By the end of this chapter you should be able to
：
■ Describe basic networking technologies
■ List network infrastructure devices _ List networking media
_ List types of networks (LAN,MAN,WAN, etc)
■ List the issues in online branch banking connectivity ■ List various networking trends (WiFi, Broadband,VPN)
置 Techt\oloq\/ in Financial Services \ Reference Book
What is a Computer Network?
Network Value • Metcalfe's Law
Discrete computers provide prospects for tremendous productivity gains, but they become many times more potent when they're connected to one another in data networks that give them the ability to share data and processing resources. With a network, coworkers can read and edit an evolving document from their own computer with minimal effort and coordination. Without a network, these colleagues have to share time on the same computer or work out a process for exchanging removable storage media. In a similar fashion, networks can create economies of scale by running resource-hungry applications on high-power hardware. In the broadest sense, a network is an interconnected group of 'items' capable of sharing meaningful information with one another. In a technology context, network is usually short for "computer network" or "data network" and implies that computers are the items sharing the meaningful information. At a conceptual level, all data networks consist of nodes, which refer to any computer or digital device using the network and links, the physical connections (either wired or wireless) that carry messages between nodes.
Data networks are important to all present-day organizations because they provide quicker, easier access to any message or data that can be represented and stored in digital format. In many contemporary organizations, large distances separate coworkers, and data sharing becomes a major logistical problem in the absence of a network. In addition to data sharing, computer networks also allow resource sharing, an important consideration in all budget-conscious organizations. Rather than buying one printer for every employee and replacing them when they wear out, an organization with a network can buy a single printer, connect it to the network and configure it in such a way that every computer user in the organization can print to it. The initial cost of a networked printer is typically more than the cost of a single desktop printer, but when considering costs on a per-user basis, the average cost of the networked printer is often much less than the cost of buying a printer for every employee. While some networked devices such as printers, scanners and fax machines have predetermined, specialized functions, one can also network and share generic, unspecialized computing power in the form of servers. Servers are large, powerful computers that can handle resource-intensive tasks more efficiently than desktop computers. As with the networked printer, the initial expenditure for a server is more than that for a desktop computer, but across the organization, it's often cheaper to run the server-based version of a program since individual users won't need expensive, high-performance desktop and laptop computers. Servers can also deploy software to other networked machines at a lower cost.
A pioneer in creating computer networking technology, engineer Robert Metcalfe developed a theory concerning the usefulness of networks that became popular during the 1990s. Metcalfe's Law claims that the possible value of a communications network increases exponentially with its size. Metcalfe's Law was intended to be an approximation and a relative measure of value for comparing two networks or the growth of one. For example, under this Law, a network with 10 endpoints or nodes (value =
10x10=100) is approximately 4 times more useful than a network half the size (5 endpoints with value 5x5=25). Metcalfe's Law characterizes many of the network effects of communication technologies and networks such as the Internet, social networking and the World Wide Web. Websites and blogs such as Twitter, Facebook and Myspace are the most prominent modern examples of Metcalfe's Law.
Marc Andreesen, one of the founders of the Web, said
：
A network in general behaves in such a way that the more nodes that are added to it, the whole thing gets more valuable for everyone on it because all of a sudden there's all this new stuff that wasn't there before. You saw it with the phone system. The more phones that are on the network, the more valuable it is to everyone because then you can call these people. Federal Express, in order to grow their business, would add a node in Topeka and business in New York would spike. You see it on the Internet all the time. Every new node, every new server, every new user expands
the possibilities br ei/e/yone else who's already there.
Data Packets A packet is a fundamental unit of communication over a digital network. A packet is also called a datagram, a segment, a block, a cell or a frame, depending on the protocol. Packets vary in structure depending on the protocols implementing them. When data has to be transmitted, it is broken down into smaller and similar structures of data - the packets, which are reassembled to the original data chunk once they reach their destination.
A packet consists of two kinds of data
：
control information and user data (also known as payload). The control information provides data the network needs to deliver the user data, for example：
source and destination addresses, i.e. the sender's IP address, the intended receiver's IP address, error detection codes and sequencing information- something that tells the network how many packets this message has been broken into and the number of this particular packet. Typically, control information is found in packet headers and trailers, with user data in between.Network A computer network is comprised of a large number of communication Infrastructure devices. Computer networking devices are units that arbitrate data in a Devices computer network. Computer networking devices are also called network equipment, Intermediate Systems (IS) or Interworking Unit (IWU). Units which are the last receiver or generate data are called hosts or data terminal equipment. The simplest device that is used in the communication is the NIC (Network Interface Card) adapter which is attached to every computer in a network. NIC and other more advanced devices are discussed below.
Network Interface Card:
Network Interface Cards (NIC) are adaptors attached to a computer or
other network devices to provide the connection between the devices
and the network. Each NIC is designed for a specific type of network sudi
as Ethernet, Token Ring, or wireless LAN. NIC basically defines the physical connection methods with the cable and the framing methods used to transmit bit streams over the network. It also defines the control signals that provide the tinning of data transfers across a network. In new computers, NICs are now mostly pre-installed by the
置 Techt\oloq\/ in Financial Services \ Reference Book
manufacturers.
Hubs：
A hub, sometimes known as a concentrator or repeater hub, refers to a networking component which acts as a merging point of a network, allowing the transfer of data packets. In its simplest form, a hub works by repeating the data packets received via one port and making it available to all ports, therefore allowing data sharing between all devices connected to the hub.
A network hub is a fairly unsophisticated broadcast device. Hubs do not manage any of the traffic that comes through them and any packet entering any port is regenerated and broadcast out on all other ports in the network. Since every packet is being sent out through all other ports, packet collisions result which greatly hinders the smooth flow of traffic. This feature of hubs also creates security concerns as the message is
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