The components of a Network Pt 1.

Information and images

1. A Router

A router is a device that forwards data packets between computer networks, creating an overlay internetwork. A router is connected to two or more data lines from different networks. When a data packet comes in one of the lines, the router reads the address information in the packet to determine its ultimate destination. Then, using information in its routing table or routing policy, it directs the packet to the next network on its journey. Routers perform the "traffic directing" functions on the Internet. A data packet is typically forwarded from one router to another through the networks that constitute the internetwork until it reaches its destination node.

The most familiar type of routers are home and small office routers that simply pass data, such as web pages, email, IM, and videos between the home computers and the Internet. An example of a router would be the owner's cable or DSL modem, which connects to the Internet through an ISP. More sophisticated routers, such as enterprise routers, connect large business or ISP networks up to the powerful core routers that forward data at high speed along the optical fiber lines of the Internet backbone. Though routers are typically dedicated hardware devices, use of software-based routers has grown increasingly common.

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2. Network Switch



A network switch, commonly referred to as just a switch, is a network device that is used to connect segments of a LAN (local area network) or multiple LANs and to filter and forward packets among them. Switches have an appearance similar to hubs (because both are box-like devices ) but they are actually multi-port bridges.


A bridge is a device that functions at the data link layer (the second layer) of the seven-layer OSI model to connect and control the flow of data between two LANs or two segments of the same LAN. Bridges have three main functions: 1, creating a bridging table to keep track of devices on each segment, 2, filtering packets based on their MAC addresses and 3, dividing a single network into multiple collision domains, thereby reducing the number of collisions on each segment and effectively increasing its bandwidth.



Switches also improve network performance over hubs by providing full duplex (i.e., data flow in both directions simultaneously) operation instead of half-duplex (data flow in only one direction at a time) operation. This results in a doubling of the maximum bandwidth. Switches can operate in full duplex mode because they prevent collisions, and thus no collision detection system is needed. Switches thus eliminate the conventional CSMA/CD (carrier-sense multiple-access with collision detection) method and utilize a far more efficient communication method.

LANs that use switches to join segments are called switched LANs. In the case of Ethernet LANs, which account for most LANs, they are also called switched Ethernets.

Switches can also include the functionality of routers, which are devices and/or software that connect at least two networks and forward packets among them according to the information in the packet headers and routing tables. However, in general, switches are simpler and faster than routers, which require knowledge about the network and how to determine the route. Routing occurs at the network layer (i.e., the third layer) of the OSI model, in contrast to the data link layer operation of switches.



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3. Hub

In computer networking, a hub is a small, simple, inexpensive device that joins multiple computers together. Many network hubs available today support the Ethernet standard. Other types including USB hubs also exist, but Ethernet is the type traditionally used in home networking. Hubs, as is the case with repeaters and in contrast to switches and bridges, operate at the physical layer (i.e., the bottom layer) of the OSI model. This layer provides no filtering of packets. Switches, however, because of their operation at the data link layer, provide a greater degree of control, including the filtering of packets by their MAC addresses so that they are forwarded only to their destination network segments rather than just broadcasting them to all segments. This limits the collision domain, and thereby conserving system bandwidth.

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4. Servers

A computer system in a network that is shared by multiple users. Servers come in all sizes from x86-based PCs to IBM mainframes. A server may have a keyboard, monitor and mouse directly attached, or one keyboard, monitor and mouse may connect to any number of servers via a switch (see KVM switch). In datacenters with hundreds and thousands of servers residing in equipment racks, all access is via the network. See server farm, blade server and rack mounted.


A User's Machine Can Be a Server

Stand-alone PCs and Macs can also function as a server to other users on the network even though they serve as a single workstation to one user (see peer-to-peer). In such cases, specific folders are typically configured for sharing rather than the entire hard drive.


Servers Can Be Software Only

The term "server" may refer to both the hardware and software (the entire computer system) or just the software that performs the service. For example, a "Web server" may refer to a dedicated computer running Web server software or to Web server software running with other applications.



below is a server in a data centre.

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5. Client

A client is a computer program that, as part of its operation, relies on sending a request to another computer program (which may or may not be located on another computer). The term "client", however, may also be applied to computers or devices that run the client software or users that use the client software. For example, web browsers are clients that connect to web servers and retrieve web pages for display. Email clients retrieve email from mail servers. Online chat uses a variety of clients, which vary depending on the chat protocol being used. Multiplayer video games or online video games may run as a client on each computer.

The term was first applied to devices that were not capable of running their own stand-alone programs, but could interact with remote computers via a network. These dumb terminals were clients of the time-sharing mainframe computer. A client is part of a client–server model, which is still used today. Clients and servers may be computer programs run on the same machine and connect via inter-process communication techniques. Combined with Internet sockets, programs may connect to a service operating on a possibly remote system through the Internet protocol suite. Servers wait for potential clients to initiate connections that they may accept.

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6. NIC (network interface controller)

A network interface card (NIC) (also known as a network interface controller) is a computer circuit board or card that is installed in a computer so that it can be connected to a network. Personal computers and workstations on a local area network (LAN) typically contain a network interface card specifically designed for the LAN transmission technology, such as Ethernet or token ring. Network interface cards provide a dedicated, full-time connection to a network. Most home and portable computers connect to the Internet through as-needed dial-up connection. The modem provides the connection interface to the Internet service provider.
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