Null modem cables allow two computers to communicate without a modem. They are often used to connect computers in head-to-head gaming, and other applications where the two terminals are in separate rooms. They are designed after the RS-232 standard, with serial cabling and two 25-pin female connectors (DB25) on either end. Cable length is usually limited to 30 feet.
Types of Null Modem Cables
Kinds of Null Modem Cables include the following:
Three-wire null modem cables
Three-wire null modem cables are used for software communication links and to connect to electronic devices lacking modem control signals.
They are also used when none of the terminals requires a handshake, or an establishment of communication protocols.
Loop back handshake cables
Loop back handshake cables are used when one device requires a handshake and the other has no handshake capabilities.
They create a "fake" handshake, which stops one side from requesting a handshake and allows data transfer.
Full handshake cables
Full handshake cables are used when both terminals require and provide a handshake.
They usually bypass the handshake request and directly permit the other to communicate.
Choosing Null Modem Cables (Buying tips)
Cable length: Choose a null modem cable that allows enough mobility for both users. Make sure the cable does not get pulled between the two terminals. If you need more than 30 feet, consider a high-speed serial extension cable to increase distance without affecting speed. Transfer rate: Choose a null modem cable with a fast transfer rate if you will use it for gaming or to send large files. Make sure it supports heavy graphics and simultaneous transfers.