Attenuation
A common issue of exceeding the design limits of a
media type is the attenuation of the bit-stream transmitted along the media.
Attenuation may occur to such an extent that the receiving device cannot always
successfully distinguish the component bits of the stream from each other. This
ends in a garbled transmission and results in a request from the receiving
device for retransmission of the missed traffic by the sender.
A far
more common source of attenuation is a poor connection resulting from a loose
cable or dirty or oxidized contacts.
Return Loss
Return loss is a measure of all reflections that are
caused by the impedance mismatches at all locations along the link. It
indicates how well the characteristic impedance of the cable matches its rated
impedance over a range of frequencies. The characteristic impedance of links
tends to vary from higher values at low frequencies to lower values at the
higher frequencies. Return loss is expressed in decibels.
The
termination resistance at both ends of the link must be equal to the
characteristic impedance of the link to avoid reflections. A good match between
characteristic impedance and termination resistance in the end equipment
provides for a good transfer of power to and from the link and minimizes
reflections.

Return
loss is of particular concern in the implementation of Gigabit Ethernet.