A technician is setting up out-of-band management for a legacy rackmount server console that exposes a male DB-9 serial port. The technician connects a USB-to-DB9 male adapter to a modern management workstation's USB Type-A port and attempts to link it to the server using a female-to-female DB-9 serial cable. Terminal emulation software shows no response. A pinout test on the female-to-female DB-9 cable reveals that pin 2 (Rx) connects directly to pin 2 (Rx), pin 3 (Tx) connects to pin 3 (Tx), and pin 5 (GND) connects to pin 5 (GND). Which of the following solutions will resolve the communication failure?
- Insert a null modem adapter that crosses the transmit (Tx) and receive (Rx) lines between the host adapter and the server port.Cevap
- BReplace the USB-to-DB9 adapter with an RJ45-to-DB9 rollover cable connected directly to the workstation's Gigabit Ethernet port.
- CRe-terminate one end of the DB-9 serial cable using the T568B wiring scheme to invert the differential signal pairs.
- DConfigure the terminal emulation software to use hardware flow control (RTS/CTS) with USB 3.2 Gen 2 dual-lane signaling rates.
Cevap
Inserting a null modem adapter (or replacing the cable with a null modem cable) that crosses transmit (Tx, pin 3) and receive (Rx, pin 2) lines between the devices.
When connecting two DTE (Data Terminal Equipment) devices—such as a PC's USB serial adapter and a server's DB-9 serial port—a straight-through cable causes both devices to transmit on pin 3 and listen on pin 2. To allow data to flow, a null modem connection must be used so that pin 3 (Tx) of the host connects to pin 2 (Rx) of the target, and pin 2 (Rx) of the host connects to pin 3 (Tx) of the target.
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RS-232 Serial Cabling and Pinouts (Straight-Through vs Null Modem)