Friday, November 20, 2015

internetwork

Internetwork
Internetworked is a term used by Cisco, BBN, and other providers of network products and services as a comprehensive term for all the concepts, technologies, and generic devices that allow people and their computers to communicate across different kinds of networks. For example, someone at a computer on a token ring local area network may want to communicate with someone at a computer on an Ethernet local area network in another country using a wide area network interconnection. The common internetwork protocols, routing tables, and related network devices required to achieve this communication constitute internetworking.
The standard reference model for internetworking is Open Systems Interconnection (OSI), which could also be used as a model for intranetworking as well. OSI enables any technology to be related to another technology because each can be related to the standard communication model. OSI provides a layering approach to the problem of exchanging data across a network or a network of networks so that the problem can be broken down into easier-to-understand components and so that boundaries between components can be more easily determined.
Internetworked is the practice of connecting a computer network with other networks through the use of gateways that provide a common method of routing information packets between the networks. The resulting system of interconnected networks is called an internetwork, or simply an internet. Internetworking is a combination of the words inter ("between") and networking; not internet-working or international-network.
The most notable example of internetworking is the Internet, a network of networks based on many underlying hardware technologies, but unified by an internetworking protocol standard, the Internet Protocol Suite, often also referred to asTCP/IP.
The smallest amount of effort to create an internet (an internetwork, not the Internet), is to have two LANs of computers connected to each other via a router. Simply using either a switch or a hub to connect two local area networks together doesn't imply internetworking, it just expands the original LAN.

Interconnection of networks

Internetworking started as a way to connect disparate types of networking technology, but it became widespread through the developing need to connect two or more local area networks via some sort of wide area network. The original term for an internetwork was catenet.
The definition of an internetwork today includes the connection of other types of computer networks such as personal area networks. The network elements used to connect individual networks in the ARPANET, the predecessor of the Internet, were originally called gateways, but the term has been deprecated in this context, because of possible confusion with functionally different devices. Today the interconnecting gateways are called routers.
Another type of interconnection of networks often occurs within enterprises at the Link Layer of the networking model, i.e. at the hardware-centric layer below the level of the TCP/IP logical interfaces. Such interconnection is accomplished withnetwork bridges and network switches. This is sometimes incorrectly termed internetworking, but the resulting system is simply a larger, single subnetwork, and no internetworking protocol, such as Internet Protocol, is required to traverse these devices. However, a single computer network may be converted into an internetwork by dividing the network into segments and logically dividing the segment traffic with routers. The Internet Protocol is designed to provide an unreliable (not guaranteed) packet service across the network. The architecture avoids intermediate network elements maintaining any state of the network. Instead, this function is assigned to the endpoints of each communication session. To transfer data reliably, applications must utilize an appropriate Transport Layer protocol, such as Transmission Control Protocol (TCP), which provides a reliable stream. Some applications use a simpler, connection-less transport protocol, User Datagram Protocol (UDP), for tasks which do not require reliable delivery of data or that require real-time service, such as video streaming [1] or voice chat.

Networking models

Two architectural models are commonly used to describe the protocols and methods used in internetworking.
The Open System Interconnection (OSI) reference model was developed under the auspices of the International Organization for Standardization (ISO) and provides a rigorous description for layering protocol functions from the underlying hardware to the software interface concepts in user applications. Internetworking is implemented in the Network Layer (Layer 3) of the model.
The Internet Protocol Suite, also called the TCP/IP model of the Internet was not designed to conform to the OSI model and does not refer to it in any of the normative specifications in Requests for Comment and Internet standards. Despite similar appearance as a layered model, it uses a much less rigorous, loosely defined architecture that concerns itself only with the aspects of logical networking. It does not discuss hardware-specific low-level interfaces, and assumes availability of a Link Layer interface to the local network link to which the host is connected. Internetworking is facilitated by the protocols of itsInternet Layer.

See also

References

  1. Jump up^ Teare, Diane (July 1999). 'Designing Cisco Networks'. Indianapolis: Cisco Press.

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browser

A browser is an application program that provides a way to look at and interact with all the information on the World Wide Web. The word "browser" seems to have originated prior to the Web as a generic term for user interfaces that let you browse (navigate through and read)text files online.
Technically, a Web browser is a client program that uses HTTP (Hypertext Transfer Protocol) to make requests of Web servers throughout theInternet on behalf of the browser user. Most browsers support e-mail and the File Transfer Protocol (FTP) but a Web browser is not required for those Internet protocols and more specialized client programs are more popular.
The first Web browser, called WorldWideWeb, was created in 1990. That browser's name was changed to Nexus to avoid confusion with the developing information space known as the World Wide Web. The first Web browser with a graphical user interface was Mosaic, which appeared in 1993. Many of the user interface features in Mosaic went into Netscape Navigator. Microsoft followed with its Internet Explorer (IE).
As of September 2006, Internet Explorer is the most commonly used browser, having won the so-called browser wars between IE and Netscape. Other browsers include:
This was first published in November 2007

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network backbone

A backbone network or network backbone is a part of computer networkinfrastructure that interconnects various pieces of network, providing a path for the exchange of information between different LANs or subnetworks.[1] 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 the networks connected to it.[2]
A diagram of a typical nationwide network backbone.
A large corporation that has many locations may have a backbone network that ties all of the locations together, for example, if a server cluster needs to be accessed by different departments of a company that are located at different geographical locations. The pieces of the network connections (for example: ethernet, wireless) that bring these departments together is often mentioned as network backbone. Network congestion is often taken into consideration while designing backbones.[3][4]
One example of a backbone network is the Internet backbone.[5]



Contents

  • 1Distributed backbone
  • 2Collapsed backbone
  • 3Parallel backbone
  • 4Serial backbone
  • 5See also
  • 6References
  • 7External links


    Distributed backbone[edit]

    A distributed backbone is a backbone network that consists of a number of connectivity devices connected to a series of central connectivity devices, such as hubs, switches, or routers, in a hierarchy.[6] This kind of topology allows for simple expansion and limited capital outlay for growth, because more layers of devices can be added to existing layers.[6] In a distributed backbone network, all of the devices that access the backbone share the transmission media, as every device connected to this network is sent all transmissions placed on that network.[7]
    Distributed backbones, in all practicality, are in use by all large-scale networks.[8] Applications in enterprise-wide scenarios confined to a single building are also practical, as certain connectivity devices can be assigned to certain floors or departments.[6] Each floor or department possesses a LAN and a wiring closet with that workgroup's main hub or routerconnected to a bus-style network using backbone cabling .[9] Another advantage of using a distributed backbone is the ability for network administrator to segregate workgroups for ease of management.[6]
    There is the possibility of single points of failure, referring to connectivity devices high in the series hierarchy.[6] The distributed backbone must be designed to separate network traffic circulating on each individual LAN from the backbone network traffic by using access devices such as routers and bridges.[10]

    Collapsed backbone[edit]

    A collapsed backbone (inverted backbone, backbone-in-a-box) is a type of backbone network architecture. The traditional backbone network goes over the globe to provide interconnectivity to the remote hubs. In most cases, the backbones are the links while the switching or routing functions are done by the equipment at each hub. It is a distributed architecture.
    In the case of a collapsed or inverted backbone, each hub provides a link back to a central location to be connected to a backbone-in-a-box. That box can be a switch or a router. The topology and architecture of a collapsed backbone is a star or a rooted tree.
    The main advantages of the collapsed backbone approach are
    1. ease of management since the backbone is in a single location and in a single box, and
    2. since the backbone is essentially the back plane or internal switching matrix of the box, proprietary, high performance technology can be used.
    However, the draw back of the collapsed backbone is that if the box housing the backbone is down or there are reachabilityproblem to the central location, the entire network will crash. These problems can be minimized by having redundant backbone boxes as well as having secondary/backup backbone locations.

    Parallel backbone[edit]

    There are a few different types of backbones that are used for an enterprise-wide network. When organizations are looking for a very strong and trustworthy backbone they should choose a parallel backbone. This backbone is a variation of a collapsed backbone in that it uses a central node (connection point). Although, with a parallel backbone, it allows for duplicate connections when there is more than one router or switch. Each switch and router are connected by two cables. By having more than one cable connecting each device, it ensures network connectivity to any area of the enterprise-wide network.[11]
    Parallel backbones are more expensive than other backbone networks because they require more cabling than the othernetwork topologies. Although this can be a major factor when deciding which enterprise-wide topology to use, the expense of it makes up for the efficiency it creates by adding increased performance and fault tolerance. Most organizations use parallel backbones when there are critical devices on the network. For example, if there is important data, such as payroll, that should be accessed at all times by multiple departments, then your organization should choose to implement a Parallel Backbone to make sure that the connectivity is never lost.[11]

    Serial backbone[edit]

    A serial backbone is the simplest kind of backbone network.[12] Serial backbones consist of two or more internet working devices connected to each other by a single cable in a daisy-chain fashion. A daisy chain is a group of connectivity devices linked together in a serial fashion. Hubs are often connected in this way to extend a network. However, hubs are not the only device that can be connected in a serial backbone. Gateways, routers, switches and bridges more commonly form part of the backbone.[13] The serial backbone topology could be used for enterprise-wide networks, though it is rarely implemented for that purpose.[14]

    See also[edit]

    References[edit]

    1. Jump up^ What is a Backbone?, Whatis.com, Accessed: June 25, 2007
    2. Jump up^ "Backbone Networks". Chapter 8. Angelfire. Retrieved 2 October 2013.
    3. Jump up^ Turner, Brough (12 September 2007). "Congestion in the Backbone: Telecom and Internet Solutions". CircleID. Retrieved2 October 2013.
    4. Jump up^ Kashyap, Abhishek; Sun, Fangting; Shayman, Mark. "Relay Placement for Minimizing Congestion in Wireless Backbone Networks" (PDF). Department of Electrical and Computer Engineering, University of Maryland. Retrieved 2 October 2013.
    5. Jump up^ Howdie, Ben (28 January 2013). "The Backbone’s connected to the…". KashFlow. Retrieved 2 October 2013.
    6. ^ Jump up to:a b c d e Tamara Dean. Network+ Guide to Networks. Course Technology, Cengage Learning, 2010, p. 202.
    7. Jump up^ BICSI Lan Design Manual - CD-ROM, Issue 1, Distributed backbone network, p.20[1], 1996, accessed May, 7 2011.
    8. Jump up^ Dooley, Kevin. Designing Large-Scale Networks, p.23[2], O'Reilly Online Catalog, January, 2002, accessed May, 7 2011.
    9. Jump up^ Distributed Backbone[3], accessed May, 7 2011.
    10. Jump up^ Boon & Kepekci (1996). BICSI Lan Design Manual. Tampa, FL. pp. 20–21.
    11. ^ Jump up to:a b Dean, Tamara (2010). Network+ Guide to Networks 5th Edition. Boston, MA: Cengage Course Technology. pp. 203–204.ISBN 1-4239-0245-9.
    12. Jump up^ CompTIA Network+ In depth, Chapter 5 p. 169
    13. Jump up^ Dean, T. (2010) Network+ Guide to Networks, Fifth Edition
    14. Jump up^ [4], Backbone Networks

    External links[edit]

    • IPv6 Backbone Network Topology
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NSFNET


NSFNET 
was a network for research computing deployed in the mid-1980s that in time also became the first backbone infrastructure for the commercial public Internet. Created as a result of a 1985 National Science Foundation (NSF) initiative, NSFNET established a high-speed connection among the five NSF supercomputer centers and the National Center for Atmospheric Research, and provided external access for scientists, researchers, and engineers who were not located near the computing centers.
Broad access was necessary for a widely dispersed and frequently changing community of users. NSFNET became part of a hierarchical series of networks. Meanwhile, NSF supported the development of regional networks that could carry traffic from individual organizations, such as government agencies and universities, to the national backbone service. NSF commissioned Merit Network, MCI, IBM, and the State of Michigan to manage the NSFNET backbone project.
It was during this critical time that Al Gore entered the picture. Gore was roundly mocked in the press after he claimed that he "took the initiative in creating the Internet" during a 1999 broadcast interview. In fact, during the late 1980s, Gore did give political support to a funding drive aimed at expanding NSFNET. Although Gore's "creation" claim was -- to put it mildly -- an exaggeration, the subsequent expansion helped spur the development of the modern-day Internet.
By the early 1990s, as commercial networks began to build their own backbone infrastructures and their own routing mechanisms, the public service furnished by NSFNET's backbone was turned over to the newer backbones and NSFNET was shut down. The scientific and research network continued as vBNS and, more recently, Internet2.

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the ARPANET

ARPANET was the network that became the basis for the Internet. Based on a concept first published in 1967, ARPANET was developed under the direction of the U.S. Advanced Research Projects Agency (ARPA). In 1969, the idea became a modest reality with the interconnection of four university computers. The initial purpose was to communicate with and share computer resources among mainly scientific users at the connected institutions. ARPANET took advantage of the new idea of sending information in small units calledpackets that could be routed on different paths and reconstructed at their destination. The development of the TCP/IP protocols in the 1970s made it possible to expand the size of the network, which now had become a network of networks, in an orderly way.
In the 1980s, ARPANET was handed over to a separate new military network, the Defense Data Network, and NSFNet, a network of scientific and academic computers funded by the National Science Foundation. In 1995, NSFNet in turn began a phased withdrawal to turn the backboneof the Internet (called vBNS) over to a consortium of commercial backbone providers (PSINet, UUNET,ANS/AOL, Sprint, MCI, and AGIS-Net99).
Because ARPA's name was changed to Defense Advanced Research Projects Agency (DARPA) in 1971, ARPANET is sometimes referred to asDARPANET. (DARPA was changed back to ARPA in 1993 and back to DARPA again in 1996.) The history of ARPANET and developments leading up to today's Internet can be found in Where Wizards Stay Up Late, by Katie Hafner and Matthew Lyon.
Arpanet logical map, march 1977.png

Packet switching—today the dominant basis for data communications worldwide—was a new concept at the time of the conception of the ARPANET. Prior to the advent of packet switching, both voice and data communications had been based on the idea of circuit switching, as in the traditional telephone circuit, wherein each telephone call is allocated a dedicated, end to end, electronic connection between the two communicating stations. Such stations might be telephones or computers. The (temporarily) dedicated line is typically composed of many intermediary lines which are assembled into a chain that stretches all the way from the originating station to the destination station. With packet switching, a data system could use a single communication link to communicate with more than one machine by collecting data into datagrams and transmitting these as packets onto the attached network link, as soon as the link becomes idle. Thus, not only can the link be shared, much as a single post box can be used to post letters to different destinations, but each packet can be routed independently of other packets.[9]
The earliest ideas for a computer network intended to allow general communications among computer users were formulated by computer scientist J. C. R. Licklider of Bolt, Beranek and Newman (BBN), in April 1963, in memoranda discussing the concept of the "Intergalactic Computer Network". Those ideas encompassed many of the features of the contemporary Internet. In October 1963, Licklider was appointed head of the Behavioral Sciences and Command and Control programs at the Defense Department's Advanced Research Projects Agency (ARPA). He convinced Ivan Sutherland and Bob Taylor that this network concept was very important and merited development, although Licklider left ARPA before any contracts were assigned for development.[10]
Sutherland and Taylor continued their interest in creating the network, in part, to allow ARPA-sponsored researchers at various corporate and academic locales to utilize computers provided by ARPA, and, in part, to quickly distribute new software and other computer science results.[11] Taylor had three computer terminals in his office, each connected to separate computers, which ARPA was funding: one for the System Development Corporation (SDC) Q-32 in Santa Monica, one for Project Genie at the University of California, Berkeley, and another for Multics at the Massachusetts Institute of Technology. Taylor recalls the circumstance: "For each of these three terminals, I had three different sets of user commands. So, if I was talking online with someone at S.D.C., and I wanted to talk to someone I knew at Berkeley, or M.I.T., about this, I had to get up from the S.D.C. terminal, go over and log into the other terminal and get in touch with them. I said, "Oh Man!", it's obvious what to do: If you have these three terminals, there ought to be one terminal that goes anywhere you want to go. That idea is the ARPANET".[12]
Meanwhile, since the early 1960s, Paul Baran at the RAND Corporation had been researching systems that could survive nuclear war[13] and presented in the United Kingdom National Physical Laboratory (NPL) the first public demonstration of packet switching on 5 August 1968.[14]

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