document_title: Computer network

question_text: radio waves used to connect computers and other devices to the internet are known as

question_tokens: radio waves used to connect computers and other devices to the internet are known as

text: Computer network

text: History[edit]

text: The chronology of significant computer-network developments includes:

text:
In the late 1950s, early networks of computers included the U.S. military radar system Semi-Automatic Ground Environment (SAGE).
In 1959, Anatolii Ivanovich Kitov proposed to the Central Committee of the Communist Party of the Soviet Union a detailed plan for the re-organisation of the control of the Soviet armed forces and of the Soviet economy on the basis of a network of computing centres, the OGAS.[2]
In 1960, the commercial airline reservation system semi-automatic business research environment (SABRE) went online with two connected mainframes.
In 1963, J. C. R. Licklider sent a memorandum to office colleagues discussing the concept of the "Intergalactic Computer Network", a computer network intended to allow general communications among computer users.
In 1964, researchers at Dartmouth College developed the Dartmouth Time Sharing System for distributed users of large computer systems. The same year, at Massachusetts Institute of Technology, a research group supported by General Electric and Bell Labs used a computer to route and manage telephone connections.
Throughout the 1960s, Paul Baran, and Donald Davies independently developed the concept of packet switching to transfer information between computers over a network. Davies pioneered the implementation of the concept with the NPL network, a local area network at the National Physical Laboratory (United Kingdom) using a line speed of 768 kbit/s.[3][4][5]
In 1965, Western Electric introduced the first widely used telephone switch that implemented true computer control.
In 1966, Thomas Marill and Lawrence G. Roberts published a paper on an experimental wide area network (WAN) for computer time sharing.[6]
In 1969, the first four nodes of the ARPANET were connected using 50 kbit/s circuits between the University of California at Los Angeles, the Stanford Research Institute, the University of California at Santa Barbara, and the University of Utah.[7] Leonard Kleinrock carried out theoretical work to model the performance of packet-switched networks, which underpinned the development of the ARPANET.[8][9] His theoretical work on hierarchical routing in the late 1970s with student Farouk Kamoun remains critical to the operation of the Internet today.
In 1972, commercial services using X.25 were deployed, and later used as an underlying infrastructure for expanding TCP/IP networks.
In 1973, the French CYCLADES network was the first to make the hosts responsible for the reliable delivery of data, rather than this being a centralized service of the network itself.[10]
In 1973, Robert Metcalfe wrote a formal memo at Xerox PARC describing Ethernet, a networking system that was based on the Aloha network, developed in the 1960s by Norman Abramson and colleagues at the University of Hawaii. In July 1976, Robert Metcalfe and David Boggs published their paper "Ethernet: Distributed Packet Switching for Local Computer Networks"[11] and collaborated on several patents received in 1977 and 1978. In 1979, Robert Metcalfe pursued making Ethernet an open standard.[12]
In 1976, John Murphy of Datapoint Corporation created ARCNET, a token-passing 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 (as of 2016[update]). The ability of Ethernet to scale easily (such as quickly adapting to support new fiber optic cable speeds) is a contributing factor to its continued use.[12]

text: Properties[edit]

text: Computer networking may be considered a branch of electrical engineering, electronics engineering, telecommunications, computer science, information technology or computer engineering, since it relies upon the theoretical and practical application of the related disciplines.

text: A computer network facilitates interpersonal communications allowing users to communicate efficiently and easily via various means: email, instant messaging, online chat, telephone, video telephone calls, and video conferencing. A network allows sharing of network and computing resources. Users may access and use resources provided by devices on the network, such as printing a document on a shared network printer or use of a shared storage device. 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. Distributed computing uses computing resources across a network to accomplish tasks.

text: A computer network may be used by security hackers to deploy computer viruses or computer worms on devices connected to the network, or to prevent these devices from accessing the network via a denial-of-service attack.

text: Network packet[edit]

text: Computer communication links that do not support packets, such as traditional point-to-point telecommunication links, simply transmit data as a bit stream. However, most information in computer networks is carried in packets. A network packet is a formatted unit of data (a list of bits or bytes, usually a few tens of bytes to a few kilobytes long) carried by a packet-switched network. Packets are sent through the network to their destination. Once the packets arrive they are reassembled into their original message.

text: Packets consist of two kinds of data: control information, and user data (payload). The control information provides data the network needs to deliver the user data, for example: source and destination network addresses, error detection codes, and sequencing information. Typically, control information is found in packet headers and trailers, with payload data in between.

text: With packets, the bandwidth of the transmission medium can be better shared among users than if the network were circuit switched. When one user is not sending packets, the link can be filled with packets from other users, and so the cost can be shared, with relatively little interference, provided the link isn't overused. Often the route a packet needs to take through a network is not immediately available. In that case the packet is queued and waits until a link is free.

text: Network topology[edit]

text: The physical layout of a network is usually less important than the topology that connects network nodes. Most diagrams that describe a physical network are therefore topological, rather than geographic. The symbols on these diagrams usually denote network links and network nodes.

text: Network links[edit]

text: The transmission media (often referred to in the literature as the physical media) used to link devices to form a computer network include electrical cable, optical fiber, and radio waves. In the OSI model, these are defined at layers 1 and 2 — the physical layer and the data link layer.

text: A widely adopted family of transmission media used in local area network (LAN) technology is collectively known as Ethernet. The media and protocol standards that enable communication between networked devices over Ethernet are defined by IEEE 802.3. Ethernet transmits data over both copper and fiber cables. Wireless LAN standards use radio waves, others use infrared signals as a transmission medium. Power line communication uses a building's power cabling to transmit data.

text: Wired technologies[edit]

text: The orders of the following wired technologies are, roughly, from slowest to fastest transmission speed.

text:
Coaxial cable is widely used for cable television systems, office buildings, and other work-sites for local area networks. The cables consist of copper or aluminum wire surrounded by an insulating layer (typically a flexible material with a high dielectric constant), which itself is surrounded by a conductive layer. The insulation helps minimize interference and distortion. Transmission speed ranges from 200 million bits per second to more than 500 million bits per second.
ITU-T G.hn technology uses existing home wiring (coaxial cable, phone lines and power lines) to create a high-speed (up to 1 Gigabit/s) local area network
Twisted pair wire is the most widely used medium for all telecommunication. Twisted-pair cabling consist of copper wires that are twisted into pairs. Ordinary telephone wires consist of two insulated copper wires twisted into pairs. Computer network cabling (wired Ethernet as defined by IEEE 802.3) consists of 4 pairs of copper cabling that can be utilized for both voice and data transmission. The use of two wires twisted together helps to reduce crosstalk and electromagnetic induction. The transmission speed ranges from 2 million bits per second to 10 billion bits per second. Twisted pair cabling comes in two forms: unshielded twisted pair (UTP) and shielded twisted-pair (STP). Each form comes in several category ratings, designed for use in various scenarios.

text: An optical fiber is a glass fiber. It carries pulses of light that represent data. Some advantages of optical fibers over metal wires are very low transmission loss and immunity from electrical interference. Optical fibers can simultaneously carry multiple wavelengths of light, which greatly increases the rate that data can be sent, and helps enable data rates of up to trillions of bits per second. Optic fibers can be used for long runs of cable carrying very high data rates, and are used for undersea cables to interconnect continents. There are two types of transmission of fiber optics, Single-mode fiber (SMF) and Multimode fiber (MMF). Single-mode fiber has the advantage of being able to sustain a coherent signal for dozens or even a hundred kilometers. Multimode fiber is cheaper to terminate but is limited to a few hundred or even only a few dozens of meters, depending on the data rate and cable grade.[13]

text: Price is a main factor distinguishing wired- and wireless-technology options in a business. Wireless options command a price premium that can make purchasing wired computers, printers and other devices a financial benefit. Before making the decision to purchase hard-wired technology products, a review of the restrictions and limitations of the selections is necessary. Business and employee needs may override any cost considerations.[14]

text: Wireless technologies[edit]

text:
Terrestrial microwave – Terrestrial microwave communication uses Earth-based transmitters and receivers resembling satellite dishes. Terrestrial microwaves are in the low gigahertz range, which limits all communications to line-of-sight. Relay stations are spaced approximately 48 km (30 mi) apart.
Communications satellites – Satellites communicate via microwave radio waves, which are not deflected by the Earth's atmosphere. The satellites are stationed in space, typically in geosynchronous orbit 35,400 km (22,000 mi) above the equator. These Earth-orbiting systems are capable of receiving and relaying voice, data, and TV signals.
Cellular and PCS systems use several radio communications technologies. The systems divide the region covered into multiple geographic areas. Each area has a low-power transmitter or radio relay antenna device to relay calls from one area to the next area.
Radio and spread spectrum technologies – Wireless local area networks use a high-frequency radio technology similar to digital cellular and a low-frequency radio technology. Wireless LANs use spread spectrum technology to enable communication between multiple devices in a limited area. IEEE 802.11 defines a common flavor of open-standards wireless radio-wave technology known as Wifi.
Free-space optical communication uses visible or invisible light for communications. In most cases, line-of-sight propagation is used, which limits the physical positioning of communicating devices.

text: Exotic technologies[edit]

text: There have been various attempts at transporting data over exotic media:

text:
IP over Avian Carriers was a humorous April fool's Request for Comments, issued as RFC 1149. It was implemented in real life in 2001.[15]
Extending the Internet to interplanetary dimensions via radio waves, the Interplanetary Internet.[16]

text: Both cases have a large round-trip delay time, which gives slow two-way communication, but doesn't prevent sending large amounts of information.

text: Network nodes[edit]

text: Apart from any physical transmission media there may be, networks comprise additional basic system building blocks, such as network interface controllers (NICs), repeaters, hubs, bridges, switches, routers, modems, and firewalls. Any particular piece of equipment will frequently contain multiple building blocks and perform multiple functions.

text: Network interfaces[edit]

text: A network interface controller (NIC) is computer hardware that provides a computer with the ability to access the transmission media, and has the ability to process low-level network information. For example, the NIC may have a connector for accepting a cable, or an aerial for wireless transmission and reception, and the associated circuitry.

text: The NIC responds to traffic addressed to a network address for either the NIC or the computer as a whole.

text: In Ethernet networks, each network interface controller has a unique Media Access Control (MAC) address—usually stored in the controller's permanent memory. To avoid address conflicts between network devices, the Institute of Electrical and Electronics Engineers (IEEE) maintains and administers MAC address uniqueness. The size of an Ethernet MAC address is six octets. The three most significant octets are reserved to identify NIC manufacturers. These manufacturers, using only their assigned prefixes, uniquely assign the three least-significant octets of every Ethernet interface they produce.

text: Repeaters and hubs[edit]

text: A repeater is an electronic device that receives a network signal, cleans it of unnecessary noise and regenerates it. The signal is retransmitted at a higher power level, or to the other side of an obstruction, so that the signal can cover longer distances without degradation. In most twisted pair Ethernet configurations, repeaters are required for cable that runs longer than 100 meters. With fiber optics, repeaters can be tens or even hundreds of kilometers apart.

text: A repeater with multiple ports is known as an Ethernet hub. Repeaters work on the physical layer of the OSI model. Repeaters require a small amount of time to regenerate the signal. This can cause a propagation delay that affects network performance and may affect proper function. As a result, many network architectures limit the number of repeaters that can be used in a row, e.g., the Ethernet 5-4-3 rule.

text: Hubs and repeaters in LANs have been mostly obsoleted by modern switches.

text: Bridges[edit]

text: A network bridge connects and filters traffic between two network segments at the data link layer (layer 2) of the OSI model to form a single network. This breaks the network's collision domain but maintains a unified broadcast domain. Network segmentation breaks down a large, congested network into an aggregation of smaller, more efficient networks.

text: Bridges come in three basic types:

text:
Local bridges: Directly connect LANs
Remote bridges: Can be used to create a wide area network (WAN) link between LANs. Remote bridges, where the connecting link is slower than the end networks, largely have been replaced with routers.
Wireless bridges: Can be used to join LANs or connect remote devices to LANs.

text: Switches[edit]

text: A network switch is a device that forwards and filters OSI layer 2 datagrams (frames) between ports based on the destination MAC address in each frame.[17] A switch is distinct from a hub in that it only forwards the frames to the physical ports involved in the communication rather than all ports connected. It can be thought of as a multi-port bridge.[18] It learns to associate physical ports to MAC addresses by examining the source addresses of received frames. If an unknown destination is targeted, the switch broadcasts to all ports but the source. Switches normally have numerous ports, facilitating a star topology for devices, and cascading additional switches.

text: Routers[edit]

text: A router is an internetworking device that forwards packets between networks by processing the routing information included in the packet or datagram (Internet protocol information from layer 3). The routing information is often processed in conjunction with the routing table (or forwarding table). A router uses its routing table to determine where to forward packets. A destination in a routing table can include a "null" interface, also known as the "black hole" interface because data can go into it, however, no further processing is done for said data, i.e. the packets are dropped.

text: Modems[edit]

text: Modems (MOdulator-DEModulator) are used to connect network nodes via wire not originally designed for digital network traffic, or for wireless. To do this one or more carrier signals are modulated by the digital signal to produce an analog signal that can be tailored to give the required properties for transmission. Modems are commonly used for telephone lines, using a Digital Subscriber Line technology.

text: Firewalls[edit]

text: A firewall is a network device for controlling network security and access rules. Firewalls are typically configured to reject access requests from unrecognized sources while allowing actions from recognized ones. The vital role firewalls play in network security grows in parallel with the constant increase in cyber attacks.

text: Network structure[edit]

text: Network topology is the layout or organizational hierarchy of interconnected nodes of a computer network. Different network topologies can affect throughput, but reliability is often more critical. With many technologies, such as bus networks, a single failure can cause the network to fail entirely. In general the more interconnections there are, the more robust the network is; but the more expensive it is to install.

text: Common layouts[edit]

text: Common layouts are:

text:
A bus network: all nodes are connected to a common medium along this medium. This was the layout used in the original Ethernet, called 10BASE5 and 10BASE2. This is still a common topology on the data link layer, although modern physical layer variants use point-to-point links instead.
A star network: all nodes are connected to a special central node. This is the typical layout found in a Wireless LAN, where each wireless client connects to the central Wireless access point.
A ring network: each node is connected to its left and right neighbour node, such that all nodes are connected and that each node can reach each other node by traversing nodes left- or rightwards. The Fiber Distributed Data Interface (FDDI) made use of such a topology.
A mesh network: each node is connected to an arbitrary number of neighbours in such a way that there is at least one traversal from any node to any other.
A fully connected network: each node is connected to every other node in the network.
A tree network: nodes are arranged hierarchically.

text: Note that the physical layout of the nodes in a network may not necessarily reflect the network topology. As an example, with FDDI, the network topology is a ring (actually two counter-rotating rings), but the physical topology is often a star, because all neighboring connections can be routed via a central physical location.

text: Overlay network[edit]

text: An overlay network is a virtual computer network that is built on top of another network. Nodes in the overlay network are connected by virtual or logical links. Each link corresponds to a path, perhaps through many physical links, in the underlying network. The topology of the overlay network may (and often does) differ from that of the underlying one. For example, many peer-to-peer networks are overlay networks. They are organized as nodes of a virtual system of links that run on top of the Internet.[19]

text: Overlay networks have been around since the invention of networking when computer systems were connected over telephone lines using modems, before any data network existed.

text: The most striking example of an overlay network is the Internet itself. The Internet itself was initially built as an overlay on the telephone network.[19] Even today, each Internet node can communicate with virtually any other through an underlying mesh of sub-networks of wildly different topologies and technologies. Address resolution and routing are the means that allow mapping of a fully connected IP overlay network to its underlying network.

text: Another example of an overlay network is a distributed hash table, which maps keys to nodes in the network. In this case, the underlying network is an IP network, and the overlay network is a table (actually a map) indexed by keys.

text: Overlay networks have also been proposed as a way to improve Internet routing, such as through quality of service guarantees to achieve higher-quality streaming media. Previous proposals such as IntServ, DiffServ, and IP Multicast have not seen wide acceptance largely because they require modification of all routers in the network.[citation needed] On the other hand, an overlay network can be incrementally deployed on end-hosts running the overlay protocol software, without cooperation from Internet service providers. The overlay network has no control over how packets are routed in the underlying network between two overlay nodes, but it can control, for example, the sequence of overlay nodes that a message traverses before it reaches its destination.

text: For example, Akamai Technologies manages an overlay network that provides reliable, efficient content delivery (a kind of multicast). Academic research includes end system multicast,[20] resilient routing and quality of service studies, among others.

text: Communication protocols[edit]

text: A communication protocol is a set of rules for exchanging information over a network. In a protocol stack (also see the OSI model), each protocol leverages the services of the protocol layer below it, until the lowest layer controls the hardware which sends information across the media. The use of protocol layering is today ubiquitous across the field of computer networking. An important example of a protocol stack is HTTP (the World Wide Web protocol) running over TCP over IP (the Internet protocols) over IEEE 802.11 (the Wi-Fi protocol). This stack is used between the wireless router and the home user's personal computer when the user is surfing the web.

text: Communication protocols have various characteristics. They may be connection-oriented or connectionless, they may use circuit mode or packet switching, and they may use hierarchical addressing or flat addressing.

text: There are many communication protocols, a few of which are described below.

text: IEEE 802[edit]

text: IEEE 802 is a family of IEEE standards dealing with local area networks and metropolitan area networks. The complete IEEE 802 protocol suite provides a diverse set of networking capabilities. The protocols have a flat addressing scheme. They operate mostly at levels 1 and 2 of the OSI model.

text: For example, MAC bridging (IEEE 802.1D) deals with the routing of Ethernet packets using a Spanning Tree Protocol. IEEE 802.1Q describes VLANs, and IEEE 802.1X defines a port-based Network Access Control protocol, which forms the basis for the authentication mechanisms used in VLANs (but it is also found in WLANs) – it is what the home user sees when the user has to enter a "wireless access key".

text: Ethernet[edit]

text: Ethernet, sometimes simply called LAN, is a family of protocols used in wired LANs, described by a set of standards together called IEEE 802.3 published by the Institute of Electrical and Electronics Engineers.

text: Wireless LAN[edit]

text: Wireless LAN, also widely known as WLAN or WiFi, is probably the most well-known member of the IEEE 802 protocol family for home users today. It is standardized by IEEE 802.11 and shares many properties with wired Ethernet.

text: Internet Protocol Suite[edit]

text: The Internet Protocol Suite, also called TCP/IP, is the foundation of all modern networking. It offers connection-less as well as connection-oriented services over an inherently unreliable network traversed by data-gram transmission at the Internet protocol (IP) level. At its core, the protocol suite defines the addressing, identification, and routing specifications for Internet Protocol Version 4 (IPv4) and for IPv6, the next generation of the protocol with a much enlarged addressing capability.

text: SONET/SDH[edit]

text: Synchronous optical networking (SONET) and Synchronous Digital Hierarchy (SDH) are standardized multiplexing protocols that transfer multiple digital bit streams over optical fiber using lasers. They were originally designed to transport circuit mode communications from a variety of different sources, primarily to support real-time, uncompressed, circuit-switched voice encoded in PCM (Pulse-Code Modulation) format. However, due to its protocol neutrality and transport-oriented features, SONET/SDH also was the obvious choice for transporting Asynchronous Transfer Mode (ATM) frames.

text: Asynchronous Transfer Mode[edit]

text: Asynchronous Transfer Mode (ATM) is a switching technique for telecommunication networks. It uses asynchronous time-division multiplexing and encodes data into small, fixed-sized cells. This differs from other protocols such as the Internet Protocol Suite or Ethernet that use variable sized packets or frames. ATM has similarity with both circuit and packet switched networking. This makes it a good choice for a network that must handle both traditional high-throughput data traffic, and real-time, low-latency content such as voice and video. ATM uses a connection-oriented model in which a virtual circuit must be established between two endpoints before the actual data exchange begins.

text: While the role of ATM is diminishing in favor of next-generation networks, it still plays a role in the last mile, which is the connection between an Internet service provider and the home user.[21]

text: Cellular standards[edit]

text: There are a number of different digital cellular standards, including: Global System for Mobile Communications (GSM), General Packet Radio Service (GPRS), cdmaOne, CDMA2000, Evolution-Data Optimized (EV-DO), Enhanced Data Rates for GSM Evolution (EDGE), Universal Mobile Telecommunications System (UMTS), Digital Enhanced Cordless Telecommunications (DECT), Digital AMPS (IS-136/TDMA), and Integrated Digital Enhanced Network (iDEN).[22]

text: Geographic scale[edit]

text:
Computer network types
by spatial scope

Nanoscale
Near-field (NFC)
Body (BAN)
Personal (PAN)
Near-me (NAN)
Local (LAN)

Home (HAN)
Storage (SAN)
Wireless (WLAN)

Campus (CAN)
Backbone
Metropolitan (MAN)
Wide (WAN)
Cloud (IAN)
Internet
Interplanetary Internet

v
t
e

text: A network can be characterized by its physical capacity or its organizational purpose. Use of the network, including user authorization and access rights, differ accordingly.

text: A nanoscale communication network has key components implemented at the nanoscale including message carriers and leverages physical principles that differ from macroscale communication mechanisms. Nanoscale communication extends communication to very small sensors and actuators such as those found in biological systems and also tends to operate in environments that would be too harsh for classical communication.[23]

text: A personal area network (PAN) is a computer network used for communication among computer and different information technological devices close to one person. Some examples of devices that are used in a PAN are personal computers, printers, fax machines, telephones, PDAs, scanners, and even video game consoles. A PAN may include wired and wireless devices. The reach of a PAN typically extends to 10 meters.[24] A wired PAN is usually constructed with USB and FireWire connections while technologies such as Bluetooth and infrared communication typically form a wireless PAN.

text: A local area network (LAN) is a network that connects computers and devices in a limited geographical area such as a home, school, office building, or closely positioned group of buildings. Each computer or device on the network is a node. Wired LANs are most likely based on Ethernet technology. Newer standards such as ITU-T G.hn also provide a way to create a wired LAN using existing wiring, such as coaxial cables, telephone lines, and power lines.[25]

text: The defining characteristics of a LAN, in contrast to a wide area network (WAN), include higher data transfer rates, limited geographic range, and lack of reliance on leased lines to provide connectivity. Current Ethernet or other IEEE 802.3 LAN technologies operate at data transfer rates up to 100 Gbit/s, standardized by IEEE in 2010.[26] Currently, 400 Gbit/s Ethernet is being developed.

text: A LAN can be connected to a WAN using a router.

text: A home area network (HAN) is a residential LAN used for communication between digital devices typically deployed in the home, usually a small number of personal computers and accessories, such as printers and mobile computing devices. An important function is the sharing of Internet access, often a broadband service through a cable TV or digital subscriber line (DSL) provider.

text: A storage area network (SAN) is a dedicated network that provides access to consolidated, block level data storage. SANs are primarily used to make storage devices, such as disk arrays, tape libraries, and optical jukeboxes, accessible to servers so that the devices appear like locally attached devices to the operating system. A SAN typically has its own network of storage devices that are generally not accessible through the local area network by other devices. The cost and complexity of SANs dropped in the early 2000s to levels allowing wider adoption across both enterprise and small to medium-sized business environments.

text: A campus area network (CAN) is made up of an interconnection of LANs within a limited geographical area. The networking equipment (switches, routers) and transmission media (optical fiber, copper plant, Cat5 cabling, etc.) are almost entirely owned by the campus tenant / owner (an enterprise, university, government, etc.).

text: For example, a university campus network is likely to link a variety of campus buildings to connect academic colleges or departments, the library, and student residence halls.

text: A backbone network is part of a computer network infrastructure that provides a path for the exchange of information between different LANs or sub-networks. A backbone can tie together diverse networks within the same building, across different buildings, or over a wide area.

text: For example, a large company might implement a backbone network to connect departments that are located around the world. The equipment that ties together the departmental networks constitutes the network backbone. When designing a network backbone, network performance and network congestion are critical factors to take into account. Normally, the backbone network's capacity is greater than that of the individual networks connected to it.

text: Another example of a backbone network is the Internet backbone, which is the set of wide area networks (WANs) and core routers that tie together all networks connected to the Internet.

text: A Metropolitan area network (MAN) is a large computer network that usually spans a city or a large campus.

text: A wide area network (WAN) is a computer network that covers a large geographic area such as a city, country, or spans even intercontinental distances. A WAN uses a communications channel that combines many types of media such as telephone lines, cables, and air waves. A WAN often makes use of transmission facilities provided by common carriers, such as telephone companies. WAN technologies generally function at the lower three layers of the OSI reference model: the physical layer, the data link layer, and the network layer.

text: An enterprise private network is a network that a single organization builds to interconnect its office locations (e.g., production sites, head offices, remote offices, shops) so they can share computer resources.

text: A virtual private network (VPN) is an overlay network in which some of the links between nodes are carried by open connections or virtual circuits in some larger network (e.g., the Internet) instead of by physical wires. The data link layer protocols of the virtual network are said to be tunneled through the larger network when this is the case. One common application is secure communications through the public Internet, but a VPN need not have explicit security features, such as authentication or content encryption. VPNs, for example, can be used to separate the traffic of different user communities over an underlying network with strong security features.

text: VPN may have best-effort performance, or may have a defined service level agreement (SLA) between the VPN customer and the VPN service provider. Generally, a VPN has a topology more complex than point-to-point.

text: A global area network (GAN) is a network used for supporting mobile across an arbitrary number of wireless LANs, satellite coverage areas, etc. The key challenge in mobile communications is handing off user communications from one local coverage area to the next. In IEEE Project 802, this involves a succession of terrestrial wireless LANs.[27]

text: Organizational scope[edit]

text: Networks are typically managed by the organizations that own them. Private enterprise networks may use a combination of intranets and extranets. They may also provide network access to the Internet, which has no single owner and permits virtually unlimited global connectivity.

text: Intranet[edit]

text: An intranet is a set of networks that are under the control of a single administrative entity. The intranet uses the IP protocol and IP-based tools such as web browsers and file transfer applications. The administrative entity limits use of the intranet to its authorized users. Most commonly, an intranet is the internal LAN of an organization. A large intranet typically has at least one web server to provide users with organizational information. An intranet is also anything behind the router on a local area network.

text: Extranet[edit]

text: An extranet is a network that is also under the administrative control of a single organization, but supports a limited connection to a specific external network. For example, an organization may provide access to some aspects of its intranet to share data with its business partners or customers. These other entities are not necessarily trusted from a security standpoint. Network connection to an extranet is often, but not always, implemented via WAN technology.

text: Internetwork[edit]

text: An internetwork is the connection of multiple computer networks via a common routing technology using routers.

text: Internet[edit]

text: The Internet is the largest example of an internetwork. It is a global system of interconnected governmental, academic, corporate, public, and private computer networks. It is based on the networking technologies of the Internet Protocol Suite. It is the successor of the Advanced Research Projects Agency Network (ARPANET) developed by DARPA of the United States Department of Defense. The Internet is also the communications backbone underlying the World Wide Web (WWW).

text: Participants in the Internet use a diverse array of methods of several hundred documented, and often standardized, protocols compatible with the Internet Protocol Suite and an addressing system (IP addresses) administered by the Internet Assigned Numbers Authority and address registries. Service providers and large enterprises exchange information about the reachability of their address spaces through the Border Gateway Protocol (BGP), forming a redundant worldwide mesh of transmission paths.

text: Darknet[edit]

text: A darknet is an overlay network, typically running on the Internet, that is only accessible through specialized software. A darknet is an anonymizing network where connections are made only between trusted peers — sometimes called "friends" (F2F)[28] — using non-standard protocols and ports.

text: Darknets are distinct from other distributed peer-to-peer networks as sharing is anonymous (that is, IP addresses are not publicly shared), and therefore users can communicate with little fear of governmental or corporate interference.[29]

text: Routing[edit]

text: Routing is the process of selecting network paths to carry network traffic. Routing is performed for many kinds of networks, including circuit switching networks and packet switched networks.

text: In packet switched networks, routing directs packet forwarding (the transit of logically addressed network packets from their source toward their ultimate destination) through intermediate nodes. Intermediate nodes are typically network hardware devices such as routers, bridges, gateways, firewalls, or switches. General-purpose computers can also forward packets and perform routing, though they are not specialized hardware and may suffer from limited performance. The routing process usually directs forwarding on the basis of routing tables, which maintain a record of the routes to various network destinations. Thus, constructing routing tables, which are held in the router's memory, is very important for efficient routing.

text: There are usually multiple routes that can be taken, and to choose between them, different elements can be considered to decide which routes get installed into the routing table, such as (sorted by priority):

text:
Prefix-Length: where longer subnet masks are preferred (independent if it is within a routing protocol or over different routing protocol)
Metric: where a lower metric/cost is preferred (only valid within one and the same routing protocol)
Administrative distance: where a lower distance is preferred (only valid between different routing protocols)

text: Most routing algorithms use only one network path at a time. Multipath routing techniques enable the use of multiple alternative paths.

text: Routing, in a more narrow sense of the term, is often contrasted with bridging in its assumption that network addresses are structured and that similar addresses imply proximity within the network. Structured addresses allow a single routing table entry to represent the route to a group of devices. In large networks, structured addressing (routing, in the narrow sense) outperforms unstructured addressing (bridging). Routing has become the dominant form of addressing on the Internet. Bridging is still widely used within localized environments.

text: Network service[edit]

text: Network services are applications hosted by servers on a computer network, to provide some functionality for members or users of the network, or to help the network itself to operate.

text: The World Wide Web, E-mail,[30] printing and network file sharing are examples of well-known network services. Network services such as DNS (Domain Name System) give names for IP and MAC addresses (people remember names like “nm.lan” better than numbers like “210.121.67.18”),[31] and DHCP to ensure that the equipment on the network has a valid IP address.[32]

text: Services are usually based on a service protocol that defines the format and sequencing of messages between clients and servers of that network service.

text: Network performance[edit]

text: Quality of service[edit]

text: Depending on the installation requirements, network performance is usually measured by the quality of service of a telecommunications product. The parameters that affect this typically can include throughput, jitter, bit error rate and latency.

text: The following list gives examples of network performance measures for a circuit-switched network and one type of packet-switched network, viz. ATM:

text:
Circuit-switched networks: In circuit switched networks, network performance is synonymous with the grade of service. The number of rejected calls is a measure of how well the network is performing under heavy traffic loads.[33] Other types of performance measures can include the level of noise and echo.
ATM: In an Asynchronous Transfer Mode (ATM) network, performance can be measured by line rate, quality of service (QoS), data throughput, connect time, stability, technology, modulation technique and modem enhancements.[34]

text: There are many ways to measure the performance of a network, as each network is different in nature and design. Performance can also be modelled instead of measured. For example, state transition diagrams are often used to model queuing performance in a circuit-switched network. The network planner uses these diagrams to analyze how the network performs in each state, ensuring that the network is optimally designed.[35]

text: Network congestion[edit]

text: Network congestion occurs when a link or node is carrying so much data that its quality of service deteriorates. Typical effects include queueing delay, packet loss or the blocking of new connections. A consequence of these latter two is that incremental increases in offered load lead either only to small increase in network throughput, or to an actual reduction in network throughput.

text: Network protocols that use aggressive retransmissions to compensate for packet loss tend to keep systems in a state of network congestion—even after the initial load is reduced to a level that would not normally induce network congestion. Thus, networks using these protocols can exhibit two stable states under the same level of load. The stable state with low throughput is known as congestive collapse.

text: Modern networks use congestion control, congestion avoidance and traffic control techniques to try to avoid congestion collapse. These include: exponential backoff in protocols such as 802.11's CSMA/CA and the original Ethernet, window reduction in TCP, and fair queueing in devices such as routers. Another method to avoid the negative effects of network congestion is implementing priority schemes, so that some packets are transmitted with higher priority than others. Priority schemes do not solve network congestion by themselves, but they help to alleviate the effects of congestion for some services. An example of this is 802.1p. A third method to avoid network congestion is the explicit allocation of network resources to specific flows. One example of this is the use of Contention-Free Transmission Opportunities (CFTXOPs) in the ITU-T G.hn standard, which provides high-speed (up to 1 Gbit/s) Local area networking over existing home wires (power lines, phone lines and coaxial cables).

text: For the Internet, RFC 2914 addresses the subject of congestion control in detail.

text: Network resilience[edit]

text: Network resilience is "the ability to provide and maintain an acceptable level of service in the face of faults and challenges to normal operation.”[36]

text: Security[edit]

text: Network security[edit]

text: Network security consists of provisions and policies adopted by the network administrator to prevent and monitor unauthorized access, misuse, modification, or denial of the computer network and its network-accessible resources.[37] Network security is the authorization of access to data in a network, which is controlled by the network administrator. Users are assigned an ID and password that allows them access to information and programs within their authority. Network security is used on a variety of computer networks, both public and private, to secure daily transactions and communications among businesses, government agencies and individuals.

text: Network surveillance[edit]

text: Network surveillance is the monitoring of data being transferred over computer networks such as the Internet. The monitoring is often done surreptitiously and may be done by or at the behest of governments, by corporations, criminal organizations, or individuals. It may or may not be legal and may or may not require authorization from a court or other independent agency.

text: Computer and network surveillance programs are widespread today, and almost all Internet traffic is or could potentially be monitored for clues to illegal activity.

text: Surveillance is very useful to governments and law enforcement to maintain social control, recognize and monitor threats, and prevent/investigate criminal activity. With the advent of programs such as the Total Information Awareness program, technologies such as high speed surveillance computers and biometrics software, and laws such as the Communications Assistance For Law Enforcement Act, governments now possess an unprecedented ability to monitor the activities of citizens.[38]

text: However, many civil rights and privacy groups—such as Reporters Without Borders, the Electronic Frontier Foundation, and the American Civil Liberties Union—have expressed concern that increasing surveillance of citizens may lead to a mass surveillance society, with limited political and personal freedoms. Fears such as this have led to numerous lawsuits such as Hepting v. AT&T.[38][39] The hacktivist group Anonymous has hacked into government websites in protest of what it considers "draconian surveillance".[40][41]

text: End to end encryption[edit]

text: End-to-end encryption (E2EE) is a digital communications paradigm of uninterrupted protection of data traveling between two communicating parties. It involves the originating party encrypting data so only the intended recipient can decrypt it, with no dependency on third parties. End-to-end encryption prevents intermediaries, such as Internet providers or application service providers, from discovering or tampering with communications. End-to-end encryption generally protects both confidentiality and integrity.

text: Examples of end-to-end encryption include HTTPS for web traffic, PGP for email, OTR for instant messaging, ZRTP for telephony, and TETRA for radio.

text: Typical server-based communications systems do not include end-to-end encryption. These systems can only guarantee protection of communications between clients and servers, not between the communicating parties themselves. Examples of non-E2EE systems are Google Talk, Yahoo Messenger, Facebook, and Dropbox. Some such systems, for example LavaBit and SecretInk, have even described themselves as offering "end-to-end" encryption when they do not. Some systems that normally offer end-to-end encryption have turned out to contain a back door that subverts negotiation of the encryption key between the communicating parties, for example Skype or Hushmail.

text: The end-to-end encryption paradigm does not directly address risks at the communications endpoints themselves, such as the technical exploitation of clients, poor quality random number generators, or key escrow. E2EE also does not address traffic analysis, which relates to things such as the identities of the end points and the times and quantities of messages that are sent.

text: SSL/TLS[edit]

text: The introduction and rapid growth of e-commerce on the world wide web in the mid-1990s made it obvious that some form of authentication and encryption was needed. Netscape took the first shot at a new standard. At the time, the dominant web browser was Netscape Navigator. Netscape created a standard called secure socket layer (SSL). SSL requires a server with a certificate. When a client requests access to an SSL-secured server, the server sends a copy of the certificate to the client. The SSL client checks this certificate (all web browsers come with an exhaustive list of CA root certificates preloaded), and if the certificate checks out, the server is authenticated and the client negotiates a symmetric-key cipher for use in the session. The session is now in a very secure encrypted tunnel between the SSL server and the SSL client.[13]

text: Views of networks[edit]

text: Users and network administrators typically have different views of their networks. Users can share printers and some servers from a workgroup, which usually means they are in the same geographic location and are on the same LAN, whereas a Network Administrator is responsible to keep that network up and running. A community of interest has less of a connection of being in a local area, and should be thought of as a set of arbitrarily located users who share a set of servers, and possibly also communicate via peer-to-peer technologies.

text: Network administrators can see networks from both physical and logical perspectives. The physical perspective involves geographic locations, physical cabling, and the network elements (e.g., routers, bridges and application layer gateways) that interconnect via the transmission media. Logical networks, called, in the TCP/IP architecture, subnets, map onto one or more transmission media. For example, a common practice in a campus of buildings is to make a set of LAN cables in each building appear to be a common subnet, using virtual LAN (VLAN) technology.

text: Both users and administrators are aware, to varying extents, of the trust and scope characteristics of a network. Again using TCP/IP architectural terminology, an intranet is a community of interest under private administration usually by an enterprise, and is only accessible by authorized users (e.g. employees).[42] Intranets do not have to be connected to the Internet, but generally have a limited connection. An extranet is an extension of an intranet that allows secure communications to users outside of the intranet (e.g. business partners, customers).[42]

text: Unofficially, the Internet is the set of users, enterprises, and content providers that are interconnected by Internet Service Providers (ISP). From an engineering viewpoint, the Internet is the set of subnets, and aggregates of subnets, which share the registered IP address space and exchange information about the reachability of those IP addresses using the Border Gateway Protocol. Typically, the human-readable names of servers are translated to IP addresses, transparently to users, via the directory function of the Domain Name System (DNS).

text: Over the Internet, there can be business-to-business (B2B), business-to-consumer (B2C) and consumer-to-consumer (C2C) communications. When money or sensitive information is exchanged, the communications are apt to be protected by some form of communications security mechanism. Intranets and extranets can be securely superimposed onto the Internet, without any access by general Internet users and administrators, using secure Virtual Private Network (VPN) technology.


document_title: List of cities in New York

question_text: city in upstate new york starts with a u

root

text: List of cities in New York

text:
Part of a series on

Regions of New York

Downstate New York[hide]

New York City
Long Island
Hudson Valley (Lower and Middle)

Upstate New York[hide]

Hudson Valley (Middle and Upper)
Capital District
North Country
Southern Tier
Mohawk Valley
Central New York
Finger Lakes
Western New York

Administrative divisions[show]

Counties
Cities
Towns
Indian reservations
Villages
Census-designated places
Places (including hamlets)

Timelines of town creation[show]

Downstate New York
Hudson Valley
Capital District
North Country
Central New York
Southern Tier
Western New York

v
t
e

tag: table

text: This list of the 62 cities in New York State contains all municipalities incorporated as cities and also gives the primary county in which each city is located.

tag: p

text: Except for Sherrill, the cities are distinct from towns. Geneva and New York City are the only cities in more than one county.

text:
Top
0–9
A
B
C
D
E
F
G
H
I
J
K
L
M
N
O
P
Q
R
S
T
U
V
W
X
Y
Z

tag: ul

text: List of cities[edit]

text:
City
County
Population [1]
(2011 census estimate)
Incorporation
date
FIPS code
(subdivision)
FIPS code
(place)
GNIS feature ID

Albany
Albany
97,660
1686
3600101000
3601000
00978659

Amsterdam
Montgomery
18,507
1830
3605702066
3602066
00978677

Auburn
Cayuga
27,590
1848
3601103078
3603078
00978695

Batavia
Genesee
15,444
1915
3603704715
3604715
00978713

Beacon
Dutchess
15,565
1913
3602705100
3605100
00978716

Binghamton
Broome
46,996
1867
3600706607
3606607
00978733

Buffalo
Erie
261,025
1832
3602911000
3611000
00978764

Canandaigua
Ontario
10,604
1913
3606912144
3612144
00978784

Cohoes
Albany
16,133
1869
3600116749
3616749
00978847

Corning
Steuben
11,187
1890
3610118256
3618256
00978867

Cortland
Cortland
19,212
1900
3602318388
3618388
00978870

Dunkirk
Chautauqua
12,511
1888
3601321105
3621105
00978911

Elmira
Chemung
29,204
1864
3601524229
3624229
00978938

Fulton
Oswego
11,906
1902
3607527815
3627815
00978979

Geneva
Ontario
Seneca[A]
13,324
1898
3606928640
3609928640
3628640
00978992

Glen Cove
Nassau
27,063
1918
3605929113
3629113
00979003

Glens Falls
Warren
14,728
1908
3611329333
3629333
00979004

Gloversville
Fulton
15,621
1890
3603529443
3629443
00979006

Hornell
Steuben
8,566
1888
3610135672
3635672
00979078

Hudson
Columbia
6,657
1785
3602135969
3635969
00979083

Ithaca
Tompkins
30,054
1888
3610938077
3638077
00979099

Jamestown
Chautauqua
31,020
1886
3601338264
3638264
00979102

Johnstown
Fulton
8,718
1895
3603538781
3638781
00979110

Kingston
Ulster
23,887
1872
3611139727
3639727
00979118

Lackawanna
Erie
18,121
1909
3602940189
3640189
00979124

Little Falls
Herkimer
5,188
1895
3604342741
3642741
00979157

Lockport
Niagara
21,119
1865
3606343082
3643082
00979164

Long Beach
Nassau
33,395
1922
3605943335
3643335
00979167

Mechanicville
Saratoga
5,227
1915
3609146360
3646360
00979207

Middletown
Orange
28,243
1888
3607147042
3647042
00979217

Mount Vernon
Westchester
67,780
1892
3611949121
3649121
00979245

New Rochelle
Westchester
77,606
1889
3611950617
3650617
00979271

New York City
Bronx, Kings, New York, Queens, and Richmond
8,550,405
1653[B]

3651000
02395220

Newburgh
Orange
29,026
1865
3607150034
3650034
00979258

Niagara Falls
Niagara
50,086
1892
3606351055
3651055
00979276

North Tonawanda
Niagara
31,501
1897
3606353682
3653682
00979293

Norwich
Chenango
7,139
1914
3601753979
3653979
00979296

Ogdensburg
St. Lawrence
11,104
1868
3608954485
3654485
00979301

Olean
Cattaraugus
14,363
1854
3600954716
3654716
00979305

Oneida
Madison
11,387
1901
3605354837
3654837
00979308

Oneonta
Otsego
13,843
1908
3607754881
3654881
00979309

Oswego
Oswego
18,158
1848
3607555574
3655574
00979325

Peekskill
Westchester
23,755
1940
3611956979
3656979
00979348

Plattsburgh
Clinton
19,949
1902
3601958574
3658574
00979376

Port Jervis
Orange
8,878
1907
3607159388
3659388
00979387

Poughkeepsie
Dutchess
32,790
1854
3602759641
3659641
00979392

Rensselaer
Rensselaer
9,391
1897
3608361148
3661148
00979414

Rochester
Monroe
210,855
1834
3605563000
3663000
00979426

Rome
Oneida
33,660
1870
3606563418
3663418
00979430

Rye
Westchester
15,834
1942
3611964309
3664309
00979445

Salamanca
Cattaraugus
5,780
1913
3600964749
3664749
00979450

Saratoga Springs
Saratoga
26,727
1915
3609165255
3665255
00979462

Schenectady
Schenectady
66,273
1798
3609365508
3665508
00979468

Sherrill
Oneida
3,147
1916
3606566993
3666993
00979493

Syracuse
Onondaga
145,151
1848
3606773000
3673000
00979539

Tonawanda
Erie
15,112
1904
3602974166
3674166
00979550

Troy
Rensselaer
50,120
1816
3608375484
3675484
00979559

Utica
Oneida
62,110
1832
3606576540
3676540
00979575

Watertown
Jefferson
27,423
1869
3604578608
3678608
00979604

Watervliet
Albany
10,230
1896
3600178674
3678674
00979606

White Plains
Westchester
57,258
1916
3611981677
3681677
00979637

Yonkers
Westchester
197,399
1872
3611984000
3684000
00979660

text: Extremes in size and population[edit]

text: The most populous and largest city by area in the state is by far New York, home to over 8.2 million people and comprising just over 300 square miles (800 km2) of land (468.87 square miles (1,210 km2) including water). The least populous city is Sherrill, with just 3,147 inhabitants in 2000. The smallest city by area is Mechanicville, which covers 0.91 square miles (2.4 km2) (of which 0.08 square miles (0.2 km2) is water).[1]

text: Gallery[edit]

text:
New York City, largest city in New York and the United States.

New York City, largest city in New York and the United States.

Buffalo, the second largest city in New York

Rochester, the third largest.

Yonkers, the fourth largest

Syracuse, the fifth largest.

Albany, the sixth largest and capital of New York.

New Rochelle, the seventh largest.

Schenectady, the ninth largest.

White Plains

Troy

Niagara Falls

Binghamton

Long Beach

Poughkeepsie

Jamestown

Watertown


document_title: Samuel de Champlain Provincial Park

question_text: samuel de champlain provincial park nipissing district on

text: Samuel de Champlain Provincial Park

text:
Samuel de Champlain Provincial Park

IUCN category II (national park)

Location
Ontario, Canada

Nearest city
Mattawa, Ontario

Coordinates
46°17′30″N 78°52′30″W / 46.29167°N 78.87500°W / 46.29167; -78.87500Coordinates: 46°17′30″N 78°52′30″W / 46.29167°N 78.87500°W / 46.29167; -78.87500

Area
25.5 km2 (9.8 sq mi)

Governing body
Ontario Parks

text: Samuel de Champlain Provincial Park is a provincial park in Ontario, Canada.

text: The park spans both sides of the Mattawa River. It has an area of 25.5 square kilometres (9.8 sq mi) and is about 14 kilometres (8.7 mi) west of Mattawa, Ontario, Canada. It is administered by Ontario Parks, which classifies it as a natural environment park.

text: This park is popular in the summer with campers, providing many recreational activities such as canoeing, swimming, hiking, wildlife viewing, and other family activities. The visitors centre houses the Voyageur Heritage Centre, which highlights the historic importance of the Mattawa River to the fur trade through interactive exhibits. The park is also home to the Canadian Ecology Centre, an outdoor education centre, which provides educational programs on sustainable forestry.

text: The park is named after Samuel de Champlain, one of the first French explorers of Canada of the 17th century.


document_title: Immunity (medical)

question_text: the type of immunity that results from a vaccination or infection

text: Immunity (medical)

text: Innate and adaptive[edit]

text: This section does not cite any sources. Please help improve this section by adding citations to reliable sources. Unsourced material may be challenged and removed. (June 2015) (Learn how and when to remove this template message)

text: Immunity is the capability of multicellular organisms to resist harmful microorganisms from entering it. Immunity involves both specific and nonspecific components. The nonspecific components act as barriers or eliminators of a wide range of pathogens irrespective of their antigenic make-up. Other components of the immune system adapt themselves to each new disease encountered and can generate pathogen-specific immunity.

text: An immune system may contain innate and adaptive components. The innate system in mammalians, for example, is composed of primitive bone marrow cells that are programmed to recognise foreign substances and react. The adaptive system is composed of more advanced lymphatic cells that are programmed to recognise self-substances and don't react. The reaction to foreign substances is etymologically described as inflammation, meaning to set on fire. The non-reaction to self-substances is described as immunity, meaning to exempt or as immunotolerance. These two components of the immune system create a dynamic biological environment where "health" can be seen as a physical state where the self is immunologically spared, and what is foreign is inflammatorily and immunologically eliminated. "Disease" can arise when what is foreign cannot be eliminated or what is self is not spared.

text: Innate immunity, also called native immunity, exists by virtue of an organisms constitution, that is its genetic make-up, without an external stimulation or a previous infection. It is divided into two types: (a) Non-Specific innate immunity, a degree of resistance to all infections in general. (b) Specific innate immunity, a resistance to a particular kind of microorganism only. As a result, some races, particular individuals or breeds in agriculture do not suffer from certain infectious diseases.

text: Adaptive immunity can be sub-divided depending on how the immunity was introduced in 'naturally acquired' through chance contact with a disease-causing agent, whereas 'artificially acquired immunity' develops through deliberate actions such as vaccination. Both naturally and artificially acquired immunity can be further subdivided depending on whether the host built up immunity itself by antigen as 'active immunity' and lasts long-term, sometimes lifelong. 'Passive immunity' is acquired through transfer (injection or infusion) of antibodies or activated T-cells from an immune host; it is short lived—usually lasting only a few months. The diagram below summarizes these divisions of immunity.

text: Adaptive immunity can also be divided by the type of immune mediators involved; humoral immunity is the aspect of immunity that is mediated by secreted antibodies, whereas cell mediated immunity involves T-lymphocytes alone. Humoral immunity is called active when the organism generates its antibodies, and passive when antibodies are transferred between individuals or species. Similarly, cell-mediated immunity is active when the organisms’ T-cells are stimulated, and passive when T cells come from another organism.

text: History of theories[edit]

text: The concept of immunity has intrigued mankind for thousands of years. The prehistoric view of disease was that supernatural forces caused it, and that illness was a form of theurgic punishment for "bad deeds" or "evil thoughts" visited upon the soul by the gods or by one's enemies.[1] Between the time of Hippocrates and the 19th century, when the foundations of the scientific methods were laid, diseases were attributed to an alteration or imbalance in one of the four humors (blood, phlegm, yellow bile or black bile).[2] Also popular during this time before learning that communicable diseases came from germs/microbes was the miasma theory, which held that diseases such as cholera or the Black Plague were caused by a miasma, a noxious form of "bad air".[1] If someone were exposed to the miasma in a swamp, in evening air, or breathing air in a sickroom or hospital ward, they could get a disease.

text: The modern word "immunity" derives from the Latin immunis, meaning exemption from military service, tax payments or other public services.[3] The first written descriptions of the concept of immunity may have been made by the Athenian Thucydides who, in 430 BC, described that when the plague hit Athens: "the sick and the dying were tended by the pitying care of those who had recovered, because they knew the course of the disease and were themselves free from apprehensions. For no one was ever attacked a second time, or not with a fatal result".[3] The term "immunes", is also found in the epic poem "Pharsalia" written around 60 B.C. by the poet Marcus Annaeus Lucanus to describe a North African tribe's resistance to snake venom.[2]

text: The first clinical description of immunity which arose from a specific disease-causing organism is probably Kitab fi al-jadari wa-al-hasbah ('A Treatise on Smallpox and Measles', translated 1848[4]) written by the Islamic physician Al-Razi in the 9th century. In the treatise, Al Razi describes the clinical presentation of smallpox and measles and goes on to indicate that exposure to these specific agents confers lasting immunity (although he does not use this term).[2] The first scientist who developed a full theory of immunity was Ilya Mechnikov after he revealed phagocytosis in 1882. With Louis Pasteur's germ theory of disease, the fledgling science of immunology began to explain how bacteria caused disease, and how, following infection, the human body gained the ability to resist further infections.[3]

text: The birth of active immunotherapy may have begun with Mithridates VI of Pontus.[5] To induce active immunity for snake venom, he recommended using a method similar to modern toxoid serum therapy, by drinking the blood of animals which fed on venomous snakes.[5] According to Jean de Maleissye, Mithridates assumed that animals feeding on venomous snakes acquired some detoxifying property in their bodies, and their blood must contain attenuated or transformed components of the snake venom. The action of those components might be strengthening the body to resist against the venom instead of exerting a toxic effect. Mithridates reasoned that, by drinking the blood of these animals, he could acquire the similar resistance to the snake venom as the animals feeding on the snakes.[5] Similarly, he sought to harden himself against poison and took daily sub-lethal doses to build tolerance. Mithridates is also said to have fashioned a 'universal antidote' to protect him from all earthly poisons.[2] For nearly 2000 years, poisons were thought to be the proximate cause of disease, and a complicated mixture of ingredients, called Mithridate, was used to cure poisoning during the Renaissance.[2] An updated version of this cure, Theriacum Andromachi, was used well into the 19th century.[6] In 1888 Emile Roux and Alexandre Yersin isolated diphtheria toxin, and following the 1890 discovery by Behring and Kitasato of antitoxin based immunity to diphtheria and tetanus, the antitoxin became the first major success of modern therapeutic Immunology.[2]

text: In Europe, the induction of active immunity emerged in an attempt to contain smallpox. Immunization, however, had existed in various forms for at least a thousand years.[3] The earliest use of immunization is unknown, however, around 1000 A.D. the Chinese began practicing a form of immunization by drying and inhaling powders derived from the crusts of smallpox lesions.[3] Around the fifteenth century in India, the Ottoman Empire, and east Africa, the practice of inoculation (poking the skin with powdered material derived from smallpox crusts) became quite common.[3] This practice was first introduced into the west in 1721 by Lady Mary Wortley Montagu.[3] In 1798, Edward Jenner introduced the far safer method of deliberate infection with cowpox virus, (smallpox vaccine), which caused a mild infection that also induced immunity to smallpox. By 1800 the procedure was referred to as vaccination. To avoid confusion, smallpox inoculation was increasingly referred to as variolation, and it became common practice to use this term without regard for chronology. The success and general acceptance of Jenner's procedure would later drive the general nature of vaccination developed by Pasteur and others towards the end of the 19th century.[2] In 1891, Pasteur widened the definition of vaccine in honour of Jenner and it then became essential to qualify the term, by referring to polio vaccine, measles vaccine etc.

text: Passive[edit]

text: Passive immunity is the transfer of active immunity, in the form of readymade antibodies, from one individual to another. Passive immunity can occur naturally, when maternal antibodies are transferred to the foetus through the placenta, and can also be induced artificially, when high levels of human (or horse) antibodies specific for a pathogen or toxin are transferred to non-immune individuals. Passive immunization is used when there is a high risk of infection and insufficient time for the body to develop its own immune response, or to reduce the symptoms of ongoing or immunosuppressive diseases.[7] Passive immunity provides immediate protection, but the body does not develop memory, therefore the patient is at risk of being infected by the same pathogen later.[8]

text: Naturally acquired[edit]

text: Maternal passive immunity is a type of naturally acquired passive immunity, and refers to antibody-mediated immunity conveyed to a fetus by its mother during pregnancy. Maternal antibodies (MatAb) are passed through the placenta to the fetus by an FcRn receptor on placental cells. This occurs around the third month of gestation. IgG is the only antibody isotype that can pass through the placenta. Passive immunity is also provided through the transfer of IgA antibodies found in breast milk that are transferred to the gut of the infant, protecting against bacterial infections, until the newborn can synthesize its antibodies. Colostrum present in mothers milk is an example of active immunity. [8]

text: Artificially acquired[edit]

text: Artificially acquired passive immunity is a short-term immunization induced by the transfer of antibodies, which can be administered in several forms; as human or animal blood plasma, as pooled human immunoglobulin for intravenous (IVIG) or intramuscular (IG) use, and in the form of monoclonal antibodies (MAb). Passive transfer is used prophylactically in the case of immunodeficiency diseases, such as hypogammaglobulinemia.[9] It is also used in the treatment of several types of acute infection, and to treat poisoning.[7] Immunity derived from passive immunization lasts for only a short period of time, and there is also a potential risk for hypersensitivity reactions, and serum sickness, especially from gamma globulin of non-human origin.[8]

text: The artificial induction of passive immunity has been used for over a century to treat infectious disease, and before the advent of antibiotics, was often the only specific treatment for certain infections. Immunoglobulin therapy continued to be a first line therapy in the treatment of severe respiratory diseases until the 1930s, even after sulfonamide lot antibiotics were introduced.[9]

text: Transfer of activated T-cells[edit]

text: Passive or "adoptive transfer" of cell-mediated immunity, is conferred by the transfer of "sensitized" or activated T-cells from one individual into another. It is rarely used in humans because it requires histocompatible (matched) donors, which are often difficult to find. In unmatched donors this type of transfer carries severe risks of graft versus host disease.[7] It has, however, been used to treat certain diseases including some types of cancer and immunodeficiency. This type of transfer differs from a bone marrow transplant, in which (undifferentiated) hematopoietic stem cells are transferred.

text: Active[edit]

text: When B cells and T cells are activated by a pathogen, memory B-cells and T- cells develop, and the primary immune response results. Throughout the lifetime of an animal, these memory cells will "remember" each specific pathogen encountered, and can mount a strong secondary response if the pathogen is detected again. The primary and secondary responses were first described in 1921 by English immunologist Alexander Glenny[10] although the mechanism involved was not discovered until later.This type of immunity is both active and adaptive because the body's immune system prepares itself for future challenges. Active immunity often involves both the cell-mediated and humoral aspects of immunity as well as input from the innate immune system.

text: Naturally acquired[edit]

text: Naturally acquired active immunity occurs when a person is exposed to a live pathogen and develops a primary immune response, which leads to immunological memory.[7] This type of immunity is "natural" because deliberate exposure does not induce it. Many disorders of immune system function can affect the formation of active immunity such as immunodeficiency (both acquired and congenital forms) and immunosuppression.

text: Artificially acquired[edit]

text: Artificially acquired active immunity can be induced by a vaccine, a substance that contains antigen. A vaccine stimulates a primary response against the antigen without causing symptoms of the disease.[7] Richard Dunning coined the term vaccination, a colleague of Edward Jenner, and adapted by Louis Pasteur for his pioneering work in vaccination. The method Pasteur used entailed treating the infectious agents for those diseases, so they lost the ability to cause serious disease. Pasteur adopted the name vaccine as a generic term in honor of Jenner's discovery, which Pasteur's work built upon.

text: In 1807, Bavaria became the first group to require that their military recruits be vaccinated against smallpox, as the spread of smallpox was linked to combat.[11] Subsequently, the practice of vaccination would increase with the spread of war.

text: There are four types of traditional vaccines:[12]

text:
Inactivated vaccines are composed of micro-organisms that have been killed with chemicals and/or heat and are no longer infectious. Examples are vaccines against flu, cholera, plague, and hepatitis A. Most vaccines of this type are likely to require booster shots.
Live, attenuated vaccines are composed of micro-organisms that have been cultivated under conditions which disable their ability to induce disease. These responses are more durable and do not generally require booster shots. Examples include yellow fever, measles, rubella, and mumps.
Toxoids are inactivated toxic compounds from micro-organisms in cases where these (rather than the micro-organism itself) cause illness, used prior to an encounter with the toxin of the micro-organism. Examples of toxoid-based vaccines include tetanus and diphtheria.
Subunit vaccines are composed of small fragments of disease-causing organisms. A characteristic example is the subunit vaccine against Hepatitis B virus.

text: Most vaccines are given by hypodermic or intramuscular injection as they are not absorbed reliably through the gut. Live attenuated polio and some typhoid and cholera vaccines are given orally in order to produce immunity based in the bowel.


document_title: List of female Indian chief ministers

question_text: who is the first woman cm of india

question_tokens: who is the first woman cm of india

text: List of female Indian chief ministers

text: Sixteen women have served as the chief minister of an Indian state. Currently, three are in office — Vasundhara Raje, Mamata Banerjee and Mehbooba Mufti. Of the thirteen states to have been headed by a female chief minister, only three—Delhi, Tamil Nadu and Uttar Pradesh—have had two woman premiers. Five of the woman chief ministers belonged to the Indian National Congress, four to the Bharatiya Janata Party and two to the All India Anna Dravida Munnetra Kazhagam.

text: In the Republic of India, a chief minister is the head of government of each of twenty-nine states and two union territories (Delhi and Puducherry). According to the Constitution of India, at the state-level, the governor is de jure head, but de facto executive authority rests with the chief minister. Following elections to the state legislative assembly, the governor usually invites the party (or coalition) with a majority of seats to form the government. The governor appoints the chief minister, whose council of ministers are collectively responsible to the assembly. Given he has the confidence of the assembly, the chief minister's term is for five years; the office is subject to no term limits.[1]

text: Chronological list of female Indian chief ministers[edit]

text: *  incumbent chief minister

text:
No
Name
Portrait
State
Term(s)
Total tenure
Party

1
Sucheta Kriplani

Uttar Pradesh
2 October 1963 – 13 March 1967
1258 days
Indian National Congress

2
Nandini Satpathy
–
Orissa
14 June 1972 – 3 March 1973
6 March 1974 – 16 December 1976
1278 days
Indian National Congress

3
Shashikala Kakodkar

Goa
12 August 1973 – 27 April 1979
2084 days
Maharashtrawadi Gomantak Party

4
Syeda Anwara Taimur
–
Assam
6 December 1980 – 30 June 1981
206 days
Indian National Congress

5
Janaki Ramachandran
–
Tamil Nadu
7 January 1988 – 30 January 1988
23 days
All India Anna Dravida Munnetra Kazhagam

6
Jayalalithaa

Tamil Nadu
24 June 1991 – 12 May 1996
14 May 2001 – 21 September 2001
2 March 2002 – 12 May 2006
16 May 2011 – 27 September 2014
23 May 2015 – 5 December 2016
5238 days
All India Anna Dravida Munnetra Kazhagam

7
Mayawati

Uttar Pradesh
13 June 1995 – 18 October 1995
21 March 1997 – 21 September 1997
3 May 2002 – 29 August 2003
13 May 2007 – 15 March 2012
2562 days
Bahujan Samaj Party

8
Rajinder Kaur Bhattal
–
Punjab
21 January 1996 – 12 February 1997
388 days
Indian National Congress

9
Rabri Devi

Bihar
25 July 1997 – 11 February 1999
9 March 1999 – 2 March 2000
11 March 2000 – 6 March 2005
2746 days
Rashtriya Janata Dal

10
Sushma Swaraj

Delhi
12 October 1998 – 3 December 1998
52 days
Bharatiya Janata Party

11
Sheila Dikshit

Delhi
3 December 1998 – 28 December 2013
5504 days
Indian National Congress

12
Uma Bharati

Madhya Pradesh
8 December 2003 – 23 August 2004
259 days
Bharatiya Janata Party

13
Vasundhara Raje *

Rajasthan
8 December 2003 – 18 December 2008
8 December 2013 – present
3336 days
Bharatiya Janata Party

14
Mamata Banerjee *

West Bengal
20 May 2011 – present
2437 days
All India Trinamool Congress

15
Anandiben Patel

Gujarat
22 May 2014 – 7 August 2016
808 days
Bharatiya Janata Party

16
Mehbooba Mufti *

Jammu and Kashmir
4 April 2016 – present
656 days
Jammu and Kashmir Peoples Democratic Party