Ethernet: Collision Domains and Switch Buffering

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A collision domain is a group of network devices that can send frames to each other that can potentially collide with frames sent by each device.  These were the types of networks that existed before modern switches were introduced.  Typically these networks were either physically shared via 10BASE2 or 10BASE5 cabling, or shared via hubs which repeated any received signal to all other ports.

Hubs

  • Ethernet hubs operate solely on Layer 1 of the OSI model.
  • Repeat electrical signals to improve the cabling distance
  • Forward received signals on a port our all other ports

As a result, using the hubs logic, this creates a single collision domain.

Switches create different collision domains on a per port basis.  Switches have the same cabling and signal regeneration benefits as hubs do, however they are capable of buffering frames preventing any collisions from occurring.

When a switch receives frames on multiple ports, it stores those frames in memory buffers to prevent collisions.  Because switches are capable of this buffering connected devices don’t have to operate in Half Duplex mode but can instead operate in Full Duplex mode.

 

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