CANCEL protocol

IMS sends and receives the SNA CANCEL command, which allows the sender to terminate an output SNA chain without having to send all of the chain following a sender- or receiver-detected error.

The CANCEL command that is sent because of either a sender- or receiver-detected error is sent by IMS with the VTAM® indicators shown in the following table.

The CANCEL command that is received by IMS because of either a sender- or receiver-detected error can indicate whatever protocol (consistent with current DFC states) is appropriate for the message sender.

In the table the VTAM indicators that are sent with the CANCEL command are represented by the following abbreviations:
  • EB: End-Bracket
  • CD: Change-Direction
Table 1. VTAM indicators sent with the CANCEL command
Output (determined in following order) ¬CD or ¬EB CD EB
After /DEQ (LUSTATUS ABORT is next) X    

When primary half session and FIC/OIC was
  between bracket (conditional BB)

 X    

After receiving selective receiver ERP
  sense code

   X  
After receiving SIGNAL   X  

When conversational or response mode
  output is still available

 X    
FIC/OIC was EB RQD* (conditional EB)     X
While in test (echo) mode   X  
Non-MFS demand-paged output for SINGLE1 component See indicators for FIC/OIC was between bracket or FIC/OIC was EB
MFS demand-paged output for SINGLE1 component     X
Output for SINGLE2 component   X  
Output for MULT1 or MULT2 component X