Download Troubleshooting

© 2008, QNX Software Systems GmbH & Co. KG.
Network adapters
Deferred Transmits
Commonly found on half-duplex networks, this value doesn’t mean that there are
problems. It means that the card tried to send data on the network cable, but the
network was busy with other data on the cable. So, it simply waited for a random
amount of time. This number can get high if the network is very busy.
Late Collision on Transmit errors
Late-collision errors that occur when a card has transmitted enough of a frame that the
rest of the network should be aware that the network is currently in use, yet another
system on the network still started to transfer a frame onto the line. They’re the same
as regular collision errors, but were just detected too late.
Depending on the protocol, these types of errors can be detrimental to the protocol’s
overall throughput. For example, a 1% packet loss on the NFS protocol using the
default retransmission timers is enough to slow the speed down by approximately
90%. If you experience low throughput with your networking, check to make sure that
you aren’t getting these types of errors. Typically, Ethernet adapters don’t retransmit
frames that have been lost to a late collision.
These errors are a sign that the time to propagate the signal across the network is
longer than the time it takes for a network card to place an entire packet on the
network. Thus, the offending system doesn’t know that the network is currently in use,
and it proceeds to place a new frame on the network.
The nodes that are trying to use the network at the same time detect the error after the
first slot time of 64 bytes. This means that the NIC detects late collisions only when
transmitting frames that are longer than 64 bytes. The problem with this is that, with
frames smaller than 64 bytes, the NIC can’t detect the error. Generally, if you
experience late collisions with large frames on your network, you’re very likely also
experiencing late collisions with small frames.
These types of errors are generally caused by Ethernet cables that are longer than that
allowed by the IEEE 802.3 specification, or are the maximum size permitted by the
particular type of cable, or by an excessive amount of repeaters on the network
between the two nodes.
Another thing to note is that these errors may actually be caused by a node on the
network that has faulty hardware and is sending damaged frames that look like
collision fragments. These damaged frames can sometimes appear to a network card
to be a late collision.
Transmits aborted (excessive collisions)
This error occurs if there are excessive collisions on the network. The network card
gives up on transmitting the frame after 16 collisions. This generally means that the
network is jammed and is too busy.
September 30, 2008
Chapter 15 • Connecting Hardware
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