Duplex Mismatch Errors
Network cards and switches can auto detect speed and duplex. When they don't properly negotiate the correct settings, your 10/100 Mbps network can slow down to less than 1 Mbps! When the performance matters, manually configure your equipment to ensure there are no errors.
Difference between Full Duplex and Half Duplex
Ethernet works on all sorts of physical layers, such as CAT5 cable, coax cable, fiber, wireless, and most other methods of connecting computers. Half duplex is when the physical layer is shared between connected devices, or nodes. When shared, only one device can talk at a time or the conversation can not be understood. With full duplex the physical layer is private, between only 2 nodes, so there is often a separate send and receive path for each device. In this case, both nodes can talk at the same time and understand each other.
Collisions on the Network
Half Duplex connections must take turns talking. In order to do this, they use CSMA/CD or Carrier Sense Multiple Access With Collision Detection. All this protocol does is listen to make sure that no other nodes are transmitting before they send data. If the node hears anyone else talking while it is sending data, it will send an error signal. At this point all nodes stop, wait a bit, then try again. Full duplex networks can talk at the same time and therefore, do not experience this.
Why Can't We Just Get Along
A Duplex Mismatch Error occurs when one side is full and the other is half. Suppose the half duplex side wants to send data. It waits for quiet, and takes its turn sending data. The full duplex side wants to send back a standard acknowledgement packet; rather than waiting, it just starts talking. The sending side hears the receiving side and sends a collision message, at which point both sides stop, wait a bit, and then start the whole process over again slowing your network to a crawl.
Avoiding Duplex Mismatch Errors
Many network cards can be set up manually. If you have a managed switch, you can connect to the switch and manually set the switch port as well. Most small networks use unmanaged equipment. In this case, a cheap hub will work best, it is always half duplex and there is no doubt as to how it is set. All switches can run as full or half. If you can't manage it manually, you are forced to use Auto. Larger networks will need the performance of a switch; to ensure it will work properly you should make sure it is managed.
For additional information or support please contact us at 303-482-1242.
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