The hub model
The hub is the model that has traditionally been used with CICS® dynamic transaction routing.
A routing program running in a TOR routes transactions between
several AORs. Usually, the AORs (unless they are AOR/TORs) do no dynamic
routing. Figure 1 shows a hub routing
model.
The hub model applies to the routing of:
- Transactions started from terminals.
- Transactions started by terminal-related START commands.
- Program-link requests received from outside CICS. (The receiving region acts as a hub or TOR because it routes the requests among a set of back-end server regions.)
- Bridge 3270 requests.
- CICS-to-CICS DPL requests.
The hub model is a hierarchical system; routing is controlled by one region (the TOR). Normally a routing program runs only in the TOR.
Advantage of the hub model
It is a relatively simple model to implement. For example, compared to the distributed model, there are few inter-region connections to maintain.
Disadvantages of the hub model
- If you use only one “hub” to route transactions and program-link requests across your AORs, the “hub” TOR is a single point-of-failure.
- If you use more than one “hub” to route transactions and program-link requests across the same set of AORs, you may have problems with distributed data. For example, if the routing program keeps a count of routed transactions for load-balancing purposes, each “hub”-TOR will need access to this data.