IMO, always put TN on an IS in the internal network. TN must have access to its DB tables. If TN is in the DMZ, then either DB server must also be there or the internal firewall would need to be configured to allow the access from IS/TN to the internal DB–neither are good options.
Use a proxy of some sort, such as the IS Gateway (formerly Reverse Invoke Server), in the DMZ and put everything else in the internal/protected network.
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