FAQs: 3270 Bridge
The list is by no means exhaustive, so please feel free to mail us questions about any topics we fail to cover here.
Here are some of the topics covered in our FAQ.
- What is the "3270 bridge"?
- How does HostBridge handle the shortcomings of the "3270 Bridge", such as not supporting dynamic modification of field attributes from CICS programs?
- Have you overcome the 3270 Bridge "problem" when the 3270 application performs and EXEC CICS START?
What is the "3270 Bridge"?
The term "3270 Bridge" has been a source of confusion since IBM came out with CICS TS 1.3. Technically, 3270 Bridge is simply an interface that allows a program to START a transaction and then intercept the terminal I/O commands issued by that transaction. When IBM introduced this interface they also provided a sample program that used the interface. This program, called WBTTA (Web Terminal Transaction Access), uses the 3270 Bridge interface to allow access to CICS transactions via a web browser.
Unfortunately, IBM's documentation sometimes used the phrase "3270 Bridge" to refer to both the 3270 Bridge interface and WBTTA. To deal with this confusion, IBM now refers to the functionality provided by WBTTA as the "3270 Web Bridge". However, since "3270 Web Bridge" and "3270 Bridge" are so similar it has done little to clarify matters.
Why is this important?
WBTTA (aka "3270 Web Bridge") has certain functional and performance characteristics - not all of which are appropriate or preferable in certain circumstances. For example, the IBM Redbook "A Performance Study of Web Access to CICS" (SG24-5748) analyzes the performance of WBTTA (aka "3270 Web Bridge"). Suffice it to say that it was not the fastest horse in the stable. And, if you think the "3270 Web Bridge" is the same as the 3270 Bridge interface, you would probably draw the erroneous conclusion that these performance characteristics apply to anything that uses the 3720 Bridge interface. But they do not!
A clear understanding of all this really helps when you examine CICS enhancement products. HostBridge XML-enables CICS transactions. HostBridge uses the 3270 Bridge interface, but does not have anything to do with the 3270 Web Bridge. As a result, HostBridge does not inherit the functional or performance limitations of 3270 Web Bridge. On the other hand, there are some CICS enhancement products that do layer on top of 3270 Web Bridge (WBTTA) and they will inherit these limitations.
How does HostBridge handle the shortcomings of the "3270 Bridge", such as not supporting dynamic modification of field attributes from CICS programs?
The shortcoming you refer to (not supporting dynamic modification of attributes), is not a shortcoming of 3270 Bridge. Instead, it is a shortcoming of the component within CWS provides HTML access to 3270 applications. (Read the question and answer above.)
HostBridge has no such shortcomings for two reasons. First, HostBridge has absolutely no interaction with that particular component of CWS. Second, we wrote our own programs and modules to overcome the perceived problems with CWS support for HTML enablement of CICS applications. The WBTTA component of CWS is satisfactory for browser-based access, but it has several limitations that make it unsuitable for application-to-application communication.
Have you overcome the 3270 Bridge "problem" when the 3270 application performs and EXEC CICS START?
This is not a limitation of the 3270 Bridge Interface. Rather, it is a limitation of the sample bridge exit provided by IBM (DFH0CBRE). IBM and some third party vendors use DFH0CBRE as their bridge exit. HostBridge does not. HostBridge has its own bridge exit, formatter, monitor, and converter. HostBridge does not rely on any of the IBM-supplied components (other than the 3270 Bridge APIs). We also support INITIAL values, static field attributes, fields on MAPONLY, DATAONLY merging, and many other things that the default exits do not support.
Thus, HostBridge supports EXEC CICS START IMMEDIATE and EXEC CICS START TRANSID() TERMID().