Radio waves are widespread in telecommunications because they can easily be produced and, given a large range of buildings, pass through obstacles and buildings, radio waves are all-round, that is, they are released in all directions, so there is no need to The exact setting of the sender and receiver is not.

The characteristics of radio waves depend on their frequency. At low frequencies, waves easily pass through obstacles, but their power decreases rapidly in distance. At high frequencies, radio waves travel in a straight line and are reflected in the collision with obstacles. There is also a loss of path, but the signal strength of the received signal depends on how it reflects, even the raindrops absorb high-frequency waves

The radio waves VLF, LF, MF follow the curvature of the earth, these waves are nearly 1000 km long, the AM radio stations work in the MF band, so their range is high. Radio waves in this gang easily cross obstacles and buildings. The only problem with these waves is the small bandwidth. In the HF and VHF bands, part of the waves that move close to the ground absorb the surface of the earth, and that portion of the waves that go into space after the collision with the ion spree again These types of bands have a wider bandwidth but a wider range, amateur radios and military communications use HF, VHF bands.

The development and advancement of telecommunication networks over the past two decades has been following a single target, which is a gradual change from packet switched circuit networks. Today, a huge amount of network operations are trying to transform the public telephone networks into the packet switches Multipurpose. Given that the process of deregulation and liberalization has fueled competition in the telecommunications market, prices have fallen and innovations have peaked.

Inactive equipment (passive): The function of this equipment is without any electrical power. These eَquipment include: cable types, connectors, ducts or ducts.

Active network equipment:Equipment that requires electrical current. These equipment include: NIC card, switch,Router, firewall, fiber optic converter (Media Convertor) and print server.

The most important task of distribution companies in addition to timely supply of electricity to customers is to maintain a good quality of electricity for subscribers. To this end, it is necessary to implement the automation system in distribution networks. In distribution networks without an automation system after the occurrence of any shutdown , A lot of time is spent to find the location of the fault and isolate that location from the rest of the network, which may increase for several hours at high-frequency networks.

With the advancement of video surveillance systems from their traditional (CCTV analogue) system to IP systems, many companies are looking for ways to bring video surveillance to their core. Now, with familiarity with its old regulatory systems and knowledge and skills in IP systems, it offers new and diverse solutions for video surveillance and secure transmission in the TCP / IP network. Today, network cameras are used in a variety of environments, small businesses, large organizations and industrial plants.