WAN- AREA NET WORK WORKING

Wide area network

 

A wide area network (WAN) is a telecommunications network or computer network that extends over a large geographical distance. Wide area networks are often established with leased telecommunication circuits.

Business, education and government entities use wide area networks to relay data to staff, students, clients, buyers, and suppliers from various locations across the world. In essence, this mode of telecommunication allows a business to effectively carry out its daily function regardless of location. The Internet may be considered a WAN..

Related terms for other types of networks are personal area networks (PAN), local area networks (LAN), campus area networks(CAN), or metropolitan area networks (MAN) which are usually limited to a room, building, campus or specific metropolitan area respectively.

Design options

The textbook definition of a WAN is a computer network spanning regions, countries, or even the world. However, in terms of the application of computer networking protocols and concepts, it may be best to view WAN as computer networking technologies used to transmit data over long distances, and between different LAN, MAN and other localised computer networking architectures. This distinction stems from the fact that common LAN technologies operating at lower layers of the OSI model (such as the forms of Ethernet or  are often designed for physically proximal networks, and thus cannot transmit data over tens, hundreds or even thousands of miles or kilometres.

WANs do not just necessarily connect physically disparate LANs. A CAN, for example, may have a localized backbone of a WAN technology, which connects different LANs within a campus. This could be to facilitate higher bandwidth applications or provide better functionality for users in the CAN.

WANs are used to connect LANs and other types of networks together so that users and computers in one location can communicate with users and computers in other locations. Many WANs are built for one particular organization and are private. Others, built by Internet service providers, provide connections from an organization's LAN to the Internet. WANs are often built using leased lines. At each end of the leased line, a router connects the LAN on one side with a second router within the LAN on the other. Leased lines can be very expensive. Instead of using leased lines, WANs can also be built using less costly circuit switching or packet switching methods. Network protocols including TCP/IP deliver transport and addressing functions. Protocols including Packet over SONET SDH, Multiprotocol Label Switching (MPLS), Asynchronous Transfer Mode (ATM) and Frame Relayare often used by service providers to deliver the links that are used in WANs. X.25 was an important early WAN protocol, and is often considered to be the "grandfather" of Frame Relay as many of the underlying protocols and functions of X.25 are still in use today (with upgrades) by Frame Relay.

Academic research into wide area networks can be broken down into three areas: mathematical models, network emulation and network simulation.

Performance improvements are sometimes delivered via wide area file services or WAN optimization.

Connection technology

Many technologies are available for wide area network links. Examples include circuit switched telephone lines, radio wave transmission, and optic fiber. New developments in technologies have successively increased transmission rates. In ca. 1960, a 110 bit/s (bits per second) line was normal on the edge of the WAN, while core links of 56 kbit/s to 64 kbit/s were considered fast. As of 2014, households are connected to the Internet with Dial-Up, ADSL, Cable, Wimax, 4G or fiber. The speeds that people can currently use range from 28.8 Kilobits per second through a 28K modem over a telephone connection to speeds as high as 100 Gigabits per second over an Ethernet 100GBaseY connection.

AT&T plans to start conducting trials in the year 2017 for businesses to use 400 Gigabit Ethernet. Researchers Robert Mather, Alex Alvarado, Domain Lavery & Polina Bayvel of University College London were able to increase networking speeds to 1.125 Terabits per second. Christos Santis, graduate student Scott Steger, Amnon Yariv, Martin and Eileen Summerfield developed a new laser that quadruples transfer speeds over fiber optic cabling. If these two technologies were combined, then a transfer speed of up to 4.5 Terabits per second could potentially be achieved, although it is unlikely that this will be commercially implemented in the near future.

LAN NET WORK

Local area network:

A local area network (LAN) is a computer network that interconnects computers within a limited area such as a residence, school, laboratory, university campus or office building. By contrast, a wide area network (WAN) not only covers a larger geographic distance, but also generally involves leased telecommunication circuits.

Ethernet and Wi-Fi are the two most common technologies in use for local area networks. Historical technologies include ARCNET, Token ring, and AppleTalk.

 History :

The increasing demand and use of computers in universities and research labs in the late 1960s generated the need to provide high-speed interconnections between computer systems. A 1970 report from the Lawrence Radiation Laboratory detailing the growth of their "Octopus" network gave a good indication of the situation

A number of experimental and early commercial LAN technologies were developed in the 1970s. Cambridge Ring was developed at Cambridge University starting in Ethernet was developed at Xerox PARC in 1973–1975, and filed as In 1976, after the system was deployed at PARC, Robert Metcalfe and David Boggs published a seminal paper, "Ethernet: Distributed Packet-Switching for Local Computer Networks". ARCNET was developed by Datapoint Corporation in 1976 and announced in 1977 It had the first commercial installation in December 1977 at Chase Manhattan Bank in New York.

The development and proliferation of personal computers using the CP/M operating system in the late 1970s, and later DOS-based systems starting in 1981, meant that many sites grew to dozens or even hundreds of computers. The initial driving force for networking was generally to share storage and printers, which were both expensive at the time. There was much enthusiasm for the concept and for several years, from about 1983 onward, computer industry pundits would regularly declare the coming year to be, “The year of the LAN”.

In practice, the concept was marred by proliferation of incompatible physical layer and network protocol implementations, and a plethora of methods of sharing resources. Typically, each vendor would have its own type of network card, cabling, protocol, and network operating system. A solution appeared with the advent of Novell NetWare which provided even-handed support for dozens of competing card/cable types, and a much more sophisticated operating system than most of its competitors. Netware dominated the personal computer LAN business from early after its introduction in 1983 until the mid-1990s when Microsoft introduced Windows NT Advanced Server and Windows for Workgroups.

Of the competitors to NetWare, only Banyan Vines had comparable technical strengths, but Banyan never gained a secure base. Microsoft and 3Com worked together to create a simple network operating system which formed the base of 3Com's 3+Share, Microsoft's LAN Manager and IBM's LAN Server - but none of these was particularly successful.

During the same period, Unix workstations were using TCP/IP networking. Although this market segment is now much reduced, the technologies developed in this area continue to be influential on the Internet and in both Linux and Apple Mac OS X networking—and the TCP/IP protocol has replaced IPX, AppleTalk, NBF, and other protocols used by the early PC LANs.

Cabling :

Early LAN cabling had generally been based on various grades of coaxial cable. Shielded twisted pair was used in IBM's Token Ring LAN implementation, but in 1984, StarLANshowed the potential of simple unshielded twisted pair by using Cat3 cable—the same simple cable used for telephone systems. This led to the development of 10BASE-T (and its successors) and structured cabling which is still the basis of most commercial LANs today.

While fiber-optic cabling is common for links between switches, use of fiber to the desktop is rare

Wireless media:

Many LANs use wireless technologies that are built into Smartphones, tablet computers and laptops. In a wireless local area network, users may move unrestricted in the coverage area. Wireless networks have become popular in residences and small businesses, because of their ease of installation. Guests are often offered Internet access via a hotspotservice.

Technical aspects:

Network topology describes the layout of interconnections between devices and network segments. At the data link layer and physical layer, a wide variety of LAN topologies have been used, including ring, bus, mesh and star. At the higher layers, NetBEUI, IPX/SPX, AppleTalk and others were once common, but the Internet Protocol Suite (TCP/IP) has prevailed as a standard of choice.

Simple LANs generally consist of cabling and one or more switches. A switch can be connected to a router, cable modem, or ADSL modem for Internet access. A LAN can include a wide variety of other network devices such as firewalls, load balancers, and network intrusion detection. Advanced LANs are characterized by their use of redundant links with switches using the spanning tree protocol to prevent loops, their ability to manage differing traffic types via quality of service (QoS), and to segregate traffic with VLANs.

LANs can maintain connections with other LANs via leased lines, leased services, or across the Internet using virtual private network technologies. Depending on how the connections are established and secured, and the distance involved, such linked LANs may also be classified as a metropolitan area network (MAN) or a wide area network(WAN).

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Java objects Basis

         Object :

The reference values (often just references) are pointers to these objects, and a special null reference, which refers to no object.

A class instance is explicitly created by a class instance creation expression.

An array is explicitly created by an array creation expression.

Other expressions may implicitly create a class instance  or an array.

 Object Creation

class Point {
    int x, y;
    Point() { System.out.println("default"); }
    Point(int x, int y) { this.x = x; this.y = y; }

    /* A Point instance is explicitly created at 
       class initialization time: */
    static Point origin = new Point(0,0);

    /* A String can be implicitly created 
       by a + operator: */
    public String toString() { return "(" + x + "," + y + ")"; }
}

class Test {
    public static void main(String[] args) {
        /* A Point is explicitly created
           using newInstance: */
        Point p = null;
        try {
            p = (Point)Class.forName("Point").newInstance();
        } catch (Exception e) {
            System.out.println(e);
        }

        /* An array is implicitly created 
           by an array constructor: */
        Point a[] = { new Point(0,0), new Point(1,1) };

        /* Strings are implicitly created 
           by + operators: */
        System.out.println("p: " + p);
        System.out.println("a: { " + a[0] + ", " + a[1] + " }");
    
        /* An array is explicitly created
           by an array creation expression: */
        String sa[] = new String[2];
        sa[0] = "he"; sa[1] = "llo";
        System.out.println(sa[0] + sa[1]);
    }
}

This program produces the output:

default
p: (0,0)
a: { (0,0), (1,1) }
hello

The operators on references to objects are:

• Field access, using either a qualified name or a field access expression 
• Method invocation
• The cast operator 
• The string concatenation operator + , which, when given a String operand and a reference, will convert the reference to a String by invoking the to String method of the referenced object (using "null" if either the reference or the result of to String is a null reference), and then will produce a newly created String that is the concatenation of the two strings
• The instanceof operator
• The reference equality operators == and !=
• The conditional operator ?

There may be many references to the same object. Most objects have state, stored in the fields of objects that are instances of classes or in the variables that are the components of an array object. If two variables contain references to the same object, the state of the object can be modified using one variable's reference to the object, and then the altered state can be observed through the reference in the other variable.