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54-548: The ticker tape revolutionized financial markets, as it relayed information from trading floors continuously and simultaneously across geographical distances. Paper ticker tape became obsolete in the 1960s, as television and computers were increasingly used to transmit financial information. The concept of the stock ticker lives on, however, in the scrolling electronic tickers seen on brokerage walls and on news and financial television channels. Ticker tape stock price telegraphs were invented in 1867 by Edward A. Calahan , an employee of

108-756: A protocol stack , often constructed per the OSI model, communications functions are divided up into protocol layers, where each layer leverages the services of the layer below it until the lowest layer controls the hardware that sends information across the media. The use of protocol layering is 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

162-503: A diverse set of networking capabilities. The protocols have a flat addressing scheme. They operate mostly at layers 1 and 2 of the OSI model. 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

216-469: A group of rushing messenger boys which inspired him to improve exchange communications. These young men called runners had to dash from the Stock Exchange to their offices to report the changes in share values. Calahan realized that the prices could be sent directly via telegraph to each broker's office much more quickly and efficiently in a permanent stream of information. With the idea, he invented

270-440: A large, congested network into an aggregation of smaller, more efficient networks. A router is an internetworking device that forwards packets between networks by processing the addressing or routing information included in the packet. The routing information is often processed in conjunction with the routing table . A router uses its routing table to determine where to forward packets and does not require broadcasting packets which

324-516: A long distance via telegraph wiring. In its infancy, the ticker used the same symbols as Morse code as a medium for conveying messages. One of the earliest practical stock ticker machines, the Universal Stock Ticker developed by Thomas Edison in 1869, used alphanumeric characters with a printing speed of approximately one character per second. Previously, stock prices had been hand-delivered via written or verbal messages. Since

378-440: A multi-port bridge. Switches normally have numerous ports, facilitating a star topology for devices, and for cascading additional switches. Bridges and switches operate at the data link layer (layer 2) of the OSI model and bridge traffic between two or more network segments to form a single local network. Both are devices that forward frames of data between ports based on the destination MAC address in each frame. They learn

432-457: A repeater hub assists with collision detection and fault isolation for the network. Hubs and repeaters in LANs have been largely obsoleted by modern network switches. Network bridges and network switches are distinct from a hub in that they only forward frames to the ports involved in the communication whereas a hub forwards to all ports. Bridges only have two ports but a switch can be thought of as

486-418: 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. Therefore, most network diagrams are arranged by their network topology which is the map of logical interconnections of network hosts. Common topologies are: The physical layout of the nodes in a network may not necessarily reflect

540-403: A standard voice telephone line. Modems are still commonly used for telephone lines, using a digital subscriber line technology and cable television systems using DOCSIS technology. A firewall is a network device or software for controlling network security and access rules. Firewalls are inserted in connections between secure internal networks and potentially insecure external networks such as

594-441: A stock is trading higher than the previous day's (green), lower than previous (red), or has remained unchanged (blue or white). In the early days of baseball , before electronic scoreboards, manual score turners used a ticker to get the latest scores from around the league. Today, computers and electronic scoreboards have replaced the manual scoreboard and the ticker. Used ticker tape was repurposed as confetti , to be thrown from

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648-877: A transmission medium. Power line communication uses a building's power cabling to transmit data. The following classes of wired technologies are used in computer networking. Network connections can be established wirelessly using radio or other electromagnetic means of communication. The last two cases have a large round-trip delay time , which gives slow two-way communication but does not prevent sending large amounts of information (they can have high throughput). Apart from any physical transmission media, networks are built from additional basic system building blocks, such as network interface controllers , repeaters , hubs , bridges , switches , routers , modems, and firewalls . Any particular piece of equipment will frequently contain multiple building blocks and so may perform multiple functions. A network interface controller (NIC)

702-406: A variety of network topologies . The nodes of a computer network can include personal computers , servers , networking hardware , or other specialized or general-purpose hosts . They are identified by network addresses and may have hostnames . Hostnames serve as memorable labels for the nodes and are rarely changed after initial assignment. Network addresses serve for locating and identifying

756-495: A variety of different sources, primarily to support circuit-switched digital telephony . However, due to its protocol neutrality and transport-oriented features, SONET/SDH also was the obvious choice for transporting Asynchronous Transfer Mode (ATM) frames. 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

810-657: A virtual system of links that run on top of the Internet . Overlay networks have been used since the early days of networking, back when computers were connected via telephone lines using modems, even before data networks were developed. 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 . 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

864-522: Is computer hardware that connects the computer to the network media and has the ability to process low-level network information. For example, the NIC may have a connector for plugging in a cable, or an aerial for wireless transmission and reception, and the associated circuitry. In Ethernet networks, each NIC has a unique Media Access Control (MAC) address —usually stored in the controller's permanent memory. To avoid address conflicts between network devices,

918-422: Is a virtual 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

972-566: Is also found in WLANs ) – it is what the home user sees when the user has to enter a "wireless access key". Ethernet is a family of technologies used in wired LANs. It is described by a set of standards together called IEEE 802.3 published by the Institute of Electrical and Electronics Engineers. Wireless LAN based on the IEEE 802.11 standards, also widely known as WLAN or WiFi, is probably

1026-478: 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 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. Repeaters work on

1080-412: Is inefficient for very big networks. 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. Early modems modulated audio signals sent over

1134-404: 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 is not 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. The physical link technologies of packet networks typically limit

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1188-459: Is used between the wireless router and the home user's personal computer when the user is surfing the web. There are many communication protocols, a few of which are described below. The Internet protocol suite , also called TCP/IP, is the foundation of all modern networking. It offers connection-less and connection-oriented services over an inherently unreliable network traversed by datagram transmission using Internet protocol (IP). At its core,

1242-529: The American Telegraph Company who later founded The ADT Corporation . Although telegraphic printing systems were invented by Royal Earl House in 1846, early models were fragile, required hand-cranked power, frequently went out of synchronization between sender and receiver, and did not become popular in widespread commercial use. David E. Hughes improved the printing telegraph design with clockwork weight power in 1856, and his design

1296-462: 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. A repeater

1350-477: The World Wide Web , digital video and audio , shared use of application and storage servers , printers and fax machines , and use of email and instant messaging applications. Computer networking may be considered a branch of computer science , computer engineering , and telecommunications , since it relies on the theoretical and practical application of the related disciplines. Computer networking

1404-706: The ticker tape in 1867. After many years of work he started the company ADT security, which still stands today. He was inducted to the National Inventors Hall of Fame in 2006 for this invention. Computer network A computer network is a set of computers sharing resources located on or provided by network nodes . Computers use common communication protocols over digital interconnections to communicate with each other. These interconnections are made up of telecommunication network technologies based on physically wired, optical , and wireless radio-frequency methods that may be arranged in

1458-537: The " Canyon of Heroes " in Manhattan, most often when local sports teams win a championship. However, actual ticker tape is not used any longer during these parades; often, pieces of paper from paper shredders are used as a convenient source of confetti. Ticker tape was also incorporated into some of the weaver Dorothy Liebes ' unusual art textiles. Edward A. Calahan Edward Augustin Calahan (1838–1912)

1512-440: The Internet protocol suite or Ethernet that use variable-sized packets or frames . ATM has similarities 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

1566-574: The Internet. 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 . A communication protocol is a set of rules for exchanging information over a network. 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. In

1620-627: The actual data exchange begins. ATM still plays a role in the last mile , which is the connection between an Internet service provider and the home user. 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). Routing

1674-468: The association of physical ports to MAC addresses by examining the source addresses of received frames and only forward the frame when necessary. If an unknown destination MAC is targeted, the device broadcasts the request to all ports except the source, and discovers the location from the reply. Bridges and switches divide the network's collision domain but maintain a single broadcast domain. Network segmentation through bridging and switching helps break down

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1728-419: The company. The shares traded is the volume for the trade being quoted. Price traded refers to the price per share of a particular trade. Change direction is a visual cue showing whether the stock is trading higher or lower than the previous trade, hence the terms downtick and uptick . Change amount refers to the difference in price from the previous day's closing. Many today include color to indicate whether

1782-494: The first time, trades were being done in what is now thought of as near real-time . By the 1880s, there were about a thousand stock tickers installed in the offices of New York bankers and brokers. In 1890, members of the exchange agreed to create the New York Quotation Co., buying up all other ticker companies to ensure accuracy of reporting of price and volume activity. Stock ticker machines are an ancestor of

1836-620: The keyboard of a piano with black keys indicating letters and the white keys indicating numbers and fractions, corresponding to two rotating type wheels in the connected ticker tape printers. Newer and more efficient tickers became available in the 1930s, but these newer and better tickers still had an approximate 15- to 20-minute delay. Ticker machines became obsolete in the 1960s, replaced by computer networks ; none have been manufactured for use for decades. However, working reproductions of at least one model are now being manufactured for museums and collectors. Simulated ticker displays, named after

1890-668: The literature as the physical medium ) used to link devices to form a computer network include electrical cable , optical fiber , and free space. In the OSI model , the software to handle the media is defined at layers 1 and 2 — the physical layer and the data link layer. A widely adopted family that uses copper and fiber media in local area network (LAN) technology are collectively known as Ethernet. The media and protocol standards that enable communication between networked devices over Ethernet are defined by IEEE 802.3 . Wireless LAN standards use radio waves , others use infrared signals as

1944-665: The means that allow mapping of a fully connected IP overlay network to its underlying network. 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. Overlay networks have also been proposed as a way to improve Internet routing, such as through quality of service guarantees 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

1998-404: The modern computer printer , being one of the first applications of transmitting text over a wire to a printing device , based on the printing telegraph . This used the technology of the then-recently invented telegraph machines , with the advantage that the output was readable text, instead of the dots and dashes of Morse code . A special typewriter designed for operation over telegraph wires

2052-415: The most well-known member of the IEEE 802 protocol family for home users today. IEEE 802.11 shares many properties with wired Ethernet. 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

2106-412: 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. With packets, the bandwidth of the transmission medium can be better shared among users than if the network were circuit switched . When one user

2160-420: The network topology. As an example, with FDDI , the network topology is a ring, but the physical topology is often a star, because all neighboring connections can be routed via a central physical location. Physical layout is not completely irrelevant, however, as common ducting and equipment locations can represent single points of failure due to issues like fires, power failures and flooding. An overlay network

2214-729: The network. 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 . For example, Akamai Technologies manages an overlay network that provides reliable, efficient content delivery (a kind of multicast ). Academic research includes end system multicast, resilient routing and quality of service studies, among others. The transmission media (often referred to in

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2268-494: The nodes by communication protocols such as the Internet Protocol . Computer networks may be classified by many criteria, including the transmission medium used to carry signals, bandwidth , communications protocols to organize network traffic , the network size, the topology, traffic control mechanisms, and organizational intent. Computer networks support many applications and services , such as access to

2322-473: The original machines, still exist as part of the display of television news channels and on some websites—see news ticker . One of the most famous outdoor displays is the simulated ticker scrolling marquee called " The Zipper " located at One Times Square in New York City. Ticker tapes then and now contain generally the same information. The ticker symbol is a unique set of characters used to identify

2376-520: The physical layer of the OSI model but still 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 used in a network, e.g., the Ethernet 5-4-3 rule . An Ethernet repeater with multiple ports is known as an Ethernet hub . In addition to reconditioning and distributing network signals,

2430-456: 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. The Internet protocol suite is the defining set of protocols for the Internet. IEEE 802 is a family of IEEE standards dealing with local area networks and metropolitan area networks. The complete IEEE 802 protocol suite provides

2484-515: The sharing of files and information, giving authorized users access to data stored on other computers. Distributed computing leverages resources from multiple computers across a network to perform tasks collaboratively. Most modern computer networks use protocols based on packet-mode transmission. A network packet is a formatted unit of data carried by a packet-switched network . Packets consist of two types of data: control information and user data (payload). The control information provides data

2538-493: The size of packets to a certain maximum transmission unit (MTU). A longer message may be fragmented before it is transferred and once the packets arrive, they are reassembled to construct the original message. The physical or geographic locations of network nodes and links generally have relatively little effect on a network, but the topology of interconnections of a network can significantly affect its throughput and reliability. With many technologies, such as bus or star networks,

2592-426: The useful time-span of individual quotes is very brief, they generally had not been sent long distances; aggregated summaries, typically for one day, were sent instead. The increase in speed provided by the ticker allowed for faster and more exact sales. Since the ticker ran continuously, updates to a stock's price whenever the price changed became effective much faster and trading became a more time-sensitive matter. For

2646-463: The windows above parades either cut up into scraps or thrown as whole spools, primarily in lower Manhattan ; this became known as a ticker tape parade . Ticker tape parades generally celebrated some significant event, such as the end of World War I and World War II , or the safe return of one of the early astronauts . Ticker tape parades are still held in New York City , specifically in

2700-663: Was an American inventor, credited with invention of a ticker tape , gold and stock tickers, and a multiplex telegraph system. Calahan was born in Boston, Massachusetts . He left school at the age of 11 to pursue his interest to be part of a modern business. Calahan came to New York in 1861 and made his residence in Brooklyn . He joined as chief telegrapher in Western Union telegraph company's New York office at Manhattan . While working with Western Union , he encountered

2754-473: Was called ticker tape . The word ticker comes from the distinct tapping (or ticking ) noise the machines made while printing. Pulses on the telegraph line made a letter wheel turn step by step until the correct symbol was reached and then printed. A typical 32-symbol letter wheel had to turn on average 15 steps until the next letter could be printed resulting in a very slow printing speed of one character per second. In 1883, ticker transmitter keyboards resembled

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2808-407: Was further improved and became viable for commercial use when George M. Phelps devised a resynchronization system in 1858. The first stock price ticker system using a telegraphic printer was invented by Edward A. Calahan in 1863; he unveiled his device in New York City on November 15, 1867. Early versions of stock tickers provided the first mechanical means of conveying stock prices ("quotes"), over

2862-462: Was influenced by a wide array of technological developments and historical milestones. Computer networks enhance how users communicate with each other by using various electronic methods like email, instant messaging, online chat, voice and video calls, and video conferencing. Networks also enable the sharing of computing resources. For example, a user can print a document on a shared printer or use shared storage devices. Additionally, networks allow for

2916-411: Was used at the opposite end of the telegraph wire connection to the ticker machine. Text typed on the typewriter was displayed on the ticker machine at the opposite end of the connection. The machines printed a series of ticker symbols (usually shortened forms of a company's name), followed by brief information about the price of that company's stock; the thin strip of paper on which they were printed

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