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• María Belén Gómez

# Online Codes

In-line codes are very frequently used when the digital transfer of data from one point to another is required. It can be said that these codes are made up of sets of bits, which are minimum units of information that are quantified on the basis of a binary numbering system comprised of zero and one. When we refer to the unit of measurement of the speed at which data is transmitted, the bit per second reflects the relationship between the space the information travels and the time it takes to do so. Online codes are packets that in the field of electromagnetic communication systems make it possible to connect individuals who are separated by space in a linear perspective.

## Codes and coding

To begin with, what is a code, when inquiring about its basic concepts you may find that in the characteristic rigidity of norms, laws and rules a common denominator is obtained. Codes are a set of rules and norms on any subject, and based on this, it can be said that the code in line part and is due to a convention so that it can be channeled by each of the parties in the same way.

Coding refers to the act of gathering information in an orderly manner in a code, through this process information can be recorded or the expression of the message can be modified. Coding implies that the information being worked on is in equivalence with the original information.

## Digital coding

In the case of digital coding, the electrical voltage values are reflected in the binary system. The digital signal is made up of sequences of voltage pulses that are discrete and discontinuous; each voltage pulse is considered a signal element. The data in its binary form is transmitted by encoding the data bits into voltage pulses.

The number zero (0) is represented by low voltage levels and the number one (1) is represented by higher voltage levels. This relationship is called the encoding scheme. After the information is encoded the signal is sent through what is called the physical layer.

## Online code transmission

Using different voltage levels for each bit is a very common way of transmitting digital signals. The codes that are transmitted based on this method have the faculty that during the duration of the bit the voltage level is constant, without transitions and do not return to zero voltage levels.

Normally, the number one (1) represents positive and constant pressure levels, while the number zero (0) is given by the absence of voltage. Due to the simplicity of these NRZ codes, they are normally used in magnetic recordings, but some limitations do not make them ideal for signal transmission.

• Multilevel Binary

In this system more than two signal levels are used. The number zero (0) is represented by the absence of the signal, and the number one (1), for this case, is included when a negative or positive pulse is present. Due to the alternating polarity there is no continuous component in the representation of the number one (1) in the binary system.

• Biphase

In this system there is a transition in the middle of the bit duration, this allows synchronization to occur when data is transmitted. Transitions from low to high are represented by the number one (1), and those from high to low are represented by the number zero (0). There is at least one transition per bit and may occur up to two times in each of the phases.