Under control of the LANIC card firmware, this command causes a designated local or remote card to transmit a special loopback test packet from the card to the LAN coaxial cable, and to receive it back again.
Loopback results are displayed on the user's terminal. Loopback failure indications can be used to help isolate a hardware problem to the node or network level.
The syntax of this command is:
| EL[,[ADR][,[LU#][,Rep]]] |
where: | |
ADR | This is the •target" Station Address of the node whose LANIC card transmits and |
| receives a loopback test packet. It is entered as 6 pairs of hexadecimal digits |
| separated by hyphens. See Table 5"1 for default addresses. |
LU# | This is the Logical Unit number that identifies the LANIC card through which a |
| command is transmitted and from which a response is received. LU# is a number |
| in the range 2 to 255 (decimal) established during system generation; hence, it |
| always applies to a local LANIC card. See Table 5"1 for default values. |
Rep | This parameter specifies the number of consecutive times this command is |
| executed. Values from •0" to •9999" may be specified. When set to •0", the |
| command is repeated indefinitely unless a failure occurs or until the NM module |
| break flag is set (see •The Rep Parameter" earlier in this section). |
The EL command is conducted through PROM"based intelligence on the card. When initiated, the LANIC card attempts to transmit a special loopback test packet onto the LAN. From the card, the packet proceeds through the AUI (Attachment Unit Interface) cabling and MAU (Medium Attachment Unit), and onto the LAN. Subsequently, it is received by the LANIC card. Any monitored failures during this process are reported to the driver.
Node Manager software interprets the external loopback test results; on failure of monitored parameters, a •[failed]" indication and status word are returned to the user. Each relevant bit in the status word is identified by one or two characters. The applicable bits are defined in Table 5"9. (Also, see Example 2 below.)
The H bit, when set, indicates that the LANIC card did not receive a heartbeat (Signal Quality Error test signal) from the MAU. Most MAUs return this temporary signal to the LANIC card on each transmission to ensure proper operation of collision detection circuitry. Although a
•[failed]" indication is returned, the lack of a heartbeat, by itself, does not positively identify a failed component. The LANIC card, AUI cabling and MAU may still be functioning properly.
5%38 Using Node Manager