IEEE 802.3 1000Base-CX
The CX variant (1000Base-CX) is standardized as a GbE interface for Gigabit Ethernet via a balanced twinaxial cable with 150 Ohm. To reduce possible interference caused by voltage differences, the transmitter and receiver are connected to the same ground line.
To minimize distortion, the connectors must not exceed a permissible return loss of 20 dB. The DB9 sub-D connector or the HSSDC connector can be used as connectors.
According to the IEEE nomenclature, the number 1000 stands for 1 Gbit/s, base for baseband, the letters "C" for copper and "X" for local area networks( LAN). 1000Base-CX supports full duplex and is suitable for end device connections with a distance of 25 meters via STP cable. For line coding, 1000Base-CX uses 8B/10B coding.
The 1000Base-CX interface is technically realized by an SFP module, which is a transceiver for optical fibers or metallic conductors. The specifications for 1000Base-CX were developed by IEEE 802.3z. The 1000Base-CX interface is a transitional solution and will be replaced by 1000Base-T.