Collision Domains - In Ethernet segments, devices connnect to the same physical medium. Because of this, all devices receive all signals sent out across the wire. If two devices send a packet at the same time, a collision occurs. When a collision happens , the two devices run a backoff algorithm and resent the packet. The devices retransmit up to 15 times. The first station to detect a collision issues a jam singnal. The more collisions that occur in your network will have to resend the packet. A collision domain defines a group of devices connected to the same physical medium.