Communications protocols

To share data over the network, prior communication is necessary, and this communication is governed by certain protocols that, subject to compliance, allow communication. We are going to see the most important ones on the Net.

A communications protocol is a set of standards that all machines and programs involved in data communication between computers must comply with, without which communication would be chaotic and therefore impossible.

Some examples of communication protocols are outlined below with the intention of clarifying the concept and their evolution:

• Point-to-point protocols.
• Communication between networks.
• packet transmission protocols.
• The TCP/IP protocol.

Point-to-point protocols.

They are the oldest and most elementary protocols used for communication through a data line between only two computers. Some of its basic rules establish the following criteria:

Role assumed by each of the two parties during a communications session, identifying and defining the role corresponding to the computer that started the session and to which it responds. The first is called a “command” and the second is called a “response”.

Way to control the correct reception of the data. For example, adding a character to the end of each message that is the sum total of BITs used.

Maximum time that must elapse between sending a message and receiving the acknowledgment from the receiving station.

Number of times a message must be repeated if, after the corresponding times, the acknowledgment message is not received.

Communication between networks.

In addition to the rules in the previous section, they must specify how to identify the specific network terminal with which communication must be established in the event that the machines that are communicating directly are servers on a local network (LAN). . For example assigning a number to each of the terminals.

Polling systems: These systems control communications in a network managed by a central computer, and are organized in such a way that it is the one that sequentially asks all the computers in the network if they have something to communicate, and urges them to do so. If so, no other components of the network take, at any time, the initiative of communication.

Packet transmission protocols:

In the packet transmission protocols, the transmission is supported by the information contained in the data that transits through the communications networks, while in the previous protocols, the responsibility for the proper functioning of the communications falls on the equipment and the transmission lines. data. To do this, the data is “chopped” and organized into packages, such as ordinary mail letters, with their origin and destination data and they go from team to team like letters go from post office to post office, from mail train to delivery truck and from another post to the postman’s bag who finally makes it reach its addressee.

The equipment that makes up the networks is limited to reading the addresses contained in the data packets and delivering the packet to the next post, who in turn will deliver it to another and so on until it finally reaches its destination.

The TCP/IP protocol.

TCP/IP stands for “Transfer Control Protocol / Internet Protocol” and this is the set of established transport standards and defined language established for the Internet and incorporated by other networks.

TCP/IP is a packet transmission protocol. When a computer wants to send a data file to another, the first thing it does is break it into small pieces (around 4 Kb) and then send each piece separately. Each information packet contains the address in the network where it has to arrive, and also the address of the sender, in case a response is to be received. The packets travel through the network independently.

As between two points in the Network there are usually many possible paths, each packet chooses the one that is optimal at that moment, depending on factors such as route saturation or traffic jams. Thus, it can happen that part of a file that is sent from the US to Spain passes by submarine cable to Northern Europe and from there to Spain, and another part comes directly by satellite. This allows the Internet to be a stable network, since, due to its own dimension and complexity, there are hundreds of alternative routes for a specific destination, so that, even if intermediary computers fail or some information channels do not work correctly, practically, there is always communication between two points on the network.

Another consequence of the structure and way of acting of TCP/IP is that it admits the eventuality that some information packet is lost along the way due to some undesired event such as an intermediary computer shutting down or saturating when a piece is passing through it. of a certain file in transmission. If this happens, the possibility of re-requesting the lost packet is always open, and completing the information without the need to transfer the entire data set again. In some Internet services, such as FTP, the sending of the lost packet is automatically requested again, so that the requested file reaches its destination in its entirety. However, in other services such as browsing the World Wide Web, the loss of one of these packets implies that an image or text does not appear on the receiver’s screen where it should be, but there is always the possibility of request this information again.