Non-MFS bracket and half-duplex protocol examples

The following series of examples illustrate ISC data flow control protocols.

In the examples, the items in parentheses are optional on the flow.

For simplicity, the examples in this topic assume only-in-chain SCHEDULER messages for flows in both directions, and the response, ATTACH, and SCHEDULER protocols have been excluded. Also, the bracket protocol is considered symmetrical in that either the primary half session (PHS) or the secondary half session (SHS) can initiate the bracket as illustrated.

Figure 1. Example of bracket protocol for a PHS component defined to IMS as SINGLE1
Flow 1: SHS to PHS with OIC, BB, and CD, then from PHS to SHS with OIC, EB, and (msg/LUSTATUS). Flow 2: Two arrows from PHS to SHS both with OIC,BB,EB.

Sample flow 1 shows the PHS ending a bracket on the first output following receipt of change-direction. When no output exists and the input cannot guarantee output, the bracket is ended through a stand-alone LUSTATUS.

Sample flow 2 shows the PHS sending output that occurs while in a between-brackets state.

Figure 2. Example of bracket protocol for a PHS component defined to IMS as SINGLE2
Flow 1 and flow 2 show numerous arrows alternating directions between PHS (IMS) and SHS. Each arrow is labelled with OIC and combinations of the following: BB, EB, CD, (LUSTATUS), (msg), and (msg/LUSTATUS).

Sample flow 1 shows the PHS returning the flow to a bracket initiator after receipt of a change-direction. The bracket initiator can optionally continue input or end the bracket. When no output exists and the input cannot guarantee output, the flow is returned to the bracket initiator using a stand-alone LUSTATUS.

Sample flow 2 shows the PHS sending asynchronous output. Also, IMS detects a potential LUSTATUS CD loop and forces end-bracket using LUSTATUS.

Figure 3. Example of bracket protocol for a PHS component defined to IMS as MULT1
Flow 1: 1 arrow from SHS to PHS and 3 arrows from PHS to SHS. Flow 2: 4 arrows pointing from PHS to SHS. In both, OIC labels each arrow alone or with some of the following: BB, EB, CD, and (LUSTATUS).

Sample flow 1 shows the PHS ending a bracket using an LUSTATUS. The bracket ends following the last output from a queue after receipt of change-direction. If no output exists and the input cannot guarantee output, the bracket is ended immediately by using a stand-alone LUSTATUS.

Sample flow 2 shows the PHS both beginning and ending a bracket by using an LUSTATUS following the last output from a queue. Additional output available from other queues causes subsequent brackets to be initiated.

Figure 4. Example of bracket protocol for a PHS component defined to IMS as MULT2
Flow 1 and flow 2 are similar to the flows in example 3, except that each ends with an arrow from SHS to PHS labelled with OIC,EB (msg/LUSTATUS).

Sample flow 1 shows the PHS returning the flow to the bracket initiator using an LUSTATUS. The bracket ends following the last output from a queue after receipt of a change-direction. The bracket initiator can optionally continue input or end the bracket. If no output exists and the input cannot guarantee output (that is, the input is not in conversational or response mode), the flow is returned by using a stand-alone LUSTATUS.

Sample flow 2 shows the PHS sending output that occurs in a between-brackets state.