Network collision domain

colisão de redes
network collision

What is a collision domain (Source wikipedia)

In a computer network, the collision domain is a logical area where packets can collide against each other, particularly in the Ethernet protocol. The more collisions that occur, the less efficient the network will be.

A collision domain can exist in a single network segment (such as a bus network) or in a portion or total of a larger network (note that the use of hubs propagates the collision domain to all its segments). In Ethernet networks, when using a hub, we have a logical bus topology and the stations behave as if they were all connected to a single physical medium. This simplifies data transmission and reduces investment in intermediary equipment, but in compensation it brings a serious problem: packet collisions that occur whenever two (or more) stations try to transmit data at the same time.

The CSMA/CD communication protocol that controls access to the medium in Ethernet networks minimizes this problem through a set of relatively simple measures: before transmitting a packet, the station “listens” to the physical medium to check if another station is already transmitting . In fact each host, through CSMA/CD, checks for a carrier wave indicating transmission. If the physical medium is busy it waits, if it is free it transmits. In the event of a collision, it immediately interrupts the transmission, sending a Jam Signal that repeats the collision, informing the hosts involved. On these hosts the jam signal will activate a backoff algorithm that will make each host wait for a random and increasing amount of time, in case of a collision recurrence, to retransmit.

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