This command allows the user to transmit an •IEEE 802.2/802.3 XID command packet" that solicits an •IEEE 802.2/802.3 XID response packet" from a program or process in the target node. It may be used as a loopback tool to help communication integrity with a remote program or process over the LAN.
The syntax of this command is:
XID,[ADR],DSAP[,[LU#][,Rep]]
where: |
|
ADR | This is the •target" Station Address of the node to which the XID command packet |
| is sent. It is entered as 6 pairs of hexadecimal digits separated by hyphens. See |
| Table 5"1 for default addresses. |
DSAP | This is the Destination Service Access Point (DSAP) that specifies the program or |
| process (on the ADR node) for which the IEEE 802.2 XID command packet is |
| directed and from which the XID response packet is desired. This parameter is |
| required and entered as a two"digit hexadecimal number. |
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" discussed earlier in this chapter). |
Recall from Chapter 2, an IEEE 802.2/802.3 XID command packet issued from a program contains a predefined value in its Control field (BF hex with the P, or Poll, bit set). In addition, the Information field contains data that identifies the type of service (Type 1 and/or Type 2) the station provides.
The corresponding IEEE 802.2/802.3 XID response packet returned by a responding program contains the same Control field value (BF hex with the F, or Final, bit set), and an Information field that identifies the type of service supplied by the responding station.
When the Node Manager XID command is issued, a valid IEEE 802.2/802.3 XID command packet is constructed and transmitted. The user"specified DSAP parameter is inserted into the packet's DSAP field. The SSAP field contains F8 hex which identifies the Node Manager software's SAP while also identifying the packet as a command packet (C/R bit not set). The Control field contains BF hex. The Information field contains three bytes of data: 81, 01, and 00 hex, indicating Type 1 service (unacknowledged, connectionless).
The response to the XID command is checked by Node Manager to ensure the same Control field is returned (BF hex). The Information field is checked for the type of service (see Chapter 2 for bit definitions in the XID packet Information field).
If the Node Manager software receives an XID command, it constructs a similar packet. The Source Address and SSAP fields of the command are used to determine the destination of the
5%44 Using Node Manager