XOT and all other options have one disadvantage: the X.25 protocol spans across the Internet/intranet. There is an overhead in the protocol headers, and there are timing issues caused by latency of the X.25 protocol. The application at the branch offices is still burdened using a proprietary X.25 API. This may be a temporary solution to replace at least the X.25 PSDN with a TCP/IP WAN. Even if legacy X.25 hardware in the branch offices cannot be eliminated, the X.25-to-TCP/IP gateway is still the better option, because the X.25 does not have to traverse the Wide Area Network (WAN). Our solution is the PXSe XGate (X.25↔TCP/IP).
If the legacy hardware in the branch offices is already an X.25-to-TCP/IP gateway (depicted above) and can be removed, this is the most cost effective option. The PXSe can terminate the X.25 connection directly at the legacy system. Data received from the TCP/IP WAN, is forwarded via X.25 to the legacy mainframe. As in XOT, a 2 byte header defines the length of the data.