2.5.1 Two Phases of an IMS Client Request

Because of the design philosophy of IMS, processing of an IMS client request occurs in two distinct “phases.”

1. A request phase wherein the request is issued during the execution of one transaction (T1).
2. A corresponding response phase wherein the response is processed during the execution of a second transaction (T2).

Transactions T1 and T2 may in fact be the same transaction ID (with appropriate logic to perform the required request or response processing, based on execution context). T1 and T2 must be two distinct transaction executions. This distinction is necessary because T1 can only initiate a request; it cannot “wait” on the response to that request because the architecture and design philosophy of IMS does not permit this.