SEQUENTIALLU

Telnet, by default, uses a sequential method to choose LUs from a group.

From the previous example, the first LU assigned is LU001, second is LU002, and so on. If five clients repeatedly connect and disconnect, they will be assigned new LUs farther into the range each time:

• When the end of the first range is reached, selection goes to the beginning of the second range.
• At the end of the second range, selection goes to the beginning of the third range.
• At the end of the third range, selection goes to the beginning of the fourth range.
• At the end of the fourth range, selection goes to the beginning of the first range again.

Telnet does not enforce an overall ascension in LU name selection. The selection process begins at the first name of the first range and progresses to the last name of the last range. In the example, after LU250 is assigned from range 2, LU240 from range 3 is attempted next. After LU280, LU010 is attempted. After LU050, the process starts over and LU001 is attempted.

The SEQUENTIALLU function can be turned off by coding NOSEQUENTIALLU. In this case, the five LUs that are repeatedly connecting and disconnecting would never use any LU names other than LU001, LU002, LU003, LU004, and LU005. NOSEQUENTIALLU might degradate LU lookup performance when a large range is specified and only LUs at the end of the range are available. Every connection has to relearn that most of the LUs are already in use. SEQUENTIALLU allows Telnet to start its search near the last chosen LU where LUs are more likely to be available. SEQUENTIALLU and NOSEQUENTIALLU parameters can be coded at all three parameter block levels for different levels of granularity.

If several clients are connecting at the same time, the order of LU assignment might not be in exactly the same order as the connection IDs due to process timing between connection ID assignment and LU name assignment.

If single LU names are in a group with LU ranges, the single LU names are selected before any LU range names are selected, regardless of their order. In the example below, LUAAA, LUBBB, LUCCC, and LUDDD are all processed before any of the range LU names.