| Description | The best estimate of the total number of collisions
on this Ethernet segment (in transmition).
Only for Ethernet Interfaces.
The value returned will depend on the location of
the RMON probe. Section 8.2.1.3 (10BASE-5) and
section 10.3.1.3 (10BASE-2) of IEEE standard 802.3
states that a station must detect a collision, in
the receive mode, if three or more stations are
transmitting simultaneously. A repeater port must
detect a collision when two or more stations are
transmitting simultaneously. Thus a probe placed on
a repeater port could record more collisions than a
probe connected to a station on the same segment
would.
Probe location plays a much smaller role when
considering 10BASE-T. 14.2.1.4 (10BASE-T) of IEEE
standard 802.3 defines a collision as the
simultaneous presence of signals on the DO and RD
circuits (transmitting and receiving at the same
time). A 10BASE-T station can only detect
collisions when it is transmitting. Thus probes
placed on a station and a repeater, should report
the same number of collisions.
Note also that an RMON probe inside a repeater
should ideally report collisions between the
repeater and one or more other hosts (transmit
collisions as defined by IEEE 802.3k) plus receiver
collisions observed on any coax segments to which
the repeater is connected. |