Information and Communications

Previous knowledge

sinusoidal wave

In the first place we are going to study the basic parameters of a sine signal, very used in engineerings.

In the signal of the left, we have:

  • To as the amplitude of the signal, or the maximum value that can reach throughout the time.
  • T is the period, that is the time that takes a wave in being developed.
  • Perhaps the signal does not begin from zero, in which case it says that she is out of phase. To that angle phase angle is denominated to him
  • Another one of the used parameters is the frequency of the signal, that it is the wave number that is repeated in a second. For example, if we have 10 cycles in a second, we have 10 Hertz, if we have 100 cycles in a second, we have 100 Hertz.
  • A relation exists between which it lasts the signal (period) and the frequency. This relation comes given by

Before entering matter, he is advisable to know how the units go from a scale to another one. The system always is the same, that is to say, is worth for the frequency, distances, weight, etc.

In the case of the frequency of a signal and defined this as the number of times that a wave is repeated per second, we have united it is Hertz with the following multiples and submultiple

  • Superficially we have the Khz that is 1000 Kz (10 Hertz)
  • The mega Hertz (MHz) corresponds to a million Hertz, (10 Hertz)
  • The Giga Hertz (GHZ) is or trillion of Hertz (10 Hertz)
  • The Tera Hertz (THz) is a trillion of Hertz (10 12 Hertz)

For the frequency they are not used the sub-multiple, although they are possible to be defined of the same form that before. We have

  • Thousand small times but mHZ is the milihercios = 10 -3 Hertz
  • A million but small one is microHertz Î¼Hz = 10 -6 Hertz
  • If we followed with the process we have the nanoHercios nHZ = 10 -9 Hertz
  • The picohercios (pHz) is thousand times but small that previous, that is to say, 10 -12 Hertz

Of this form, already we can make some changes from one to another one.

Activity. To pass to Hertz the following values

  1. 23 KHz
  2. 45.7 Hertz
  3. 356 mHz

To pass to milihercios the following values

  1. 467 Ghz
  2. 87.34 Khz
  3. 68000 pHz

Activity If we have a signal of 400 Kz and added a 2.5 signal to him of Mhz, that result we have. To express it in exponential form.

Activity. To calculate the frequency of a signal of whose period it is 2 microseconds and of another one of 45 milliseconds

1,2 Analog signals and digitalises.

The difference between one and the other are in the form and the possible values that each can take throughout the time. In the case of the analogical natural signal * , the values that can take are infinite, whereas the digitalis (two digits) can take only two values (0 and 1). so that it is possible, the transition being a value and another one must be immediate possible.

1 Activity. In page 6 of the book we have an example of both signals. Something that to object.

Difference between analog signal and digitalis?

Codification of analogical to Digitalis

  • Before we spoke of natural signal referring us to the analog signal. I appeal to this denomination because it is the representation of each physical variable in the nature.
  • When the electronic components work, factors as the heat, constitution, interferences, etc, cause that those values are distorted and, therefore, would be better than they worked of digital way, (two values) so that to happen from a value to another one a Gap exists important (it happens, for example, of 0 volts to 5 volts)
  • Therefore, it is necessary to find each analogical value to his corresponding digitalis. For it, the signal is sampled once in a while (sampling frequency) and is assigned a value of 0 and 1 to each sampling. In the example of figure 1,9, for example, for the first sampling value 000100 can be assigned, indicating the first digit that are a positive value, and the other the value in binary of the tension. For the second negative sample, value 1 01011 is taken. The first value means that he is negative and the rest indicates the value of that signal.
  • signal sampling

Bauds and Bps

When we thought about transmitting data by a digital network, we thought typically in terms of bps. In first of the images, we have two logical values 0 and 1, that tensions 0 and 3 volts are represented by.

If we took 8 from those values, we would have a byte, (for example, the 10010011). Each byte is going to be able to represent a character as the letter, the b, the c, etc (This comes prevailed by several standards, as the ASCII)

In the first image, each sent electrical pulse denominates symbol. In this first case, if we defined M as the number of possible values that the symbol can take, we have M is worth 2, reaching the conclusion that the bps envoys are equal to the symbols per second (Bauds)

Logical values 0€ and 1€ are represented by values 0 and 3 volts.
In this case, we have but tension to represent but values of bits

In 2 image, designs a system so that the tension can take 4 different values (- 1.5v, 0v, +1.5v, +3v).  In this case, M=4, and the line can represent the associate logical values:

  •  -1.5v = 00€
  •   0v=€ 01 €³
  •   +1.5v=€ 10 €³
  •    +3v=€ 11 €³

For the same clock of work, for the same bauds, we have doubled the information capacity, since before we had only the possibility of transmitting a bit, but now have 2 bits for the same baud.

Binary system and decimal

In order to represent a value usually we make it in the decimal system (3, 7, 4.567, etc) but the digital machines work with numeral systems binary (0 and 1).

Any symbol that we want to represent (the 3, letter b, *, the key \ {, etc) can be represented by a binary code. With 8 bits they are sufficient for all of them and to or the bit a byte is called to him.

Activity: It looks for in Internet what is ASCII and how each value is obtained.

We are going to see how to happen of a system to the other and for it we must review the subject seen in 4 of THAT on the introduction the digital electronics 

  • As activity, to pass numbers 68 and 104 to the binary system and to verify that the operation is correct

Emitter, receiver and circuit

Their names indicate to us what function has within a system of communications. To emit a signal, to receive it (Emitting) and to establish a suitable system so that it happens (circuit). Within the circuit we have two 3 forms which the connections (elements of the circuit), deal with the signal.

  1.  If they are limited to take it and to propagate it in a single sense (of the emitter to the receiver) is called simplex.  We are speaking of a unidirectional communication
  2. If in addition to receiving it can emit but only one thing simultaneously (or it emits or it receives, following the issued order) we are speaking of a half-duplex
  3. When to the communication he is bidirectional and each connection can emit and to receive simultaneously, we are in a system full-duplex

Activity. Search, at least an example, of each one of the systems

Communications networks.

We have in that section a classification of the networks, taking care of its extension (PAN, LAN, MAN and WAN). If we know the words of each abbreviation, we have the answer to each, is enough to know that all ends in AN that comes from Area Network (area network) preceded of P (personal), L (Local), M (Metropolitan) and W (Wide).

On the other hand, based on who can use it we have the private one, public and dedicated. (To see book description). It is possible to add more than it is not in the book. The network

Deep Web

As exercise, search in Internet what is that network, how it accedes, that uses it, that there is in her, what dangers entail their use, etc

Important: it is necessary to have much taken care of in this network because we can be found any thing. In addition, if we are not careful, we can take of gift some type to us of virus, normally a spyware. As precaution, to create a point of restoration of the system and when finishing the session, recovering the system to that point.



To study this question by this blog.

Multiplexer is called to the system that it makes possible to transmit several information channels from two distant points, using only a communication channel.

Several types of multiplexers exist. First that we will see is perhaps simplest, the multiplexer per time, where each channel has a time to overturn data in the other part of the system of communications.

In the image we have a multiplexer using the technique of the time splitter.

multiplexer per time

2 of them is the multiplexer by frequency, where we are going to use several carriers of different frequencies, we modulated them and we passed them to the channel. We see in the image following east system:

multiplexer by frequency

If we observed the image superior, we have exist three oscillating of 12, 16 and 20 kHZ. Those frequencies are modulated in frequency€ by the signals that we want to transmit and that they have a 3.4 rank from 0.3 to KHz.

A.M. and FM

In the following image is a modulation in frequency (also in Amplitude of the signal (A.M.))

As we see in the modulation in frequency, the frequency of the carrier wave (blue) is modulated by the signal that we want to transmit (signal in the image). We add another image to see how it is modulated the carrying signal by moduladora praise.

modulation by frequency

In this case, we see as it varies the carrying signal on the basis of the moduladora. We have indicated two square zones (blue and red) to see as they vary the values of the frequency.

The frequency of the carrier can arrive at 12000 Hertz €“ 300 = 11700 = 11.7 Khz and the minimum frequency can arrive a (12000 €“ 3400) = 8600 Hertz.

The same takes control of the second signal, that we only left from another carrier of 16000 and 3 of 20000 Hertz. 4000 Hertz rise so that the signals are not overlapped.

Once the three are transmitted signals by the cable are arrived at the receiving system, that separates them by three filters of step band soon to demodulate and to obtain the origin signal.

Topologies of network

The way to connect several computers is diverse with its advantages and disadvantages. We will see a little in detail the network in enmeshes (the rest to see them by the book)

This topology does not require of a node that collate data as it happens more with others as the star topology, with the advantage of a considerable reduction in the failures and of maintenance.

The simple network has a routing cable to cable, thus, the breakage of a cable causes that the computers that are connected stop communicating.

If it is had dynamic routing, we give rise to a system autoenrutables€.  In this case, the communication between two devices of the network can even be carried out with broken cables (whenever an alternative way exists and, thanks to the dynamic routing, the information can re-be directed by alternative ways.  The problem of this network is that they turn out expensive to install, due to the amount of necessary material (cables, repeaters, cards of ports, etc) and the manpower required for its installation

Activity: 1 Leer the question of page 11 of the book. Time 25 minutes. In case of not having book, to make work groups of 2 people and to obtain the necessary data in Internet to each one of the networks, including how the computers, advantages and disadvantages are connected.

2 Intentar to deduce the formula by which the number of connections in enmeshes complete is: I connect = \ tailcoat {n * (n-1))}{2}

 (time 30 minutes)

Solution: It is possible to be calculated of easy way for a network of few computers so that:

  • The first computer connects with all, therefore we have n-1 already cables (being n the number of computers)
  • 2 computer has a cable less than connection because the previous one already has connected to him with one). Therefore we have n-2 cables.
  • Of that form, the result is the sum of (n-1) + (n-2) + (n-3)

The following image is to a development for diverse groups of n computers and X cables.

deduction of formula I number connections Mayan completes

We represent with a line curves the cable difference that exists between each network, for example, that agrees with n-1

In order to obtain cables of, for example 5 computers, turn out 10 is obtained to multiply the 5, by the previous difference (4) divided by two. for that reason we have been able to deduce the previous formula

Activity 3. To realise the exercises of proposal 1.1

Activity 4. We have a building of 4 plants and 30 computers by plant. You consider that the topology of enmeshes complete is adapted. Because and on the contrary, what enmeshes but is adapted. The answer reasons.

Modelo OSI.

When two computers, that normally have different hardware and software, must communicate, it is necessary to establish a series of norms so that communication is effective. One can be connected with fiber and another one with a pair of cables. One can be a Mac and another Windows, one can be in Holland and the other in Spain and thus a series of things that make necessary a series of protocols and functions of communication so that Internet is possible.

We have this video that can clarify a little but the subject to us

We are going to make a summary on the 7 layers that form the model OSI (summary of the content of the book). We leave from the idea that this one model must as objective establish the necessary conditions so that two distant devices can be communicated. The 7 layers are, to simplified way:

1. It castrates Physics.  Like to communicate two points in the real space, we needed a highway, a route of the train, etc and in them some settle down traffic norms, the physical layer has as an aim the one to establish the conditions so that by means (air, cable. ) data can to transmit, and for it, aside from to specify as they must be cables and connectors, it says us as they must be the 0 and 1 (that electrical values correspond to them), felt of the information, etc.

2. Layer of data link. When we sent a postal letter, on it has an adressee and a sender. This makes the layer of data, to add information to each package of data so that it is known from where it comes and where it goes. In addition it adds synchronization information.

3. Layer of network.  It is the GPS of the car. It indicates to us that way is the optimum one to send each package of data.

In this layer, 4 processes take place, that are

Address: Capa of network must provide a mechanism to direccionar the equipment that is wanted to communicate

Encapsulation. The data (information) for their later shipment are packed and, this way, to have a more effective system.

Routing. The in charge device (to router) must select the routes and direct packages towards its destiny.

Desencapsulamiento. When the package arrives at host destiny, it is processed. The arrival device (host) examines the destiny direction to verify that, indeed, this package comes to host suitable. Soon the desencapsulado one in this layer of Network takes place

4. Layer of transport. If we want to transport a very great object, what we do. To section it and to send it in several packages. Then that is what this layer does. One is in charge to section the information in the side of the emitter and to assemble it in the receiver.

5. Layer of session. When I close the warehouse. The information has a time to transmit it and we do not have to close it until everything arrives at destiny. If it is closed by some reason, the session layer is in charge to continue receiving data since it cut the connection

6. Layer of presentation. One is in charge to translate suitably the data when the devices are not equal, of that form we made sure that they are understood. It is as a language translator so that two people with different languages can be understood. It can go beyond and encriptar the data.

7 Capa of application. They are the programs in himself that allow the user to accede to the network


Activity 5. To carry out the tasks from 1,1 to 1,22 of the book.

To carry out the following tasks of the subject Information and Communications