Cabletron Systems EMM-E6 - Manual (Page 40)

Using the EMM-E6 Hub View
2-24 Monitoring Hub Performance
Runt Frames
The total number of received packets smaller than the minimum Ethernet frame
size of 64 bytes (excluding preamble). This minimum size is tied to the maximum
propagation time of an Ethernet network segment — the maximum propagation
time is 51.2
µ
s, and it takes approximately 51.2
µ
s to transmit 64 bytes of data;
therefore, every node on the segment should be aware that another node is
transmitting before the transmission is complete, providing for more accurate
collision detection. Runts can sometimes result from collisions, and, as such, may
be the natural by-product of a busy network; however, they can also indicate a
hardware (packet formation), transmission (corrupted data), or network design
(more than four cascaded repeaters) problem.
Giant Frames
The total number of received packets that are longer than the maximum Ethernet
size of 1518 bytes (excluding preamble). Giant packets typically occur when you
have a jabbering node on your network — one that is continuously transmitting,
or transmitting improperly for short bursts — probably due to a bad transmitter
on the network interface card. Giant packets can also result from packets being
corrupted as they are transmitted, either by the addition of garbage signal, or by
the corruption of the bits that indicate frame size.
The EMM-E6 Error Priority Scheme
Each Cabletron device employs an error priority scheme which determines how
packets with multiple errors will be counted, and ensures that no error packet is
counted more than once. The priority scheme for the EMM-E6 counts errors in the
following order:
1. OOW Collisions
2. Runts
3. Giants
4. Alignment Errors
5. CRC Errors
Knowing the priority scheme employed by the EMM-E6 can tell you a lot about
the error counts you are seeing. For example, you know that the number of
packets counted as CRC errors had only CRC errors — they were of legal size (not
runts or giants) and had no truncated bytes. You also know that any packet less
than 64 bytes long has been counted as a runt, even if it also had alignment
and/or CRC problems (which is likely if the runt is the result of a collision or
other transmission problem).