User manual

154 Publication ENET-UM001I-EN-P - January 2010
Chapter 11 Troubleshoot an EtherNet/IP Module
Ethernet Media Counters
Media Counter Definition
Alignment Errors A frame containing bits that do not total an integral multiple of eight.
Alignment errors often result from:
• starting or stopping of module.
• MAC-layer packet formation problems.
• cabling problems that corrupt or eliminate data.
• packets passing through more than two cascaded multiport transceivers.
FC
S Errors A frame containing eight bits, at least one of which has been corrupted.
FCS errors often result from:
• s
tarting or stopping the module.
• cabling problems that corrupt data.
Impo
rtant: Even though the acceptable Ethernet bit-error rate is 1 in 108, the ty
pical rate is 1 in 1012 or better.
Single Collisions The number of outgoing packets that encountered only one collision during transmission.
Multiple C
ollisions The number of outgoing packets that encountered 2...15 collisions during transmission.
SQE Test Errors A test to detect the collision-present circuit between a transceiver and a network interface card (NIC).
Impo
rtant: Because most NICs now have an integrated transc
eiver, the SQE test is unnecessary. Ignore this media
counter.
Deferred
Tr
ansmissions
The number of outgoing packets whose transmission is deferred because the network is busy when the first attempt
is made to send them.
Important: The module will
only defer the first attempt to transmit a packet. After the first attempt, the module will
transmit the packet without checking. However, if the network is still busy, a collision will be recorded.
Late Collisions The number of times two devices transmit data simultaneously.
Neither device detects a collision because the time it takes to send the signal from one end of the network to the
o
ther exceeds the time needed to put the entire packet on the network. Consequently, neither device senses the
other’s transmission until the entire packet is out on the network.
Late collisions often result from:
• ex
cessive network segment length.
• repeaters between devices.
Impo
rtant: Large and small packets can be affected by
late collisions. However, the transmitter cannot detect late
collisions between small packets. Consequently, a network that experiences measurable late collisions between
large packets will also lose small packets.
Excessive
C
o
llisions
The number of frames that experience 16 consecutive collisions.
MAC Transmit
Errors
T
he number of frames for which transmission via a particular interface fails due to an internal MAC sublayer
transmission error.
Important: MAC transmit errors
are only counted if either late collisions, excessive collisions, or carrier sense errors
are not counted.