The data transmissions by telephone route are based on a series of international standards that must fulfill the devices involved in the communication. Every norm defines a series of such parameters that allow the correct communication at a certain speed.

This way, when it is said that a modem expires with the norm "V.34", it means that it is a modem that fulfills a such series of specifications that allows him to communicate with modems of this speed (and usually of any speed lower than that one). The most important norms are:

In addition to these standards, there exist two pseudo-standards (they are not official) for the transmissions to 55.600 bps: the "K56flex" and "x2". They are incompatible between themselves; that of more success in Spain was the K56flex of Rockwell, although x2 it was used very much in the United States; these pseudo-standards refused to be substituted very much with the official norm V.90 due to the excessive time that was late in this one appeared.

For lack of a better name, it is as we will designate at the speed with which they communicate to themselves between themselves the PC and the modem, good is this one internally (in whose case ISA will do by means of the bus), well be external (by means of a cable connected to a port COM).

This speed can (and it has to) be bigger than that one than the one that our modem and the remote modem are communicating to themselves. Major all that is the information flow between our computer and our modem, freer will be this one to be giving the information that receives from the exterior and the yield will be better, without necks of bottle that slow down it.

For example, if both speeds were equal (for example of 28.800 bps), if the modem would be receiving an equal constant wealth to this 28.800 bps and we wanted to give him an order ("say to the remote servant that I want another page", for example), part of this 28.800 should transfer us bps so that we could "speak" to him, what would cause a phase lag in the transmission and a slowing down of the process. And if for some motive we were lucky to connect a few moments at more speed of the normal one (what is named a "peak" in the transmission), we might not make use of it because we have put the ceiling in the nominal speed.

Being practical, let's say that the ideal internal speed for a modem 55.600, 33.600 or 28.800 are 115.200 bps (as we see, much major than the face-value), while for a modem 14.400 is 57.600 bps. Nevertheless, sometimes they turn out to be excessively difficult to control these values and low values must be selected, as for example 38.400 bps for a modem 14.400. In Windows 95 they are selected like one more option of the modem, with the cryptic name of "maximum speed".

The one who limits these values, providing or do not support at these speeds, it is such a commented UART, about which we will treat further on.

Hayes is the name of a company that in the origins of the communication for modem (when 2.400 bps could look like an enormity) defined a series of commands or orders so that the communications software could communicate with the modem. These commands were successful that turned into the virtual communications standard, and the modems that comprise them (99,99 % of the modern modems) are named compatible Hayes.

The commands the most common Hayes are:

• ATZ: inicializa or resetea the modem.
• ATH: it hangs the line.
• ATM: it extinguishes the loudspeaker of the modem.
• ATDP number: it marks a phone for pulses (method of marking of the analogical phone lines ancient, that assigns so much noises of marked like values of the numbers of the number; this way, "055 it would be marked doing 10+5+5=20 sounds).
• ATDT number: it marks a phone for tones (method of marking of the analogical phone lines modern, that assigns a noise of marked by every number of the number; this way, "055 it would be marked doing 1+1+1=3 sounds).

For example, the following commands sequence: ATMDT055 it would serve to us to call by tones to the telephone number 055, without having to hear the loudspeaker of the modem. In Windows these commands would get (if it is that there need) in the pigeonhole additional Configurations that one finds in Control panel-> Modems-> Properties-> Connection-> Advanced post.