SDT
From MythTV Official Wiki
SDT (Service Description Table) is a service information element carried within a DVB transport stream, it gives user-oriented information about services in the transport stream.
The SDT typically contains information such as the name of the service, the service ID, the status of the service (e.g. running/not running/starting in a few seconds) and whether the service is scrambled or not.
For further information see http://www.interactivetvweb.org/tutorials/dtv_intro/dtv_intro
