Crossover Cables
Switches can also connect to each other via special twisted-pair cables called crossover cables. A standard cable cannot be used to connect two switches without using an uplink port because both switches will attempt to send data on the second pair of wires (3 and 6) and will listen for data on the first pair (1 and 2). A crossover cable reverses the sending and receiving pairs on one end of the cable. One end of the cable is wired according to the T568A standard, whereas the other end is wired according to the T568B standard (Figure 4.12). With the sending and receiving pairs reversed, the switches can hear each other; hence, the need for two standards for connecting RJ-45 jacks to UTP cables.
FIGURE 4.12   A crossover ...

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