Rollover is network cable which is used to connect serial port of a computer with console port or serial port of network router or switch. It is usually flat or yellow or light blue in color to distinguish it from other network cables, it is also called cisco console cable because it permits a network programmer to make changes in the network by connecting it to console port of routing or switching device.
It is a type of null modem cable. Null modem communication method is between two directly connect DTEs (i.e. computer, terminal, printer, etc.) using an RS-232serial cable.
A rollover cable has four pairs which are colored and is wired with each pin on one end of the cable connected to the reverse pin on the other end. So the cable on Pin 1 on one end of the cable connects to Pin 8 at the other end, etc. The wiring scheme of rollover cable is shown in the figure:
Figure 1: Rollover Cable Pin Configuration
Data communication is asymmetric as to the definitions of two ends of communication link, assuming that one end is DTE and other one is DCE i.e. Modem. Transmitting and receiving end is cross linked as shown in the figure. Since data communication is serial its length can be extended to more than 400ft with the help of modern cables like CAT-5 etc. The cable has short transmission distance due to presence of noise in limiting transmission because of high numbers of bits per second when its length is more than 180ft. Other serial communication standards are better adopted to drive hundreds or thousands of meters of cable.