Ethernet Networking


Ethernet is a contention media access method that allows all hosts on a network to share the same bandwidth of a link.

Ethernet networking uses Carrier Sense Multiple Access with Collision Detection (CSMA/CD), A protocol that helps devices share the bandwidth evenly without having two devices transmit at the same time on the network medium. CSMA/CD was created to overcome the problem of those collisions that occur when packets are transmitted simultaneously from different nodes

  • Carrier Sense Multiple Access with Collision Detection (CSMA/CD)

    When a host wants to transmit over the network, it first checks for the presence of a digital signal on the wire. If all is clear (no other host is transmitting), the host will then proceed with its transmission. But it doesn’t stop there. The transmitting host constantly monitors the wire to make sure no other hosts begin transmitting. If the host detects another signal on the wire, it sends out an extended jam signal that causes all nodes on the segment to stop sending data (think busy signal). The nodes respond to that jam signal by waiting a while before attempting to transmit again. Back off algorithms determine when the colliding stations can retransmit. If collisions keep occurring after 15 tries, the nodes attempting to transmit will then timeout. 

    When a collision occurs on an Ethernet LAN, the following happens:
     
    1. A jam signal informs all devices that a collision occurred.
    2. The collision invokes a random back off algorithm.
    3. Each device on the Ethernet segment stops transmitting for a short time until the timers expire.
    4. All hosts have equal priority to transmit after the timers have expired.

    The following are the effects of having a CSMA/CD network sustaining heavy collisions:
     
    1. Delay
    2. Low throughput
    3. Congestion
  • Ethernet at the Data Link Layer

    Ethernet at the Data Link layer is responsible for Ethernet addressing, commonly referred to as hardware addressing or MAC addressing. Ethernet is also responsible for framing packets received from the Network layer and preparing them for transmission on the local network through the Ethernet contention media access method.
  • Ethernet Addressing

    It uses the Media Access Control (MAC) address burned into each and every Ethernet network interface card (NIC). The MAC, or hardware, address is a 48-bit (6-byte) address written in a hexadecimal format.

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