Cabletron Systems Spectrum EMM-E6 User Manual

Also see for SPECTRUM: User guide User guide User guide User guide User guide

Contents

Cabletron Systems Spectrum EMM-E6 User Manual Manual pdf 40 page image

Using the EMM-E6 Hub View2-24Monitoring Hub PerformanceRunt FramesThe total number of received packets smaller than the minimum Ethernet framesize of 64 bytes (excluding preamble). This minimum size is tied to the maximumpropagation time of an Ethernet network segment — the maximum propagationtime is 51.2 μs, and it takes approximately 51.2 μs to transmit 64 bytes of data;therefore, every node on the segment should be aware that another node istransmitting before the transmission is complete, providing for more accuratecollision detection. Runts can sometimes result from collisions, and, as such, maybe the natural by-product of a busy network; however, they can also indicate ahardware (packet formation), transmission (corrupted data), or network design(more than four cascaded repeaters) problem.Giant FramesThe total number of received packets that are longer than the maximum Ethernetsize of 1518 bytes (excluding preamble). Giant packets typically occur when youhave a jabbering node on your network — one that is continuously transmitting,or transmitting improperly for short bursts — probably due to a bad transmitteron the network interface card. Giant packets can also result from packets beingcorrupted as they are transmitted, either by the addition of garbage signal, or bythe corruption of the bits that indicate frame size.The EMM-E6 Error Priority SchemeEach Cabletron device employs an error priority scheme which determines howpackets with multiple errors will be counted, and ensures that no error packet iscounted more than once. The priority scheme for the EMM-E6 counts errors in thefollowing order:1. OOW Collisions2. Runts3. Giants4. Alignment Errors5. CRC ErrorsKnowing the priority scheme employed by the EMM-E6 can tell you a lot aboutthe error counts you are seeing. For example, you know that the number ofpackets counted as CRC errors had only CRC errors — they were of legal size (notrunts or giants) and had no truncated bytes. You also know that any packet lessthan 64 bytes long has been counted as a runt, even if it also had alignmentand/or CRC problems (which is likely if the runt is the result of a collision orother transmission problem).