Testing a nonswitched SDLC line

A link level 2 test is used to test a nonswitched SDLC communication line between one of the following pairs of items:

NCP and one of its peripheral PUs
VTAM® and one of its peripheral PUs
Two NCPs
Two VTAMs (The command must be initiated from the VTAM with the highest subarea number.)
NCP and VTAM (The command must be issued from the NCP domain.)

You can specify:

A continuous link test or the number of test transmissions to be sent
The cancelation of an ongoing link test
Any user data to be included in the test transmissions

The test data is returned from the remote station (NCP, host node, or peripheral PU) to the controlling NCP or to VTAM. The data received by the NCP or VTAM is compared with the data sent, and the following information is displayed by VTAM:

Number of test messages sent
Total number of test messages returned (including those in error)
Number of test messages returned without error

The SDLC link must be active, and the physical unit must be inactive. You must specify the name of the physical unit on the ID operand of the MODIFY LL2 command. You can run this test on a point-to-point line or on a multipoint line without affecting any other physical units on the line.

Before you request a link level 2 test between two NCPs, ensure that the link station at the originating end is inactive and the link station at the receiving end is active. In a multiple-domain network with shared host ownership of link stations, both link stations must be inactive to all SSCPs. The name of the link station in the NCP initiating the test must be specified on the ID operand of the MODIFY LL2 command.