Collisions and collision detection – What are collisions in Ethernet?


What are collisions and how they happen? In Ethernet world, the result of two nodes transmitting in the same time. The frames from each machine impact and collide when they meet on the physical media.This contention-based methods allow any device to try to access the medium whenever it has data to send. To prevent complete “choking” on the media, these methods use a Carrier Sense Multiple Access (CSMA) process to first detect if the media is transmitting any signal in that moment. If there is a signal on the media from another computer, it means that another device is talking. When the device attempting to transmit sees that the media is in use, it will wait and try again after a short period of time. If no carrier signal is detected, the device transmits its data. Ethernet and wireless networks use contention-based media access control.

It is possible that the CSMA process will fail and two devices will transmit at the same time. This is called a data collision. If this occurs, the data sent by both devices will be corrupted and will need to be resent. As the number of nodes increases on a shared media, the probability of successful media access without a collision decreases. Additionally, The recovery mechanisms required to correct errors due to these collisions further diminishes the overall throughput.

Collision detection mechanism (Just a word for every of them, they will have the whole post just for them later in this blog): 

  • CSMA/CD Protocol

It is used when more that two computers are sharing the same medium tipicaly something that is happening in LAN networks when computers are connected trough hub. CSMA/CD is a practice used for multiple access control protocols. Transmission will be taken place by a particular station at a time but when more than one station will transmit at the same time as a result collision can be occurred. In that moment

  • CSMA/CA Protocol

CSMA/CA (Carrier Sense Multiple Access/Collision Avoidance) that has been introduced to get better the CSMA performance. According to that a station will sense the transmission medium before sending the frame. CASMA/CA protocol is used in wireless (802.11) LANs. Moreover, when a station sense collision in case of CSMA/CA, it first waits for some time after that but before packets transmission, it will listen to the channel for its idleness, if so packets transmission will start otherwise it will waits for the medium to become unoccupied.

Note that above mentioned both CSMA/CD and CSMA/CA protocols are the best example of Physical Protocols.

  • In some other worlds beside networking…

Anyway besides this, computational problem “collision detection” can also be described as the process of uncovering the two or more than two object’s intersection. So whenever the words “video games” or “robotics” will be used, that term will too come in front of you. Thus in order to understand the under-discussion issue well, it will be good to put some light on the use of collision detection in 3D video games as well.

This process is enclosed in it TOI (time of impact) calculation and a set of meeting points, known as report a contact manifold. But the purpose of this detection system is to determine that, either the objects in a game are overlapped with each other or not. With the introduction of 3D technology, far-reaching changes are made by the programmers especially in the gaming applications by keeping in mind their better effectiveness and efficiency. Collision detection as an essential part of the 3D technology can give you the assurance of a game physics practicality.

The two main portions in the process of collision detection are:

  • Detecting that whether a collision is occurred or not
  • And if yes, then responding to that collision

The physics of the billiard balls bouncing can be elaborated best with the “rigid body motion” plus with the “elastic collisions”. But a computer program relating billiard can be developed by dividing its logical design into different portions so actual game can come into existence with real features to play. Each subdivision of this program will performs its own task such as one portion will be in charge for the precise impacts calculation between the game balls. Anyhow, programming requires full concentration of the developer because any small slip up in the calculation can be resulted in the drastic changes in the ball’s final position.

In this regard, physical simulation can play an important role in a game development. That means collision detection copes with simulating. But in the physical simulation, collision detection involves certain phases. Some amongst them are as following:

  • Posteriori or discrete Vs  Priori or continuous
  • Optimization
  • Make use of temporal coherence
  • Pairwise pruning
  • Spatial partitioning etc

In short, a well structured application can detect collisions while poor implementation of this detection system may collapse a product. Thus excellent ccollision detection implementation means a product amazing success. But the solution of a collision detection problem is required the usage of linear algebra and computational geometry’s concepts knowledge.

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