UNIT 4 (GLOBAL COMMUNICATION NETWORKS)

Telephone networks

A telephone network is a large group of interconnected elements, with the objective of transmitting and receiving voice communication between different locations.

With the basic infrastructure of a telephone network, any user can use the internet, and mobile phones have become a communication phenomenon around the world.

Transmission via telephone networks uses two different systems; analogical transmission and digital transmission. They are two completely different methods:

• Analogical telephone: A voice is directly transformed into electrical signals that are transmitted through a medium. The emitter generates these signals, and the receptor changes them into sound once again.                                                                                                                                           

          - Basic telephone network: The traditional telephone network. A system of circuits takes the electric signals from the emitter to the receptor.

          - First generation mobile telephone: This uses analogical systems to transmit data which have great coverage and reach.

• Digital telephone: This is a great advancement when it comes to voice transmission, as it permits better quality and is more reliable than the original signal. Also, it can generate some additional services.                                                                                                                                                                                                                            - RDSI fixed telephone : This uses the same system as the basic telephone networks, the difference is that it has a digital transmission.                                                                                                           - Second generation mobile phone: The first digital mobile phone. It permits a high-speed voice transmission.                                                                                                                                             - Third generation mobile phone: This marks a great improvement of data transmission. Among other features, it permits internet access. 
• Telephone and data services: Telephone systems offer many more services than simple voice communications. They include SMS, EMS, MMS videocall, videomessage, the ability to surf the internet, chat and news.
• Security in data transmission: First generation mobile phones were analogical, and they weren't very secure. Second generation mobile phones use digital voices, which meant that information was more secure. Third generation mobile phones use IP technology to transmit data, which uses encrypted data. This means that the information is very secure.

Proteccion of mobile terminals: There are many items used to protect mobiles such as:             

- Sim cards: Small circuits used to connect the terminal to the telephone network.                                   

- PIN code: A four-numbered code used to activate the terminal.                                                               

- PUK code: Used to unblock the SIM card when the Pin code has been introduced incorrectly more than twice.                                                                                                                              

- IMEI code: A code that has fifteen digits and is used by the operators to identify their terminals in the network.

Emission and reception of radios and televisions

Television and radio are the two communication networks that can get to all the population. They are based on the emission of electromagnetic waves from an emitting station to various receiving stations. In Spain, the system of signal transmission was analogic, but, in 2010 it became digital. The digital signal can be sent from a satelite, an antena or an emitting centre.

Radio and television services: There are certain services that come with radio and television. They include teletext, GUIDE Plus, RDS and digital services.

Brief history of the internet

Internet was created by the USA defense department with the aim of developing a communication network capable of supporting the destruction of a large part of devices that it formed and keep working. The agency ARPA had to develop innovative ideas and one of them was the internet. Industry and the academic world have also contributed to its creation. In 1966 Lawrence Robinson came up with ARPANET, the idea of a large communication network for computers. The communication protocol TCP/IP was adopted by ARPANET. In 1986, NSFNET was created. This system intergrated all small networks. This caused the dissappereance of ARPANET, in 1990.

Internet is the group of all the public computer network which use the protocole TCP/IP.

Commutation of packages and of circuits

With package commutation, information is fragmented, and each package is sent on different paths.

A communication network is an agreement that is adopted so that different devices can understand each other, it is like another language. TCP/IP is a protocol that permits computers with different operating systems to communicate through communication networks that are different.

           -TCP: Its job is to divide messages into small portions, package them, number them, and add    some information to them, so that the computer knows how to organize these messages.
            -IP: It sends the packages through the different networks that form internet and it identifies teams. To do so, it employs IP directions.

The problems that have to be resolved for us users not to appriciate the work these protocols do are, amongst others: Identifying the computers that send and receive messages, making the PCs agree with each other, seeing if the integrity of the information that gets to the internet is adecuate and organize this information.Computers do this with the help of routers and modems: 

            -Routers: They are machines that decide what the route the the data packages must follow.               

            -Modems: Devices that permit the transmission of data through analogical telephone lines.

• IP adresses: In the internet, there are thousands of uses connected simultaniosly. This is a grave problem when you have to identify the PCs and direct the data packages. IP addresses solve this problem, by identifying every host connected to the internet. A host is a PC conceted to the internet. Each host has an IP address, which is formed by four groups of numbers that are separated by points. There can't be two computers with the same IP address.
• Types of IP addresses: They can be:                                                                                                      - Public IP directions: They are accesible from any computer that is connected to the internet.       - Private IP directions: They permit configurations of hosts in LAN networks. They are only visible from their own network.                                                                                                       - Loopback addresses: They permit a PC to send packages to itself. It tends to be 127.0.0.1            - Automatic private direccionate IP: They are reserved for a PC that obtains an IP direction, even though it hasn't been assigned.                                                        

     Also, they can be:

         - Static IPs: Used for hosts that connect to the internet using the same IP. They are used by             Internet servers.

         - Dynamic IPs: Used for PCs that use a different IP every time they connect to the Internet.

Subnetwork masks: Not all networks have the same size, but all IP directions always have 32 bits. This is a new problem, and to solve it different type of networks were created, and to distinguish them, the subnetwork mask was created. The subnetwork mask is a number of 32 bits, joined in four groups of eight. It indicates the network which part of the IP adress indentifies the network and which represent the PC inside its own network. The first three groups of eight of the IP address correspond to the network, and the last group indicates the number of the PC inside the network.

• Special directions: Network directions and the Broadcast direction are some of the directions that must be used in TCP/IP networks.

                - Network directions: It is an IP address that represents that network. It is indicated by the numbers of the IP that use a 1 in the subnetwork mask, adding a 0 in the part due to the number of the PC.

              -Broadcast directions: It is the direction used by the protocole TCP/IP to identify every PC in a network. It is used to send a message to all the network.

Names of the domain and management of directions

When you navigate through the internet without using IP addresses you use names of domain. Names of the domain are an identifying system of hosts that is based in words that are separated by dots that indicate the  position of the host inside its network and that let it be indentified in the Internet. 

The DNS is a data base distributed by lots of computers around the world that can turn IP addresses into names of domain and vice versa. Currently, the ICANN is the organization in charge of the register of names of the domain. It is the same with the assiging of IP addresses.

Communication lines and internet

To connect to the Internet you need to employ extended communication connection. Depending on the type of connection that someone has hired, you obtain a quality service. The type of connections are RTB, ADSL, PLC, RDSI, cable, satelite and wireless broadband.

• Types of internet connection

          - RTB: The data packages are transmitted analogicaly for normal telephone networks

          -  RDSI: It employs the usual network, but the last part is digitalised

          - ADSL: It employs a normal telephone network together with a ADSL router.

          - Cable: This technology is developed exclusively to offer a series of services to someones home and someones office

          - PLC: The information gets to houses and businesses through a conventional electricity connection.

          - Satelite: In this case, information is  received via satelite.

          - Wireless broadband: It is a fairly expenssive solution.

Hardware necessary to connect to the Internet

   

• Modem: It modulates and changes the digital signal into an analogical system and viceversa.
• Router: It is a network device whos job is to look for the best routes to direct the data packages it receives.