Before starting with the use of some Linux commands, I want to remind the importance of reviewing the reference manual for each command, because this is the place where you can find all the possible options. The reference manual can be displayed on a terminal using the "man" command, for example, if we see the manual of the "man" command in a terminal, we should write "man man" and we would see something like this:

Figure # 1: Linux terminal displaying the manual of the man command.

I present you my favorite applications to capture packets on the network, although they are well known for their features, I decided to give a little space to discuss some of their features. In addition to data capture, these applications are useful for certain packets analysis with the obtained data, on the other hand, when the analysis that we need to do is a bit complex or very specific, it is always advisable to build our own scripts, but there is no doubt that no matter for what we use them, this applications will help us to obtain useful network information. This applicacions can also be combined with traffic generators in order to analyze some network issues.

TCPDUM

TCPDUMP [1] is a tool for capturing traffic flowing through the network in real time, this includes packets transmitted and received on a specific network interface. This tool has no graphical interface, this makes for one of the favorite applications when you want to use minimum resources as possible, also be suitable for unattended packet capture, because it can be managed by command line as it can seen in Figure # 1.

Figure # 1: View of the contents of various packets for command line using TCPDUMP.

For some time I have been using various traffic generators, and today I want to share 3 of the that I most use for their interesting features. The traffic generators are useful for injecting traffic of certain applications or network services and not have the need to run such applications, in my case I used to generate the traffic of VoIP, video streaming, video surveillance, and even to make some reverse engineering on certain commercial devices. Then I leave a short review of each of them:

The Propagation of radio signals has a number of inherent problems of electromagnetic waves, of which LTE or 4G is not exempt. Aspects such as absorption, refraction, diffraction, fading, and other properties can cause serious problems of coverage, interference, and general degradation of the transmitted signal. Some of these parameters are largely unpredictable, mainly those arising from meteorological phenomena or the ground, and therefore, fewer steps may be taken in such cases.

Moreover, the free space loss (FSL) is directly related to the system operating frequency and the distance between transmitter and receiver. The case of frequency is a parameter already defined for this type of technology by the International Telecommunication Union [1], also depends on the frequency assignments of each country, and therefore it is not something that operators can easily handle to increase the coverage of their mobile systems.

The case of multipath is a problem that is associated with the spread of radio beam by several pathways, supported by the phenomena of reflection, diffraction and scattering. This type of phenomenon produces a difference in the distance that a beam that travels with sight line over another who has suffered the effect of reflection (to name one example) and consequently there is a difference between the arrival times of the signals and the receiver, which may cause the overlap of the signals at the receiving antenna causing inter-symbol interference (ISI), or too low power to be demodulated, it is also possible that even a given beam incident on the receiving antenna as shown in the following Figure # 1.

Figure # 1: Multipath example.

Mobile communications have had an exponential increase due to the high level of acceptance due to the need for information and access to different services from the world community, for this reason wireless devices such as PDA's, smartphones and other devices have a growth in sales, extremely high in recent years, as it is shown in Figure # 1.

Figure # 1: Amounts of mobile devices sold per year [1].