When both ends of the network cable use the same standard crystal head, it is the direct connection mode. (Most of them adopt T568B standard. )
When the two ends of the network cable are different standards, that is, one end is T568A and the other end is T568B, then it is a cross-connection mode.
Straight lines connect different devices together. Such as: computer to switch, computer to cat, computer to router.
The function of the cross line is to connect the same kind of equipment together. Such as: computer to computer, switch to switch.
But now all kinds of devices basically adopt adaptive methods, which can automatically identify whether they are through or cross-connected, so cross-connected methods are rarely used.
Crystal head line sequence icon: