Port Error Counters UPDATED: August 31, 1999 SUMMARY: The PortMaster (TM) keeps count of errors detected on its ports which are useful when when trying to detect a problem or debugging a problem. Below are sample screen shots of some PortMaster ports with links to definitions of the various errors. Sample synchronous port output Command> show w1 ----------------------- Current Status - Port W1 -------         Status: ESTABLISHED          Input: 915287284          Abort Errors: 56/1         Output: 3214289999           CRC Errors: 27        Pending: 0                Overrun Errors: 0      TX Errors: 0                  Frame Errors: 15   Modem Status: DCD+  CTS+ Sample asynchronous port output Command> show s10 ----------------------- Current Status - Port S10 ------         Status: ESTABLISHED          Input: 1392900           Parity Errors: 0         Output: 453743           Framing Errors: 0        Pending: 0                Overrun Errors: 0   Modem Status: DCD+  CTS+ Abort Errors An abort error means that a connection did not establish on the synchronous port and it is trying again. Each time it tries again it increments the error count by one. When you see a slash in the Abort Error (Abort Errors: 56/1) count the first number represents framing errors, the second number represents device errors. Framing Errors count is incremented when: The receiver chip reports a framing error The receiver chip reports an abort Device Errors count is incremented when: When frame size is 0. When frame size is greater than the maximum size of a PPP frame. When frames overlap each other CRC Errors Means the data received did not pass a verification routine. Cyclical Redundancy Check - Is a check on the data to make sure that it has arrived fine. The checking mechanism is a hashing algorithm. The CRC hashes the large set of all possible binary numbers onto the smaller set of all possible CRC codes. Hashing by nature loses data so at least two different blocks must produce identical CRC. So CRC is very good at detecting changes in data blocks during serial transmission (Which is what PortMasters use it for). Overrun Errors If a character is received sent to the buffer to be processed before the previous character has been read by the processor the previous character is destroyed or overwritten. Basically someone is force-feeding characters to a port greater than the port speed. Frame Errors Basically, the frame was munged in transit. Almost always caused by a hardware failure in a line or modem, etc. A frame is considered invalid if it does not terminate with at least 1 STOP bit. If a framing error occurs the counter is incremented, and the PortMaster automatically attempts to resynchronize by assuming that the incorrect STOP bit was actually the start bit for the next character. A new character is then constructed beginning with this new START bit. On synchronous ports the "Frame errors" is sometimes followed by two numbers separated by a slash. Frame Errors: small packets/large packets Large packets count is incremented when receive character counter overflow (packet too big - drop it). Small error count is incremented when a short frame is received. Troubleshooting Framing Errors What to watch for? See if the framing errors are rising constantly or just sometimes. You need to know if your framing errors are incrementing at a constant rate or if your framing errors are occurring all at once. If they are incrementing at a constant rate, by how much? How quickly? If they happen all at once and are not on the rise then they were probably caused by a single event. Unplugging a serial cable from the PortMaster can result in a jump of framing errors. Determine if the framing errors are limited to one port If you notice a particular port has numerous framing errors on the rise then swap the serial cable, device (modem, CSU/DSU), phone wire with that of another port. If the problem follows the port then check the Lucent box. If the problem follows the line then begin swapping cables, modems, etc. to narrow down the source of the framing errors. What to do? Make sure your power cables are perpendicular to your data cables. Electricity passing through a cable generates a magnetic field. The electro-magnetic fields generated by the power cables can disrupt information passing through the data cables. By running your power cables perpendicular to your data cables you minimized the contact with the electro-magnetic fields.   Check your serial cables The cable (and possibly connectors and adapters) between the PortMaster and (modem or CSU/DSU) should be shielded to minimize noise from other serial cables and power connectors. Try swapping the cable and/or adapters. Sometimes a cable will have a short-circuit. Usually serial cables come bad in batches since they are all manufactured at the same time. When swapping cables try to use store bought cables to prevent human error. Be especially suspicious of DB25 to RJ45 connects as these often have problems. Have your lines tested for noise Analog, ISDN, T1, etc. lines are all susceptible to noise at the telephone company. This is OFTEN the cause of many framing errors and the noise test is generally free. Noise can come and go so you will want to see when the framing errors are occurring. Check the environment Other devices can cause noise as well that can result in framing errors. Be sure to keep your data cables away from monitors, magnets, old color TV's, arc welders and low flying UFOs. Verify Modem/CSU/DSU Modems and CSU/DSU's can also cause framing errors if they are defective or misconfigured. Verify Phone Wire and block Check the wiring in your building, in the block and from the block to the modem. If this is wired poorly, or you have bare copper running or ordinary phone wiring running for a few feet will make you susceptible to framing errors.