There are two possible dynamic routing models.
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 14 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.
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.
In the distributed model, each region may be both a routing region and
a target region. A routing program runs in each region. Figure 15 shows
a distributed routing model.
The distributed model applies to the routing of:
- CICS business transaction services processes and activities
- Method requests for enterprise beans and CORBA stateless objects
- Non-terminal-related START requests
- CICS-to-CICS DPL requests
The distributed model is a peer-to-peer system--each
participating CICS region may be both a routing region and a target region.
A routing program runs in each region.
Advantage of the distributed model
There is no single point-of-failure.
Disadvantages of the distributed model
- Compared to the "hub" model, there are a great many inter-region
connections to maintain.
- You may have problems with distributed data. For example, any data used
to make routing decisions must be available to all the regions. (CICSPlex® SM solves
this problem by using dataspaces.)
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