Components of computer networks

to move data between computer networks are logical and physical components required ..• logical connection by network software, which is a set of programs through which the user has access to network facilities• physical connection made through physical media for data transmission (cable, radio) and specific network equipment. The most used transmission media used in a network: twisted pair, fiber optic, radio

The most common equipment in a network are:• Network Adapters (NIC Network Interface Card) or NICs are tile interface which can connect one computer to another computer in the network. It is mandatory that all networked computers have the network card configuration.Modems are required to connect a computer to the network via telephone line. The modem is a device necessary because:- within the computer the signal is digital (in the form of electrical pulses, which correspond to binary 0 and 1), and the transmission line (which is usually a normal telephone line) signal is analog (in the form of amplitude modulated sinusoidal currents or phase).The transmitter computer, the modem performs signal modulation, ie converting the digital signal into analog and computer modem receiver performs signal demodulation, ie converting the analog signal into a digital signal.

-Hubs

-Switches

-Bridge

- Routers

- Wireless Access Points

- Firewall

-VPN

Fig 1

Cards are shown in Figure 1. These are electronic devices with an interface between the computer and network cable. Network card installed inside each computer on the network.

Functions of cards are:

- Prepare data to be transmitted by cable network;

- Transmit data to another computer;

- Control the flow of data between the computer and the network cable.

Hubs

Hubs are shown in Figure 2. These are devices that extend the range of a network, receiving data on a port and then sending data to all other ports. Thus, all traffic from a device connected to the hub is sent to all other equipment connected to the hub whenever hub transmits data. In this way it generates a large amount of traffic on the network. Hubs are also called concentrators, because they act as a central point for a LAN connection.

In Figure 3 is the symbol of a hub and a few computers connected to a hub.

Fig 3

Fig 2

Fig 5

Switch şi Bridge

Local networks are usually divided into sections called segments, similar to how a company is divided into departments. The boundaries between segments can be defined using a bridge.

The data is transmitted between network segments are organized into files. They are divided into bite-sized pieces called packets before being transmitted over the network. Destination information packets are added at the beginning and end of packets before being transmitted.

A bridge (Figure 5) is a device used to filter network traffic between a LAN segments.

Typically, a bridge can only have two ports connecting two segments of the same network.

A switch has multiple ports, depending on how many network segments to be connected. A switch is a device more complex than a bridge. A switch maintains a table of addresses of computers that are connected to each port.

In computer science, a Media Access Control address (MAC address) is a 6-byte integer (48 bits) on token ring or Ethernet networks used to identify a computer on a local network. When a frame is received on a port, the switch compares the address

information of the frame to the MAC address table. The switch determines which port to use to send the frame.

In Figure 6 we realize extend a network using a bridge and a switch.

Routers

To better understand the role of routers, you make a comparison between the switch and the router. We learned earlier that the role of a switch is to connect segments of a network.

Routers, shown in Figure 7, are devices that interconnect multiple networks. Switches use MAC addresses to transmit a frame within a network. Routers use IP addresses to forward frames to other networks. A router can be a computer that has installed special software or equipment can be designed for network equipment manufacturers. Routers contain tables of IP addresses with the optimal routes to other networks destination.

Fig 7

Segment 2

To Segment 2

Segment 1

To Segment 1

Fig 6

Wireless Access Points

Wireless access points are shown in Figure 9. They provide network access for wireless devices such as laptops and PDAs. Wireless access point uses radio waves to perform communication with computers, PDAs and other wireless access points. An access point has a range of limited coverage. Large networks need more access points to ensure adequate coverage.

Firewall

In computer networks, a firewall , also called firewall (or firewall, the firewall English) is a device or set of devices configured in such a way that the filter, encrypt or to intermediate traffic between different security domains based on predefined rules.

Fig 9

VPN

A virtual private network (in English from the virtual private network, abbreviated VPN) extends a private network over a public network such as the Internet. Allows a computer or a device that can be connected to the network to send and receive data over public networks or shared as would be connected to the private network, while benefiting from the functionality, security and public network policies. VPN traffic messages can be transmitted via a public data network infrastructure (eg the Internet) using standard protocols, or via a private network to the Internet service provider (ISP), made available publicly.

These types of connections provides a low-cost alternative compared to dedicated networks of private WAN, enabling telecom switches connecting to the internal network of a company Cable, xDSL, or dial-up. VPN connections are easier to implement than existing public infrastructure, and provides an alternative to dedicated private networks such as Frame Relay or ATM type, which are generally more expensive.

VPNs offers several advantages: low prices for implementation / operation / management / maintenance, enhanced information security (as close to the actual private networks, traditional), scalability, simplified and, finally, compatibility with high-speed public networks .