Collision domain

The term collision domain a portion of subscriber stations on OSI Model Layer 1 will be described in a computer network. A collision domain includes all network devices that compete together to provide access to a transmission medium. Basic idea is that all network participants have the chance to equal use of the network. The transmission medium is therefore a split between all network stations resource. Nevertheless, it can transmit information only one station at the same time. Catch in such a common layer -1 segment to transmit simultaneously at two stations, there will be collisions. They arise because both stations operate on a common physical medium ( cable or radio frequency). The signals ( voltage pulses ) are mixed / superimposed in the medium and the information is destroyed.

Emergence of collisions

In a constructed with coaxial network ( for example, 10Base2 and 10Base5 ) all stations are often physically attached to a single cable. Come add a repeater, it still remains in the common collision domain, since repeater signals only recycle electrical and do not respond to collisions. Although a 10BaseT Ethernet looks star-shaped, it is but when using hubs - logically speaking - yet from a single medium to which all stations are connected together. All stations are located in a single collision domain. If simultaneously start to transmit at least two stations, a collision occurs. For Ethernet you tried using the Carrier Sense Multiple Access / Collision Detection method ( CSMA / CD) to avoid collisions and to minimize their effects.

---- x ------- PC1 PC2 PC3 ------- ------- PC4 ---- x Such a network can thus be divided, for example, with a bridge into different segments and in collision domains.

X ---- PC1 ------- PC2 ------- [Bridge ] ------- ------- PC3 PC4 --- x PC1 and PC2 and PC3 and PC4 and the respective side of the bridge are each located in a separate collision domain. That is, PC1 to PC2 and PC3 can communicate simultaneously with PC4. Only within a segment, it may still come to collisions: If PC1 wants to send something to PC3, the packet is first stored and analyzed in the bridge. You then sends it to the lower segment. If something send at this moment PC3 or PC4, arises in the lower segment of a collision.

Therefore, the next step is to hang each PC to a dedicated port on the bridge. We speak to a bridge with more than two terminals is usually of a switch. If all devices are full duplex, no collisions occur more on:

PC1 | PC4 ---- [ Switch ] ---- PC2 | PC3 Extended Definition: A collision domain is a network segment in a CSMA / CD network. All stations (physical layer, physical layer ) are interconnected at layer 1, are located in the shared collision domain. Repeaters and hubs do not separate collision domains.

Bridges separate collision domains, since they operate on layer 2. In a switched network in half-duplex mode, there is a collision domain of only two stations, the client and the switch port at full duplex there is no collision domain.

Treatment of transmission conflicts

There are two ways to deal with this issue:

Carrier Sense Multiple Access / Collision Avoidance (collision avoidance)
Carrier Sense Multiple Access / Collision Detection ( Collision Detection )