- Access Glossary
Alignment Errors
Auto Partitioning
Broadcast Frames
Buffer Full Errors
Carrier Sence
Carrier Sence Loss Errors
Number of times lost
Collisions
Continual during transmit
Collision Rate
Cyclic Redundancy Check
Cyclic Redundany Check(CRC) Errors
(# of packets w/ an incorrect CRC)
Data Rate Mismatch Errors
Excessive Collision Errors
Frame
Frame Check Sequence(FCS) Errors
Framing Errors
(# of frames lost)
Framing Length Errors
Frame Too Long Errors
Giant Frame Errors
Heartbeat Errors
HST - Host Address
If - Interface #
Input Discards (ID)
Input Discard Errors
Input Drop Errors
Input Errors
(# of errors)
Input FIFO Overruns Errors
Input Overrun Errors
Input Packets
Input Queue (buffer) Full
Input Traffic (IKPk)
Counted in Megabytes
Inter Packet Gap(IPG) Errors
Jabber Condition
Jams
Late Collision Errors
Lost Frame Errors
Maintenance Fail(MT Fail)
Maintenance Media test (MT) (# of times failed)
Media Access Control(MAC) Frame
Miscellanous errors
Missing Start Frame Delimiter(SFD) Errors
Multicast Frames
Non-Unicast Packets
Octets
Out Success With Retry Errors
Out Of Window Collision Errors
Detecting
Output discards (OD)
Output Discard Errors
Output Errors
(# of errors)
Output FIFO Overrun Errors
Output Packets
Output Traffic(OKPk)
Counted in Megabytes
Packet Framing Error
Percent Collisions
Preamble Field
Readable Frames
Readable Octets
Runt Errors
Self-Test Fail (ST Fail)
(# of times failed)
Short Event Errors
Signal Quality Error(SQE) Test
Start Frame Delimiter(SFD) Field
Transmit Collision Errors
Transmitted Frames
Transmitted Octets
Unicast Packets
Glossary of Ethernet Terminology
- Alignment Errors
- Frame misalignments are input error and indicate damaged frames. A frame
has an alignment error if the number of bits received is not a multiple of
eight; since there are eight bits in one byte, frames must be received on
byte boundaries. A misaligned frame also has a Frame Check Sequence (FCS)
error. The causes of alignment errors include bad wiring, broken Ethernet
cards, and cable runs that are out of specification.
- Auto Partitioning
- Auto Partitioning is an IEEE 802.3 specification which may be optionally
implemented by the vendor. Auto Partitioning means that the hardware has
automatically separated a port from the rest of the network. In accordance
to the specifications, the hardware attempts to recover automatically when
the condition clears. The port may be partitioned because too many
collisions are occurring from the port (greater than 31 consecutive
collisions) or because a single collision from the port is too long (greater
than 1024 bit times in duration). Auto Partitioning can occur when a station
is disconnected from a port or the wrong type of wiring is used, drastically
increasing the number of collisions. Auto Partitioning may also occur if the
attached device is sending a jamming signal which could bring down the
entire network.
- Broadcast Frames
- Broadcast frames are frames that are directed to the broadcast group
address. This does not include received frames which contained a framing
error. Multicast packets are not included.
- Buffer Full Errors
- Buffer Full errors are input errors which indicate that the hardware has
asserted an overwrite warning, signaling that the receive buffer is full. It
does not mean, however, that a frame was necessarily lost.
- Carrier Sense
- Carrier Sense is the process used by devices on Ethernet to determine
whether the cable is currently being used by a transmitting station. If
electrical signals are detected on the cable, then carrier has been detected
and a station is currently transmitting on the cable.
- Carrier Sense Loss Errors
- Carrier Sense Losses are output errors which indicate that carrier sense
was lost or never appeared when the device was attempting to transmit a
packet. A station listens on the wire as it transmits a frame in order to
detect collisions. Carrier sense loss occurs when the hardware is
transmitting a frame onto the wire and does not see its own carrier wave on
the Ethernet. Carrier sense loss can occur if the optical power is marginal
to a Fiber Optic Transceiver (FOT) on a router, for example. Loss of carrier
sense may also be the result of plugging and unplugging the cable
connections on a network.
- Collisions
- On an Ethernet, only one station may transmit at a time. Any computer
wishing to transmit checks whether the cable is busy by using carrier sense.
If carrier is not detected and the cable has not been busy for a specified
period of time, then the station begins transmitting its data. While it is
transmitting a frame, a computer listens to ensure that no other station
starts transmitting. If any other station begins transmitting at the same
time, a collision occurs. In other words, a collision is a condition where
two devices detect that the network is idle and try to send packets at
approximately the same time. Since only one device can transmit at a time,
both devices must back off and attempt to retransmit again. The
retransmission algorithm requires each device to wait a random amount of
time, so the two stations are very likely to retry at different times; thus,
the second station will sense that the network is busy and wait until the
frame is finished being transmitted. If the two devices retry at the same
time again, they will colliding once more. This process repeats until either
the packet finally makes it onto the network without collisions, or 16
consecutive collision occur and the packet is aborted. (See Excessive
Collisions.)
Collisions which occur due to two stations transmitting at the same time
are normal events on an Ethernet. As the amount of traffic on a network
increases, the number of collisions on a network also increases. However,
collisions due to two stations transmitting at different times is not
considered normal. (See Late Collisions.) Unusual numbers of collisions on a
network may indicate a pathological problem and should be examined.
Oftentimes, these collisions are the result of either a misconfigured
network or a device transmitting when it should not be and stepping on other
packets. Most likely, the collisions are the result of reflections or other
problems with the physical plant, such as a bad transceiver. A ground loop
is another possible cause of collisions if the cable is grounded at two
points. Collisions can also happen if there is a bad cable or a station is
incorrectly connected to the network.
- Collision Rate
- The collision rate is calculated by dividing the total number of packets
by the total number of collisions and multiplying the result by 100. What is
an acceptable level of collisions? This depends on your application and
protocol along with the physical design of your network. In some cases,
collision rates of 50% will not cause a large decrease in perceived
throughput. If your network is slowing down and you notice the percentage of
collisions is consistently above 10%, you may want your network examined.
- Cyclic Redundancy Check
- The Cyclic Redundancy Check (CRC) is a an error-checking algorithm used to
check for the validity of a frame. A transmitting station uses the algorithm
to compute a CRC value based on the bits in the frame and sets the Frame
Check Sequence field of the frame to the calculated CRC value. A station
receiving the frame can then use the same algorithm to determine whether or
not the frame has been corrupted. If the computed CRC value of a frame
received by a station does not match the value in its Frame Check Sequence
field, then the frame is bad.
- Cyclic Redundancy Check (CRC) Errors
- See Frame Check Sequence (FCS) Errors.
- Data Rate Mismatch Errors
- Data Rate Mismatches are input errors which occur when the incoming data
rate is not with in the tolerance level of 10MHZ + or - 0.01%. In other
words, an Ethernet device on the network is not transmitting at the correct
10 million/bits per second on the network and is breaking the
specifications.
- Excessive Collision Errors
- Excessive Collisions are output errors which indicate that frames were not
transmitted due to jams on the network. Excessive collision errors are the
number of times that a frame destined for the network incurred 16 collisions
and was discarded. Excessive collision errors are cases where the router,
for example, tries several times to transmit a frame, but is collided with
each time; eventually the router gives up and throws the frame away. The
usual cause of jams is an exceedingly busy network. If the jam count
fluctuates between being zero and a huge number, an intermittent problem is
occurring on the network which causes the devices to repeat collisions at a
high rate, such that the router transmit any frames.
- Frame
- See Media Access Control (MAC) Frame.
- Frame Check Sequence (FCS) Errors
- Frame Check Sequence (FCS) errors are input error that are aligned but
fail the Cyclic Redundancy Check (CRC). FCS errors indicate damaged frames.
There can be many causes for FCS errors, including flaky in-room wiring,
broken Ethernet cards, and cable runs which are too long.
- Framing Errors
- See Alignment Errors.
- Frame Length Errors
- Frame Length errors are input errors due to frames that have a length
field value greater than the maximum allowed data size. Unfortunately, if
both IEEE 802.3 Ethernet and Ethernet Type 2 coexist on the same network,
the Frame Length errors will show a misleadingly high error rate. This is
because Ethernet Type 2 frames do not have a length field similar to IEEE
802.3 Ethernet frames.
- Frame Too Long Errors
- Frame Too Long errors are input errors where the frame has a valid Start
Frame Delimiter (SFD) and Frame Check Sequence (FCS), but it is longer than
the maximum allowable size of an Ethernet frame.
- Giant Frame Errors
- See Frame Too Long Errors.
- Heartbeat Errors
- Heartbeat errors are output errors which indicate that a heartbeat was not
detected after transmitting a frame. In Ethernet Version 2, heartbeat is a
test of the collision functionality of the transceiver. The term heartbeat
is often used interchangeably with Signal Quality Error (SQE). See Signal
Quality Error Test.
- Input Discard Errors
- Input Discards are input errors, which occur when the hardware attempts to
receive a packet, but the local receive packet buffer is full. Input discard
errors usually indicate that the network has more traffic than it can
handle. They may also indicate a software discard such as an unhandled
protocol.
- Input Drop Errors
- See Buffer Full Errors.
- Input Errors
- Input Errors is the sum of all the input errors on an interface.
- Input FIFO Overruns Errors
- Input FIFO Overruns are input errors indicating that the input queue
overflowed while copying received frames. The problem is that the hardware
is unable to store bytes in the local packet buffer as fast as they come off
the wire.
- Input Overrun Errors
- See Frame Too Long Errors.
- Input Packets
- See Readable Frames.
- Inter Packet Gap (IPG) Errors
- The Inter Packet Gap (Inter Frame Gap or IFG) is an enforced quiet time
between transmitted Ethernet frames. The Inter Frame Gap is required so that
listening stations are provided with enough time to detect that there is no
carrier sense on a wire. Inter Packet Gap errors are usually the result of a
device that is not adhering to the Ethernet specifications.
- Jams
- If a workstation detects a collision while it is transmitting, the station
does not immediately stop transmitting. Instead, the workstation puts out a
jam so all other stations will detect the collision. When a repeater detects
a collision on one of its ports, it also puts out a jam on all its ports.
This ensures that the transmitting stations detect the collision and that
the stations on the other repeater ports see the collision. (See excessive
collisions.) The purpose of a workstation to continue transmitting after
detecting a collision for a short period of time ensures that every station
on the network has time to see the collision.
- Late Collision Errors
- Late Collisions are input errors due to a collision which occurs after a
station has been transmitting for some period of time. The device has
transmitted enough of a frame that every other station on the wire should
know that the media has been acquired. Late Collisions indicate that the
time to propagate the signal from one end of the network to another is
longer than the time to put the entire packet on the network; therefore, the
two devices that cause the Late Collision never detect that the other
station is sending data until after both stations put entire frames on the
network. Late collisions are detected by the transmitter after the first Òslot
timeÓ of 64 byte times. Late Collisions, as a result, are only detected
during transmissions of frames longer than 64 bytes. Late Collisions are
similar to normal collisions; it just happens too late.
Typical causes of late collisions are that either the entire network is
temporally larger in diameter than is allowed by the IEEE 802.3
specification; the cable lengths of segments may be in excess of the maximum
length permitted for the cable type or that there are excessive numbers of
repeaters between network devices. Another cause of late collisions is that
there are defective Ethernet transceivers or controllers. Some damaged
frames on the net look enough like collision fragments to fool the
hardware`s controller chip. One bad thing about late collisions is that
collisions involving small frames cannot be detected by the transmitter. A
network suffering a measurable rate of late collisions (on large frames) is
also suffering loss of small frames. Some higher protocols do not cope well
with packet losses, no matter how small. A 1% packet loss is enough to
reduce the speed of NFS by 90% with the default retransmission timers.
Additionally, Ethernet controllers do not retransmit frames lost to late
collisions.
- Lost Frame Errors
- Lost Frames are input errors which indicate that frames have been lost due
to insufficient buffer space. Lost frames are packets missed by the station
because it was either too busy to take the interrupt in time or because the
queue of packets in memory waiting for processing overflowed. Both indicate
that the device is being swamped with traffic. If the traffic on the network
is not overloaded, then there may be a machine causing sporadic packet
floods of the network.
- Maintenance Fail (MT Fail)
- Every few seconds, the router sends out a signal on its interfaces
checking for an open cable. After a certain number of failed maintenance
checks, the interface is brought down for self-testing.
- Media Access Control (MAC) Frame
- A frame is a packet that is transmitted on the physical wire. IEEE 802.3 (IEC
8802-3) protocol standard is an ANSI specification for Ethernet. An IEEE
802.3 frame consists of a Preamble, Start Frame Delimiter, Destination
Hardware Address, Source Hardware Address, Data, and Frame Check Sequence:
Preamble (7 Octets)
Start Frame Delimeter (1 Octet)
Destination Address (6 Octets)
Source Address (6 Octets)
Length Field (2 Octets)
Payload (46 to 1500 Octets)
Frame Check Sequence (4 Octets)
If the protocol being used is Ethernet Type 2, then the frame has a field
indicating the packet type instead of a length field. Ethernet Type 2 is an
older protocol developed by Xerox which is still in common use today.
- Missing Start Frame Delimiter (SFD) Errors
- Missing Start Frame Delimiters are input errors which occur when a burst
of data greater than or equal to 10 bytes in length is received with no SFD.
A Start Frame Delimiter is required to indicate to the listening stations
that the beginning of a frame is being transmitted.
- Multicast Frames
- Multicast frames are frames that are directed to an active multicast group
address. This does not include frames received which had a framing error.
Broadcast packets are also not included.
- Non-Unicast Packets
- Non-Unicast Packets are frames that are addressed to either broadcast or
multicast addresses.
- Octet
- A byte of data, which contains eight 0 or 1 bits.
- Out Success With Retry Errors
- Out Success With Retry errors are output errors which indicate that a
frame successfully transmitted after one or more collisions. Out Success
With Retry Errors are the number of frames that experienced a a collision
and retransmit before success. The total collisions divided by the number of
Out Success With Retry errors will provide the average number of collisions
per packet transmitted with collisions.
- Out of Window Collisions Errors
- Out of Window Collisions are a type of output error. Out of window
collision errors occur when a frame in the process of being transmitted
collides with another frame. This error usually occurs either when some
interface on the network fails to defer or the network has too many
stations. (See Late Collisions.)
- Output Discard Errors
- Output Discards are output errors that occur when the router has to throw
a packet out instead of queuing it for transmission on the Ethernet. Output
discard errors usually indicate that the network has more traffic than it
can handle. They may also indicate a software discard such as no route to
destination.
- Output Errors
- Output errors are the sum of all the output errors that occur on an
interface.
- Output FIFO Overrun Errors
- FIFO Overruns are a type of output error. Output FIFO Overruns occur when
the output queue in the adapter underflowed while putting a frame on the
wire. This problem occurs when the interface is not receiving bits of the
frame fast enough.
- Output Packets
- See Transmitted Packets.
- Preamble Field
- The preamble field synchronizes the timing of all listening devices on the
network. The preamble field is 7 bytes and consists of a series of 56
alternating zero and one bits.
- Readable Frames
- A good or Readable Frame is a frame between 64 and 1518 bytes in length
and has an SFD and good FCS. In other words, Readable Frames are the number
of frames that are successfully received by the port, including broadcast
and multicast frames.
- Readable Octets
- Readable Octets are the total number of data and padding octets in frames
that are successfully received by the device, including broadcast and
multicast frames. This does not include frames received with a framing
errors. The number of Readable Octets does not include the octets in the
address, length/type and CRC fields.
- Runt Errors
- Runt Errors are input errors in which the received frames are smaller than
64 bytes, but have no CRC or alignment errors. Frames must be a minimum
length in order ensure that all stations on the network will detect possible
collisions. Runt errors are likely the result of a faulty device on the
network, or defective software.
- Self-Test Fail (ST Fail)
- The total number of self test failures on this interface. A self-test is a
internal card diagnostic procedure that is performed when the router is
restarted or the interface is brought into a self-test mode.
- Short Event Errors
- See Missing Start Frame Delimiter (SFD) Errors.
- Signal Quality Error (SQE) Test
- Signal Quality Error (SQE) is the IEEE term for a collision. The term SQE
is often used interchangeably with heartbeat. Signal Quality Error Test is
an IEEE 802.3 function that tests the transceiver. The SQE Test is a means
of detecting a transceiver`s inability to detect collisions. Without SQE
Test, it is not possible to determine if your collision detector is
operating properly. SQE Test is implemented by generating a test signal on
the collision pair from the transceiver following every transmission on the
network. It does not generate any signal on the common medium.
IEEE 802.3 specifications state that IEEE 802.3 compliant repeaters must
not be attached to transceivers that generate a heartbeat, because a jam
signal prevents redundant collisions from occurring on the network.
Therefore, the SQE Test between the transceiver and an 802.3 repeater
usually must be disabled. See Heartbeat.
- Start Frame Delimiter (SFD) Field
- The Start Frame Delimiter field of a frame signals the beginning of a
frame being transmitted.
- Transmit Collision Errors
- Transmit Collision Errors are output errors which indicate the total
number of collisions that the device encountered when attempting to transmit
frames.
- Transmitted Frames
- Transmitted Frames are the number of frames that are transmitted. This is
incremented when a frame is successfully transmitted, even if a collision
occurs. In other words, Transmitted Frames include transmissions that
succeeded after some number of collisions. This also includes multicast and
broadcast frames.
- Transmitted Octets
- Transmitted Octets are the number of data and padding octets of frames
that are transmitted. This includes octets in broadcast and multicast frames
that are transmitted. This does not include the address fields, length/type
field, and CRC field of the frame.
- Unicast Packets
- Unicast Packets are frames that are not addressed to either broadcast or
multicast addresses.