The LANCOM access switches of the types GS-3510XP and GS-3528XP have, among other things, Ethernet downlink ports on which maximum transfer rates of 2.5 Gb/s are possible.
However, if network components are connected to these ports via PoE and the CAT cabling has been incorrectly selected (e.g. unshielded CAT5 / UTP cable), it can happen that a maximum of 1 Gb/s is transmitted on these ports . "Aliennoise" disturbances caused by radiation from unknown sources.
The downshifts from 2.5 Gb / s to 1 Gb / s always occur during runtime. The link is initially negotiated with 2.5 Gb/s, but at some point it drops back to 1 Gb/s during operation.
If network components are not operated with PoE but by connection to the power supply at these ports, no downshift effects occur!
LANCOM Systems therefore recommends the use of shielded CAT5e or CAT6e Ethernet cables (each of the type STP or FTP) in order to minimize the risk of a downshift from 2.5 Gb/s to 1 Gb/s.
Further technical information on this topic can be found in the NBASE-T Alliance whitepaper at: