Understanding the network.pdf - Back to Home

NOTE
On switched Ethernet segments that are operating in full-duplex mode (a single
end-station attached to switch port or an inter-switch link), there should be no
collisions. This is because full-duplex operation disables the collision detection
aspect of CSMA/CD used by Ethernet in order for the end-station to send and
receive data simultaneously. If you do see collisions on a link you believe is
configured for full-duplex operation, chances are that, either the end-station or the
switch port is misconfigured.
As part of Ethernet's CSMA/CD implementation, Ethernet has defined minimum and
maximum packet sizes. The minimum packet sizes are 72 bytes, 64-bytes data,
including the frame header, the data PDU and the frames CRC, plus an 8-byte
preamble. The maximum packet sizes are 1,526 bytes (802.3) or 1,530 bytes
(802.3ac) (1,518-byte, including the CRC and header, plus an 8-byte preamble).
Ethernet frames that are less than the minimum size are known as runts, and
excessively long packets are known as jabs. Illegal packet sizes are caused by a bad
NIC or corrupted NIC driver. Another indication of a bad NIC is a condition called
jabbering, which occurs when a NIC sends continuous stream bits that are longer
than 1,526/1,530 bytes in length. Jabbering can bring the entire segment to halt
because the jabbering station typically cannot hear collisions on the segment, and it
just continues transmitting streams of random bits, consuming all the segment's
available bandwidth.
Token Ring Errors
Token Ring has two types of error conditions: soft and hard. Soft errors are error
conditions of an intermittent nature that only impact data transmission on a
temporary basis. When a soft error is encountered on a Token Ring system, an error
recovery process is initiated. This process begins with the detecting station
collecting error type information and then generating a report indicating the type of
error (and the station at fault, if possible) and sends it to the Ring Error Monitor
(REM). REM is collects ring error information to troubleshoot error conditions on the
ring. Each station keeps track of the errors it detects on the ring and, when an error
is detected, it increments it's internal soft error counter. The remainder of the
recovery process depends on the category and type of soft error that occurs.
Token Ring soft errors are divided into two categories: isolating and non-isolating.
Isolating soft errors (ISEs) are soft errors that can be attributed to a specific Token
Ring fault domain. A fault domain is a logical area of the ring that consists of the
station that has detected the error, it's nearest active upstream neighbor (NAUN),