ISO-TCP Header
| Byte | Description | |
| 0 | version number (for S7 communication always 0x03) | |
| 1 | reserved (always 0x00) | |
| 2-3 | size of ISO-TCP message (including this header) in byte |
| Byte | Description | |
| 0 | version number (for S7 communication always 0x03) | |
| 1 | reserved (always 0x00) | |
| 2-3 | size of ISO-TCP message (including this header) in byte |