stoptimetable is the scheduled departures surface for a stop within a requested departure window. It is a stop-centric scheduled view rather than a route-centric timetable view.
StopMonitoring
StopMonitoring provides current and forthcoming arrivals and departures at a stop.
The transit specification warns that omitting the stop filter can lead to very slow responses because the service may return all monitored stops for an agency.
VehicleMonitoring
VehicleMonitoring provides the current location and expected activities of a vehicle, along with current and subsequent journey context.
Other SIRI service families in the PDFs
The transit specification also documents several additional SIRI families that are not presented as stable primary surfaces here:
- Announcement: documented as discontinued
- General Announcements: documented as discontinued
- Transit Schedule Updates: documented as possible future implementation using SIRI Production Timetable
- Transit Addition and Cancellation of Trips: documented as possible future implementation using SIRI Estimated Timetable
Message structures
Appendix C of the transit specification is the best source for the nested SIRI message structures behind realtime responses. It covers stop monitoring, vehicle monitoring, stop timetables, announcements, schedule updates, estimated timetables, general messages, and service alerts. 
