Before we start talking about the radio or the Internet we have to explain what do we exactly mean by "telecommunication networks", in order to make sure that we have a clear idea about this concept. There are lots of different networks, each of them integrated by diverse elements and with different uses. However, we could say that, in general terms, a telecommunication network is made up by several links and nodes that enable communication between two or more terminals in long distances. Depending on the network we are talking about, there will be different types of terminals, links, nodes..., concerning the uses the network might have, the distance that separates the terminals, the number of terminals de communication is directed to, the kind of communication we want to send or receive, etc.
Nowadays, telecommunication networks are integrated by complex structures and elements such as satellites or big terrestrial stations, which enable communication from one pole to the other. But, of course, it hasn't always been like that. In the last hundred years they have appeared some revolutionary networks which have even changed our habits and which have made our daily-life easier than never before. As clear examples of this, we should mention the impact that networks such as the telephone, the radio or the television -which have reached billions or users all over the world- have made in society. But, of course, this is nothing compared to the huge revolution that the appearance of the Internet meant in the telecommunications field.
A telephone network is made up by a number of linked elements by which we can send or receive voice or other sounds from different locations. Although the land phone was the first to appear, the invention of the mobile phone has supposed a worldwide revolution in telephony.
·Digital or analogical?
Telephone communication is transmitted via two different systems: analogical and digital transmission. Both land telephony and mobile telephony can use this two systems.
ØIn analogical telephony voice is directly turned into electric impulses that are send by a transmitter. The emissary terminal generates this impulses, and the receptor terminal turns then again into sound. There are different systems of analogical transmission:
-Telephoning Basic Net (TBN): a chain of circuits carries the electric impulses from the emissary to the receptor. Nodes are used to link the different telephones with other nodes and telephones.
-First Generation Mobile Telephony: it uses analogical systems of transmission, providing a better covering than any other mobile telephony.
ØIn digital telephony voice is transmitted with a higher quality, and better services can be offered. In this system, voice is codified.
The main systems of digital transmission are:
-RDSI Land Technology.
-Second Generation Mobile Telephony: it transmits voice at a higher speed.
- Third Generation Mobile Telephony: it allows Internet connection, files download, multimedia messages, etc.
·Telephony Services and Security:
As time goes on, telephony offers more and more services than the simple voice communication. Among this services we should mention the SMS (Short Message Service) -used to send messages of less than 160 letters-, the EMS (Enhanded Multimedia Service) -used to send messages with images or little melodies-, the MMS (Multimedia Messaging Service) -used to send messages with no limit of words-, Internet Navigation, chats...
At the same time that telephony offers different functions, it provides more security to the users. Since the appearance of the digital transmission, in which the information is codified, calls have become safer. Besides, the data we want to send can be encrypted by using pairs of codes. Finally, they exist several elements created in order to protect mobile phones: the PIN (Personal Identification Code), PIN2 and PUK codes, the SIM target (Subscriber Identity Module), etc.
Since almost 100% of the population has access to both of them, we could say that radio and television are perhaps the most used communication networks. Their transmission system is based on electromagnetic waves, which are sent from a transmitting station to a receptor one. Radio waves can be distinguished according to their frequencies, what is to say, according to the number of times that the wave vibrates per second.
In Spain, since the year 2010, digital transmission has substituted the analogical one, due to the great advantages that the former offers when compared with the latter. On the one hand, while in the analogical system the quality of the reception is highly influenced by the distance between the transmitter and the receptor, the climatic conditions, and the interferences often produced by the saturation of the radio-electric space, in the digital transmission system the quality of the reception is always quite good. On the other hand, when we use the digital transmission, television and radio can offer parallel services, such as the Teletext, the Guide Plus or Programming Guide, Digital Services (entertainment, information...), etc.
Internet has meant the biggest revolution ever in telecommunications. Internet is a wonderful resource for information, knowledge, entertainment, discussion...Since the development of its use, it has changed the daily-life of millions of users all over the world, who use it for e-mails, chats, world wide webs (www)... In fact, you wouldn't be reading this right now without the Internet. But did the Internet suddenly appear? What do you know about its history?And how does the Internet really work?
A computer net is a connection between different computers which allows us to exchange information, share a common software or hardware, etc. Internet is a group of linked computer nets (in fact, the word "Internet" comes from Interconnected Networks.
·Brief History of the Internet
If you want to learn a bit more about the history of the Internet, you should watch this video:
Internet was at first created as a proposal of the Defense Department of the USA. In the 1950's the agency ARPA (Advanced Research Projects Agency) was asked to create a strong communications net which would remain operative under any conditions. In 1966 Lawrence G. Roberts created ARPANET, a wide-area communication net for computers and by 1969 he was able to connect four computers to this net at the same time. During the 1980's they were developed several nets of computers which, together with the already mentioned ARPANET, contributed to the creation of the protocol of communication TCP/IP, which we will explain later. As time went on, the number of users and nets that were connected to ARPANET highly increased. This led to the creation of NSFNET, a net that integrated the rest of the small nets. By 1990 ARPANET disappeared, leading to the apparition of Internet.
·How does the Internet really work?
If you want to learn a bit more about how does the Internet work, you should watch this video:
During the development of the Internet, they were several key concepts that allowed its success. One of them was Packet Switching. Packet Switching means that the complete message or information is divided into different portions, each of them travelling to the destination computer by different routes. By using this system, we improve the communication nets' flexibility. One of the other key concepts we mentioned, was the creation of a protocol of communications, that is to say, a "universal agreement" which is adopted in order to allow and guarantee communication between completely different devices. This protocol was the TCP/IP:
-TCP: Transmission ControlProtocol. It divides the messages into different packets, codes them and adds some information in order to reorganize the information after it has reached its final destination.
-IP: Internet Control. It drives the packets inside the nets and identifies the computers by using the IP directions.
IP directions are made up by four octets of numbers and are used to identify unequivocally each host (a computer connected to the Internet). Each host receives a unique IP direction, which identifies at the same time the net the computer belongs to and, inside that net, the computer itself.
Although all IP directions are made up by 32 bits, not all the nets are of the same size. In order to solve this new problem, they were created different kinds of nets, according to the number of computers that each net could connect. The Net Mask -a number of 32 bits- was then created in order to differentiate the diverse nets. The role of this Net Mask is to indicate the devices which fragments of the IP direction of the computer identifies the net the computer belongs to, and the fragments which represent the computer itself inside the net.
Up to now, we have been talking about the IP directions and their uses. However, whenever we are surfing the Internet, we use Domain Names instead of directly using IP directions. Domain Names are words separated with full stops which identify and indicate us the position of a computer or host inside its net. This concept is similar to the idea of IP, so Domain Names are mainly used because it is easier to remember, for example, www.google.es than its matching IP: 66.102.11.104. The DNS (Domain Name System) is a data base which turns Domain Names into IP directions and vice verse.
·How can I connect the Internet?
Up to now, the most used communication lines used to connect the Internet have been the telephone lines. However, nowadays they exist different ways to connect the Internet, such as the optical fiber lines. Depending on the kind of line we have, we will enjoy a different quality (which is mainly reflected in the bandwidth -the number of data transferred during a particular unit of time- and in the parallel services we are offered). Some examples of Internet connections are the BTL (Basic telephone Line), the ADSL (Asymmetric Digital Subscriber Line), the Optical Fiber Line (which offers the greatest bandwidth) or the Satellite.
In order to connect the Internet, we need to use specific hardware. This hardware is mainly:
-A modem: which turns the analogical information into a digital one and vice versa, in order to "translate" the information that our computer needs to send or receive into the signal that travels by the telephone lines.
-A router: which drives the packets of information it receives (remember Packet Switching) by the fastest ways to the final destination.
Exercise 10)Where are there more local radio stations, in the FM band or in the AM one? In Spain there are more local radio stations in the FM band. In the FM band there are 837 local stations, while in the AM there are only 197.
Exercise 11)Where are there more music radio stations, in the FM band or in the AM one? Nowadays, in Spain there is more music radio stations in the FM band than in than AM one.
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Exercise 21)Complete the following tables.
Computer 1:
Decimal number
Binary number
IP direction
192
168
1
36
11000000
10101000
00000001
000100100
Net Mask
255
255
255
0
11111111
11111111
11111111
0000000
Computer 2:
Decimal number
Binary number
IP direction
192
168
1
33
11000000
10101000
00000001
00100001
Net Mask
255
255
255
0
11111111
11111111
11111111
00000000
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Exercise 39)which protocol is in charge of making sure that the information arrives to the right destination? The TCP/IP protocol.
Exercise 40)The Net Mask is an IP number which allows us to... ...know which part of the IP direction matches with the identification of the net and which part identifies the host.
Exercise 42)what do we mean when we say that the access to the Internet via ADSL is an asymmetric? This means that the bandwidth devoted to the emission of data is wider than the bandwidth devoted to the sending of information.
Exercise 39) what do we use a router for? To organize the traffic of data in the different nets.
Exercise 45)
1.
Blu-Ray:The first consumer device arrived in stores on April 10, 2003
DVD: DVD is an optical disc storage format, invented and developed by Philips, Sony, Toshiba, and Panasonic in 1995
2. Sony ps3 and other special players are able to read
Blu-ray discs
3.High-definition optical disc formats: Blu-ray Disc versus HD DVD. Several disc formats that were intended to improve on the performance of the DVD were developed, including Sony's Blu-ray and Toshiba's HD-DVD, as well as HVD, FVD and VMD. The first HD-DVD player was released in March 2006, followed quickly by a Blu-ray player in June 2006. In addition to the home video standalone players for each format, Sony's PlayStation 3 video game console offers a Blu-ray Disc player and its games use that format as well.[5] The format war went largely in Blu-ray's favour after the largest movie studio supporting HD DVD, Warner Brothers, decided to abandon releasing films on HD-DVD in January 2008.[6] Shortly thereafter, several major North American rental services and retailers such as Netflix, Best Buy, Wal-Mart, etc. and disc manufacturers such as CMC Magnetics, Ritek, Anwell, and others, announced the exclusive support for Blu-ray products, ending the format war.
4.If the two formats have compete in the same market we would have suffered the problems of the incompatible formats and the need to purchase specific readers for each format.
