Communication

== Computer ==
{{main|Computer networks}}
[[File:Example of computer communication.svg|thumb|upright=1.8|alt=Diagram of computer communication from a personal computer to a server using modems and the public telephone network|Example of computer communication: modems act as transmitter and receiver while the public telephone network is used as a transmission system.<ref>{{harvnb|Stallings|2014|p=40}}</ref>]]
Computer communication concerns the exchange of data between computers and similar devices.<ref>{{multiref | {{harvnb|Stallings|2014|p=39}} | {{harvnb|Wittmann|Zitterbart|2000|p=[https://books.google.com/books?id=bRyEfBCxIRsC&pg=PA1 1]}} }}</ref> For this to be possible, the devices have to be connected through a [[transmission system]] that forms a network between them. A [[transmitter]] is needed to send messages and a receiver is needed to receive them. A personal computer may use a [[modem]] as a transmitter to send information to a server through the public telephone network as the transmission system. The server may use a modem as its receiver.<ref>{{multiref | {{harvnb|Stallings|2014|pp=39–40}} | {{harvnb|Hura|Singhal|2001|pp=49, 175}} }}</ref> To transmit the data, it has to be converted into an electric signal.<ref>{{harvnb|Stallings|2014|p=44}}</ref> Communication channels used for transmission are either [[Analog signal|analog]] or [[Digital signal|digital]] and are characterized by features like [[Bandwidth (computing)|bandwidth]] and [[Network latency|latency]].<ref>{{multiref | {{harvnb|Hura|Singhal|2001|pp=49–50}} | {{harvnb|Hura|Singhal|2001|pp=142, 175}} | {{harvnb|McGuire|Jenkins|2008|p=[https://books.google.com/books?id=swvSgicJM5IC&pg=PA373 373]}} }}</ref>

There are many forms of [[computer network]]s. The most commonly discussed ones are [[Local area network|LANs]] and [[Wide area network|WANs]]. ''LAN'' stands for ''local area network'', which is a computer network within a limited area, usually with a distance of less than one kilometer.<ref>{{multiref | {{harvnb|Hura|Singhal|2001|pp=4–5, 14}} | {{harvnb|Stallings|2014|pp=46–48}} }}</ref> This is the case when connecting two computers within a home or an office building. LANs can be set up using a wired connection, like Ethernet, or a wireless connection, like [[Wi-Fi]].<ref>{{multiref | {{harvnb|Nawrocki|2016|p=[https://books.google.com/books?id=vW2PCwAAQBAJ&pg=PA340 340]}} | {{harvnb|Grigorik|2013|p=[https://books.google.com/books?id=KfW-AAAAQBAJ&pg=PA93 93]}} }}</ref> ''WANs'', on the other hand, are ''wide area networks'' that span large geographical regions, like the [[internet]].<ref>{{multiref | {{harvnb|Hura|Singhal|2001|pp=4–5, 14}} | {{harvnb|Shinder|2001|p=[https://books.google.com/books?id=ZMizSUW7XF4C&pg=PA37 37]}} | {{harvnb|Stallings|2014|pp=46–48}} }}</ref> Their networks are more complex and may use several intermediate connection nodes to transfer information between endpoints.<ref>{{multiref | {{harvnb|Stallings|2014|p=295}} | {{harvnb|Hura|Singhal|2001|p=542}} }}</ref> Further types of computer networks include [[Personal area network|PANs]] (personal area networks), [[Campus area network|CANs]] (campus area networks), and [[Metropolitan area network|MANs]] (metropolitan area networks).<ref>{{multiref | {{harvnb|Palmer|2012|p=[https://books.google.com/books?id=-QELAAAAQBAJ&pg=PA33 33]}} | {{harvnb|Hura|Singhal|2001|pp=4–5}} }}</ref>

For computer communication to be successful, the involved devices have to follow a common set of conventions governing their exchange. These conventions are known as the [[communication protocol]]. They concern various aspects of the exchange, like the format of messages and how to respond to transmission errors. They also cover how the two systems are synchronized, for example, how the receiver identifies the start and end of a signal.<ref>{{multiref | {{harvnb|Stallings|2014|pp=29, 41–42}} | {{harvnb|Meinel|Sack|2014|p=[https://books.google.com/books?id=5O25BAAAQBAJ&pg=PA129 129]}} }}</ref> Based on the flow of informations, systems are categorized as [[Simplex communication|simplex]], half-[[Duplex (telecommunications)|duplex]], and full-duplex. For simplex systems, signals flow only in one direction from the sender to the receiver, like in radio, cable television, and screens displaying arrivals and departures at airports.<ref>{{harvnb|Hura|Singhal|2001|p=142}}</ref> Half-duplex systems allow two-way exchanges but signals can only flow in one direction at a time, like [[walkie-talkie]]s and [[police radio]]s. In the case of full-duplex systems, signals can flow in both directions at the same time, like regular telephone and internet.<ref>{{harvnb|Hura|Singhal|2001|p=143}}</ref> In either case, it is often important for successful communication that the connection is [[Cyber security|secure]] to ensure that the transmitted data reaches only the intended destination and is not intercepted by an unauthorized third party.<ref>{{harvnb|Stallings|2014|pp=41–42}}</ref> This can be achieved by using [[cryptography]], which changes the format of the transmitted information to make it unintelligible to potential interceptors.<ref>{{multiref | {{harvnb|Saha|Manna|Mandal|2013|p=[https://books.google.com/books?id=iUI8BAAAQBAJ&pg=PA231 231]}} | {{harvnb|Bruen|Forcinito|McQuillan|2021|p=[https://books.google.com/books?id=BPcyEAAAQBAJ&pg=PA49 49]}} }}</ref>

Human-computer communication is a closely related field that concerns topics like how [[Human-computer interaction|humans interact with computers]] and how data in the form of inputs and outputs is exchanged.<ref>{{multiref | {{harvnb|Guzman|2018|pp=[https://books.google.com/books?id=ML1OtAEACAAJ 1, 5]}} | {{harvnb|Riekert|1990|p=[https://books.google.com/books?id=kOU5wrsqvcgC&pg=PA42 42]|loc=[https://books.google.com/books?id=kOU5wrsqvcgC&pg=PA42 What Does Knowledge Look Like?]}} }}</ref> This happens through a [[user interface]], which includes the hardware used to interact with the computer, like a [[Computer mouse|mouse]], a [[Computer keyboard|keyboard]], and a [[Computer monitor|monitor]], as well as the software used in the process.<ref>{{multiref | {{harvnb|Twidale|2002|p=414}} | {{harvnb|Riekert|1990|p=[https://books.google.com/books?id=kOU5wrsqvcgC&pg=PA42 42]|loc=[https://books.google.com/books?id=kOU5wrsqvcgC&pg=PA42 What Does Knowledge Look Like?]}} }}</ref> On the software side, most early user interfaces were [[command-line interface]]s in which the user must type a command to interact with the computer.<ref>{{harvnb|Rao|Wang|Zhou|1996|p=[https://books.google.com/books?id=Ec3sfGyC_q8C&pg=PA57 57]}}</ref> Most modern user interfaces are [[graphical user interfaces]], like [[Microsoft Windows]] and [[macOS]], which are usually much easier to use for non-experts. They involve graphical elements through which the user can interact with the computer, commonly using a design concept known as [[skeumorphism]] to make a new concept feel familiar and speed up understanding by mimicking the real-world equivalent of the interface object. Examples include the typical computer folder icon and recycle bin used for discarding files.<ref>{{multiref | {{harvnb|Twidale|2002|p=411}} | {{harvnb|Green|Jiang|Isaacs|2023|p=[https://books.google.com/books?id=HGjKEAAAQBAJ&pg=PA16 16]}}}}</ref> One aim when designing user interfaces is to simplify the interaction with computers. This helps make them more user-friendly and accessible to a wider audience while also increasing productivity.<ref>{{harvnb|Twidale|2002|pp=411–413}}</ref>