1.
Computer network
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A computer network or data network is a telecommunications network which allows nodes to share resources. In computer networks, networked computing devices exchange data with other using a data link. The connections between nodes are established using either cable media or wireless media, the best-known computer network is the Internet. Network computer devices that originate, route and terminate the data are called network nodes, nodes can include hosts such as personal computers, phones, servers as well as networking hardware. Two such devices can be said to be networked together when one device is able to exchange information with the other device, Computer networks differ in the transmission medium used to carry their signals, communications protocols to organize network traffic, the networks size, topology and organizational intent. In most cases, application-specific communications protocols are layered over other more general communications protocols and this formidable collection of information technology requires skilled network management to keep it all running reliably. The chronology of significant computer-network developments includes, In the late 1950s, in 1960, the commercial airline reservation system semi-automatic business research environment went online with two connected mainframes. Licklider developed a group he called the Intergalactic Computer Network. In 1964, researchers at Dartmouth College developed the Dartmouth Time Sharing System for distributed users of computer systems. The same year, at Massachusetts Institute of Technology, a group supported by General Electric and Bell Labs used a computer to route. Throughout the 1960s, Leonard Kleinrock, Paul Baran, and Donald Davies independently developed network systems that used packets to transfer information between computers over a network, in 1965, Thomas Marill and Lawrence G. Roberts created the first wide area network. This was an precursor to the ARPANET, of which Roberts became program manager. Also in 1965, Western Electric introduced the first widely used telephone switch that implemented true computer control, in 1972, commercial services using X.25 were deployed, and later used as an underlying infrastructure for expanding TCP/IP networks. In July 1976, Robert Metcalfe and David Boggs published their paper Ethernet, Distributed Packet Switching for Local Computer Networks, in 1979, Robert Metcalfe pursued making Ethernet an open standard. In 1976, John Murphy of Datapoint Corporation created ARCNET, a network first used to share storage devices. In 1995, the transmission speed capacity for Ethernet increased from 10 Mbit/s to 100 Mbit/s, by 1998, Ethernet supported transmission speeds of a Gigabit. Subsequently, higher speeds of up to 100 Gbit/s were added, the ability of Ethernet to scale easily is a contributing factor to its continued use. Providing access to information on shared storage devices is an important feature of many networks, a network allows sharing of files, data, and other types of information giving authorized users the ability to access information stored on other computers on the network
2.
Application-specific integrated circuit
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An application-specific integrated circuit /ˈeɪsɪk/, is an integrated circuit customized for a particular use, rather than intended for general-purpose use. For example, a designed to run in a digital voice recorder or a high-efficiency Bitcoin miner is an ASIC. Application-specific standard products are intermediate between ASICs and industry standard integrated circuits like the 7400 or the 4000 series, as feature sizes have shrunk and design tools improved over the years, the maximum complexity possible in an ASIC has grown from 5,000 gates to over 100 million. Modern ASICs often include entire microprocessors, memory blocks including ROM, RAM, EEPROM, flash memory, such an ASIC is often termed a SoC. Designers of digital ASICs often use a hardware description language, such as Verilog or VHDL, for smaller designs or lower production volumes, FPGAs may be more cost effective than an ASIC design even in production. The non-recurring engineering cost of an ASIC can run into the millions of dollars, the initial ASICs used gate array technology. An early successful commercial application was the gate array circuitry found in the 8-bit ZX81 and ZX Spectrum low-end personal computers and these were used by Sinclair Research essentially as a low-cost I/O solution aimed at handling the computers graphics. Customization occurred by varying the metal interconnect mask, Gate arrays had complexities of up to a few thousand gates. Later versions became more generalized, with different base dies customised by both metal and polysilicon layers, some base dies include RAM elements. In the mid-1980s, a designer would choose an ASIC manufacturer, most designers ended up using factory-specific tools to complete the implementation of their designs. A solution to problem, which also yielded a much higher density device, was the implementation of standard cells. Standard-cell design is the utilization of these blocks to achieve very high gate density. Standard-cell design fits between Gate Array and Full Custom design in terms of both its non-recurring engineering and recurring component cost, by the late 1990s, logic synthesis tools became available. Such tools could compile HDL descriptions into a gate-level netlist, the design team constructs a description of an ASIC to achieve these goals using an HDL. This process is analogous to writing a program in a high-level language. This is usually called the RTL design, suitability for purpose is verified by functional verification. This may include such techniques as logic simulation, formal verification, emulation, each technique has advantages and disadvantages, and often several methods are used. Logic synthesis transforms the RTL design into a collection of lower-level constructs called standard cells
3.
X.25
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X.25 is an ITU-T standard protocol suite for packet switched wide area network communication. An X.25 WAN consists of packet-switching exchange nodes as the networking hardware, X.25 is a family of protocols that was popular during the 1980s with telecommunications companies and in financial transaction systems such as automated teller machines. X.25 was originally defined by the International Telegraph and Telephone Consultative Committee in a series of drafts and finalized in a publication known as The Orange Book in 1976. While X.25 has, to an extent, been replaced by less complex protocols, especially the Internet protocol. X.25 is one of the oldest packet-switched services available and it was developed before the OSI Reference Model. The protocol suite is designed as three conceptual layers, which correspond closely to the three layers of the seven-layer OSI model. It also supports functionality not found in the OSI network layer, X.25 was developed in the ITU-T Study Group VII based upon a number of emerging data network projects. Various updates and additions were worked into the standard, eventually recorded in the ITU series of books describing the telecommunication systems. These books were published every year with different-colored covers. The X.25 specification is only part of the set of X-Series specifications on public data networks. The public data network was the name given to the international collection of X.25 providers. Their combined network had large global coverage during the 1980s and into the 1990s, publicly accessible X.25 networks were set up in most countries during the 1970s and 1980s, to lower the cost of accessing various online services. Beginning in the early 1990s, in North America, use of X.25 networks started to be replaced by Frame Relay, most systems that required X.25 now use TCP/IP, however it is possible to transport X.25 over TCP/IP when necessary. X.25 networks are still in use throughout the world, a variant called AX.25 is also used widely by amateur packet radio. Racal Paknet, now known as Widanet, is still in operation in many regions of the world, running on an X.25 protocol base. Additionally X.25 is still under heavy use in the business even though a transition to modern protocols like X.400 is without option as X.25 hardware becomes increasingly rare. As recently as March 2006, the United States National Airspace Data Interchange Network has used X.25 to interconnect remote airfields with Air Route Traffic Control Centers, france was one of the last remaining countries where commercial end-user service based on X.25 operated. Known as Minitel it was based on Videotex, itself running on X.25, as planned, service was terminated 30 June 2012
4.
Telephone call
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A telephone call is a connection over a telephone network between the called party and the calling party. The first telephone call was made on March 10,1876 by Alexander Graham Bell, Bell demonstrated his ability to talk with electricity by transmitting a call to his assistant, Thomas Watson. The first words transmitted were Mr Watson, come here and this event has been called Bells greatest success, as it demonstrated the first successful use of the telephone. Although it was his greatest success, he refused to have one in his own home because it was something he invented by mistake, the call may use land line, mobile phone, satellite phone or any combination thereof. When a telephone call has more than one called party it is referred to as a conference call, when two or more users of the network are sharing the same physical line, it is called a party line or Rural phone line. If the callers wireline phone is connected directly to the party, when the caller takes their telephone off-hook. This is called a hot line or ringdown, otherwise, the calling party is usually given a tone to indicate they should begin dialing the desired number. In some cases, if the party cannot dial calls directly. Calls may be placed through a public network provided by a telephone company or a private network called a PBX. In most cases a private network is connected to the network in order to allow PBX users to dial the outside world. Most telephone calls through the PSTN are set up using ISUP signalling messages or one of its variants between telephone exchanges to establish the end to end connection, calls through PBX networks are set up using QSIG, DPNSS or variants. Some types of calls are not charged, such as local calls dialed directly by a subscriber in Canada. In most other areas, all calls are charged a fee for the connection. Fees depend on the provider of the service, the type of service being used, in most circumstances, the calling party pays this fee. However, in circumstances such as a reverse charge or collect call. In some circumstances, the caller pays a flat charge for the telephone connection. The caller then rotary dials or presses buttons for the number needed to complete the call. The second phone makes a noise to alert its owner
5.
Asynchronous Transfer Mode
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ATM was developed to meet the needs of the Broadband Integrated Services Digital Network, as defined in the late 1980s, and designed to unify telecommunication and computer networks. It was designed for a network that must handle both traditional high-throughput data traffic, and real-time, low-latency content such as voice and video. The reference model for ATM approximately maps to the three lowest layers of the ISO-OSI reference model, network layer, data link layer, and physical layer. ATM is a protocol used over the SONET/SDH backbone of the public switched telephone network and Integrated Services Digital Network. This differs from approaches such as the Internet Protocol or Ethernet that use variable sized packets, ATM uses a connection-oriented model in which a virtual circuit must be established between two endpoints before the actual data exchange begins. ATM eventually became dominated by Internet Protocol only technology, in the ISO-OSI reference model data link layer, the basic transfer units are generically called frames. In ATM these frames are of a length and specifically called cells. Under normal queuing conditions the cells might experience maximum queuing delays, to avoid this issue, all ATM packets, or cells, are the same small size. In addition, the cell structure means that ATM can be readily switched by hardware without the inherent delays introduced by software switched and routed frames. Thus, the designers of ATM utilized small data cells to reduce jitter in the multiplexing of data streams.544 to 45 Mbit/s in the USA, at this rate, a typical full-length 1500 byte data packet would take 77.42 µs to transmit. In a lower-speed link, such as a 1.544 Mbit/s T1 line, a queuing delay induced by several such data packets might exceed the figure of 7.8 ms several times over, in addition to any packet generation delay in the shorter speech packet. This was clearly unacceptable for speech traffic, which needs to have low jitter in the stream being fed into the codec if it is to produce good-quality sound. This allows smoothing out the jitter, but the delay introduced by passage through the buffer would require echo cancellers even in local networks, also, it would have increased the delay across the channel, and conversation is difficult over high-delay channels. Build a system that can provide low jitter to traffic that needs it. Operate on a 1,1 user basis, the design of ATM aimed for a low-jitter network interface. However, cells were introduced into the design to provide short queuing delays while continuing to support datagram traffic, ATM broke up all packets, data, and voice streams into 48-byte chunks, adding a 5-byte routing header to each one so that they could be reassembled later. The choice of 48 bytes was political rather than technical, most of the European parties eventually came around to the arguments made by the Americans, but France and a few others held out for a shorter cell length. With 32 bytes, France would have been able to implement an ATM-based voice network with calls from one end of France to the other requiring no echo cancellation,48 bytes was chosen as a compromise between the two sides
6.
Packet switching
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Packet switching increases network efficiency and robustness, and enables technological convergence of many applications operating on the same network. Packets are composed of a header and payload, Information in the header is used by networking hardware to direct the packet to its destination where the payload is extracted and used by application software. This concept contrasted and contradicted then-established principles of pre-allocation of network bandwidth, the new concept found little resonance among network implementers until the independent work of British computer scientist Donald Davies at the National Physical Laboratory in the late 1960s. Packet mode communication may be implemented with or without intermediate forwarding nodes, in case of a shared physical medium, the packets may be delivered according to a multiple access scheme. In the late 1950s, the US Air Force established a wide area network for the Semi-Automatic Ground Environment radar defense system and they sought a system that might survive a nuclear attack to enable a response, thus diminishing the attractiveness of the first strike advantage by enemies. Report P-2626 described a general architecture for a large-scale, distributed, Barans work was known to Robert Taylor and J. C. R. Licklider at the Information Processing Technology Office, who advocated wide area networks, starting in 1965, Donald Davies at the National Physical Laboratory, UK, independently developed the same message routing methodology as developed by Baran. He called it packet switching, a more accessible name than Barans and he gave a talk on the proposal in 1966, after which a person from the Ministry of Defence told him about Barans work. A member of Davies team met Lawrence Roberts at the 1967 ACM Symposium on Operating System Principles, Davies had chosen some of the same parameters for his original network design as did Baran, such as a packet size of 1024 bits. In 1966, Davies proposed that a network should be built at the laboratory to serve the needs of NPL, the NPL Data Communications Network entered service in 1970. In 1974, Vint Cerf and Bob Kahn published the specifications for Transmission Control Protocol, Packet switching may be classified into connectionless packet switching, also known as datagram switching, and connection-oriented packet switching, also known as virtual circuit switching. Examples of connectionless protocols are Ethernet, Internet Protocol, and the User Datagram Protocol, connection-oriented protocols include X.25, Frame Relay, Multiprotocol Label Switching, and the Transmission Control Protocol. In connectionless mode each packet includes complete addressing information, the packets are routed individually, sometimes resulting in different paths and out-of-order delivery. Each packet is labeled with an address, source address. It may also be labeled with the number of the packet. At the destination, the original message/data is reassembled in the correct order, connection-oriented transmission requires a setup phase in each involved node before any packet is transferred to establish the parameters of communication. The packets include a connection identifier rather than address information and are negotiated between endpoints so that they are delivered in order and with error checking, the signaling protocols used allow the application to specify its requirements and discover link parameters. Acceptable values for service parameters may be negotiated, routing a packet requires the node to look up the connection id in a table
7.
Frame Relay
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Frame Relay is a standardized wide area network technology that specifies the physical and data link layers of digital telecommunications channels using a packet switching methodology. Originally designed for transport across Integrated Services Digital Network infrastructure, it may be used today in the context of other network interfaces. Network providers commonly implement Frame Relay for voice and data as a technique used between local area networks over a wide area network. Each end-user gets a line to a Frame Relay node. The Frame Relay network handles the transmission over a frequently changing path transparent to all end-user extensively used WAN protocols and it is less expensive than leased lines and that is one reason for its popularity. The extreme simplicity of configuring user equipment in a Frame Relay network offers another reason for Frame Relays popularity. With the advent of Ethernet over fiber optics, MPLS, VPN and dedicated broadband services such as cable modem and DSL, however many rural areas remain lacking DSL and cable modem services. In such cases, the least expensive type of non-dial-up connection remains a 64-kbit/s Frame Relay line, thus a retail chain, for instance, may use Frame Relay for connecting rural stores into their corporate WAN. Frame Relay puts data in units called frames and leaves any necessary error-correction up to the end-points. This speeds up overall data transmission, an enterprise can select a level of service quality, prioritizing some frames and making others less important. Frame Relay can run on fractional T-1 or full T-carrier system carriers.520 Mbit/s to 622.080 Mbit/s, Frame Relay has its technical base in the older X.25 packet-switching technology, designed for transmitting data on analog voice lines. When a Frame Relay network detects an error in a frame, the end points have the responsibility for detecting and retransmitting dropped frames. Frame Relay often serves to connect local area networks with major backbones, as well as on public wide-area networks and it requires a dedicated connection during the transmission period. Frame Relay does not provide a path for voice or video transmission. However, under circumstances, voice and video transmission do use Frame Relay. Frame Relay originated as an extension of integrated services digital network and its designers aimed to enable a packet-switched network to transport over circuit-switched technology. The technology has become a stand-alone and cost-effective means of creating a WAN, Frame Relay switches create virtual circuits to connect remote LANs to a WAN. The Frame Relay network exists between a LAN border device, usually a router, and the carrier switch, the technology used by the carrier to transport data between the switches is variable and may differ among carriers
8.
General Packet Radio Service
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General Packet Radio Service is a packet oriented mobile data service on the 2G and 3G cellular communication systems global system for mobile communications. GPRS was originally standardized by European Telecommunications Standards Institute in response to the earlier CDPD and it is now maintained by the 3rd Generation Partnership Project. GPRS usage is typically charged based on volume of data transferred, contrasting with circuit switched data, sometimes billing time is broken down to every third of a minute. Usage above the cap is charged per megabyte, speed limited. In 2G systems, GPRS provides data rates of 56–114 kbit/second, 2G cellular technology combined with GPRS is sometimes described as 2. 5G, that is, a technology between the second and third generations of mobile telephony. It provides moderate-speed data transfer, by using unused time division multiple access channels in, for example, GPRS is integrated into GSM Release 97 and newer releases. The GPRS core network allows 2G, 3G and WCDMA mobile networks to transmit IP packets to external networks such as the Internet, the GPRS system is an integrated part of the GSM network switching subsystem. This is much faster using the ordinary SMS over GSM. GPRS supports the protocols, Internet Protocol. In practice, built-in mobile browsers use IPv4 since IPv6 was not yet popular, in this mode PPP is often not supported by the mobile phone operator but if the mobile is used as a modem to the connected computer, PPP is used to tunnel IP to the phone. This allows an IP address to be assigned dynamically to the mobile equipment and this is typically used for applications like wireless payment terminals, although it has been removed from the standard. When TCP/IP is used, each phone can have one or more IP addresses allocated, GPRS will store and forward the IP packets to the phone even during handover. The TCP handles any packet loss, devices supporting GPRS are divided into three classes, Class A Can be connected to GPRS service and GSM service, using both at the same time. Such devices are known to be available today, Class B Can be connected to GPRS service and GSM service, but using only one or the other at a given time. During GSM service, GPRS service is suspended, and then resumed automatically after the GSM service has concluded, most GPRS mobile devices are Class B. Class C Are connected to either GPRS service or GSM service, must be switched manually between one or the other service. A true Class A device may be required to transmit on two different frequencies at the time, and thus will need two radios. To get around this requirement, a GPRS mobile may implement the dual transfer mode feature
9.
Stream Control Transmission Protocol
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In computer networking, the Stream Control Transmission Protocol is a transport-layer protocol, serving in a similar role to the popular protocols TCP and UDP. It is standardized by IETF in RFC4960, in the absence of native SCTP support in operating systems it is possible to tunnel SCTP over UDP, as well as mapping TCP API calls to SCTP ones. The reference implementation was released as part of FreeBSD version 7 and it has subsequently been widely ported. The IETF Signaling Transport working group defined the protocol in 2000, SCTP applications submit their data to be transmitted in messages to the SCTP transport layer. SCTP places messages and control information into separate chunks, each identified by a chunk header, the protocol can fragment a message into a number of data chunks, but each data chunk contains data from only one user message. SCTP bundles the chunks into SCTP packets, the SCTP packet, which is submitted to the Internet Protocol, consists of a packet header, SCTP control chunks, followed by SCTP data chunks. One can characterize SCTP as message-oriented, meaning it transports a sequence of messages, as in UDP, in SCTP a sender sends a message in one operation, and that exact message is passed to the receiving application process in one operation. In contrast, TCP is a protocol, transporting streams of bytes reliably. However TCP does not allow the receiver to know how many times the application called on the TCP transport passing it groups of bytes to be sent out. The term multi-streaming refers to the capability of SCTP to transmit several independent streams of chunks in parallel, in essence, it involves bundling several connections into a single SCTP association, operating on messages rather than bytes. TCP preserves byte order in the stream by including a number with each segment. SCTP, on the hand, assigns a sequence number to each message sent in a stream. This allows independent ordering of messages in different streams, however, message ordering is optional in SCTP, a receiving application may choose to process messages in the order of receipt instead of in the order of sending. Features of SCTP include, Multihoming support in one or both endpoints of a connection can consist of more than one IP address, enabling transparent fail-over between redundant network paths. Delivery of chunks within independent streams eliminate unnecessary head-of-line blocking, as opposed to TCP byte-stream delivery, path selection and monitoring to select a primary data transmission path and test the connectivity of the transmission path. Validation and acknowledgment mechanisms protect against flooding attacks and provide notification of duplicated or missing data chunks, improved error detection suitable for Ethernet jumbo frames. The designers of SCTP originally intended it for the transport of telephony over Internet Protocol and this IETF effort is known as SIGTRAN. In the meantime, other uses have been proposed, for example, TCP has provided the primary means to transfer data reliably across the Internet
10.
Application software
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An application program is a computer program designed to perform a group of coordinated functions, tasks, or activities for the benefit of the user. Examples of an application include a processor, a spreadsheet, an accounting application, a web browser, a media player, an aeronautical flight simulator. The collective noun application software refers to all applications collectively and this contrasts with system software, which is mainly involved with running the computer. Applications may be bundled with the computer and its software or published separately. Apps built for mobile platforms are called mobile apps, in information technology, an application is a computer program designed to help people perform an activity. An application thus differs from a system, a utility. Depending on the activity for which it was designed, an application can manipulate text, numbers, graphics, some application packages focus on a single task, such as word processing, others, called integrated software include several applications. User-written software tailors systems to meet the specific needs. User-written software includes templates, word processor macros, scientific simulations, graphics. Even email filters are a kind of user software, users create this software themselves and often overlook how important it is. The delineation between system software such as operating systems and application software is not exact, however, and is occasionally the object of controversy. As another example, the GNU/Linux naming controversy is, in part, the above definitions may exclude some applications that may exist on some computers in large organizations. For an alternative definition of an app, see Application Portfolio Management, the word application, once used as an adjective, is not restricted to the of or pertaining to application software meaning. Sometimes a new and popular application arises which only runs on one platform and this is called a killer application or killer app. There are many different ways to divide up different types of application software, web apps have indeed greatly increased in popularity for some uses, but the advantages of applications make them unlikely to disappear soon, if ever. Furthermore, the two can be complementary, and even integrated, Application software can also be seen as being either horizontal or vertical. Horizontal applications are more popular and widespread, because they are general purpose, vertical applications are niche products, designed for a particular type of industry or business, or department within an organization. Integrated suites of software will try to handle every aspect possible of, for example, manufacturing or banking systems, or accounting
11.
Transmission Control Protocol
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The Transmission Control Protocol is one of the main protocols of the Internet protocol suite. It originated in the initial implementation in which it complemented the Internet Protocol. Therefore, the suite is commonly referred to as TCP/IP. TCP provides reliable, ordered, and error-checked delivery of a stream of octets between applications running on hosts communicating by an IP network, major Internet applications such as the World Wide Web, email, remote administration, and file transfer rely on TCP. Applications that do not require reliable data stream service may use the User Datagram Protocol, during May 1974, the Institute of Electrical and Electronic Engineers published a paper titled A Protocol for Packet Network Intercommunication. The papers authors, Vint Cerf and Bob Kahn, described a protocol for sharing resources using packet-switching among the nodes. A central control component of this model was the Transmission Control Program that incorporated both connection-oriented links and datagram services between hosts, the model became known informally as TCP/IP, although formally it was henceforth termed the Internet Protocol Suite. The Transmission Control Protocol provides a service at an intermediate level between an application program and the Internet Protocol. It provides host-to-host connectivity at the Transport Layer of the Internet model, an application does not need to know the particular mechanisms for sending data via a link to another host, such as the required packet fragmentation on the transmission medium. At the transport layer, the protocol handles all handshaking and transmission details, at the lower levels of the protocol stack, due to network congestion, traffic load balancing, or other unpredictable network behaviour, IP packets may be lost, duplicated, or delivered out of order. TCP detects these problems, requests re-transmission of lost data, rearranges out-of-order data, If the data still remains undelivered, the source is notified of this failure. Once the TCP receiver has reassembled the sequence of octets originally transmitted, thus, TCP abstracts the applications communication from the underlying networking details. TCP is optimized for accurate delivery rather than timely delivery and can incur relatively long delays while waiting for messages or re-transmissions of lost messages. Therefore, it is not particularly suitable for applications such as Voice over IP. For such applications, protocols like the Real-time Transport Protocol operating over the User Datagram Protocol are usually recommended instead, TCP is a reliable stream delivery service which guarantees that all bytes received will be identical with bytes sent and in the correct order. Since packet transfer by many networks is not reliable, a known as positive acknowledgement with re-transmission is used to guarantee reliability. This fundamental technique requires the receiver to respond with an acknowledgement message as it receives the data, the sender keeps a record of each packet it sends and maintains a timer from when the packet was sent. The sender re-transmits a packet if the timer expires before receiving the message acknowledgement, the timer is needed in case a packet gets lost or corrupted
