Perbezaan antara semakan "Rangkaian komputer"

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{{kegunaanlain|Rangkaian}}
'''Rangkaian komputer''' adalah sekumpulan peranti, dikenali juga sebagai nod, yang berhubungan dengan media penghubung. Nod boleh terdiri dari komputer, pencetak atau lain-lain peranti yang menghantar dan menerima data yang dihasilkan oleh nod-nod lain dalam rangkaian. Media penghubung juga dikenali sebagai media komunikasi.
 
== Perkembangan ==
Rangkaian bermula dengan binaan yang kecil, dengan penyambungan lebih kurang sepuluh komputer dan satu pencetak. Teknologi yang wujud di masa itu menghadkan bilangan komputer yang disambung dan panjang kabel komunikasi yang boleh dibenarkan dalam rangkaian. Di awal tahun sembilan puluhan kabel komunikasi boleh ditarik sejauh kira-kira 600 kaki dengan penyambungan sebanyak lebih kurang 30 komputer sahaja. Rangkaian seperti ini sesuai untuk organisasi yang kecil dan dikenali sebagai [[rangkaian kawasan setempat]] (LAN).
 
LAN biasanya menghubungkan peranti dalam satu pejabat atau satu bangunan. Satu LAN boleh dibina hanya dengan dua komputer dan satu pencetak sahaja atau boleh diperluaskan dalam satu bangunan dengan memasukkan perisian audio dan video. Saiz LAN adalah terhad kepada jarak beberapa kilometer sahaja. LAN mempunyai kadar data daripada 4 Mbps sehingga 100 Mbps.
 
Perhubungan pengguna rangkaian dari berlainan negara telah mewujudkan perkembangan LAN kepada [[rangkaian kawasan luas]] (WAN). WAN boleh menghantar data, audio dan video pada jarak yang jauh sehingga merangkumi sebuah negara atau benua atau seluruh dunia.
 
== Tujuan rangkaian ==
Sebelum kewujudan rangkaian komputer yang berasaskan jenis sistem telekomunikasi tertentu, perhubungan antara mesin pengira dan komputer awal dilaksanakan oleh pengguna manusia dengan melaksanakan arahan antara mereka. Kebanyakan tingkah laku yang dilihat di Internet pada hari ini ditujukkkan pada abad ke-19 dan boleh dikatakan pada rangkaian lebih awal menggunakan isyarat boleh dilihat.
 
* Pada September 1940, [[George Stibitz]] menggunakan mesin Teletaip bagi menghantar arahan bagi set masalah daro Modelnya di Kolej Dartmouth ke Mesin Kira Nombor Rumit (“Complex Number Calculator”) di New York dan menerima balasan melalui cara yang sama. Menyambung masukan sistem seperti teletaip kepada komputer merupakan minat Agensi Projek Penyelidikan Maju (“Advanced Research Projects Agency - ARPA) apabila salah seorang juruteranya J. C. R. Licklider mengambil dan membangunkan kumpulan kerja yang digelar "Rangkaian Intergalaktik", suatu awalan kepada [[ARPANET]], pada tahun 1962.
* Jaringan awal komunikasi komputer termasuk sistem radar tentera Persekitaran Darat Separa Automatik (''Semi-Automatic Ground Environment'' - SAGE), bermula lewat tahun 1950-an
* Sistem penempahan penerbangan komersial persekitaran penyelidikan business separa automatik (''semi-automatic business research environment'' – SABRE) yang mula dalam talian dengan dua kerangka komputer pada tahun 1960.<ref>
{{cite book
* Pada tahun 1964, penyelidik di Dartmouth membangunkan Sistem Perkongsian Masa Dartmouth bagi penguna tersebar sistem komputer besar. Pada tahun yang sama, di Institut Teknologi Massachusetts, satu kumpulan penyelidik yang disokong oleh General Electric dan Bell Labs menggunakan komputer bagi mengarah dan mengurus sambungan telefon.
| title = On the way to the web: the secret history of the internet and its founders
| author = Michael A. Banks
| publisher = Apress
| year = 2008
| isbn = 9781430208693
| page = 1
| url = http://books.google.com/books?id=P9wbSjO9WMMC&pg=PA1
}}</ref><ref>
{{cite book
| title = History of the Internet: a chronology, 1843 to the present
| author = Christos J. P. Moschovitis
| publisher = ABC-CLIO
| year = 1998
| isbn = 9781576071182
| page = 36
| url = http://books.google.com/?id=Hu5SAAAAMAAJ&dq=intitle%3A%22history+of+the+internet%22+sage+sabre&q=sage+sabre%27s#search_anchor
}}</ref>
* Pada tahun 1964, penyelidik di Dartmouth membangunkan Sistem Perkongsian Masa Dartmouth bagi penguna tersebar sistem komputer besar. Pada tahun yang sama, di Institut Teknologi Massachusetts, satu kumpulan penyelidik yang disokong oleh [[General Electric]] dan [[Bell Labs]] menggunakan komputer bagi mengarah dan mengurus sambungan telefon.
* Sepanjang tahun 1960-an Leonard Kleinrock, Paul Baran dan Donald Davies secara bebas membangunkan konsep dan sistem jaringan yang menggunakan paket yang boleh digunakan dalam jaringan antara sistem komputer.
* 1965: ahli sains Thomas Merrill dan Lawrence G. Roberts mencipta jaringan kawasan luas (''wide area network'' - WAN).
* Suis telefon pertama yang digunakan secara meluas yang menggunakan kawalam komputer sebenar diperkenalkan oleh Western Electric pada tahun 1965.
* 1969: Universiti California di Los Angeles, Institut Penyelidikan Stanford, Universiti California di Santa Barbara, dan Universiti Utah disambung pada permulaan jaringan [[ARPANET]] menggunakan litar 50 kbit/sesaat.<ref>{{cite web |title=Internet Began 35 Years Ago at UCLA with First Message Ever Sent Between Two Computers |url=http://www.engineer.ucla.edu/stories/2004/Internet35.htm |author=Chris Sutton|publisher=''[[UCLA]]''| archiveurl=http://web.archive.org/web/20080308120314/http://www.engineer.ucla.edu/stories/2004/Internet35.htm |archivedate=March 8, 2008}}</ref>
* Perkhidmatan komersial menggunakan [[X.25]] dilaksanakan pada tahun 1972, dan kemudiannya digunakan sebagai struktur asas bagi mengembangkan jaringan [[TCP/IP]].
 
Pada masa kini, jaringan komputer merupakan teras perhubungan moden. Kesemua aspek moden bagi jaringan ibu sawat telefon (“public switched telephone network-PSTN”) adalah dikawal komputer, dan komputer semakin kerap melalui Protokol Internet, sungguhpun tidak semestinya Internet awam. Rangkuman perhubungan telah meningkat dengan banyaknya pada abad lalu, dan ledakan pada perhubungan tidak mungkin boleh terjadi tanpa kemajuan meningkat rangkaian komputer. Jaringan komputer, dan teknologi yang diperlukan bagi menyambung dan berhubung melalui dan antara mereka, teres memancu perkakasan, perisian dan atal tambahan komputer. Perkembangan ini selari dengan pertumbuhan dalam jumlah dan jenis pengguna rangkaian dari penyelidik kepada pengguna di rumah.
 
Salah satu ''keluarga'' media perhubungan yang terkenal adalah secara keseluruhannya dikenali sebagai [[Ethernet]]. Ia ditakrifkan oleh [[IEEE 802]] dan menggunakan pelbagai piwaian dan media yang membolehkan perhubungan antara peranti. Teknologi LAN tanpa wayar direka bagi menyambung peranti tanpa pendawaian. Peranti ini menggunakan isyarat gelombang radio atau [[IrDA|infra]] sebagai perantaraan pemancaran.
 
== Teknologi dengan wayar ==
<!----
 
===Wired technologies===
*''[[Twisted pair]] wire'' is the most widely used medium for 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 networking 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 (electronics)| 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 which are Unshielded Twisted Pair (UTP) and Shielded twisted-pair (STP) which are rated in categories which are manufactured in different increments for various scenario.
 
*''[[Coaxial cable]]'' is widely used for cable television systems actually, office buildings, and other work-sites for local area networks. The cables consist of copper or aluminum wire wrapped with insulating layer typically of a flexible material with a high dielectric constant, all of which are surrounded by a conductive layer. The layers of insulation help minimize interference and distortion. Transmission speed range from 200 million to more than 500 million bits per second.
 
*[[ITU-T]] [[G.hn]] technology uses existing [[home wiring]] ([[Ethernet over coax|coaxial cable]], phone lines and [[Power line communication|power lines]]) to create a high-speed (up to 1 Gigabit/s) local area network.
 
*''[[Optical fiber]] cable'' consists of one or more filaments of glass fiber wrapped in protective layers that carries data by means of pulses of light. It transmits light which can travel over extended distances. Fiber-optic cables are not affected by electromagnetic radiation. Transmission speed may reach trillions of bits per second. The transmission speed of fiber optics is hundreds of times faster than for coaxial cables and thousands of times faster than a twisted-pair wire. This ''capacity'' may be further increased by the use of colored light, i.e., light of multiple wavelengths. Instead of carrying one message in a stream of monochromatic light impulses, this technology can carry multiple signals in a single fiber.
 
===Wireless technologies===
*''Terrestrial [[microwave]]''&nbsp;– Terrestrial microwaves use Earth-based transmitter and receiver. The equipment looks similar to satellite dishes. Terrestrial microwaves use low-gigahertz range, which limits all communications to line-of-sight. Path between relay stations spaced approx, {{convert|48|km|mi|abbr=on}} apart. Microwave antennas are usually placed on top of buildings, towers, hills, and mountain peaks.
 
*''Communications [[satellite]]s''&nbsp;– The satellites use microwave radio as their telecommunications medium which are not deflected by the Earth's atmosphere. The satellites are stationed in space, typically {{convert|35,400|km|mi|abbr=on}} (for geosynchronous satellites) above the equator. These Earth-orbiting systems are capable of receiving and relaying voice, data, and TV signals.
 
*''Cellular and PCS systems''&nbsp;– Use several radio communications technologies. The systems are divided to different geographic areas. Each area has a low-power transmitter or radio relay antenna device to relay calls from one area to the next area.
 
*''Wireless LANs''&nbsp;– Wireless local area network 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. An example of open-standards wireless radio-wave technology is [[IEEE 802.11]].
 
*[[Infrared communication]] can transmit signals between devices within small distances of typically no more than 10 meters. In most cases, [[line-of-sight propagation]] is used, which limits the physical positioning of communicating devices.
 
*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 the user communications from one local coverage area to the next. In IEEE Project 802, this involves a succession of terrestrial [[wireless LAN]]s.<ref>[http://grouper.ieee.org/groups/802/20/ Mobile Broadband Wireless connections (MBWA)]</ref>
 
===Exotic technologies===
There have been various attempts at transporting data over more or less exotic media:
 
* [[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.<ref> [http://www.blug.linux.no/rfc1149 Bergen Linux User Group's CPIP Implementation]</ref>
 
* Extending the Internet to interplanetary dimensions via radio waves.<ref>[http://www.ipnsig.org/reports/ISART9-2000.pdf Interplanetary Internet], 2000 Third Annual International Symposium on Advanced Radio Technologies, A. Hooke, September 2000</ref>
 
A practical limit in both cases is the [[round-trip delay time]] which constrains useful communication.
 
==Communications protocol==
{{main|Communications protocol}}
A communications protocol defines the formats and rules for exchanging information via a network and typically comprises a complete [[protocol suite]] which describes the protocols used at various [[OSI model|usage levels]]. An interesting feature of communications protocols is that they may be – and in fact very often are – stacked above each other, which means that one is used to carry the other. ''The'' example for this is [[HTTP]] running over [[transmission control protocol|TCP]] over [[Internet protocol|IP]] over [[IEEE 802.11]], where the second and third are members of the [[Internet Protocol Suite]], while the last is a member of the [[Ethernet]] protocol suite. This is the stacking which exists between the [[wireless router]] and the home user's personal computer when surfing the World Wide Web.
 
Communication protocols have themselves various properties, such as whether they are [[Connection-oriented communication|connection-oriented]] versus [[Connectionless communication|connectionless]], whether they use [[circuit mode]] or [[packet switching]], or whether they use hierarchical or flat addressing.
 
There exist a multitude of communication protocols, a few of which are described below.
 
===Ethernet===
{{main|Ethernet}}
Ethernet is a family of connectionless protocols used in LANs, described by a set of standards together called [[IEEE 802]] published by the [[Institute of Electrical and Electronics Engineers]]. It has a flat addressing scheme and is mostly situated at levels 1 and 2 of the [[OSI model]]. For home users today, the most well-known member of this protocol family is [[IEEE 802.11]], otherwise known as [[Wireless LAN]] (WLAN). However, the complete protocol suite deals with a multitude of networking aspects not only for home use, but especially when the technology is deployed to support a diverse range of business needs. [[Media access control|MAC]] [[Bridging (networking)|bridging]] ([[IEEE 802.1D]]) deals with the routing of Ethernet packets using a [[Spanning Tree Protocol]], [[IEEE 802.1Q]] describes [[Virtual LAN|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 also found in WLANs – it is what the home user sees when they have to enter a "wireless access key".
 
===Internet Protocol Suite===
The [[Internet Protocol Suite]], often also called TCP/IP, is the foundation of all modern internetworking. It offers connection-less as well as connection-oriented services over an inherently unreliable network traversed by datagram transmission at the [[Internet protocol]] (IP) level. At its core, the protocol suite defines the addressing, identification, and routing specification in form of the traditional [[IPv4|Internet Protocol Version 4]] (IPv4) and IPv6, the next generation of the protocol with a much enlarged addressing capability.
 
===SONET/SDH===
{{main|Synchronous optical networking}}
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 [[Pulse code modulation|PCM]] 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.
 
===Asynchronous Transfer Mode===
{{main|Asynchronous transfer mode}}
Asynchronous Transfer Mode (ATM) is a switching technique for telecommunication networks. It uses asynchronous [[time-division multiplexing]] and encodes data into small, fixed-sized [[cell relay|cells]]. This differs from other protocols such as the [[Internet Protocol Suite]] or [[Ethernet]] that use variable sized packets or [[Frame Relay|frames]]. ATM has similarity with both [[Circuit switching|circuit]] and [[Packet switching|packet]] switched networking. This makes it a good choice for a network that must handle both traditional high-throughput data traffic, and real-time, [[Latency (engineering)|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.
 
While the role of ATM is diminishing in favor of [[Next generation network|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. For an interesting write-up of the technologies involved, including the deep stacking of communications protocols used, see.<ref>{{cite web|last=Martin|first=Thomas|title=Design Principles for DSL-Based Access Solutions| url=http://www.gsi.dit.upm.es/~legf/Varios/XDSL_MARTI.PDF|accessdate=18 June 2011}}</ref>
 
==Scale==
{{Area networks}}
Networks are often classified by their physical or organizational extent or their purpose. Usage, trust level, and access rights differ between these types of networks.
 
===Personal area network===
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.<ref>{{cite web | url=http://searchmobilecomputing.techtarget.com/sDefinition/0,,sid40_gci546288,00.html |title=personal area network (PAN) |accessdate=January 29, 2011}}</ref> A wired PAN is usually constructed with USB and Firewire connections while technologies such as Bluetooth and infrared communication typically form a wireless PAN.
 
===Local area network===
A [[local area network]] (LAN) is a network that connects computers and devices in a limited geographical area such as home, school, computer laboratory, office building, or closely positioned group of buildings. Each computer or device on the network is a node. Current wired LANs are most likely to be based on [[Ethernet]] technology, although new standards like [[ITU-T]] [[G.hn]] also provide a way to create a wired LAN using existing home wires (coaxial cables, phone lines and power lines).<ref>[http://www.itu.int/ITU-T/newslog/New+Global+Standard+For+Fully+Networked+Home.aspx New global standard for fully networked home], ITU-T Press Release</ref>
 
[[Image:NETWORK-Library-LAN.png|thumb | Typical library network, in a branching tree topology and controlled access to resources]]
 
All interconnected devices must understand the network layer (layer 3), because they are handling multiple subnets (the different colors). Those inside the library, which have only 10/100 Mbit/s Ethernet connections to the user device and a Gigabit Ethernet connection to the central router, could be called "layer 3 switches" because they only have Ethernet interfaces and must understand [[Internet Protocol|IP]]. It would be more correct to call them access routers, where the router at the top is a distribution router that connects to the Internet and academic networks' customer access routers.
 
The defining characteristics of LANs, in contrast to WANs (Wide Area Networks), include their higher data transfer rates, smaller geographic range, and no need for leased telecommunication lines. Current Ethernet or other [[IEEE 802.3]] LAN technologies operate at speeds up to 10 Gbit/s. This is the data transfer rate. [[IEEE]] has projects investigating the standardization of 40 and 100 Gbit/s.<ref>[http://www.ieee802.org/3/ba/ IEEE P802.3ba 40Gb/s and 100Gb/s Ethernet Task Force]</ref>
LANs can be connected to Wide area network by using routers.
 
===Home network===
A [[home network]] is a residential LAN which is 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.
 
===Storage area network===
 
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.
 
===Campus network===
A [[campus network]] is a computer network made up of an interconnection of LANs within a limited geographical area. The networking equipment (switches, routers) and transmission media (optical fiber, copper plant, [[Category 5 cable|Cat5]] cabling etc.) are almost entirely owned (by the campus tenant / owner: an enterprise, university, government etc.).
 
In the case of a university campus-based campus network, the network is likely to link a variety of campus buildings including, for example, academic colleges or departments, the university library, and student residence halls.
 
===Backbone network===
A [[backbone network]] is part of a computer network infrastructure that interconnects various pieces of network, providing a path for the exchange of information between different LANs or subnetworks. A backbone can tie together diverse networks in the same building, in different buildings in a campus environment, or over wide areas. Normally, the backbone's capacity is greater than that of the networks connected to it.
 
A large corporation which has many locations may have a backbone network that ties all of these locations together, for example, if a server cluster needs to be accessed by different departments of a company which are located at different geographical locations. The equipment which ties these departments together constitute the network backbone. [[Network performance management]] including [[network congestion]] are critical parameters taken into account when designing a network backbone.
 
A specific case of a backbone network is the [[Internet backbone]], which is the set of wide-area network connections and [[core router]]s that interconnect all networks connected to the [[Internet]].
 
===Metropolitan area network===
A [[Metropolitan area network]] (MAN) is a large computer network that usually spans a city or a large campus.
[[File:EPN Frame-Relay and Dial-up Network.svg|thumb|upright=1.5| Sample EPN made of [[Frame relay]] WAN connections and dialup remote access.]]
 
[[File:Virtual Private Network overview.svg|thumb|upright=1.5|Sample VPN used to interconnect 3 offices and remote users]]
 
===Wide area network===
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, using a communications channel that combines many types of media such as telephone lines, cables, and air waves. A WAN often uses transmission facilities provided by common carriers, such as telephone companies. WAN technologies generally function at the lower three layers of the [[OSI model|OSI reference model]]: the [[physical layer]], the [[data link layer]], and the [[network layer]].
 
===Enterprise private network===
An [[enterprise private network]] is a network built by an enterprise to interconnect various company sites, e.g., production sites, head offices, remote offices, shops, in order to share computer resources.
 
===Virtual private network===
A [[virtual private network]] (VPN) is a computer 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.
 
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.
 
===Internetwork===
An [[internetwork]] is the connection of multiple computer networks via a common routing technology using routers. The [[Internet]] is an aggregation of many connected internetworks spanning the [[Earth]].
 
==Organizational scope==
Networks are typically managed by organizations which own them. According to the owner's point of view, networks are seen as intranets or extranets. A special case of network is the [[Internet]], which has no single owner but a distinct status when seen by an organizational entity – that of permitting virtually unlimited global connectivity for a great multitude of purposes.
 
===Intranets and extranets===
Intranets and extranets are parts or extensions of a computer network, usually a LAN.
 
An [[intranet]] is a set of networks, using the [[Internet Protocol]] and IP-based tools such as web browsers and file transfer applications, that is under the control of a single administrative entity. That administrative entity closes the intranet to all but specific, authorized users. Most commonly, an intranet is the internal network of an organization. A large intranet will typically have at least one web server to provide users with organizational information.
 
An [[extranet]] is a network that is limited in scope to a single organization or entity and also has limited connections to the networks of one or more other usually, but not necessarily, trusted organizations or entities—a company's customers may be given access to some part of its intranet—while at the same time the customers may not be considered ''trusted'' from a security standpoint. Technically, an extranet may also be categorized as a CAN, MAN, WAN, or other type of network, although an extranet cannot consist of a single LAN; it must have at least one connection with an external network.
 
===Internet===
Internet merupakan sebuah sistem sejagat terdiiri daripada rangkaian komputer pemerintah, akademi, korporat, awam dan persendirian berdasarkan teknologi perangkaian [[Suit Protokol Internet]]. Ia merupakan pengganti kepada [[ARPANET|Rangkaian Agensi Projek Penyelidikan Maju]] (''Advanced Research Projects Agency Network'', ARPANET) developed by [[Defense Advanced Research Projects Agency|DARPA]] of the [[United States Department of Defense]]. Ia juga merupakan tulang belakang komunikasi yang tersembunyi dalam [[Jaringa Sejagat]] (''World Wide Web'', WWW).
 
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 address]]es) administered by the [[Internet Assigned Numbers Authority]] and [[Regional Internet Registry|address registries]]. Service providers and large enterprises exchange information about the [[routing|reachability]] of their address spaces through the [[Border Gateway Protocol]] (BGP), forming a redundant worldwide mesh of transmission paths.
 
==Network topology==
===Common layouts===
A [[network topology]] is the layout of the interconnections of the nodes of a computer network. Common layouts are:
* 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]].
* A [[star network]]: all nodes are connected to a special central node. This is the typical layout found in 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 neighbor 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 neighbors 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.
 
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 a star, because all neighboring connections are routed via a central physical location.
 
===Overlay network===
An [[overlay network]] is a virtual computer network that is built on top of another network. Nodes in the overlay are connected by virtual or logical links, each of which 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.
[[File:Network Overlay.svg|thumb|upright=1.5| A sample overlay network: IP over SONET over Optical]] For example, many [[peer-to-peer]] networks are overlay networks because they are organized as nodes of a virtual system of links run on top of the Internet. The Internet was initially built as an overlay on the [[telephone network]] .<ref>D. Andersen, H. Balakrishnan, M. Kaashoek, and [[Robert Tappan Morris|R. Morris]]. [http://nms.csail.mit.edu/ron/ Resilient Overlay Networks]. In Proc. ACM SOSP, Oct. 2001.
</ref>
 
The most striking example of an overlay network, however, is the Internet itself: At the IP layer, each node can reach any other by a direct connection to the desired IP address, thereby creating a fully connected network; the underlying network, however, is composed of a mesh-like interconnect of subnetworks of varying topologies (and, in fact, technologies). [[Address Resolution Protocol|Address resolution]] and [[routing]] are the means which allows the mapping of the fully connected IP overlay network to the underlying ones.
 
Overlay networks have been around since the invention of networking when computer systems were connected over telephone lines using [[modem]]s, before any data network existed.
 
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 [[associative array|map]]) indexed by keys.
 
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 [[Router (computing)|router]]s in the network.{{Citation needed|date=August 2010}} On the other hand, an overlay network can be incrementally deployed on end-hosts running the overlay protocol software, without cooperation from [[Internet service provider]]s. The overlay 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 a message traverses before reaching its destination.
 
For example, [[Akamai Technologies]] manages an overlay network that provides reliable, efficient content delivery (a kind of [[multicast]]). Academic research includes [http://esm.cs.cmu.edu/ end system multicast] and overcast for multicast; RON ([[resilient overlay network]]) for resilient routing; and OverQoS for quality of service guarantees, among others.
 
==Basic hardware components==
Apart from the physical communications media themselves as described above, networks comprise additional basic hardware building blocks interconnecting their terminals, such as [[Network interface controller|network interface cards (NICs)]], [[Ethernet hub|hubs]], [[Network bridge|bridges]], [[Network switch|switches]], and [[Router (computing)|router]]s.
 
===Network interface cards===
A [[network card]], network adapter, or NIC (network interface card) is a piece of [[computer hardware]] designed to allow computers to physically access a networking medium. It provides a low-level addressing system through the use of [[MAC address]]es.
 
Each [[Ethernet]] network interface has a unique MAC address which is usually stored in a small memory device on the card, allowing any device to connect to the network without creating an address conflict. Ethernet MAC addresses are composed of six [[Octet (computing)|octets]]. Uniqueness is maintained by the [[Institute of Electrical and Electronics Engineers|IEEE]], which manages the Ethernet address space by assigning 3-octet prefixes to equipment manufacturers. The [http://standards.ieee.org/regauth/oui/oui.txt list of prefixes] is publicly available. Each manufacturer is then obliged to both use only their assigned prefix(es) and to uniquely set the 3-octet suffix of every Ethernet interface they produce.
 
===Pengulang dan paksi===