Although some type 2.1 peripheral nodes do not support adaptive-session pacing, an independent logical unit in that node can still act as the primary LU and therefore sends the BIND. The primary pacing values in the BIND are established by the independent logical unit (primary). However, the value of the primary send count might be so large that it can impact the subarea node to which it is attached. For example, a PS/2 attached to an NCP using a token ring (NTRI) can specify a value of 0 (no pacing) as the primary send count, which if not altered, can cause the NCP to enter slowdown. VTAM®, in conjunction with NCP, allows you to control the primary pacing values used by an independent logical unit for which adaptive-session pacing is not supported. If a type 2.1 peripheral node that supports adaptive session pacing is attached directly to VTAM, VTAM honors the pacing-window-size value included in the pacing response from the peripheral node but continues to use the appropriate receive count for its fixed-window-size value.

The primary send count specified in the logon mode entry of the primary logical unit is used by VTAM to control the rate at which a peripheral node acting as a primary logical unit sends data to an NCP. This value is then used by NCP or VTAM for a directly attached type 2.1 peripheral node to control the primary send pacing. If a negotiable BIND is used, the smaller value (other than 0) is used. If the BIND is nonnegotiable and the primary send value in the original BIND (other than 0) is larger than the value VTAM obtained from the logon mode entry or PACING specification, VTAM or NCP may reject the session setup request. For a directly attached type 2.1 peripheral node, VTAM performs the same type of operation.

Therefore, you must specify proper pacing values in VTAM for any type 2.1 independent logical unit. If the type 2.1 peripheral node supports adaptive-session pacing, this procedure is not necessary.