Which field of VideoOS.Platform.Data.BaseEvent contains the original string send in from external party through port 1234?If it is not inside BaseEvent , where it is?Could you provide a sample which can get this external string through SDK?

[Peter_Posselt_Vergmann (Peter Posselt Vergmann (Milestone Systems))]

The original string is not available. If you need to pass in more information that should be available afterwards you can use analytics events instead. These consists of an XML format with predefined fields that will be available in the event class afterwards. You can, however, still not access the string as such - only the recognized fields.