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Difficulty: MediumNetwork Cable Types and Connectors

A network technician is terminating an unshielded twisted-pair (UTP) Ethernet cable to connect a user workstation directly to a network switch. The wall outlet jack connected to the switch is pre-wired according to the T568B standard. When attaching the RJ-45 connector on the workstation end, the technician accidentally follows the T568A pinout standard instead. Assuming the network switch ports are older legacy hardware that does NOT support Auto-MDIX, which of the following best describes the cable type created and its operational result?

  1. A
    It creates a straight-through cable that operates normally at full Gigabit Ethernet speed.
  2. It creates a crossover cable that fails to establish a network link with the switch port.Answer
  3. C
    It creates a rollover cable that restricts the connection to out-of-band serial management traffic.
  4. D
    It creates a loopback plug adapter that redirects transmitted frames back to the workstation network card.

Answer

The cable constructed is an Ethernet crossover cable, which will fail to establish a link when connecting a host computer to a standard switch port that lacks Auto-MDIX support.
When one end of an Ethernet patch cable is terminated with T568A and the other end with T568B, the transmit wire pair (pins 1 and 2) on one end connects to the receive wire pair (pins 3 and 6) on the other end, creating an Ethernet crossover cable. Connecting a workstation (MDI device) to a switch port (MDI-X device) requires a straight-through cable. Because the legacy switch does not support Auto-MDIX (Automatic Medium Dependent Interface Crossover), it cannot automatically swap signals in hardware, resulting in a complete failure to establish a physical link.

Step-by-Step Solution

1
Analyze the pinout configuration on both cable ends.
One end is wired to T568A and the opposite end is wired to T568B.
T568A and T568B swap the positions of the green pair (pins 1 and 2 in T568A, pins 3 and 6 in T568B) and orange pair (pins 3 and 6 in T568A, pins 1 and 2 in T568B).
2
Determine the resulting cable type created by combining T568A and T568B on opposite ends.
The resulting cable is an Ethernet crossover cable.
By swapping pins 1/2 with pins 3/6 between opposite ends, the transmit signals on one end connect directly to transmit pins on the other end.
3
Evaluate the operational impact on legacy switch hardware lacking Auto-MDIX.
The physical link will fail to negotiate or establish communication.
Standard host-to-switch (MDI to MDI-X) links require straight-through cabling so host transmit pins connect to switch receive pins. Without Auto-MDIX to automatically detect and correct transposed pairs, the crossover cable causes transmit-to-transmit collision and link failure.

Key Concept

T568A vs T568B Wiring Standards & Crossover Cable Behavior
Estimated Time:1m 15s
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Topics

Network Cable Types and Connectors

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