When setting up a network, knowing the difference between cross-over cables and straight-through cables is crucial for ensuring devices communicate properly. Both types use Ethernet cables with RJ45 connectors, but the wiring inside differs.
What is Straight-Through Cabling?
Straight-through cables are used to connect different types of devices, such as:
A computer to a switch or hub
A switch to a router
A computer to a router
In a straight-through cable, the wires inside the cable follow the same wiring standard on both ends (usually T568A or T568B).
When to Use Straight-Through Cable:
Connecting hosts (PCs, printers) to network devices (switches, routers)
Connecting switches to routers
What is Cross-Over Cabling?
Cross-over cables are used to connect similar devices directly without a switch or hub in between, such as:
Connecting one computer directly to another computer
Connecting one switch to another switch
Connecting one router to another router
In a crossover cable, the transmit and receive pairs are crossed — meaning one end follows the T568A standard and the other end follows T568B.
When to Use Cross-Over Cable:
Direct device-to-device connection of the same type (PC to PC, switch to switch)
In older network devices without auto-MDI/MDIX support (modern devices often auto-detect and adjust)
Understanding T568A and T568B Wiring Standards
Both standards define the order of the wires inside an Ethernet cable:
| Pin | T568A | T568B |
|---|---|---|
| 1 | White/Green | White/Orange |
| 2 | Green | Orange |
| 3 | White/Orange | White/Green |
| 4 | Blue | Blue |
| 5 | White/Blue | White/Blue |
| 6 | Orange | Green |
| 7 | White/Brown | White/Brown |
| 8 | Brown | Brown |
How to Make a Straight-Through Cable (T568B on both ends)
Materials Needed:
Ethernet cable (Cat5e, Cat6, etc.)
RJ45 connectors
Crimping tool
Wire stripper/cutter
Step-by-Step:
Strip about 1-1.5 inch of outer cable jacket off both ends of the cable to expose the wires.
Untwist the pairs and arrange the wires in the T568B order:
White/Orange
Orange
White/Green
Blue
White/Blue
Green
White/Brown
Brown
Flatten the wires in this order and trim the ends evenly about 1/2 inch from the jacket.
Insert the wires carefully into the RJ45 connector, making sure each wire goes into its respective channel.
Use the crimping tool to crimp the connector tightly to the cable.
Repeat the process on the other end of the cable, using the exact same wiring order (T568B).
Test the cable with a cable tester to ensure correct wiring.
How to Make a Cross-Over Cable (T568A on one end, T568B on the other)
Step-by-Step:
Strip the cable jacket off both ends as before.
Prepare one end with the T568A wiring standard:
White/Green
Green
White/Orange
Blue
White/Blue
Orange
White/Brown
Brown
Prepare the other end with the T568B wiring standard:
White/Orange
Orange
White/Green
Blue
White/Blue
Green
White/Brown
Brown
Flatten the wires and trim as before, then insert into RJ45 connectors and crimp on both ends.
Test the cable with a tester to verify the crossover.
Quick Reference Table: Which Cable to Use?
| Devices Connecting | Cable Type |
|---|---|
| PC to Switch | Straight-Through |
| Switch to Router | Straight-Through |
| PC to PC | Cross-Over |
| Switch to Switch | Cross-Over |
| Router to Router | Cross-Over |
Tips for Modern Networks
Many modern devices support Auto-MDI/MDIX, which automatically adjusts for crossover or straight-through cables.
However, knowing the difference and how to make each cable is essential for troubleshooting and legacy equipment.
Summary
Straight-through cables use the same wiring standard on both ends (commonly T568B).
Cross-over cables use T568A on one end and T568B on the other.
Use straight-through cables to connect different devices (PC to switch), cross-over cables to connect similar devices directly (PC to PC).
Always test cables after crimping to avoid connectivity issues.
