas of unallocated address space are called the bogon space. These are that are not in any range allocated the Internet Assigned Numbers Authority (IANA) or a regional Internet registry (RIR) for public internet use. Bogon IPs al ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
CIDR Notation
Classless Inter-Domain Routing (CIDR ) is a method for allocating IP addresses for IP routing. The Internet Engineering Task Force introduced CIDR in 1993 to replace the previous classful network addressing architecture on the Internet. Its goal was to slow the growth of routing tables on router (computing), routers across the Internet, and to help slow the rapid IPv4 address exhaustion, exhaustion of IPv4 addresses. IP addresses are described as consisting of two groups of bits in the address: the most significant bits are the network prefix, which identifies a whole network or subnet, and the least significant bit, least significant set forms the ''host identifier'', which specifies a particular interface of a host on that network. This division is used as the basis of traffic routing between IP networks and for address allocation policies. Whereas classful network design for IPv4 sized the network prefix as one or more 8-bit groups, resulting in the blocks of Class A, B, or C ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Bit Error Rate Test
In digital transmission, the number of bit errors is the number of received bits of a data stream over a communication channel that have been altered due to noise, interference, distortion or bit synchronization errors. The bit error rate (BER) is the number of bit errors per unit time. The bit error ratio (also BER) is the number of bit errors divided by the total number of transferred bits during a studied time interval. Bit error ratio is a unitless performance measure, often expressed as a percentage. The bit error probability ''pe'' is the expected value of the bit error ratio. The bit error ratio can be considered as an approximate estimate of the bit error probability. This estimate is accurate for a long time interval and a high number of bit errors. Example As an example, assume this transmitted bit sequence: 1 1 0 0 0 1 0 1 1 and the following received bit sequence: 0 1 0 1 0 1 0 0 1, The number of bit errors (the underlined bits) is, in this case, 3. The BER ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
D-subminiature
The D-subminiature or D-sub is a common type of electrical connector. They are named for their characteristic D-shaped metal shield. When they were introduced, D-subs were among the smallest connectors used on computer systems. Description, nomenclature, and variants A D-sub contains two or more parallel rows of pins or sockets usually surrounded by a D-shaped metal shield, or shell, that provides mechanical support, ensures correct orientation, and may screen against electromagnetic interference. Calling that shield a shell (or D-shell) can be ambiguous, as the term shell is also short for the cable shell, or backshell. D-sub connectors have gender: parts with pin contacts are called ''male connectors'' or ''plugs'', while those with socket contacts are called ''female connectors'' or ''sockets''. The socket's shield fits tightly inside the plug's shield. Panel-mounted connectors usually have #4-40 UNC (as designated with the Unified Thread Standard) jackscrews that ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Open Sound System
The Open Sound System (OSS) is an interface for making and capturing sound in Unix and Unix-like operating systems. It is based on standard Unix devices system calls (i.e. POSIX read, write, ioctl, etc.). The term also sometimes refers to the software in a Unix kernel that provides the OSS interface; it can be thought of as a device driver (or a collection of device drivers) for sound controller hardware. The goal of OSS is to allow the writing of sound-based applications that are agnostic of the underlying sound hardware. OSS was created by Hannu Savolainen and is distributed under four license options, three of which are free software licences, thus making OSS free software. API The API is designed to use the traditional Unix framework of open(), read(), write(), and ioctl(), via device files. For instance, the default device for sound input and output is /dev/dsp. Examples using the shell: cat /dev/random > /dev/dsp # plays white noise through the speaker c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Routing Protocol
A routing protocol specifies how routers communicate with each other to distribute information that enables them to select paths between nodes on a computer network. Routers perform the traffic directing functions on the Internet; data packets are forwarded through the networks of the internet from router to router until they reach their destination computer. Routing algorithms determine the specific choice of route. Each router has a prior knowledge only of networks attached to it directly. A routing protocol shares this information first among immediate neighbors, and then throughout the network. This way, routers gain knowledge of the topology of the network. The ability of routing protocols to dynamically adjust to changing conditions such as disabled connections and components and route data around obstructions is what gives the Internet its fault tolerance and high availability. The specific characteristics of routing protocols include the manner in which they avoid ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Martian Packet
A Martian packet is an IP packet seen on the public Internet that contains a source or destination address that is reserved for special use by the Internet Assigned Numbers Authority (IANA) as defined in , Appendix B Glossary (Martian Address Filtering). On the public Internet, such a packet either has a spoofed source address, and it cannot actually originate as claimed, or the packet cannot be delivered. The requirement to filter these packets (i.e. not forward them) is found in , Section 5.3.7 (Martian Address Filtering). Martian packets commonly arise from IP address spoofing in denial-of-service attacks, but can also arise from network equipment malfunction or misconfiguration of a host. In Linux terminology, a Martian packet is an IP packet received by the kernel on a specific interface, while routing tables indicate that the source IP is expected on another interface. The name is derived from ''packet from Mars'', meaning that packet seems to be not of this Earth. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Datagram
A datagram is a basic transfer unit associated with a packet-switched network. Datagrams are typically structured in header and payload sections. Datagrams provide a connectionless communication service across a packet-switched network. The delivery, arrival time, and order of arrival of datagrams need not be guaranteed by the network. History In the early 1970s, the term ''datagram'' was created by combining the words ''data'' and ''telegram'' by the CCITT rapporteur on packet switching, Halvor Bothner-By. While the word was new, the concept had already a long history. In 1964, Paul Baran described, in a RAND Corporation report, a hypothetical military network having to resist a nuclear attack. Small standardized ''message blocks'', bearing source and destination addresses, were stored and forwarded in computer nodes of a highly redundant meshed computer network. Baran wrote: "The network user who has called up a ''virtual connection'' to an end station and has trans ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Multiprotocol Label Switching
Multiprotocol Label Switching (MPLS) is a routing technique in telecommunications networks that directs data from one node to the next based on labels rather than network addresses. Whereas network addresses identify endpoints, the labels identify established paths between endpoints. MPLS can encapsulate packets of various network protocols, hence the ''multiprotocol'' component of the name. MPLS supports a range of access technologies, including T1/ E1, ATM, Frame Relay, and DSL. Role and functioning In an MPLS network, labels are assigned to data packets. Packet-forwarding decisions are made solely on the contents of this label, without the need to examine the packet itself. This allows one to create end-to-end circuits across any type of transport medium, using any protocol. The primary benefit is to eliminate dependence on a particular OSI model data link layer (layer 2) technology, and eliminate the need for multiple layer-2 networks to satisfy different types of tra ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Internet Engineering Task Force
The Internet Engineering Task Force (IETF) is a standards organization for the Internet standard, Internet and is responsible for the technical standards that make up the Internet protocol suite (TCP/IP). It has no formal membership roster or requirements and all its participants are volunteers. Their work is usually funded by employers or other sponsors. The IETF was initially supported by the federal government of the United States but since 1993 has operated under the auspices of the Internet Society, a non-profit organization with local chapters around the world. Organization There is no membership in the IETF. Anyone can participate by signing up to a working group mailing list, or registering for an IETF meeting. The IETF operates in a bottom-up task creation mode, largely driven by working groups. Each working group normally has appointed two co-chairs (occasionally three); a charter that describes its focus; and what it is expected to produce, and when. It is open ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
