Cabletron Systems manual Runt Frames, Giant Frames, The EMM-E6 Error Priority Scheme, 2-24

Using the EMM-E6 Hub View

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 ∝s, and it takes approximately 51.2 ∝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).

2-24 Monitoring Hub Performance