When you’re studying to pass the CCNA exam and earn your certification, you happen to be introduced to a great numerous terms that are either completely new to you or seem familiar, but you are not fairly certain what they are. The term “collision domain” falls into the latter category for a lot of CCNA candidates.
What specifically is “colliding” in the very first location, and why do we care? It really is the information that is being sent out onto an Ethernet segment that we’re concerned with right here. Ethernet uses Carrier Sense Numerous Access / Collision Detection (CSMA/CD) to avoid collisions in the initial location. CSMA/CD is a set of guidelines dictating when hosts on an Ethernet segment can and cannot transmit data. Essentially, a host that desires to transmit data will “listen” to the ethernet segment to see if another host is presently transmitting. If no a single else is transmitting, the host will go forward with its own transmission.
This is an efficient way of avoiding a collision, but it is not foolproof. If two hosts adhere to this procedure at the precise very same time, their transmissions will collide on the Ethernet segment and each transmissions will turn into unusable. The hosts that sent those two transmissions will then send a jam signal out onto the segment, indicating to all other hosts that they must not send information. The two hosts will each and every begin a random timer, and at the finish of that time each and every host will commence the listening approach once again.
Now that we know what a collision is, and what CSMA/CD is, we need to have to be able to define a collision domain. A collision domain is any region where a collision can theoretically take place, so only one particular device can transmit at a time in a collision domain.
In one more free CCNA certification tutorial, we saw that broadcast domains have been defined by routers (default) and switches if VLANs have been defined. Hubs and repeaters did practically nothing to define broadcast domains. Well, they do not do something here, either. Hubs and repeaters do not define collision domains.
Switches do, even so. A Cisco switchport is truly its own unshared collision domain! Consequently, if we have 20 host devices connected to separate switchports, we have 20 collision domains. All 20 devices can transmit simultaneously with no danger of collisions. Evaluate this to hubs and repeaters – if you have 5 devices connected to a single hub, you nonetheless have one particular huge collision domain, and only one particular device at a time can transmit.
Mastering the definition and creation of collision domains and broadcast domains is an essential step toward earning your CCNA and becoming an powerful network administrator. Ideal of luck to you in each these worthwhile pursuits!
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