Cabletron Systems SEHI-22/24 Multicast Packets, Total Errors, Alignment Errors, CRC Errors, 2-17

Using the SEHI Hub View

Multicast Packets

The number of multicast packets received by this device, module, or port since the window was last opened or reset. Multicast packets are simultaneously addressed to more than one address, but fewer than all addresses.

Collisions

The number of collisions recorded by this device, module, or port since the window was last opened or reset. The SEHI counts both receive collisions — those detected while a port is receiving data — and transmit collisions — those detected while a port is transmitting data (i.e., the port has transmitted one of the colliding packets); however, these counts are combined and a single total value is displayed. Collisions of this type (called “legal” collisions, as opposed to the OOW collisions described below) are a natural by-product of a busy network; if you are experiencing high numbers of collisions, it may be time to redirect network traffic by using bridges or routers. Extremely high collision rates can also indicate a data loop (redundant connections) or a hardware problem (some station transmitting without listening first).

Total Errors

The number of errors of all types recorded by this device, module, or port since the window was last opened or reset.

Alignment Errors

The number of misaligned packets recorded since the window was last opened or reset. Misaligned packets are those which contain any unit of bits which is less than a byte — in other words, any group of bits fewer than 8. Misaligned packets can result from a packet formation problem, or from some cabling problem that is corrupting or losing data; they can also result from packets passing through more than two cascaded multi-port transceivers (a network design which does not meet accepted Ethernet spec).

CRC Errors

CRC, or Cyclic Redundancy Check, errors occur when packets are somehow damaged in transit. When each packet is transmitted, the transmitting device computes a frame check sequence (FCS) value based on the contents of the packet, and appends that value to the packet. The receiving station performs the same computation; if the FCS values differ, the packet is assumed to have been corrupted and is counted as a CRC error. CRC errors can result from a hardware problem causing an inaccurate computation of the FCS value, or from some other transmission problem that has garbled the original data. The CRC error counter shows the total number of CRC errors recorded since the window was last opened or reset.

OOW Collisions

The number of out-of-window collisions recorded since the window was last opened or reset. OOW collisions occur when a station receives a collision signal while still transmitting, but more than 51.2 ∝sec (the maximum Ethernet propagation delay) after the transmission began. There are two conditions which can cause this type of error: either the network’s physical length exceeds IEEE

Monitoring Hub Performance 2-17